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Grazing systems and management strategies for lactating Holstein cows in Florida

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Grazing systems and management strategies for lactating Holstein cows in Florida
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Fike, John Herschel
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English
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xiii, 214 leaves : ill. ; 29 cm.

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Cattle ( jstor )
Dairy cattle ( jstor )
Feed intake ( jstor )
Forage ( jstor )
Grasses ( jstor )
Grazing ( jstor )
Milk ( jstor )
Milk production ( jstor )
Pastures ( jstor )
Stocking rate ( jstor )
Dairy and Poultry Sciences thesis, Ph. D ( lcsh )
Dissertations, Academic -- Dairy and Poultry Sciences -- UF ( lcsh )
Forage plants -- Florida ( lcsh )
Holstein-Friesian cattle -- Feeding and feeds -- Florida ( lcsh )
Milk yield ( lcsh )
Range management -- Florida ( lcsh )
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bibliography ( marcgt )
non-fiction ( marcgt )

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Thesis:
Thesis (Ph. D.)--University of Florida, 1999.
Bibliography:
Includes bibliographical references (leaves 184-213).
General Note:
Printout.
General Note:
Vita.
Statement of Responsibility:
by John Herschel Fike.

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GRAZING SYSTEMS AND MANAGEMENT STRATEGIES FOR LACTATING
HOLSTEIN COWS IN FLORIDA












By

JOHN HERSCHEL FIKE
















A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

1999













ACKNOWLEDGMENTS

This work could not have been completed without the assistance of several

people. Thanks first go to my wife, Wonae, without whose patience, assistance and

understanding this work could not have been completed. The support and encouragement

of the author's parents and family also were instrumental in making this dissertation

possible.

The author wishes to express his gratitude for the teaching, direction and patience

received from his advisors Dr. Charles R. Staples and Dr. Lynn E. Sollenberger. The

Churchillian words of encouragement from Dr. Staples that came during some dark hours

will not be forgotten.

Thanks also go to Dr. John E. Moore for encouragement, mentoring, and excellent

teaching. Drs. Mary Beth Hall and Peter J. Hansen also were instrumental to this work

by providing excellent teaching and assistance whether in or out of the classroom.

To my plastic-sleeved compatriots, Bisoondat Maccoon and Renato Fontanelli,

the wish is extended that though you have adequate sample, your fecal-sample cups will

never runneth over.

Others to be recognized for their help include D. Hissem, J. Lindsay, and M.

Russell for farm support, Drs. R. E. Littell and C. R. Wilcox for statistical assistance, and

Dr. H. H. Head for assistance with immunoassays. Thanks to O. A. Carrijo, Jr., J. Hayen,

E. M. Hirchert, and J. P. Jennings for assistance in the laboratory, at the farm, or both.




ii








Thanks for the generous financial assistance given by the Dean for Academic

Programs for the first year and the Department of Dairy and Poultry Sciences for the

remaining years. Thanks also go to American Farm Bureau, CBAG, and Monsanto for

their financial assistance of the research.












































iii















TABLE OF CONTENTS
page

ACKNOWLEDGMENTS ........................................................ .................................. ii

LIST O F T A B LE S ............................................................................................................ vii

LIST O F FIG U RES ..................................................................................................... ix

KEY TO ABBREVIATIONS ........................................... ......................................... xi

A B STR A C T ................................................................................................................ xii

CHAPTER 1. INTRODUCTION ................................................... ............................. 1

CHAPTER 2. LITERATURE REVIEW ................................... ................................3

Climatic Challenges to Southeastern Dairies...............................................................4
Clim atic Anim als. ........................................................................................................... 6
Energy Considerations for the Grazing Ruminant.......................................................7
Some Animal and Nutritional Factors Influencing Feed Intake ........................................9
Some Non-Nutritional Factors Affecting Behavior and Forage Intake of Grazing
R um inants .............................................................................................................. 13
Mechanistic Components of Forage Intake .......................................... ............... 13
Daylight and Temperature ...................................................................................17
Measurement of Forage Intake in Grazing Ruminants..............................................18
Herbage Allowance and Stocking Rate Effects on Forage Intake and Performance
of Rum inants.................................................. . ....................................................... 21
Supplement Effects on Animal Performance with Particular Emphasis on
Lactating Cows in Pasture-Based Dairy Systems................................................25
Supplement Effects on Production.......................................................................26
Supplement Effects on Intake ..............................................................................29
Supplement Effects on Forage Digestibility ...........................................................33
Synchronizing Nitrogen and Carbohydrate Supplements to Increase Microbial
Protein Synthesis in the Rumen..............................................................................37
Loss of Feed Nitrogen in Ruminants ......................................................................37
Responses to Supplemental Carbohydrate..............................................................39
Effects of Supplement Feeding Frequency .............................................................42
Effects of Timing of Supplement Provision Relative to Forage Intake.....................44
Additional Energy and Protein Supplements for Animals on Pasture.............................45
Fats.................................................................................................... . . ................... 45
Escape Proteins ......................................................................................................46

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Effect of Supplements on Grazing Behavior ..................................................................47
Interactions of Supplement and Herbage Allowance on Performance of Lactating
Cows in Pasture-Based Dairy Systems.....................................................................49
Two Perennial Forages for Lactating Cows in Pasture-Based Dairy Systems in the
Southeast...................................................................................................................... 51
B erm udagrass.........................................................................................................51
Comparisons of Grasses and Legumes .....................................................................60
R hizom a Peanut..................................................................................................... 63
Some Management Strategies for the Improvement of Milk Production in
Subtropical Environments Systems..........................................................................67
Bovine Somatotropin (bST)................................................................................. 67
Effects of Heat on Milk Production and Cooling Strategies for Pastured Cows.........70
bST in Hot Environments ....................................................................................72

CHAPTER 3. PASTURE-BASED DAIRY PRODUCTION SYSTEMS:
INFLUENCE OF FORAGE, STOCKING RATE, AND
SUPPLEMENTATION RATE ON ANIMAL PERFORMANCE............................75
Introduction.........................................................................................................................75
M aterials and M ethods................................................................................................. 77
Cows, Design, and Treatments ............................................................................ 77
Experimental Procedures ....................................................................................... 81
Statisitical A nalyses............................................................................................... 86
Results and D iscussion ................................................................................................ 87
Forage Com position............................................................................................... 87
Milk Production and Composition per Cow...........................................................89
Milk Production per Land Area ................................................................................100
Body Weight and Condition ......................................................................................101
Respiration, Temperature, and Blood Metabolites ............................................105
Intake of Organic Matter and Nutrients................................................................... 109
Treatment Effects on Forage Nutritive Value Estimates......................................... 117
Treatment Effects on Herbage Mass, Availability, and Intake Estimates as
Determined by Pasture Sampling.................................................................... 120
Simple Economic Assessment of Supplementation...................................................125
Conclusions........................................................................................................ . . 127

CHAPTER 4. PASTURE-BASED DAIRY PRODUCTION SYSTEMS:
INFLUENCE OF HOUSING, bST, AND FEEDING STRATEGY ON
ANIMAL PERFORMANCE ................................................................................. 130
Introduction .................................................................................. ............................ 130
M aterials and M ethods............................................ ................................................. 31
Cows, Design, and Treatments .............................................................................131
Experimental Measurements................................................................................134
Statistical A nalysis............................................ ..................................................142
Results and D iscussion ............................................................................................... 145
Grazing Time and Intake of Organic Matter ......................................................... 145
Milk Production and Composition........................................................................150


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Body Weight and Composition..........................................................................155
Plasm a IGF- 1 and Insulin .................................................................................... 157
Respiration Rates and Body Temperatures.................................................................59
C onclusions................................................................................................................ 163

CHAPTER 5. FINAL SUMMARY AND CONCLUSIONS ........................................167

APPENDIX 1. SAS PROGRAM OF POND ET AL. (1987) FOR THE
ESTIMATION OF FECAL OUTPUT............................. ......................................181

APPENDIX 2. SAS PROGRAM TO ADJUST FORAGE INTAKE UNTIL
FECAL OUTPUT OBSERVED AND FECAL OUTPUT PREDICTED
DIFFER BY LESS THAN ONE-HUNDREDTH OF A KILOGRAM PER
D A Y ..................................................................................................................... 182
APPENDIX 3. RAINFALL AND TEMPERATURE DATA FOR GRAZING
TRIALS IN 1995, 1996, AND 1997..........................................................................183

LIST OF REFEREN CES ............................................................................................ 184

BIOGRAPHICAL SKETCH .....................................................................................214































vi














LIST OF TABLES

Table page

3.1 Ingredient and chemical composition of supplements fed to lactating Holstein cows
on pasture............................................................................................................79

3.2 Nutritive value characteristics, chemical composition, and calculated net energy of
lactation (NEL) and total digestible nutrients (TDN) of Tifton 85 bermudagrass and
Florigraze rhizoma peanut pastures. Samples were hand-plucked once each period,
based on visual appraisal of forage consumed by grazing cows.
............ .............. . . .................................................................... ....... ...............88

3.3 Effect of forage, stocking rate (SR), and supplementation rate (SUP) on milk
production and composition of Holstein cows grazing Tifton 85 bermudagrass and
Florigraze rhizoma peanut during the summers of 1995 and 1996..........................90

3.4 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on
body weight (BW) and body condition score change (ABCS), respiration rate (RR),
body temperature (TEMP), and plasma urea nitrogen (PUN) and plasma glucose of
Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut
during the summers of 1995 and 1996................................................................ 102

3.5 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on
forage, supplement and total organic matter intake (OMI), and on forage,
supplement, and total organic matter intake as a percent of bodyweight (OMIPBW)
of Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut
during the summers of 1995 and 1996. ................................................................. 110

3.6 Calculated daily intake of nutrients by cows grazing Tifton 85 bermudagrass (BG)
or Florigraze rhizoma peanut (RP) pastures. Cows received supplement (SUP) at
either 0.33 kg (Low) or 0.5 kg (High) (as-fed) per kg of daily milk production..... 114

3.7 Effect of forage, stocking rate (SR), and supplementation rate (SUP) on bodyweight
(BW) change, 4% fat corrected milk (FCM) production, and measures of energy (E)
status of Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma
peanut during the summers of 1995 and 1996 ....................................................115

3.8 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on
forage, supplement and crude protein (CP), in vitro organic matter digestibility
(IVOMD), and neutral detergent fiber (NDF) concentrations in Tifton 85

vii








bermudagrass and Florigraze rhizoma peanut during the summers of 1995 and 1996.
Samples were hand-plucked once each period based on visual appraisal of forage
consum ed by grazing cows. .....................................................................................118

3.9 Regression groupings and regression coefficients for predicting 1995 and 1996 pre-
and post-graze herbage mass of Tifton 85 bermudagrass and Florigraze rhizoma
peanut pastures...................................................................................................... 121

3.10 Disk meter estimates of the effect of forage species, stocking rate (SR), and
supplementation rate (SUP) on forage pre- and post-graze herbage mass (HM),
herbage allowance (HA), and dry matter intake (DMI) of grazing, lactating Holstein
cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut during the
sum m ers of 1995 and 1996......................................................................................122

3.11 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on milk
income minus supplement costs (MIMSC), assuming supplement intake
proportionate to LS means of milk production within a given SUP treatment and
calculated on both per cow and per land area bases.. .............................................126

4.1 Supplem ent ingredients......................................................................................... 133

4.2 Chemical composition, and nutritive value of supplement, corn silage and
berm udagrass pasture............................................................................................ 133

4.3 Influence of housing (0800 to 1500 h on pasture or in barns with fans and
sprinklers), bST, and bST with supplemental silage on organic matter intake (OMI)
of Holstein cows grazing Tifton 85 bermudagrass pastures. ................................146

4.4 Influence of housing (0800 to 1500 h on pasture or in barns with fans and
sprinklers), bST, and bST with supplemental silage on milk production and
composition of Holstein cows grazing Tifton 85 bermudagrass pastures .............151

4.5 Calculated daily intake of nutrients by cows grazing Tifton 85 bermudagrass (BG)
pastures and not treated (-bST) or treated (+bST) with exogenous growth hormone.
An additional treatment tested the effect of feeding corn silage (Silage) to cows
treated w ith bST.........................................................................................................153

4.6 Influence of housing (0800 to 1500 h on pasture or in barns with fans and
sprinklers), bST, and bST with supplemental silage on body weight (BW), body
condition score (BCS), respiration rates (RR), and concentrations of plasma insulin
and insulin-like growth factor-1 (IGF-1) of Holstein cows grazing Tifton 85
berm udagrass pastures.............................................................................................156






viii















LIST OF FIGURES

Figure page

3.1 Interaction of forage [Tifton 85 bermudagrass (BG) or Florigraze rhizoma peanut
(RP)] and year (1995 or 1996) on production of milk, 4% fat corrected milk (FCM),
and m ilk fat and milk fat percent. .........................................................................92

3.2 Interaction of forage, stocking rate (SR), and year on milk and 4% fat corrected milk
(FCM) yields and body weight change (DBW). Forages were Tifton 85
bermudagrass and Florigraze rhizoma peanut. Low and high SR for BG were 5.0
and 7.5 cows/ha in 1995 and 7.5 and 10.0 cows/ha in 1996. Low and high SR for
RP were 2.5 and 5.0 cows/ha in 1995 and 5.0 and 7.5 cows/ha in 1996. .................93

3.3 Interaction of supplementation rate and forage species on production of milk, 4% fat
corrected milk (FCM), milk fat, and protein. Supplementation rates were 0.33 (Lo)
and 0.5 (Hi) kg of supplement per kg of daily milk production. Forage species were
Tifton 85 bermudagrass and Florigraze rhizoma peanut ........................................95

3.4 Interaction of supplementation rate and year on production of 4% fat corrected milk
and milk fat, and percentages of milk fat and protein. Low (Lo) and high (Hi)
supplementation rates were 0.33 and 0.5 kg of supplement per 1 kg of daily milk
production, respectively......................................................................................98

3.5 Interaction of parity, year, and supplementation rate on production of milk, 4% fat
corrected milk (FCM), and milk fat and milk fat percent. Low (Lo) and high (Hi)
supplementation rates were 0.33 kg and 0.5 kg of supplement per kg of daily milk
production. Supplementation rates did not differ by year (1995 or 1996)...............99

3.6 Interaction of parity, forage, and stocking rate on body weight change (ABW).
Average low (Lo) and high (Hi) stocking rates were 6.25 and 8.75 cows/ha for
Tifton 85 bermudagrass (BG) and 3.75 and 6.25 cows/ha for Florigraze rhizoma
peanut (RP) pastures. Stocking rates were the same across parities ...................104

3.7 Interaction of supplementation rate and year on changes of body condition score
(ABCS - 5 point scale) and body weight (ABW). Low (Lo) and high (Hi)
supplementation rates were 0.33 and 0.5 kg of supplement per kg of daily milk
production. .........................................................................................................104



ix









3.8 Interaction of forage, supplementation rate, and year on body weight change (ABW).
Forages were Tifton 85 bermudagrass and Florgraze rhizoma peanut. Low (Lo) and
high (Hi) supplementation rates were 0.33 and 0.5 kg of supplement per 1 kg of
daily milk production. Supplementation rates did not differ by year (1995 or
1996)........................................................................................................................106

3.9 Interactions of parity, forage, and stocking rate (SR) on forage and total organic
matter intake (OMI) and forage and total OMI as a percent of body weight
(OMIPBW). Forages were Tifton 85 bermudagrass (BG) or Florigraze rhizoma
peanut (RP). Average low and high SR for BG pastures were 6.25 and 8.75
cows/ha. Average low and high SR for RP pastures were 3.75 and 6.25 cows/ha.
..................................................... . . . .................................................................112

4.1 Vibracorder charts for cows treated with bST and housed in barns from 0800 to
1500 h (A) and for cows housed on pasture (B). Note the greater grazing intensity
for cows housed in the barn during the day...................................................147

4.2 Effect of housing on body temperatures of cows measured over a 24-h period and
averaged over bST treatment regimes...................................................................... 160

4.3 Effect of bST on body temperatures of cows measured over a 24-h period and
averaged over daytime barn and daytime housing regimes...................................162

4.4 Regression equation estimates of body temperatures of cows measured over a 24-h
period and showing interaction of bST (+ or -) and housing treatments .................164

4.5 Effect of barn plus bST (B+) vs. barn plus bST plus silage (B+S) treatment on body
temperatures of cows measured over a 24-h period...............................................165




















x














KEY TO ABBREVIATIONS
ADF - acid detergent fiber
ADG - average daily gain
BCS - body condition score
BG - Tifton 85 bermudagrass
bST - bovine somatotropin
BW - body weight
CP - crude protein
DE - digestible energy
DM - dry matter
DMI - dry matter intake
FCM - fat corrected milk
FI - forage intake
GT - grazing time
HA - herbage allowance
HM - herbage mass
IB - intake per bite
IGF-1 - insulin-like growth factor 1
IVDMD - in vitro dry matter digestibility
IVOMD - in vitro organic matter digestibility
ME - metabolizable energy
MUN - milk urea nitrogen
MY - milk yield
N - nitrogen
NAN - non-ammonia nitrogen
NDF - neutral detergent fiber
NEL - net energy of lactation
NEFA - non-esterified fatty acid
NRC - National Research Council
NSC - non-structural carbohydrate
OM - organic matter
OMI - organic matter intake
PUN - plasma urea nitrogen
RB - rate of biting
RP - Florigraze rhizoma peanut
SCC - somatic cell count
SR - stocking rate
SUP - supplementation rate
THI - temperature-humidity index
TMR - totally mixed ration
TT - temperature transponder

xi














Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

GRAZING SYSTEMS AND MANAGEMENT STRATEGIES FOR
LACTATING HOLSTEIN COWS IN FLORIDA

By

John Herschel Fike

December, 1999


Chairman: Charles R. Staples
Major Department: Dairy and Poultry Sciences

Two experiments tested effects of two pasture forage species, the legume rhizoma

peanut (RP; Arachis glabrata) or bermudagrass (BG; Cynodon spp. cv. 'Tifton 85'), two

supplementation rates (SUP; 0.33 or 0.5 kg/kg of milk), and two stocking rates (SR) on

performance of mid-lactation Holstein cows.

The RP supported more milk per cow (17.3 vs. 16.3 kg/d), but less milk per

hectare than BG pastures. With each additional kg of supplement fed above the low SUP,

cows produced an additional 0.87 kg of milk/d if grazing BG vs. an additional 0.43 kg of

milk/d if grazing RP.

Respiration rates and body weight (BW) losses generally were greater when

treatments stimulated milk production. Optimum SR for BG and RP pastures were

approximately 10 and 5 cows/ha. Cows grazing RP had greater forage (11.3 vs. 7.6 kg/d;



xii








2.26 vs. 1.52% of BW) and total (17.7 vs. 13.5 kg/d; 3.54 vs. 2.70% of BW) organic

matter intakes (OMI). Increased supplement provision increased daily OMI, but

decreased forage intake. Substitution of forage with supplement (kg/kg) was 0.51 for RP

and 0.18 for BG.

A third experiment tested the effects of housing pasture-based cows in barns or on

pasture from 0800 to 1530 h. Within housing treatments, cows did or did not receive

bST. A fifth treatment tested the effect of feeding silage to barn-housed cows injected

with bST.

Intake of pasture and milk production were similar for both housing managements

although cows housed in barns spent less time grazing. Treatment with bST increased

milk production (18.1 vs. 16.6 kg/d). Production was unaffected by silage intake.

Housed cows and bST-treated cows maintained or gained BW. Respiration rates

and body temperatures were greater for pastured cows, and body temperatures were

greater in cows given bST.

Improved grasses in combination with large amounts of supplemental feeds are

likely most suited for pasture-based dairy production systems in Florida. Providing fans

and sprinklers to relieve heat stress and injecting with bST was only moderately effective

to stimulate milk production of midlactation cows in a pasture-based system.












xiii














CHAPTER 1
INTRODUCTION


While use of pasture-based production systems is the norm for beef production in

the U.S., pasture use for dairy production was all but abandoned until the mid- to late

1980s when management of pastures using intensive rotational stocking began to be

adopted. During a time of financial duress, pasture systems garnered renewed interest,

primarily due to perceptions that they have reduced production costs, require less initial

investment, have less demanding labor requirements, and are more environmentally

sound than production with confined-housing.

Information regarding their use is limited, however, particularly for producers in

the Southeast. Regardless of the production system, producers in the Southeast must

overcome several challenges to be successful. The lesser quality of perennial forages

adapted to the region and the negative effects of high heat and humidity on animal

performance are the primary limitations to production. Thus, information in this arena is

vital because the challenges to production likely are more formidable for pasture-based

dairies.

Forages adapted to the region typically are of less quality than cool-season species

due to greater concentrations of fiber and lower concentrations of digestible nutrients.

Other potential limitations of pasture-based systems include variability in forage supply

and nutritive value, both of which are highly dependent upon climatological conditions.




1






2

Pasture-based production systems are energetically demanding of the animal.

Cows face greater energy requirements for walking and foraging in addition to energy

demands for dissipation of heat load during periods of high ambient temperature and high

humidity. Such requirements may limit severely the nutrients available for production.

Production potential of pasture-based dairies may also be affected by numerous

management practices. Issues of particular concern include suitability of available forage

species, types and amounts of supplement to feed, appropriate stocking rates, effects of

management strategies upon animal production and physiology, and the interactions of

these factors.

The studies described herein were conducted to test the effects of forage species,

supplementation rate, stocking rate, and some potential management practices on animal

intake and performance. Some simple estimates of income are also reported along with

concluding statements regarding the viability of such systems.














CHAPTER 2
LITERATURE REVIEW

Since the 1980s, the economics of dairying in the United States has put farmers in

a severe cost-price squeeze (Muller et al., 1995). Reducing feed costs has become critical

because these costs are estimated to account for 50 to 60% of operating costs (Elbehri

and Ford, 1995). To cope with this economic reality, many dairies using confined

housing have increased herd size. Technological advances have helped drive this change

(Lanyon, 1995), and typically are most profitable when employed on a large scale

(Thomas et al., 1994). Increasing herd size can help farmers reduce feed costs per cow

by increasing purchasing power with larger commodity purchases (Lanyon, 1995).

Further, fixed costs can be reduced by increased use of farm equipment and greater

throughput of cows through the milking parlor. These management changes rely upon

increased efficiencies and greater milk production to increase profit but both "increased

herd size and increased technological sophistication have resulted in dairy production

becoming an even more capital-intensive agribusiness" (Thomas et al., 1994, p. 1).

Facing the same economic and environmental pressures as other dairies but

without the ability or desire to expand the size of their herd and facilities, some producers

have opted for another way to improve profitability. Their strategy relies on reduced

levels of inputs and lower cost structures (Parker et al., 1993). This is attempted by use

of alternative forage feeding systems, particularly, intensive grazing (Elbehri and Ford,

1995). "Smaller farms have been subjected to greater financial stress than properties



3






4

supporting large herds" (Parker et al., 1992, p. 2587, citing Hallberg and Partenhiemer,

1991, and citing Kaffka, 1987), thus it is understandable that "most interest in grazing

systems has been shown by dairy producers with herds of fewer than 100 cows" (Parker

et al., 1992, p. 2587).

Milk production per cow or farm may decrease in grazing herds as producers

change from management of confined housing to management of grazing systems, but

graziers assume that the decrease in production costs is greater than the cost of lost milk

production, thus garnering greater net profit. Some studies (Emmick and Toomer, 1991;

Parker et al., 1992) have indicated returns per cow can increase from $85 to $165 with

the use of pasture (Muller and Holden, 1994). Other reasons cited for choosing pasture-

based production systems include reduced labor, best land use, improved cow health, and

reduced manure handling, as well as improved quality of lifestyle for the owner/manager

(Loeffler et al., 1996). One survey indicated that total hours of labor were not decreased

in grazing-based systems, but that time devoted to various tasks changed as that activity's

importance in the system changed (Loeffler et al., 1996).

Climatic Challenges to southeastern Dairies

Regardless of the production system, the climate of the Southeast presents unique

challenges for producers in the region. Of particular concern is the effect of heat and

humidity on both plants and livestock. The effect of the climate may be more adverse for

animals on pasture.

Climatic Effects on Forages

The perennial, warm-season forages adapted to the Southeast are typically of

lower nutritive value than either cool-season perennials or warm-season annuals






5

[National Research Council (NRC), 1989]. Even at similar NDF and lignin

concentrations, warm-season grasses are less digestible than cool-season grasses (Barton

et al., 1976; Mertens and Lofton, 1980). Minson and McLeod (1970) reported that the

mean DM digestibility coefficient for tropical grasses was 13 percentage units less than

that of temperate grasses. When grown at warmer temperatures, forages have greater

concentrations of fiber and are less digestible than those grown under more temperate

conditions (Deinum and Dirven, 1976; Fales, 1986). Greater humidity also creates

potential for additional plant stresses via increased phytopathogen load.

For southeastern producers using confined-housing systems, growing high quality

forages may be of limited concern. Despite the climatological challenges, acceptable

quality maize (Zea mays L.) silage can be grown locally and high quality alfalfa

(Medicago sativa L.) hay is available for purchase from growers in western states.

Moreover, producers in the region using confined-housing frequently use by-product

feeds such as brewer's and distiller's grains, whole cottonseed, and cottonseed hulls.

These feeds may supply substantial portions of the diet's roughage, potentially reducing

the need for homegrown forages.

The ability to grow superior quality forages is of particular concern for graziers

(producers using grazing systems). Perennial, warm-season forages typically are of

lower quality than cool-season forages as measured by comparisons of animal

performance (Galloway et al., 1993b). Stobbs (1976, cited by Ruiz, 1983) showed that

Jersey cows grazing immature tropical pastures produced approximately 60% as much

milk as those grazing temperate pastures. Cool season species generally are considered

to be of greater quality due to greater digestibility because of differences in the relative






6

amount and arrangement of tissues (Akin, 1986a,b, p. 194). However, warm-season

species do have the agronomic advantage of being adapted to the region. Thus, despite

their lower quality, forages such as bahiagrass (Paspalum notatum) and bermudagrass

(Cynodon dactylon (L.) Pers.) are the foundation of forage production systems for

grazing animals in the Southeast.

Other forage quality concerns for graziers may include pasture variability in

supply and nutritive value over the course of the growing season (Holt and Conrad,

1983). Changes may correspond with changes in climatic conditions, such as

temperature, soil moisture, leaf/stem ratio and the proportions of dead leaves in the sward

(Beaty et al., 1982; Henderson and Robinson, 1982). Grazing dairies, reliant upon locally

grown perennial forages, thus are likely more susceptible to changing forage quality than

many dairy farms using confined housing.

Climatic Effects on Animals

Higher environmental heat and humidity affect dairy cows negatively by limiting

their ability to dissipate body heat. In such circumstances, cows are likely to decrease

DMI, and in more severe conditions may also suffer from heat-related disorders such as

respiratory alkalosis/metabolic acidosis, ketosis related to excessive decrease of DMI,

and laminitis associated with feeding diets of large concentrations of grain (Sanchez et

al., 1994; Nocek, 1997; Orskov, 1999). Heat stress also impairs the cow's reproductive

performance and embryo survival (Thatcher and Collier, 1986; Wolfenson et al., 1988;

Ealy et al., 1993).

Heat stress can be mitigated with cooling technologies. The technological

advances in confined-housing systems include well-ventilated barns with high roofs and






7

high-speed fans with wetting mechanisms (Flamenbaum et al., 1986; Chen et al., 1993;

Chan et al., 1997). Such facilities increase shade and evaporative cooling, providing

relief from excessive ambient temperatures.

Ways to cool cows on pasture are limited, however. Fixed and mobile shade

structures, trees, cooling ponds, and strategic movement (e.g. allowing cows access to

cooling barns during times of high ambient temperature) represent the major methods

used to reduce heat stress of pastured animals. In addition, pastured cows face additional

heat stress from the heat of activity caused by grazing and walking to and from the parlor.

Thus, the effect of heat stress is likely of greater concern for graziers.

Recent literature regarding grazing dairy systems in the southeastern United

States is limited, although results with beef steers on pasture may have application. The

majority of data pertaining to dairy cow grazing in North America has been published by

researchers working in the Northeast and Midwest under very different environmental

conditions. Some research from Australia and other tropical areas may be applicable to

the southeastern environment, but the forages grown are typically of different genera and

the amounts of concentrate fed are less than the amounts provided by U.S. producers.

Thus, while pasture-based dairies may be a viable alternative to confined housing

systems in the Southeast, more information on factors affecting their viability is needed.

Energy Considerations for the Grazing Ruminant

Energy requirements for grazing cattle are likely greater than requirements for

cattle housed in confinement (Van Es, 1974; NRC, 1989). For lactating cows housed in

confinement, the NRC (1989) estimates that the maintenance requirement is 80 kcal of

NEL/kg of BW 0.75 (Moe et al., 1972) which includes an activity requirement of 10%.






8

Based on work by Brody (1945), the NRC (1989) recommends an additional allowance

of 3%/km walked per day and an added 10% maintenance allowance/d for cows grazing

"good pasture." Brody (1945) estimated that standing (vs. lying down) increases energy

expenditure by 9%, but research that is more recent suggests this is an underestimate

(Clark et al., 1972; Vercoe, 1973). Robbins (1993) suggested that a better estimate of the

cost of standing versus lying (including small position changes) would be 20%. This

does not mean to suggest that the grazing animal necessarily stands more than an animal

in confined housing, but it does emphasize the point that energy needs for grazing

ruminants are likely underestimated by some current energy system recommendations.

Depending on the pasture or environmental conditions, the requirements might be

expected to be much greater (Osuji, 1974; DiMarco and Aello, 1996; Noller, 1997, cited

by Reis, 1998). Noller (1997, cited by Reis, 1998) estimated that increasing the energy

requirements by 10 to 20% is probably not enough for cattle grazing tropical forages

under tropical conditions. DiMarco and Aello (1996, cited by Reis, 1998) indicated that

for grazing cattle, maintenance energy might need to be increased 27 to 30%.

The energy requirements of grazing animals may be expected to increase if

animals require more time for foraging, if topography is hilly, or if environmental

conditions compromise thermoregulation (Robbins, 1993). Additionally, the efficiency

associated with consuming the diet is likely reduced. Osuji (1974) reported that sheep

fed fresh grass required approximately 12% more metabolizable energy than those fed an

equivalent amount of dry matter as dried grass. The increase was due primarily to the

additional time required to achieve equal DMI.






9

Grazing is energetically expensive for the cow, and "any improvement in

performance will hinge upon increasing energy intake or increasing the efficiency with

which ingested energy is utilized" (McCollum and Horn, 1990, p. 1). Even with

relatively high quality cool-season pastures, animal performance is often less than might

be expected given the chemical composition and nutritive value of the forage. This may

be due to the lower efficiency of utilization of fresh forage (Osuji, 1974) or to differences

in energy intake (Kolver and Muller, 1998). Kolver and Muller (1998) examined the

reason behind performance differences of cows consuming high quality pasture and those

eating a totally mixed ration (TMR) primarily composed of corn and legume silages,

high moisture shelled corn, whole cottonseed, soybean meal, legume hay and wheat

middlings. The concentration of NEL of the diets was similar (1.63 and 1.65 Mcal/kg of

DM for pasture and TMR), but NEL intake was less (32.4 vs. 40.2 Mcal/d) for cows

grazing pasture. The apparent DM digestibility of the diets was approximately equal (77

and 76% for pasture and TMR, respectively), but dietary NDF and ADF concentrations

were 40 and 20% greater for the pasture diets. The authors reported that differences in

intake rather than differences in energy between pasture and TMR limited energy intake

by pastured cows.

Some Animal and Nutritional Factors Influencing Feed Intake

Understanding the mechanisms regulating feed intake historically has been a key

research objective, because the "amount of forage consumed is the major determinant of

production by animals fed forage-based diets" (Buxton et al., 1995, p. 10). As much as

60 to 90% of the variation in digestible energy intake may be due to animal variability,

with 10 to 40% due to diet digestibility (Crampton et al., 1960; Reid, 1961). Though






10

intake and digestibility may be strongly correlated (Anderson et al., 1973), intake of

digestible nutrients "is affected more by differences in intake than by differences in

digestibility" (Waldo, 1986, p. 618).

Much effort has been made to determine whether voluntary intake was limited

primarily through physical or physiological control mechanisms. Conrad et al. (1964)

examined results from 114 trials with lactating cows and reported the relative importance

of physical and physiological factors regulating feed intake changes as diet digestibility

increases. Intake of diets having between 50 and approximately 67% digestibility was

thought to be limited by physical factors such as digestibility of a feed and its rate of

passage through the digestive tract. Intake of diets having a digestibility greater than

67% was limited primarily by physiological control mechanisms. This "breakpoint

[67%] is likely a convenient mathematical simplification" (Allen, 1996, p. 3064) because

voluntary intake is likely regulated by numerous, integrated signals from the intestinal

tract and digestive organs (Forbes, 1996). Regardless of the breakpoint or precise

mechanisms of intake control, research supports the theory that intake often is restricted

by rumen distention, i.e. physical constraint (Balch and Campling, 1962; Grovum and

Phillips, 1978; Friggens et al., 1998).

Constraints on feed intake by physical mechanisms are, in part, a function of

digestive tract capacity and are related to energy balance (Allen, 1996). Voluntary DMI

of cows in negative or slightly positive energy balance decreased in response to inert fill

added to the reticulorumen but was unaffected in cows having greater positive energy

balance (Johnson and Combs, 1991, 1992; Dado and Allen, 1995). This is of particular

relevance for the grazing dairy cow which has increased maintenance energy








requirements because of increased walking and grazing activities (NRC, 1989). The

increased energy requirements of these activities may lower energy balance, putting

downward pressure on voluntary DMI.

Some have suggested that intake capacity is in part a function of the energy

required for production. For example, increased rumen volume has been attributed to the

increased energy demand of lactation (Tulloh et al., 1965), and Redmond (1988, cited by

Allen, 1996) reported that weight of reticulorumen contents increased more than 40% in

the first 2 months of lactation in dairy cows. In a comparison of rumen load and

clearance between lactating and non-lactating sheep, Weston and Cantle (1982) showed

that both were increased by lactation.

Goetsch et al. (1991, p. 2635) reviewed 18 Latin-square experiments to

"determine effects of various feedstuffs ... on intake and digestion by Holstein steer

calves ingesting bermudagrass hay ad libitum." The authors reported that fiber fractions

in the feeds were of negligible importance and the coincident "absence of strong

relationships between bermudagrass composition and digestion ... implies that variation

in chemically fractionated fiber components of bermudagrass had little impact on nutrient

status and (or) gut fill regulation of DMI" (p. 2639) further noting that growth and energy

utilization may have been involved with regulating DMI.

This remains a subject of debate, however. Friggens et al. (1998) fed constraining

or non-constraining diets over a lactation, switching the diets of half the dairy cows in

each test group at 153 days in milk. Diets were composed of grass silage and a barley-

based concentrate. The NDF concentrations of the diets were approximately 37 and 43%

and the ADF concentrations were approximately 21 and 26% for the low- and high-fill






12

diets, respectively. Milk production was greatest from cows initially fed the non-

constraining diet, but when switched to a constraining diet, intake declined rapidly "even

though, immediately prior to the changeover, cows on [the non-constraining] diet had a

much greater milk yield and thus a much greater presumed energy requirement," (p.

2236). The authors concluded that milk "yield had no effect on the capacity of the cow to

consume a constraining diet... [and] intake capacity is independent of cow

performance" (p. 2237). The authors noted that intake capacity might be expected to

change during very early and very late phases of lactation as others have shown (Hunter

and Siebert, 1986; Stanley et al., 1993).

The results of Friggens et al. (1998) underscore the importance of dietary factors

that affect gut fill. Of a forage's intrinsic characteristics, fiber is thought to be the main

component limiting voluntary intake due to its "filling properties" (Jung and Allen,

1995). In 1965, Van Soest reported large negative correlation between percent of plant

cell wall constituents (NDF) and voluntary intake. Neutral detergent fiber represents the

total cell wall fraction of a feedstuff, and is considered a mechanism controlling forage

intake by ruminants (Waldo, 1986; Jung and Allen, 1995).

Intake of perennial, warm-season grasses in the Southeast typically is considered

limited by physical (fill) effects due to their high fiber concentrations and low

digestibilities. The National Research Council recommends dietary NDF concentrations

of 25 to 28% in rations for lactating cows (NRC, 1989), but the majority of summer,

perennial grasses common to the region generally have concentrations of NDF in excess

of 70% (DM basis). If warm-season perennial grasses are the sole forage source in the

diet, their large NDF concentrations might represent a steep hurdle for producers trying to






13

maintain adequate intake for high-producing dairy cows. However, the strength of the

negative relationship between fiber and intake (or digestion) for animals consuming

bermudagrass has been questioned (Golding et al., 1976a; Jones et al., 1988; Goetsch et

al., 1991) and bears further investigation.

Some Non-Nutritional Factors Affecting Behavior and Forage Intake Of Grazing
Ruminants

Mechanistic Components of Forage Intake

A mechanistic or mathematical model of forage intake by the grazing ruminant

was first put forth by Allden and Whittaker (1970) following the work of Allden (1962).

The model reduces forage intake (FI; kilograms) to the product of the main components

of grazing behavior; that is time spent grazing (GT; minutes or hours), rate of biting

during grazing (RB; bites per minute), and the intake of forage per bite (IB; grams).

Hence the equation: FI = (IB*RB*GT)/1000.

Research indicates that if herbage mass is maintained above amounts which

restrain intake, animals can maintain fairly constant amounts of intake by adjusting IB,

RB, and GT (Willoughby, 1959; Allden and Whittaker, 1970). Of these three variables,

IB is the most affected by sward conditions (Hodgson, 1985). Intake per bite "normally

falls sharply as herbage mass or sward height declines" (Hodgson, 1985, p. 340, citing

Allden and Whittaker, 1970 and Hodgson, 1981). Negative correlations between IB and

herbage on offer (r = -0.61) and sward bulk density (r = -0.70) have been shown with

tropical pastures (Stobbs, 1973). Sward height may be positively related to intake of

warm-season species (Flores et al., 1993), though universality is unlikely when one

considers the range in morphologies of tropical forages.






14

Leaf distribution in the canopy has the greatest influence on IB, (Stobbs, 1973;

Hodgson, 1985) because IB is the product of "bite volume (depth x area) and the bulk

density (weight per unit volume) of herbage within the sward horizons encompassed in a

bite" (Hodgson, 1985, p. 342-343). Other factors that influence IB include sward height,

presence of stem and pseudostem horizons, and the height of these horizons relative to

total sward height, all of which affect ease of prehension and depth of biting into the

canopy (Flores et al., 1993).

Sward maturity has strong effects on efficiency of the grazing activity due to its

effect on leaf distribution in the canopy (Stobbs, 1973; 1974a). Stobbs (1973) studied IB

in dairy cows grazing tropical swards at 2, 4, 6, or 8 wk of regrowth. The IB was limited

by the low yield and density of herbage at 2 wk of age even though pastures contained

82% leaf. Intake per bite increased at 4 wk with increasing available herbage, but

decreased with increasing maturity (6 and 8 wk) primarily due to decreasing leaf:stem

ratio. Mean IB at 2, 4, 6, and 8 wk were approximately 0.23, 0.27, 0.17, and 0.15 g

OM/bite. This research also compared responses between species (Setaria anceps and

Chloris gayana) that showed that sward maturity affected IB differently between species

(Stobbs, 1973). Mayne et al. (1997) reported intakes of 0.4 to 1.1 g of DM/bite for cows

grazing ryegrass pastures. These values are quite high, but their estimates were made

indirectly. Pulido and Leaver (1997) did not report IB but reported rates of intake of

perennial ryegrass of 20 to 30 g of OM/min. Assuming a bite rate of 55 bites/min, IB

ranged from 0.36 to 0.55 g of OM/bite.

Research into the effect of progressive defoliation on intake of tropical pastures

showed that cows selected more than 80% leaf from the upper layers of the sward in the






15

early stages of defoliation (Chacon and Stobbs, 1976). Work by Roth et al. (1990)

showed that cattle continued to select large proportions of leaf even as leaf percentage of

the canopy decreased. As the quantity of leaf decreases, animals increased GT, RB, and

total number of eating bites, but these activities were not sustained as pastures became

severely defoliated (Chacon and Stobbs, 1976). Chacon and Stobbs (1976) suggested

that leaf yield would give a better expression of forage on offer than the more commonly

used "grazing pressure".

Biting rates between 51 and 63 bites/min were reported by Chacon and Stobbs

(1976) when cows grazed warm-season forages. Rates as great as 90 bites/min on

temperate pasture were reported by Hodgson (1985) but this likely represents total jaw

movements. Rates of biting declined linearly with increasing length of grazing period

when forage was not limiting (Stobbs, 1974b). Greenwood and Demment (1988)

compared intake behavior ofunfasted steers or those fasted for 36 h. They reported that

ingestive bites increased approximately 30% (38.9 vs. 29.7 bites/min) due to fasting, but

this response was seen during the morning only.

Under forage-limiting conditions with temperate pastures, RB increases as IB

decreases, but RB rarely increases enough to maintain herbage intake (Allden and

Whittaker, 1970; Hodgson, 1981). Moreover, the changes in RB likely are due to the

manipulative jaw movements required to harvest the forage (Stobbs, 1974b; Chambers et

al., 1981). With temperate pastures, RB may increase when forage is limited due to a

reduction in manipulative jaw movements (Hodgson, 1985), but low availability of

herbage would likely decrease ingestive RB with most tropical pastures, as animals

would spend more time selecting leaf material.






16

In a comparison of grazing of cool- and warm-season grasses, Stobbs (1974b)

reported that RB was much less with Abyssinian barley (Hordeum vulgare) than with S.

anceps, and the decline in RB over time was less with the tropical grass. Cows grazing

barley were observed grasping large mouthfuls of forage with their tongues and chewing

the forage several times before swallowing, whereas cows grazing S. anceps took small

amounts of herbage and their mastication bites accounted for less than 5% of total

grazing bites.

A more apparent behavioral response to decreasing IB is an increase in GT, but

the degree of this compensatory mechanism is also limited, such that daily FI variations

may reflect closely the observed variations in IB (Hodgson, 1985). Stobbs (1974a)

reported that cows rarely take more than 36,000 prehension bites in a day. Based on this

value and the biting rates reported by Chacon and Stobbs (1976), the upper limit to daily

grazing time would be 10 to 12 h, though the latter authors reported 39,600 prehension

bites/d in one study, and GT as great as 800 min/d with cattle grazing tropical legumes

have been reported (Smith, 1959; Stobbs, 1970). In the study by Chacon and Stobbs

(1976), average maximum GT reported was 10.75 h/day, and GT patterns were

curvilinear. Cows grazed approximately 9 h during the first few days on a new pasture.

Grazing time increased to a maximum between days 3 through 6 then subsequently

declined "despite a reduction in the quantity of herbage on offer in the later stages of

defoliation" (Chacon and Stobbs, 1976, p. 714).

Work by Pulido and Leaver (1997) has shown that level of performance affects

intake. The authors measured intake of cows having initial milk yields of 21 or 35 kg/d.






17

On average, cows grazed an additional 2.45 min for each additional kg of daily milk

produced.

Grazing time also may be dependent upon the system of grazing management

utilized. Le Du et al. (1979) reported that with rotational stocking, cows did not

compensate for decreased herbage availability with increased GT. Rapid defoliation with

strip-grazed pastures would be expected to make large alterations in canopy structure,

requiring animals to increase manipulative jaw movements (Hodgson, 1981) in order to

consume a large proportion of leaf material.

Daylight and Temperature

In general, cows graze primarily during daylight hours, exhibiting strong

periodicity in grazing behavior (Hughes and Reid, 1951; Stobbs, 1970). Adams (1985)

noted that most grazing behavior studies show that cows typically have a major grazing

period occurring early in the morning and one later in the afternoon. Additional

intermittent grazing bouts occur throughout other periods of the day and night.

Phillips (1989) reported marked reluctance of cattle to eat at night (Phillips and

Denne, 1988) even in hot climates (Alhassan and Kabuga, 1988), but this may be true

more for steers than for lactating animals which likely are under greater heat strain.

Stobbs (1970, p. 242) reported that "during the night cows grazing tropical pastures

behave more as individuals" and that "high yielding cows can spend a considerable

length of time grazing during this period." While Stobbs (1970) indicated that night

grazing might be limited to 30% of grazing time, work by Seath and Miller (1947)

indicated that in hot, humid environments (Louisiana), cows would graze more during

night time. Part of the differences in these studies may be in the designation of night,






18

however, and Stobbs (1970) noted that greater than 50% of grazing would often occur

between a.m. and p.m. milkings which occurred after dawn and before dusk, respectively.

Measurement of Forage Intake in Grazing Ruminants

Several methods of intake estimation for animals on pasture have been explored.

Each method employs different assumptions which must be met if the estimates are to be

valid (Moore, 1996).

Early attempts to estimate intake from individual animals included use of fecal

collection bags for total fecal collection. In addition to the potential for loss or urine

contamination due to poor design or lack of fit, the bags also have the potential to stress

the animal and to alter intake by changing grazing behavior.

To avoid such problems, other researchers cut and carried green pasture to

animals kept in confinement. Though this approach affords a great degree of precision, it

may be highly inaccurate because it reduces both the opportunity for selection and the

work required to harvest the forage. Experimental results are likely most affected when

swards are highly heterogeneous or when environmental factors or sward density would

have large effects on grazing behavior.

Marker technologies for the estimate of FI of grazing animals have been used

extensively. Markers are reference compounds used to investigate both chemical

(hydrolysis and synthesis) and physical (flow) digestive processes (Owens and Hanson,

1992). Fecal output (flow) is the measure of interest in the grazing animal because it can

be used to calculate intake using the following equation: FI (kg) = Fecal output (kg)/(100

- diet digestibility (%)).






19

Characteristics of an ideal marker were outlined by Owens and Hanson (1992)

and include the following traits: 1) it should be unabsorbable, 2) it should not affect or be

affected by animal or microbial digestive processes, 3) its flow should closely mimic that

of the material it marks, and 4) it must be analyzable with a specific and sensitive

methodology. No single marker currently meets all these criteria.

Both internal (a dietary fraction such as lignin or plant alkanes) and external (e.g.,

colored plastic chips or rare earth metals) markers have been employed. Use of either

type of marker relies upon an accurate estimate of its intake. This is controlled by the

researcher using external markers, but calculation of internal marker intake depends upon

accurate estimates of what the animal consumes. This may be a particular problem in

grazing situations where herbage consumed may not be the same as selected by the

researcher.

The external marker, Cr203, has been used extensively but its suitability has been

questioned (Ellis et al., 1980). The Cr203 does not associate with a particular liquid or

feed fraction and thus may settle out of the rumen contents and flow with large

variability, particularly when animals consume forage diets. Holden et al. (1995, p. 158)

worked with Cr203 and noted that significant "daily variation in DMI indicates that

analysis of composited samples of forages and feces for intake determination may not be

adequate for estimation of intake under grazing conditions." Another disadvantage of

using Cr203 is the multiple doses required over several days in order for Cr to reach

equilibrium concentrations in the digestive tract. Additional handling of animals is

undesirable, particularly when it has potential to disturb established patterns of grazing

behavior






20

More recently, use of pulse-dosed markers has gained acceptance. Animals are

dosed once with labeled feed fractions, and numerous fecal samples are collected over a

period of time long enough for the label source to have cleared the animal (typically 96 or

more hours). A nonlinear equation relating time after dosing to fecal [Cr] is used to

generate parameters for the estimation of fecal output (Pond et al., 1987). This method

has advantages in that the animals observed need only be handled once for dosing.

Fiber mordants, especially Cr-mordanted fiber, have been used as markers due to

the tenacity with which heavy metals bind the fiber particles. Disadvantages to this

method include the amount of effort involved in preparing mordanted fiber and the

potential negative effects of mordanting upon passage characteristics of the fiber particles

(Ellis et al., 1980).

Estimation of intake using external markers also requires an accurate estimate of

diet digestibility. Pasture samples may be obtained with surgically altered animals

(esophogeally- or ruminally-fistulated) or by hand plucking. Estimates of diet

digestibility are then obtained with in vitro techniques. Either method can be inaccurate

because potential exists for the sampling animal or for the researcher to select plant

material that is different from the plant material chosen by the animals being studied. If

supplements are fed, they may further alter diet digestibility, thwarting accuracy of

estimation.

With each of these methods, care must be taken during the laboratory analysis,

since feces must go through several preparation steps prior to the Cr analysis. An

additional difficulty with marker methodologies is the large number of samples which

must be collected and processed to make reasonable estimates of intake.






21

Herbage intake for individual animals also can be estimated with measurements

of grazing behavior, where FI = GT*RB*IB. This method may be beneficial in

overcoming any effects that supplemental feeds may have on estimates of diet

digestibility. However, all three measures for the estimate are quite variable over time,

especially with changes in sward conditions (Stobbs, 1973; Chacon and Stobbs, 1976;

Hodgson, 1985). Further, it is unlikely that a researcher would have access to more than

a few esophogeally-fistulated animals, limiting the number of estimates of IB, and the

fistulated animals may not be representative of the population of interest.

Another common method of estimating intake is by disappearance of herbage

mass (HM). On rotationally stocked pastures with short (1 to 3 d) grazing periods, HM is

estimated both pre- and post-graze with devices such as sward sticks, rising plate meters

or capacitance meters that allow rapid collection of numerous measurements. The

difference between pre- and post-graze HM (disappearance) is the herbage assumed eaten

by the grazing animal(s). Such estimates are more suitable when measuring group

intakes and are advantageous with respect to eliminating effects of supplement on forage

digestibility (Milne et al., 1981). However, their usefulness is limited to conditions

where pastures are uniform.

Herbage Allowance or Stocking Rate Effects on Forage Intake and Performance of
Ruminants

Due to the complexity of plant-animal interactions and the difficulty of obtaining

such information, most research regarding these relationships considers only the gross

effects of herbage allowance (HA; kg of forage DM/kg of animal live weight), grazing

pressure, or stocking rate (SR) on animal performance. Several models have been

proposed to describe these effects (Mott, 1960; Jones and Sandland, 1974; Mott and






22

Moore, 1985). In all the models, as SR increases, animal gain decreases but gain per land

area increases. A variant model by Jones (1981) suggested that at very low SR,

gain/animal also might be compromised, and Stuth et al. (1981) reported that at high

amounts of daily HA of bermudagrass pastures, defoliation efficiency is reduced.

Much of the debate among researchers appears to center on the nature of the

animal responses at the extremes of HA. Hart (1972) stated that animal gain decreases

linearly in response to increasing SR (animals/land area), and thus gain to land area is

necessarily curvilinear. Matches and Mott (1975, p. 205) noted that "the exact form of

trends reported in the literature have differences depending on the researcher and

circumstances of experimentation." The rapid declines in output (per animal or land

area) proposed by Mott (1960) are likely most applicable to limited-input, extensive

grazing systems (Pearson and Ison, 1997) unsuited for intensive milk production.

Contention also has arisen over the nature of DMI in response to HA. Hodgson

(1975, cited by Stockdale, 1985) reported that intake followed HA in a linear fashion.

Others have reported asymptotic intake responses to HA (Allden and Whittaker, 1970;

Stuth et al., 1981). Stockdale (1985) reviewed eight experiments under Australian

conditions and noted that though DMI of grazing dairy cows was reduced with

decreasing HA, the relationship was not always curvilinear. He noted that combining the

data from all the experiments resulted in a significant quadratic term. The intake

response to increasing HA reported by Le Du et al. (1979) was positive and asymptotic

and similar responses were reported in a review by Phillips (1989). However, the nature

of the response likely is linear over the range of SR typically used (Jones and Sandland,

1974).






23

As HA increases, forage intake increases, primarily due to increased opportunities

for diet selection (Le Du et al., 1979). Thus the nutritive value of forage consumed also

increases, though nutritive value of the total sward may decrease due to accumulation of

senescing or senescent leaves and stems (Hamilton et al., 1973; Hodgson, 1985).

Piaggio and Prates (1997) noted good correlation between steer gains and HA

within season on range pastures. The nature of the response was quadratic, but a

regression equation explaining the relationships between intake and HA or between gain

and HA over an entire year could not be fitted. Thus, the authors created a new variable,

corrected energy pressure. The product of HA and metabolizable energy (ME) of

herbage, corrected energy pressure was scaled for availability and possibility of selection

which was simplified to the proportion of green material in the sward. The relationships

between intake or gain and corrected energy pressure were strong (R2 > 0.82) and

curvilinear.

Phillips (1989) reviewed studies of lactating cows grazing temperate pastures and

producing approximately 15 to 18 kg ofmilk/d. He reported that to prevent a decline in

individual performance, minimum HA should allow for DMI of at least 40 g of OM/kg of

liveweight per day. This is in contrast with a value of 60 g of OM/kg of liveweight per

day suggested by Minson and Wilson (1994). Studies of cool-season pasture grasses

suggest that maximum intake occurs when HA is approximately twice intake (Le Du et

al., 1979), but HA required for maximum yield/cow may be greater with tropical pastures

(Stobbs, 1977). Cowan and O'Grady (1976) indicated that DMI was depressed due to

decreased grazing time when HM was less than 2000 kg/ha in tropical grass-legume

pastures.






24

The response of DMI to HA appears to vary depending upon length of the

experiment. Stockdale (1985) reported that average DMI was 2.9 kg/d greater with long-

term experiments than short-term experiments, regardless of the HA. The author

suggested that greater intake in long-term experiments was due to adaptation.

Stocking rate may have both short and long-term consequences for both pasture

and animal production, particularly for forage species that exhibit seasonal growth habits.

Intense grazing bouts during initial periods of growth may reduce reproductive tillering

and the deleterious effects of accumulated dead material in the sward later in the grazing

season (Michell and Fulkerson, 1987). Michell and Fulkerson (1987) observed that the

quantities of available green herbage were the same in pastures that had been subjected to

low or high SR (1.9 or 3.4 cows/ha) on ryegrass (Lolium perenne L.)-white clover

(Trifolium repens) pastures. However, quantities of dead herbage were greater in the low

SR pastures over most of the grazing season. Diet digestibilities between treatments were

similar, but production from cows on the low SR appeared compromised due to a

reduction of DMI.

Grazing intensity also affects botanical composition and herbage yield of grasses,

legumes, and weeds (Brougham, 1960; Michell and Fulkerson, 1987). Composition and

yield changes in response to SR are variable depending upon grazing events through the

season and emphasize the importance of management in maintaining high quality

pastures (Brougham, 1960). Because dead plant tissue (Hodgson, 1985) and fecal matter

(Phillips and Leaver, 1985) negatively affect intake and are more prevalent in the fall

than in the spring, Phillips (1989) suggested managing pastures for greater sward height

as the grazing season progresses.






25

Fales et al. (1995, p. 88) reported that SR was "a key management variable in

determining productivity and profitability of grazing systems but it has not been

adequately researched in the USA with high producing dairy cows." Castle et al. (1968)

reported that by increasing SR with lactating dairy cows on mixed temperate pastures

(primarily ryegrass, timothy, and white clover), herbage utilization was increased; output

per land area was increased approximately 28%, though at the expense of individual

animal performance. Stockdale et al. (1987, p. 927, citing Stockdale, 1985) stated that "it

is not possible to feed cows well on pasture alone if the herbage is to be adequately

utilized," and thus SR must of necessity be high. In order to maintain milk production

while optimizing pasture utilization, supplements must be fed.

Supplement Effects on Animal Performance with Particular Emphasis on Lactating
Cows in Pasture-Based Dairy Systems

Mott (1959) proposed that comparisons of forage quality are best expressed in

terms of differences in animal performance and gave guidelines for these comparisons,

including (but not limited to) no provision of supplemental energy or protein. However,

cows consuming only well-managed temperate pasture had intakes capable of supporting

as much as 28 kg of milk/d (Muller et al., 1995), yet the genetic potential of dairy cows

for milk production is much greater than this amount (NRC, 1989). Maximizing milk

production per animal has been the goal of most of the U.S. dairy industry, and this has

been facilitated by the availability of relatively inexpensive concentrate feeds. Thus,

forage quality for lactating dairy cows is rarely evaluated by Mott's (1959) guidelines.

The energy requirements of high producing dairy cows cannot be met by forages

alone (Galyean and Goetsch, 1993; NRC, 1989). Several studies have shown energy to

be the first dietary limitation to optimum performance of cows grazing N-fertilized






26

pastures (Royal and Jeffrey, 1972; Delgado and Randel, 1989; Davison et al., 1991;

Reeves et al., 1996).

To maximize the performance of animals on pasture, supplemental feeds

(primarily energy feeds) are required to balance or increase the nutrient supply (Leaver,

1985a,b; NRC, 1989; Muller et al., 1995). Without supplemental energy, milk

production may be maintained by excessive mobilization of fat stores. This may have

potentially negative consequences in that it may result in metabolic disorders such as

ketosis or fatty liver syndrome.

Although milk yield is the typical performance variable measured, reproduction

has been shown to be compromised in beef cattle when energy intake is limited

(Wiltbank et al., 1964). Muller et al. (1995) noted that reproductive performance of dairy

cows also may be compromised without supplemental energy if pastures are high in CP

due to the negative relationship between high rumen degradable protein and fertility in

the lactating cow (Ferguson and Chalupa, 1989).

Supplement Effects on Production

Though the feeding of supplements is a common practice, production responses to

supplement are inconsistent and may not be profitable. Citing Leaver et al. (1968) and

Journet and Demarquilly (1979), Meijs and Hoekstra (1984) reported that typical

responses were approximately 0.3 to 0.4 kg of milk per kg of supplement fed to cows

grazing adequate temperate pasture. In a summary of 12 papers, Combellas et al. (1979)

reported similar responses (0.34 kg of milk per kg of supplement) when cows grazed

tropical pastures. Davison et al. (1991) reported similar results but speculated that cows






27

were not adapted to high amounts of supplement (8 kg of DM/d) and that abundant

available herbage resulted in greater than normal substitution effects.

Ruiz (1983) suggested that one reason for "poor response to supplementation of

grazing cows [in some experiments] is the stage of lactation at which comparisons were

made." Ruiz noted that cows on research trials were often beyond peak of lactation and,

as cows approached the end of lactation, nutrients may have been more readily

partitioned to replenishment of body reserves rather than milk synthesis.

Studies by Jennings and Holmes (1984a) and Stockdale et al. (1987) confirmed

the theory of Ruiz (1983). Jennings and Holmes (1984a) found increased total intake and

increased milk production with supplement, but a concomitant decrease in milk fat

concentration resulted in no difference in FCM production. Cow BW increased with

supplement, indicating that the nutritional benefit of concentrate nutrients was not

reduced per se, but that nutrients were partitioned toward body reserve repletion.

Stockdale et al. (1987, p. 936) reported that "marginal return from feeding [concentrate

supplement] decreased as lactation progressed" whereas increases in BW due to

supplement were greatest for cows in the latter stage of lactation.

Feeding supplement to cows in the early lactation period may have strong,

positive residual effects on milk production in later lactation (Cowan et al., 1975;

Martinez et al., 1980). A comparison of supplement provision during the first 10 wk of

lactation vs. the whole lactation period showed that when given the same rate of

supplement through the whole lactation, cows produced only an additional 181 L of milk

in response to an extra 754 kg of concentrate (Martinez et al., 1980, cited by Jennings and

Holmes, 1984b). Lack of residual effect (Martinez et al., 1980) may have resulted from






28

ample HA that provided intake adequate for lower milk production found later in

lactation, a response also reported by others (Le Du et al., 1979; Poole, 1987).

Length of study may also be an important consideration for proper interpretation

of response to supplement when cows grazed tropical grasses. Jennings and Holmes

(1984b) found that in short-term studies (n = 18, average duration = 80 d), the average

response to supplements was 0.46 kg of milk/kg of supplement though they noted no

"consistent association between level of response to supplementary feeding and stage of

lactation," (p. 270). A review by Cowan et al. (1977) suggested responses of 0.3 to 0.6

kg of FCM/kg of supplement were common for studies of less than 60 d in duration.

In studies conducted over most or all of the lactating period, responses to

supplement were typically between 0.9 to 1.2 kg of FCM/kg of supplement (Cowan et al.,

1977; Cowan, 1985, cited by Davison et al., 1991; McLachlan et al., 1994). However, a

review by Jennings and Holmes (1984b) indicates greater variability of response should

be expected with complete lactation studies. The authors found the range of response to

supplement was 0.10 to 1.80 kg of milk/kg of supplement, with an average response of

0.82 kg of milk/kg of supplement. Jennings and Holmes (1984b) further noted that mean

SR was 4.2 cows/ha and average milk yield of unsupplemented cows was 2,560 kg of

milk /lactation. Such information serves as a reminder that factors such as pasture and

animal management and animal genetic capacity should be included in consideration of

response to supplement. For example, a review by Moran and Trigg (1989) comparing

response to concentrate feeding between U.S. and Australian cattle indicated that both

groups of cows responded well to concentrate up to 2 metric ton per lactation. However,

U.S. cattle were able to respond to concentrate up to 3.5 metric ton per year.






29

Several long-term studies (2250 d) have shown linear MY increases in response

to an increasing supplement rate (Cowan et al., 1977; Davison et al., 1991; McLachlan et

al., 1994). Others have reported a curvilinear response (Balch, 1967; Coulon and

Remond, 1991, Delaby and Peyraud, 1997).

Other factors which may affect the response to supplement include quality of

pasture and supplement, amount of pasture and supplement fed, and the degree to which

supplemental feeds replace pasture intake (Stockdale et al., 1987). Although feeding

supplement can cause numerous production responses (form and magnitude), the

variability of response is associated primarily with the effect of supplement on DMI.

Supplement Effects on Intake

Provision of supplement may increase, decrease or have no effect on forage or

total DMI (Moore, 1980). Forage intake may increase if a nutrient imbalance is

corrected, leading to increased passage rate due to greater microbial degradation of the

forage or stimulation of appetite. Generally, forage intake depressions occur when

supplements are fed with forages which have greater nutritive value (Blaxter and Wilson,

1963; Holmes and Jones, 1964; Leaver, 1973; Golding et al., 1976b; Arriaga-Jordan and

Holmes, 1986). Large differences in substitution rates have been reported and the effects

have greater relation to differences among forages rather than to differences among

concentrates (Waldo, 1986).

Golding et al. (1976b) tested the effects of grain supplement on forage intake

depression when the supplement was fed at approximately 50% of total digestible energy

(DE) intake. Bermudagrass harvested at four maturities (4, 6, 8, or 10 wk) was fed as

hay to wethers with or without supplement. With increased forage maturity, DE intake






30

decreased, without or with supplement. Feeding supplement reduced DE intake from hay

at all maturities but had the greatest depressing effect on DE intake of wethers fed the

highest quality (4-wk maturity) hay. When fed supplement, wethers fed the 4-wk

maturity hay decreased hay DE intake by 80 kcal/BW075 per day, while those fed the 10-

wk maturity hay had decreased hay DE intake by 1 kcal/BW075 per day. The increase in

DE intake due to supplement for the 4-wk maturity hay was approximately half that of

the 10-wk maturity hay (26 vs. 51 kcal/BW0O75 per day for 4- and 10-wk maturities,

respectively). Intermediate decreases in hay DE intake with concomitant increases in

total DE intake occurred when supplements were fed in combination with hays of

intermediate maturity.

Concentrates had limited effects on forage intake in a study by Galloway et al.

(1993a). The researchers compared five supplement combinations fed to Holstein steers

eating bermudagrass hay in confinement. The hay was of moderate quality, averaging

11.4% CP, 75% NDF, and 52% digestibility. Supplements, fed at 0.75% of BW, were

ground corn, dried whey, dried molasses product, or a combination of corn and whey or

corn and molasses. Although intake of bermudagrass as a percent of BW was

numerically less for all of the three corn-based supplements, only the corn plus molasses

treatment significantly decreased bermudagrass intake.

Several researchers have reported forage intake depressions that varied with the

amount of supplement fed (Campling and Murdoch, 1966; Tayler and Wilkinson, 1972;

Sarker and Holmes, 1974; Cowan et al., 1977; Combellas et al., 1979). Though forage

quality may affect the response of intake to supplement, Waldo (1986) noted that "total






31

dietary DMI is affected very little by forage quality" when diets contain very large (>

80% of DM) levels of concentrate.

Sarker and Holmes (1974) fed supplement in increments of 2, 4, 6, or 8 kg OM/d

to non-lactating cows grazing ryegrass. Though total OM intake (OMI) increased with

increasing amount of supplement, the average increase in intake was 0.46 kg of OM/kg of

concentrate OM fed.

Combellas et al. (1979) fed 0, 3, or 6 kg of concentrates to lactating heifers

grazing Cenchrus ciliaris pastures. Across rainy and dry seasons, herbage intake

decreased approximately 0.52 kg with each kg of concentrate fed, and the authors noted

that this agreed with the range of 0.41 to 0.60 kg estimated from the equations of Holmes

and Jones (1964) and Holmes (1976) for a forage of 65% digestibility.

Supplements frequently are fed to animals consuming bermudagrass, and

Galloway et al. (1993a, p. 173, citing Galloway et al., 1992) stated that "moderate dietary

levels of supplemental grain (e.g., 20 to 30%) can improve nutrient intake and

performance by cattle consuming bermudagrass." At greater amounts, nutrient digestion,

intake, or both, of the forage portion of the diet can be affected negatively.

Type of supplement fed also is an important factor with respect to substitution

effects. Mould and Orskov (1983) reported that feeding large amounts of rapidly

fermentable starch led to decreased intake. Meijs (1986) fed high-starch supplements

(containing corn and cassava) or high fiber supplements (containing beet pulp, palm

kernel expeller, soybean hulls, and corn gluten feed) to cows grazing predominantly

perennial ryegrass swards. Supplement intakes were 5.5 and 5.3 kg of OM/d with forage

intakes of 11.5 and 12.6 kg of OM/d for high and low starch treatments, respectively.






32

Average forage substitution rate for animals receiving the starchy supplement was 0.45

kg of herbage/kg concentrate vs. 0.21 kg of herbage/kg of concentrate for animals

receiving the more fibrous supplement. Milk and FCM yields were greater for animals

receiving the fibrous supplement, but feeding the starch-based supplement resulted in

0.17 kg greater ADG vs. fibrous supplement.

Similar responses to type of supplement have been found with cows consuming

corn silage as the base forage (Huhtanen, 1993). Supplements were crushed barley alone

or mixed grain (40%) and pelleted fibrous by-products (60%). Cows eating the fibrous

supplement consumed 0.43 kg/d more (P < 0.10) silage and more total DM, but lower

ME (212.7 vs. 218.0 MJ/d). Milk production increased 1.5 kg/d when animals consumed

the fibrous supplement. The author suggested that positive associative effects from the

combination of different carbohydrate sources or the greater CP intake (0.20 kg/d) due to

the fibrous supplement may help explain greater milk yields. Though liveweight did not

change due to supplement and insulin concentrations were not reported, greater plasma

insulin concentration for barley supplement have been reported by Miettinen and

Huhtanen (1989). This hormonal change would suggest greater partitioning of nutrients

to body tissues and may explain the results of Meijs (1986).

Gordon et al. (1993) compared the effects of fibrous or starchy supplements on

milk production and energetic efficiency. Fibrous supplements included sugar beet and

citrus pulp as well as cottonseed while starchy concentrates contained barley and wheat.

Cows were fed the supplements with high- or low-digestibility grass silage. The authors

reported greater milk production (23.5 vs. 21.6 kg/d) by cows fed the fibrous supplement.

Milk protein percentage was greater with the starch supplement, potentially indicative of






33

greater microbial synthesis, but milk protein production did not differ due to milk

production differences. Partial efficiency of milk production was unaffected by

supplement type.

Galloway et al. (1993b) compared provision of soy hulls, corn, or a combination

of the two at equal digestible energies (differing amounts in kg/d) to steers consuming

bermudagrass hay. Providing hulls resulted in a greater decrease in bermudagrass intake

relative to corn or corn plus soy hull supplementation, but total DMI were similar for

steers fed the supplemented diets and greater than for steers fed bermudagrass alone.

Supplement increased particulate rate of passage from the rumen (avg. 4.71 vs. 4.18%/h),

which could have negative effects on digestibility of bermudagrass. However, the overall

supplement effect was an increased diet digestibility.

A comparison of a TMR or grain concentrate as a supplement for pasture-fed

dairy cattle indicated that a TMR supplement may not be an improvement over

concentrate feeds. Welch and Palmer (1997) fed 1) no supplement, 2) 7.3 kg of

concentrate/d, or 3) an equal quantity of TMR balanced for 38.5 kg of daily milk to cows

grazing unspecified cool-season pastures. Milk production was greatest for concentrate

fed cows and least for unsupplemented cows, but milk fat concentration followed an

opposite pattern. The researchers speculated that pasture intake "fiber in the TMR

probably reduced pasture DM intake" (p. 222).

Supplement Effects on Forage Digestibility

Energy supplements often affect forage digestibility and DMI in a similar manner.

Milne et al. (1981) fed sheep increasing amounts of grain concentrate and found a linear

decrease in digestibility of ingested herbage. A 9.6 percentage unit decrease (64.3 vs.






34

54.7%) in true ruminal digestion of cool-season forage DM was reported when lactating

dairy cows were fed supplemental corn at 6.4 kg/d. Total tract digestibility of DM was

less affected (71.9 vs. 69.9%), however (Berzaghi et al., 1996).

Research with steers (Vadiveloo and Holmes, 1979; Galloway et al., 1993a,b) and

sheep (Chenost et al., 1981, cited by Arriaga-Jordan and Holmes, 1986) has shown that

when forages are of low to moderate digestibility, supplement often improves overall

total diet digestibility, likely due to the greater digestibility of the supplement (Galloway

et al., 1993a). Diet digestibility is often unimproved when supplements are fed with high

quality forages, however. Arriaga-Jordan and Holmes (1986) studied the effects of

concentrate supplementation on herbage digestibility in dairy cattle. Feeding a grain-

based supplement to cows eating high quality pasture increased total intake, but reduced

herbage intake and depressed digestibility of the herbage consumed, thus reducing the

potential nutritional benefit of the concentrates.

Supplements also affect diet digestibility by affecting rates of passage of digesta

through the digestive tract. Waldo et al. (1972) were the first to model the relationship

between rates of digestion and passage on total digestion: kl/(kl +k2), where kl and k2 are

rates of digestion and passage, respectively. In theory, if passage is 0 then digestion will

equal 100% of potential extent of digestion (kl/kl = 1). Conversely, if passage is rapid, it

will have a large, depressive effect on diet digestion. For example, Tyrrell and Moe

(1972) fed increasing amounts of corn grain as a supplement to cows fed corn silage

diets. Although intakes increased with supplementation, the decreased digestibility of the

diet due to increased passage resulted in decreased concentration of dietary ME.






35

Forage intake and digestibility in response to supplement feeding also is related to

supplement effects on ruminal microbes. Growth of ruminal microbes is reduced in vitro

with decreased ruminal pH (Russell and Dombrowski, 1980). Low rates of starch

supplementation may increase numbers of cellulolytic microbes, but feeding diets with

large concentrations of rapidly fermentable starch may lead to a cascade of events

including decreased ruminal pH, reduced cellulolytic microbes, and ultimately, decreased

intake (Mould and Orskov, 1983).

Cellulolysis is decreased not only by reduced pH but also by preferential starch

digestion by the microbes (Mould et al., 1983; Hoover, 1986). Mould et al. (1983) fed

increasing amounts of barley to sheep, with or without additional bicarbonate salt to

buffer ruminal pH. Diets were fed at a fixed rate, just below maximum voluntary intake,

so passage should not have confounded the findings. Even when pH was maintained at

approximately 6.7, DM digestibility decreased with increasing concentration of barley in

the diet, and the depression in apparent DM digestion was greater in sheep fed the more

processed barley, suggesting that fiber-digesting microbes preferentially selected starch.

Moreover, reduction in cellulolysis in response to starch supplementation was greater

when roughages were of lower DM degradability (Mould et al., 1983), which has

implications for cows grazing warm-season pastures.

Caird and Holmes (1986, p. 53, citing Jennings and Holmes, 1984a) stated that

the "response in intake to concentrates depends on the influence of the concentrate on

herbage digestibility." Others have reported that extensively fermented, fiber-based

supplements have less negative effects on forage intake and digestion. For example,

when soybean hulls were used as a supplement for beef cattle, reductions in forage






36

consumption were not as evident as when starch-based supplements were fed (Martin and

Hibberd, 1990). Klopfenstein and Owen (1987) reported that supplementation with

soybean hulls had less effect on ruminal pH compared with supplementation with cereal

grains. The lack of starch in soybean hulls may prevent the decreases in fibrolytic

activity caused by preferential starch utilization by fiber-digesting microbes (Hoover,

1986).

Other supplement sources such as beet pulp and by-product feeds have also been

considered with varying results. Thus, Galloway et al. (1993b) noted that the optimum

supplement composition might vary with the forage source with which it is fed.

Though the characteristics of a forage affect both ruminal conditions and

absorption of nutrients (Minson, 1990), it should be noted again that the "effects of

[forage] quality differences may decrease and even disappear if enough grain is fed. In

such a case there would be no effect of forage quality on animal performance" (Golding

et al., 1976b). However, extent of production may confound the effect and interpretation

of responses to supplement. From work with steers, Joanning et al. (1981) reported that

at intake below twice maintenance, associative effects between forage and concentrate

might not occur, though this suggestion was based on extrapolations. Ultimately, with

high-performance dairy cows, optimizing use of feed supplements will require a balance

between improvements in intake and concomitant decreases in digestion.

Besides the changes in digestibility, additional concerns with feeding large

amounts of high-starch concentrate may include reduced milk fat concentrations (Huber

et al., 1964; Jennings and Holmes, 1984a; Polan et al., 1986; Sutton et al., 1986) and






37

negative effects due to slug feeding of supplements such as periodic reductions in intake

and ruminal acidosis.

Synchronizing Nitrogen And Carbohydrate Supplements To Increase Microbial
Protein Synthesis in the Rumen

Loss of Feed Nitrogen in Ruminants

Proteins in pasture forages can be degraded rapidly and extensively by ruminal

microbes (Beever et al., 1986a, b; Van Vuuren et al., 1991) and considerable N losses

have been reported for animals grazing pasture. For example, steers grazing ryegrass or

white clover pastures consumed approximately 0.61 and 1.18 g of N/kg of live weight,

and non-NH3-N (NAN) flow to the small intestine was greater with clover diets (0.60 vs.

0.76 g of NAN/kg of live weight for ryegrass and clover, respectively; Beever et al.,

1986b). However, the differential between intake N and NAN flow represented a 35%

loss of N prior to the duodenum for cows grazing clover pastures and little loss of N for

cows grazing ryegrass. Ruminal NH3 concentrations typically ranged between 20 and

100 mg of NH3-N/L of ruminal fluid for grass diets, but ranged from 250 to 300 mg of

NH3-N/L of rumen fluid for clover diets.

Similar ruminal N losses (37%) were reported for non-lactating cows consuming

unfertilized fresh cool-season pasture grasses (Holden et al., 1994b). Cows were fed

fresh pasture, silage, or hay and consumed similar quantities (13.0 to 13.7 kg of DM/d) of

the mixed-grass forage. The CP concentration of the forage was approximately 17% in

each forage form with the OM:CP ratio ranging from 4.5 to 5.1. Ruminal NH3

concentrations were greater for cows consuming pasture. The authors, citing work by

Ushida et al. (1986), suggested that the greater ruminal NH3 concentrations might have

been related to greater protozoal counts they observed in the pasture-fed cows. Though






38

bacterial N as a percentage of N flowing to the small intestine was greatest for cows

grazing pasture, N flow to the small intestine relative to N intake was least for cows

grazing pasture, indicative of the greater N losses. Flows of certain essential amino acids

also tended to be less with pasture-fed cows. Holden et al. (1994b) also suggested that

diet selection over time may affect fermentation patterns because intake of CP and

ruminally degradable protein likely decline with time spent grazing (Chacon and Stobbs,

1976).

Loss of N from the rumen is costly due to significant energetic expenditure

associated with urea synthesis and excretion. Urea synthesis and excretion cost

approximately 5 kcal/g of N excreted (NRC, 1989). Greaney et al. (1996) estimated that

25% or more of liver oxygen consumption was for the detoxification of ammonia to urea

when diets were pelleted alfalfa (2.7% N) or fresh white clover (4.4% N). The authors

noted that these energetic costs of N loss were likely underestimated because increased

ammonia loading would likely result in increased amino acid catabolism, sodium pump

activity and oxidative phosphorylation. In addition to the greater energetic expenditure,

additional N costs are incurred with hepatic removal of NH3 due to amino acid

catabolism (Lobley et al., 1995; Greaney et al., 1996). This may further limit animal

performance if supplies of essential amino acids are limited.

Though microbial protein is the primary protein source for lactating dairy cows

(Glenn, 1994), Leng and Nolan (1984) noted that it alone cannot provide an adequate

supply of amino acids to the small intestine for maximum growth and production by the

host, as reported by Holden et al. (1994b). This might in part account for reduced

persistency observed with grazing dairy cows (Hoffman et al., 1993). To offset these






39

limitations, some have fed rumen escape proteins, but performance responses to

ruminally undegradable intake proteins have been inconsistent, both for cows in

confinement and on pasture (Davison et al., 1991; Aldrich et al., 1993; Petit and

Tremblay, 1995a,b; Jones-Endsley et al., 1997). Such responses highlight the need for

first optimizing ruminal fermentation to maximize microbial protein synthesis (Aldrich et

al., 1993; Glenn, 1994).

To maximize "microbial cell yields per unit of nutrient input (e.g., feed materials)

the rate of ATP production from fermentation reactions must equal the usage rate by

biosynthetic reactions at all times" (Hespell and Bryant, 1979). With adequate ATP

(derived primarily from carbohydrate fermentation), rumen microbes can incorporate

amino acids into microbial protein (Nocek and Russell, 1988). Thus, providing

supplemental energy (typically grains high in carbohydrates) may be an effective way to

increase microbial yield and reduce excess N excretion.

Responses to Supplemental Carbohydrate

Responses to providing carbohydrate energy sources are mixed, however. With

continuous culture studies, Hoover and Stokes (1991) reported a high correlation (r =

0.99) between percent carbohydrate digestion and nonstructural carbohydrate (NSC) as a

percentage of dietary carbohydrate. However, the correlation of microbial efficiency to

NSC as a percentage of dietary carbohydrate was much lower (r = 0.33). These results

have been confirmed using cows on pasture by Carruthers et al. (1996) who found that

"increasing the proportion of NSC in pasture without increasing energy intake did not

increase ruminal microbial protein synthesis or increase milk solids production in early

lactation."






40

Nocek and Russell (1988) noted that even "seemingly appropriate amounts of

dietary CP and carbohydrate may not provide an ideal balance of protein and

carbohydrate to the rumen microorganisms." The authors compared four theoretical diets

that were isonitrogenous and isocaloric but which had variable concentration of ruminally

available CP and carbohydrate. Theoretical bacterial synthesis and amino acid supply to

the small intestine were markedly different among the diets and demonstrated the

potential difficulty inherent in formulating diets for maximum microbial production.

This challenge may be even greater when forage and concentrates are consumed as

individual components such as occurs in grazing systems.

A batch culture study more similar to pasture feeding conditions was conducted to

test the effects of asynchronous nitrogen and energy supplies on microbial growth

(Newbold and Rust, 1992). Cultures were supplied glucose and urea or corn and soybean

meal processed for slow or rapid microbial digestion, respectively. Regardless of

substrate, only transient effects of nutrient imbalance on cell yield were reported.

Though the mean bacterial population was greater from 5 to 8 h of incubation,

populations were similar at 12 h. However, the authors could not rule out end-product

inhibition as a reason for similar bacterial mass at the end of the experiments.

Rooke et al. (1987) studied the effects of constant-rate infusions of urea, casein,

glucose syrup, or casein and glucose syrup into the rumens of cows consuming ryegrass

silage. Infusions did not affect ruminal pH or VFA concentrations, but glucose and the

casein-glucose mixture reduced the rumen NH3-N concentration. Glucose and the casein-

glucose mixture also increased the quantities of OM, ADF, NAN, amino acid N, and

microbial N entering the small intestine, indicating that microbial yield was increased but






41

at the expense of fiber digestion. Similar results were found by England and Gill (1985)

who added sucrose to grass silage diets at 50, 75, 100, and 150 g/kg of silage DM. Silage

DMI was reduced, but not total DMI. With increasing proportions of dietary sucrose, a

corresponding decrease in cellulose digestion was observed. The results indicated that

the benefits of N utilization were offset by the decrease in diet digestibility, perhaps due

to the rapid solubility of the sucrose.

Phillips (1988) suggested corn silage would be "a suitable nutritional

complement" to herbage of variable energy and high CP concentrations. An experiment

by Holden et al. (1995) indicated that supplemental silage fed to cows grazing pasture

might have altered ruminal fermentation and reduced N load because silage supplement

also reduced concentrations of plasma urea N from 29.6 to 27.3 mg/dL. This could not

be determined by the authors, however, because the change in plasma urea N

concentration with silage treatment could have resulted from better N utilization or

decreased intake of ruminally degradable protein. Production responses were unaffected

by supplemental silage.

In some experiments, microbial utilization of forage N was not markedly

improved by supplementation with barley (Thomas et al., 1980; Rooke et al., 1985).

Greater intraruminal N recycling due to increased ruminal protozoal number has been

implicated in the lack of N utilization by microbes (Chamberlain et al., 1985).

Substitution with fibrous concentrates such as beet pulp and distiller's solubles for barley

has resulted in increased duodenal NAN primarily due to increased feed N flow

(Huhtanen, 1988, 1992) with concomitant increase in milk production and milk protein

yield (Huhtanen, 1987; Ala-Seppaili et al., 1988).






42

The effects of corn supplementation on intake and digestion characteristics in

lactating cows consuming primarily orchardgrass (Dactylis glomerata L.) and white

clover were studied by Berzaghi et al. (1996). Provision of supplement decreased

ruminal NH3 (17 vs. 22 mg/dl) and increased N recovery at the duodenum (86.7 vs.

75.3% of N intake), though total tract N recovery was reduced with supplementation

(71.9 vs. 78.8%). Digestibility of NDF also was reduced with supplementation,

suggesting that corn had negative effects on fiber digestion. Differences in microbial

flow to the duodenum were not significant.

Effects of Supplement Feeding Frequency

Feeding frequency may also alter ruminal fermentation patterns, improve nutrient

synchrony, and enhance microbial growth. Gustafsson et al. (1993) studied more than

38,000 records of Swedish cows and found that feeding concentrates 4 or more times per

day resulted in 3 and 7% (by year) increases in milk production compared with feeding

twice per day. Their study indicated that feeding frequency positively affected milk

production of primiparous cows with low ME intakes but that this was less of a factor as

ME intake increased. Increasing feeding frequency from 1 to 2 times per day for dairy

cows grazing tropical pastures was shown to increase milk production approximately

11% (McLachlan et al., 1994), but no milk production responses were observed in a

comparison of providing supplement 2 or 4 times per day to cows grazing cool-season

pastures (Hongerholt et al., 1997).

McLachlan et al. (1994) fed 0, 2, 4, 6, or 8 kg of a cracked-corn, meat-meal

supplement and reported that the FCM response was greatest with 6 kg of supplement/d

and pasture substitution rates were less when the supplement was provided twice daily.






43

From these results the authors inferred that more frequent feeding resulted in more stable

ruminal fermentation patterns, and that cellulolytic activity was closer to optimum.

However, increased milk protein percentage and greater milk fat concentrations (which

could support the hypothesis of increased microbial growth and cellulolytic activity with

increased feeding frequency) were not observed.

Kolver et al. (1995) fed a supplement either with the base forage (a cool-season

pasture grass) or four hours after forage feeding. With synchronous feeding they found

less diurnal variation in ruminal pH, but average pH was lower (6.06 vs. 6.17).

Synchronous feeding reduced concentrations of ruminal NH3 at 3 and 5 h post-feeding,

but N retention for milk and growth were unaffected.

In a review, Robinson (1989, p. 1199) noted that "although improved efficiency

of rumen fermentation in frequently fed cows seems unlikely to result in increased milk

yield in research studies, it can result in increased milk energy output due to increased fat

yield in situations where the combination of infrequent feeding and high inclusion of

rapidly fermentable dietary components results in perturbation of rumen fermentation

sufficient to depress milk fat output. In addition, some evidence suggests that

maintenance of body condition, often a critical problem in high producing herds may be

better maintained with more frequent feeding." Production benefits due to improved

ruminal fermentation efficiency are likely to be quantitatively small when compared with

production gains due to the increased intake associated with greater feeding frequency

(Robinson, 1989).






44

Though McLachlan et al. (1994) did not report changes in body condition, their

results of increased FCM and reduced forage substitution with increased feeding

frequency support the observations of Robinson (1989).

Hongerholt et al. (1997) fed a supplement 2 or 4 times per day and reported that

BW change and non-esterified fatty acids (NEFA) concentrations were unaffected when

grain intakes were similar across treatments. In contrast, feeding 6 rather than 2 times

per day resulted in greater milk fat concentrations and decreased concentrations of

plasma NEFA (Sutton et al., 1986), indicative of enhanced cellulolytic activity and

energy availability from the diet.

Effects of Timing of Supplement Provision Relative to Forage Intake

Timing of forage and concentrate provision relative to each other may affect

intake and performance. Morita et al. (1991; cited by Morita et al., 1996) reported that

steers ate more roughage when concentrate was fed after roughage provision. Work from

Germany (Voigt et al., 1978, cited by Robinson, 1989, p. 1205) indicated that providing

grain supplements before feeding roughage (chopped ryegrass) had different effects upon

ruminal pH and digestion of cellulose depending upon the fermentability of the grain.

Barley, a rapidly fermented grain, caused a greater depression in ruminal pH than corn, a

more slowly grain. Feeding the ryegrass before the grains caused a greater increase in

forestomach whole-diet cellulose digestion if barley was the grain supplement (63.6 vs.

75.0%) rather than corn (72.1 vs. 78.3%). Differences in ruminal cellulose digestion

were unaffected by feeding sequence if the ryegrass was pelleted and total diet digestion

was reduced. Morita et al. (1996) also noted that roughage consumption and fiber






45

digestibility in the rumen were greater when cows ate roughage before concentrate rather

than in the reverse order.

Timing might also be important relative to ruminal heat production. Russell

(1986) reported that adding pulses of glucose to glucose-limited cultures immediately

doubled heat production with little increase in cell protein. In addition to reduced

efficiency of microbial protein production, consumption of primarily soluble

carbohydrate-based supplements in asynchrony with dietary protein might increase

ruminal heat. Heat in the rumen negatively affects intake of DM and water and alters

ruminal fermentation patterns (Gengler et al., 1970). A 3 �C increase in rumen

temperature (from 38.0 to 41.3 oC) resulted in a 14% decrease in feed intake (13.2 vs.

11.4 kg/d for control and treatment cows, respectively) in the study by Gengler et al.

(1970).

Additional Energy and Protein Supplements for Animals on Pasture

Fats

Fat feeding may improve milk production but has potential for negative side

effects with respect to microbial fermentation, growth, and feed digestion (Emery and

Herdt, 1991). Fat feeding to lactating cows typically has been limited to mixed rations,

and information on feeding fats to cows on pasture is limited.

King et al. (1990) compared production from cows grazing ryegrass pastures and

receiving no supplement, 3.5 kg of a grain-based pelleted concentrate, or 3.8 kg of pellets

containing 0.5 kg of added fatty acids (primarily palmitic, stearic, and linoleic acids).

Diets were not isocaloric. Forage intakes were similar and were estimated at 17.0, 16.3,

and 15.6 kg of DM/d for control, concentrate, and concentrate plus fatty acid treatments.






46

Total intake was an average of 2.5 kg/d greater for supplemented cows. Production of

milk, 4% FCM, and milk protein were not different between concentrate treatments but

were greater than for the unsupplemented treatment. Cows fed fatty acids produced

greater quantities of milk fat. Volatile fatty acids in ruminal fluid were essentially

unchanged between concentrate treatments, indicating that the fatty acids used did not

affect microbial function. However the low amount of added dietary fat and the small

percentage of which was unsaturated fatty acid would not be expected to significantly

hinder microbial function (Jenkins, 1993).

Escape proteins

In a review, Oldham (1984) noted that supplemental proteins might directly affect

control of food intake in ways not directly related to improvements in digestibility. This

has been shown by Froetschel et al. (1997) who reported that ruminal undegradable

proteins contain peptide sequences that may increase gut motility.

Because of the rapid and extensive degradation of proteins in lush pastures

(Beever et al., 1986a,b), some researchers have explored the utility of supplementing

cows with less ruminally degradable sources of protein. Jones-Endsley et al. (1997)

compared amounts (6.4 vs. 9.6 kg/d) and concentrations (12 and 16% CP) of protein

supplements for lactating dairy cows. The 16% supplement appeared designed to provide

additional ruminally undegradable protein, but this was not made clear by the presented

feed analysis. Amount of supplement did not affect forage intake, but animals

consuming the 16% CP concentrate tended to consume more forage (1.6 kg/d) than did

those fed the 12% CP supplement.






47

Hongerholt and Muller (1998) also found no response of grazing, lactating cows

to increased dietary ruminally undegradable protein, but Stobbs et al. (1977) reported that

escape protein from protected casein stimulated intake. When Davison et al. (1991)

provided meat and bone meal to lactating cows, they were not able to measure forage

intake changes. However, by calculations of energy requirements for observed milk

production and weight changes, the authors determined that forage intake was likely

increased. Consumption of meat and bone meal did not result in greater milk yield, but

did result in less (P = 0.068) BW loss over the first 100 d of the trial and greater (P =

0.054) gain over the entire lactation. The authors concluded that "responses to protein

supplements ... vary with the type of pasture, the level of grain or energy supplement fed

and the level of pasture on offer" (Davison et al., 1991, p. 162).

Effect of Supplements on Grazing Behavior

Several researchers have reported reduced grazing time with supplementation.

Sarker and Holmes (1974) fed 2, 4, 6, or 8 kg of concentrate supplement/d. They

reported large decreases in GT (an average of 28 min/kg of supplement) with

supplementation. Although total OM intake increased 2 kg from the low to the high

supplementation rate (11.5 vs. 13.6 kg of OM/d), herbage OM intake decreased from 9.9

to 7.4 kg of OM/d.

Cowan et al. (1977) fed a 4:1 corn:soybean meal concentrate at 0, 2, 4, or 6 kg/d

to cows grazing green panic (Panicum maximum var. trichoglume) and glycine (Glycine

wightii cv. 'Tinaroo') pastures. They reported decreased grazing time with increased

supplement (23 min/d per kg of supplement fed) during autumn and winter months (time

of reduced HA), but not during summer. Available pasture increased with increasing






48

amount of supplement fed. Estimates of forage mass excluded dead material. Average

mass of DM harvested increased 188 kg/ha for each kg increase in concentrate fed,

indicative of reduced forage intake. Herbage on offer ranged from 4000 to 6000 kg of

green DM/ha in summer to 500 to 1500 kg of green DM/ha in winter (below the "forage

not limiting intake level"). Average length of lactation was greater for supplemented

cows (275 d) compared to those of 0 (222 d) or 2 kg/d (252 d) supplement groups. Cows

assigned to 0 or 2 kg/d treatments had to be removed from treatment early due to

excessive weight loss.

A study of heifers grazing Cenchrus ciliaris pastures showed that grazing time

decreased 11 min/kg of supplement fed (Combellas et al., 1979). Heifers received a high

energy, high protein concentrate at 0, 3, or 6 kg/d. Rate of biting, total bites, and intake

per bite were also decreased. Though not significant, the number of grazing periods was

numerically greater with increased rate of supplementation.

Pulido and Leaver (1997) reported decreased GT of 11 min/kg of concentrate,

though effects were much more dramatic when concentrate fed was greater than 6 kg/d.

For 0, 6, or ad lib kg of daily concentrate intake, GT were 531, 526, and 381 min/d and

rates of forage intake were 31.4, 25.8, and 20.7 g/min. Forage intake decreased 0.69 kg/d

for each kg of concentrate consumed.

A study with beef steers (Adams, 1985) indicated that timing of supplement

feeding affects grazing behavior and forage intake. Steers grazing Russian wild ryegrass

(Elymusjunceus) in Montana received forage only (control) or morning or afternoon

feedings of corn supplement (0.3 kg of supplement/100 kg of BW). Though

supplemented steers ate less forage than steers on the control treatment, comparison






49

between morning and afternoon feedings indicated greater forage intake with afternoon

feeding (2.6 and 2.9 percent of BW for morning and afternoon feedings, respectively).

Total intakes were not different among the three treatment groups, but forage intake and

total intake were greater for afternoon-supplemented steers in comparison with morning

supplemented animals. Feeding supplement to steers in the morning resulted in a 24%

decrease in forage intake/h of grazing time in comparison with control and afternoon

feeding treatments (Adams, 1985).

Reid (1951) noted that DMI and grazing time are not necessarily correlated.

Similarly, Krysl and Hess (1993) noted that a decrease in grazing time does not

necessarily mean a decrease in forage intake because harvest efficiency (defined as g of

forage OMI/kg of BW per min spent grazing) may change. Work of Barton et al. (1992)

confirmed these ideas. The authors observed grazing behavior of dairy steers fed

supplemental cottonseed meal at 0 or 2.5% of BW in the AM or PM. The steers reduced

grazing time on intermediate wheatgrass (Thinopyrum intermedium Host) pastures by

approximately 1.5 h when provided cottonseed meal supplement, but forage intakes were

not different across treatments. Steers receiving cottonseed meal had numerically greater

forage intake.

Interactions of Supplement and Herbage Allowance on Performance of Lactating
Cows in Pasture-Based Dairy Systems

The two main factors considered to cause the variable responses to supplement

are forage availability and forage nutritive value. Work by Blaser et al. (1960)

demonstrated that concentrate supplements were used more efficiently when herbage was

limited.






50

To investigate the interactions of herbage availability and level of concentrate

supplementation on OMI, Meijs and Hoekstra (1984) stocked lactating Friesians on

perennial ryegrass pastures at 16.3 or 24.8 kg of pasture OM/cow per d. Values for HA

are 2-yr averages within treatments. Three rates of concentrate (1, 3, or 5 kg/cow per d in

1981 and 1, 4, or 7 kg/cow per d in 1982) were fed. Greater herbage intake was reported

at the greater HA (13.6 vs. 11.3 kg of OM/cow per d for the greater and lesser HA,

respectively). Increasing concentrate intake negatively affected forage OMI. This was

primarily due to the decrease in forage intake by cows on the greater HA treatment

(forage by concentrate interaction). Forage OMI of 14.9, 13.6, and 12.3 kg/cow per d

were reported for cows fed the low, medium and high concentrate rates, respectively, for

cows on the greater HA treatment, whereas forage OMI decreased only from 11.4 to 11.0

kg/cow per d with increasing concentrate for cows on the lesser HA treatment.

"Relatively few experiments have been conducted on tropical pastures to

determine objectively the relationship between herbage availability and the performance

of dairy cattle. There is therefore little evidence on which to determine the pasture

conditions under which supplementary feeding might be most efficiently employed"

(Jennings and Holmes, 1984b, p. 270). Little research has been published on this topic in

the last 15 years.

Cowan and Davison (1978) investigated effects of supplementing maize (0 or 3

kg/d) to cows grazing tropical pastures of mixed forage species at 1800 or 3300 kg of

DM/ha. Milk production was increased from 6.5 to 9.3 kg/cow per day with supplement

offered to cows assigned to the lower level of HM but was unaffected by supplement

(13.0 kg/d) offered at the greater level of HM.






51

Two Perennial Forages for Lactating Cows in Pasture-Based Dairy Systems
in the Southeast

Bermudagrass

Bermudagrass is one of the most extensively grown improved, perennial, warm-

season forages for the Southeast. According to G. W. Burton, bermudagrasses '"occupy

more than half the pasture acreage in the southern United States"' (cited in Adams, 1992,

p. 19). First introduced to the U.S. in 1751 (Burton and Hanna, 1995, citing the diary of

Thomas Spalding), bermudagrass has been the subject of much research. Numerous

improved cultivars of the grass have been released since the 1940s (Burton and Hanna,

1995), and a review of the literature reveals improvements in both yield and digestibility

(Monson and Burton, 1982). Today, more than 5 million hectares in the Southeast have

been sprigged with improved bermudagrasses, with many more supporting common

bermudagrass (Burton and Hanna, 1995).

Though well adapted to much of the region, bermudagrasses typically have high

concentrations of NDF and low concentrations of NEL and digestible nutrients (West et

al., 1997). A compilation of 18 experiments in which bermudagrass hay "harvested at

vegetative to mature growth stages, obtained from local producers and grown with a

variety of management practices" was reported by Goetsch et al. (1991, p. 2635). Mean

NDF concentration was 74.5% with a range of 65.6 to 86.7% (DM basis). Though mean

OM digestion was 54.9 %, the range of OM digestion was quite wide, from 27.5 to

75.4%.

Bermudagrass yield responses and nutritive value characteristics are affected by

numerous factors, including frequency of defoliation (grazing or clipping), fertility,

temperature, season, and location, and responses vary by cultivar (Wilkinson et al., 1970;






52

Jolliffet al., 1979; Henderson and Robinson, 1982; Holt and Conrad, 1986; Adjei et al.,

1989). Soil moisture also has been implicated as a factor affecting quality of warm-

season grasses (Henderson and Robinson, 1982; Pitman and Holt, 1982).

Yield typically increased with decreased frequency of defoliation (Decker et al.,

1971; Holt and Conrad, 1986; Adjei et al., 1989) though this was not reported by

Ethridge et al. (1973). Conversely, in vitro digestibility decreased with decreased

defoliation frequency (Decker et al., 1971; Holt and Conrad, 1986; Jolliff et al., 1979),

but the magnitude of change in digestibility has been inconsistent (Hussey and Pinkerton,

1990). Data from Holt and Conrad (1986, p. 435) indicated "that both yield and dry

matter digestibility cannot be maximized by manipulating harvest or utilization

frequency, necessitating a compromise in one or both in any management situation."

In pasture systems, both digestibility and availability of forage influence animal

performance. As digestibility decreases, more forage must be consumed to maintain

animal gain, and the upper limit of productivity will be reduced (Duble et al., 1971).

Forage quality, as determined by intake, nutritive value and efficiency of utilization, is

well demonstrated by work of Greene et al. (1990). Stocker performance was compared

using four different bermudagrass cultivars. Though the cultivar 'Grazer' did not

produce the greatest forage DM yields, animal output per unit land area with Grazer was

approximately 18% greater than the average production with the other cultivars

('Brazos', Coastal, and Tifton 44).

The varying nature of cultivar responses makes finding an appropriate

compromise between maximum yield and greatest nutritive value more difficult.

Optimum will likely depend on production aims. For example, Adjei et al. (1989)






53

investigated the response of three bermudagrass cultivars to grazing at 2, 4, 6, and 8 wk

frequencies within seasons (Winter/Spring and Summer/Fall). Yield response of Callie

35-3 (now cv. 'Florakirk') to grazing frequency was quadratic in nature. Maximum

yields for both Callie 35-3 and Tifton 78 occurred at the 6-wk grazing interval, with

yields of 2.6 and 3.6 t/ha for the respective cultivars. A linear response to grazing was

observed for Tifton 79, with a maximum yield of 3.5 t/ha occurring at the 8-wk grazing

frequency. Conversely, as grazing frequency decreased, in vitro organic matter

digestibility (IVOMD) declined in a linear fashion for Callie 35-3 and exhibited both

linear and quadratic characteristics for Tifton 78 and 79 depending on season. For the

Tifton cultivars, greatest digestibility occurred at the 4-wk grazing frequency.

Concentration of CP also decreased with decreased grazing frequency for all cultivars

with the nature of the responses dependent on season and cultivar.

Holt and Conrad (1986) investigated yield and digestibility responses to

frequency of harvest among several varieties of bermudagrass and one stargrass (C.

nlemfuensis Vanderyst) cultivar (Tifton 68). Although Coastal bermudagrass had the

greatest seasonal yield at all clipping frequencies (average of 15.8 metric T/ha), its

IVDMD was least at all clipping frequencies (average of 54.8% IVDMD). The stargrass

cultivar had intermediate yield (average of 13.8 t/ha) and greatest digestibility (average of

65.4% IVDMD) at all clipping frequencies. The greater IVDMD for Tifton 68 resulted in

that cultivar producing the greatest quantity of digestible OM. The best compromise

between yield and digestibility for all cultivars was at approximately 4 wk of regrowth.

Many studies of the effect of fertilization on bermudagrass yield and nutritive

value have been conducted. Typically, increased CP concentrations were reported with






54

increasing N application (Monson et al., 1971; Monson and Burton, 1982; Thom et al.,

1990). Good fertilization is essential to production of quality bermudagrass. Stallcup et

al. (1986) fertilized bermudagrass pastures at 0 to 200 kg of N/ha in 50 kg increments and

reported that CP concentrations in bermudagrass fertilized with 0 and 50 kg of N/ha were

11.4 to 14.3%, respectively. Although apparent DM digestibility increased slightly (61.3

to 62.0%), CP digestibility increased from 54.2 to 63.6%. When the hays were fed to

steers, the difference in N retention (measured as a percent of N fed) was quite large (2.8

vs. 21%, respectively). Increasing the rate of N application above 50 kg of N/ha had

more modest positive effects on the variables measured. Monson and Burton (1982)

investigated the effect of two levels of N fertilization (336 or 672 kg/ha) and cutting

frequency (1, 2, 4, or 8 wk) on yield, quality, and persistence of eight bermudagrass

cultivars. Digestibility increased with increased N application with weekly harvests.

Significant interactions between harvest frequency and genotype in response to N also

were noted. Besides increasing CP and yield, N fertilization also has been shown to

increase carotene and xanthophyll concentrations in bermudagrass (Monson et al., 1971).

Ocumpaugh (1990) noted that if legumes are used, chemical N sources are not a

necessity for bermudagrass production. He reported that when Coastal bermudagrass

pastures were overseeded with sub-clover (T. subterraneum) or arrowleaf clover (T.

vesiculosum) they produced as well as similar pastures receiving two applications of 56

kg of N/ha. In years of plentiful rainfall grass-legume pastures out-yielded grass-N

pastures.

Singular use of N fertilizer may not be effective for bermudagrass production.

Welch et al. (1981, cited by Pratt and Darst, 1986) reported that yields with N





55

fertilization were 50% of those when both N and K were applied. Pratt and Darst (1986)

also indicated that response to K fertilization was not always immediate. In their work, K

deficiency was seen (vis-a-vis large decline in yield) in the third year of study, and they

emphasized the need for long-term observation.

Effects of other fertilizers on animal responses have been investigated. Mathews

et al. (1994b) fed non-lactating cows chopped Tifton 78-common bermudagrass hays

which had or had not been fertilized with S (gypsum). The authors reported a 30.4

percentage unit increase in the apparent digestibility of S (vs. unfertilized control) and a

10.6 percentage unit increase in the apparent digestibility of lignin. Apparent N

digestibility slightly increased with S fertilization. Digestibility of ADF and NDF tended

(P = 0.18) to be increased by 1.5 percentage units, and DMI also tended (P = 0.14) to be

increased with S supplementation.

Henderson and Robinson (1982) grew bermudagrass in chambers to study the

effects of differing light intensity, moisture, and temperature on bermudagrass harvested

at 14 or 21 d. Yield increased with increased temperature and with increased photon flux

density, and in vitro digestibility decreased with increased temperature. When soil

moisture was low, light level did not affect forage digestibility across the array of

temperatures. Similarly, increased age reduced digestibility to a lesser degree under

moisture-limited conditions.

Seasonal effects on digestibility have been observed. Forage digestibility

typically is greatest in spring, declines in summer and increases in late summer or early

fall (Carver et al., 1978; Holt and Conrad, 1986), though this pattern is not always

observed (Guerrero et al., 1984). Holt and Conrad (1986, p. 435-436) noted that






56

differences in digestibility were unrelated to age at harvest, and that changes in IVDMD

"apparently are related to environmental conditions not clearly understood under field

conditions." Adjei et al. (1989) also reported that forage nutritive value typically was

greater in fall than in summer and differences between cultivars within seasons were

observed as well. Animal performance often mirrors these changes (Greene et al., 1990).

Holt and Conrad (1986) investigated decreasing leaf proportion as a source of

decline in forage digestibility because leaves are usually more digestible than stems.

Leafiness decreased with age but, though the decline in leaf proportion was a significant

factor, it explained less than 50% of the decline in forage digestibility (r2 = 0.44). The

authors noted that stem digestibility was a likely factor in cultivar digestibility

differences, but this was not explored. "Genotype and seasonal effects on [IVDMD]

were greater than and largely independent of leaf effects when plant material was all the

same chronological age" (p. 435). Similar results with respect to leaf proportion were

observed by Mathews et al. (1994a). They investigated IVOMD and nutrient

concentration of 'Callie' bermudagrass in response to four methods of harvest. Pastures

were stocked continuously, rotationally stocked in short and long rotations, or cut for hay.

Leaf lamina as a percentage of the plant material sampled was least with continuous

stocking (33.5% across years) and averaged 47% with the other three methods. However,

the weighted mean of IVOMD was relatively stable (56.5%), not differing by more than

3.2 percentage units.

Location also determines the productivity and quality of bermudagrass in as much

as it combines such factors as rainfall or soil moisture, ambient temperature, soil

characteristics, and incident light. For example, though Adjei et al. (1989) did not






57

specifically test genotype by location, their research indicated that Tifton 78 was

unsuitable for central Florida conditions even though it had been released and was

"finding some use in Georgia."

Numerous investigators have studied the suitability of use of bermudagrass as an

animal feed. Typically, the grass is used more in extensive feeding systems such as

pasture for beef cattle or dry dairy stock.

Stocking rates on bermudagrass may have a large influence on animal

performance once some critical level is reached. Working with a biophysical model,

Parsch et al. (1997) simulated forage production responses to a range of beef cattle SR.

According to the model, with improved bermudagrass pastures weight gain per head is

essentially unaffected by grazing intensity until a critical SR (6 head/ha) is reached.

Bransby et al. (1988, p. 278) also reported that "grazing systems on bermudagrass appear

to be well buffered against changes in grazing intensity" across a wide range of stocking

rates and available herbage.

The interaction of forage and SR with continuously stocked bermudagrass

pastures was investigated by Guerrero et al. (1984). Forages were Callie, Coastal, and

three experimental hybrids. Stocking rates varied by cultivar but the range averaged from

4.6 to 11.0 steers/ha. Forage digestibility was increased with increasing SR, and greater

digestibility occurred primarily at medium and heavy SR. However, ADG decreased as

available herbage declined, and cultivar differences in digestibility and yield were

observed.

Roth et al. (1984, 1990) studied bermudagrass growth, morphology, and

compositional responses at four different HA under continuous stocking management.






58

Decreased HA affected leaf chemical characteristics and the proportion of leaf in the HM.

Leaf NDF decreased from 75.2 to 71.3% from high to low HA, and the average

proportion of leaf in the HM decreased by 51.6 and 39.7% for low and high HA

treatments, respectively.

Leaf proportion in the diet was unaffected across grazing pressures (82.7% for

low and 78.5% for high pressures), however, demonstrating diet selectivity of the grazing

animal. Animals also showed selectivity for leaves of greater quality as the concentration

of NDF in leaves selected was less than that in leaves in the standing herbage. With the

lower HA treatments, the proportion of dead material increased as leaf declined during

the hotter months. The dead material consisted primarily of uprooted stolons and dead

stems, and their disappearance later in the grazing season was due to consumption.

Although dead herbage is not high quality, the concentration of NDF in the dead

herbage of the low HA treatment was approximately 9.0 percentage units less than that of

the other treatments. As HA decreased, NDF concentration of the herbage was reduced

in the two pastures with the lowest HA compared with the two pastures with the greatest

HA. Moreover, reductions in NDF concentrations with decreased HA were observed in

all herbage components, and particularly in the senesced herbage.

Other studies (Arnold, 1960; Hamilton et al., 1973; Adjei et al., 1980) have not

shown the positive relationship between HA and NDF concentration of the herbage or the

diet found by Roth et al. (1990). The latter noted that the previous studies were

conducted using greater HA, however.

In 1993, a new cultivar, Tifton 85, was released (Burton et al., 1993). The grass is

actually an interspecific hybrid between bermudagrass and stargrass (Tifton 68), and it






59

produces "an abundance of stems and leaves in spring, followed by more vegetative

growth later in the season" (Hill et al., 1993, p. 3222). The authors reported greater NDF

concentrations in the forage earlier in the grazing season and suggested that this might be

due to the cultivar's growth habit.

Tifton 85 has "[r]apid growth rate and high IVDMD values relative to other

bermudagrass hybrids" (Hill et al., 1993 p. 3219). Hill et al. (1993) tested Tifton 85

grown in small plots and found that it produced greater quantities of DM with greater

digestibility than all other cultivars in the comparison. In comparison with Coastal

bermudagrass, [at one time the predominant cultivar in the Southeast (Holt and Conrad,

1983)], Tifton 85 produced more than 25% more DM (16.7 vs. 13.3 t of DM/ha) the and

forage was more than 12% more digestible (58.8 vs. 52.3% IVDMD).

Hill et al. (1993) also compared Tifton 85 with Tifton 78 in a grazing study.

Tifton 78 is a cultivar widely used because of its relatively high digestibility and yield.

The researchers maintained HM of both forages at approximately 2500 kg of DM/ha over

2 yr and sampled esophageally fistulated steers to estimate forage nutritive value

characteristics. Tester steers and variable SR also were used to determine ADG and to

calculate grazing d/ha. Steers grazed 169 d each year, and though the ADG with the two

forages were similar (0.67 vs. 0.65 kg/ for Tifton 85 and 78, respectively) Tifton 85

supported in excess of 500 more grazing days over the 3 yr of the study. The BW gain/ha

was 46% greater for steers grazing Tifton 85 as a consequence (1160 vs. 790 kg/ha). Hill

et al. (1993, p. 3224) noted "a strong tendency for Tifton 85 to remain more productive

later in the grazing season than Tifton 78 did." This translated into slightly greater rates

of BW gain in August and September.






60

Mandebvu et al. (1998) compared DM and NDF digestibilities of first and second

cuttings (3.5 wk of growth) of Tifton 85 hay with that of Coastal bermudagrass hay of 4

wk growth. The IVDMD was reported as 63.6, 59.9, and 52.0% for the first and second

cuttings of Tifton 85 and the Coastal bermudagrass hay, respectively. The NDF

digestibilities were 61.4, 58.5, and 47.5%. First-cut Tifton 85 had a greater potentially

digestible NDF fraction in whole forage (77.9 vs. 67.1%) and in extracted NDF (81.5 vs.

70.7) than did Coastal bermudagrass.

Much literature details performance of beef animals grazing bermudagrass

pastures, with some information released comparing Tifton 85 with Tifton 78 (Hill et al.,

1993), but information regarding use of bermudagrass for grazing dairy animals is

limited. A study by Martinez et al. (1980, cited by Jennings and Holmes, 1984b) may

have overpredicted the potential use of bermudagrass as a pasture forage for dairy cows.

The authors reported that cows grazing Coast-cross I bermudagrass produced 4125 kg of

milk/cow per yr without supplementation.

West et al. (1997) indicated that Tifton 85 may be suitable for confinement

dairies, but no information is presently available regarding use of Tifton 85 by lactating

cows in grazing systems without or with supplemental feeds. In the study by West et al.

(1997), 3.5% FCM yields were not different for cows fed diets of either 15 or 30%

bermudagrass or alfalfa hays. Results suggested that the NDF digestion of Tifton 85 was

more rapid and more extensive than that of alfalfa or corn silage components of the diets.

Comparisons of Grasses and Legumes

The high concentrations of NDF and low concentrations of digestible nutrients

associated with warm-season perennial grasses limit their desirability for use in animal






61

production systems. Many have looked to forage legumes for suitable alternatives to

grasses because animal performance is often greater when legumes are fed (Rattray and

Joyce, 1974; Thomas et al., 1985; Beever et al., 1986b; Hoffman et al., 1998). The

following discussion primarily will consider cool-season perennial legumes, because few

warm-season perennial legumes have proven suitable for intensive grazing systems.

Regarding chemical composition, legumes typically have greater concentrations

of protein than grasses, with a larger percentage of the protein being ruminally

degradable (Beever et al., 1986a; Glenn, 1994). The soluble portion of legume CP also is

different, having more amino acids and peptides than that of grasses (Glenn et al., 1989).

Legumes generally have less NDF than grasses, and the composition of NDF in legumes

is markedly different. Legumes have less hemicellulose, typically less cellulose, more

lignin and more pectic substances (Van Soest, 1965) than grasses.

In vitro digestibility studies indicate that legumes typically have a greater rate but

lesser extent of digestion in comparison with grasses (Smith et al., 1972). Glenn (1994)

noted that, relative to alfalfa, proportionately more grass NDF typically is digested in the

rumen. A review of several comparisons of alfalfa and orchardgrass fed to growing

animals indicated that total tract digestibility of orchardgrass was 94% that of alfalfa

(Glenn, 1994). In comparisons of alfalfa with ryegrass or orchardgrass, researchers

typically have found greater true fiber and DM digestibility for the grasses (Holden et al.,

1994a; Hoffman et al., 1998), but the greater DM digestibility may in part be related to

the lower intakes of cows on the grass-based diets.

Holden et al. (1994a) fed diets of 55 or 66% forage (orchardgrass and alfalfa hays,

respectively) which were formulated to have equivalent NDF concentrations. Lactating






62

cows consumed 17.5 and 15.1 kg of OM/d for the alfalfa and orchardgrass diets,

respectively, and total tract digestions ofNDF, ADF, and DM were greater for cows fed

the grass diets. In the study by Hoffman et al. (1998), lactating cows were fed diets based

on 70% inclusion of alfalfa or perennial ryegrass silage. Intake of DM was greater when

cows ate alfalfa silage (22.5 vs. 20.3 kg of DM/d), though true digestibility of NDF and

DM was greater for the ryegrass silage-based diet. In both studies, milk production was

greater with the alfalfa-based diet.

In a comparison of steers grazing pure stands of ryegrass or white clover, Beever

et al. (1986b) reported a nearly 25% greater DMI of the clover pasture (26.0 vs. 20.9 g/kg

of LW). Although intakes are generally greater with legumes, the better performance

typically associated with their consumption may not be only an intake effect. Glenn

(1994, citing Tyrrell et al. 1992 and Varga et al., 1990) noted that the large differences in

digestible OM composition must have some effect on the composition of absorbed

nutrients.

Differences in digestible OM composition likely contribute to the greater

efficiency of ME use associated with legume consumption (Armstrong, 1982). Greater

energetic efficiency of lactating cows fed alfalfa in comparison with orchardgrass was

reported by Casper et al. (1993). The authors fed ensiled forages (direct-cut and treated

with formaldehyde and formic acid) with two high-starch concentrate sources (barley or

corn grain). Intakes of DM and ME and the digestibility of the DM were all greater for

the alfalfa-based diets. Although heat production was greater when cows consumed

alfalfa, heat production per unit of ME intake was greater for the orchardgrass diets. The






63

greater heat production/ME likely indicated "an increased energy cost associated with

digestion" of orchardgrass.

Although the greater DMI and efficiency of utilization reported with legumes is

desirable, legume use in pasture systems in warm climates often has been limited. Few

perennial legumes have been satisfactorily productive or persistent in forage systems in

subtropical regions of the humid Southeast, and some researchers have argued that

legumes have little place in production systems in the region (Rouquette et al., 1993). To

date, insects, nematodes, phytopathogens and poor persistence under grazing conditions

have relegated tropical legumes to limited roles in forage production systems in the

tropics (Maraschin et al., 1983).

Rhizoma Peanut

One legume with promise for the region, however, is rhizoma peanut (Arachis

glabrata Benth.). The legume is fine-stemmed and leafy, with potential for use in

grazing or stored-forage production systems (Prine et al., 1981). Introduced to Florida

from Brazil in 1936 and first distributed to commercial growers in 1978 (Prine et al.,

1986), most acreage expansion has occurred since 1980 (French, 1988). In 1990, an

estimated 1200 ha of rhizoma peanut (RP) had been planted in Florida (Niles et al.,

1990), with plantings increasing to 8100 ha by 1999 (E. C. French, personal

communication). The plant is being tried in other Deep South states as well (Prine et al.,

1986; Ocumpaugh, 1990; Mooso et al., 1995). Factors slowing its use by producers

include farmer unfamiliarity with the crop and high establishment costs (Prine et al.,

1986).






64

Another reason for RP's limited use may be its slow rate of establishment. In

studies by Valentim et al. (1987) and Terrill et al. (1996), RP was slower to establish than

alfalfa. In the study by Terrill et al. (1996), RP produced less DM than did alfalfa (cv.

'Pioneer 526') in the first 2 yr (11.9 vs. 6.1 Mg/ha). In the third year of the study,

however, DM production did not differ between RP and alfalfa (10.6 vs. 11.4 t/ha), and

leaf yield was greater for RP (6.2 vs. 5.4 metric t/ha). Similarly, Valentim et al. (1987)

found that RP outyielded alfalfa (cv. 'Florida 77') in the fourth year of their trial. Florida

77 has poor stand longevity, however, and over time this may affect comparison of yield

for the two forages.

Despite its establishment and propagation difficulties, RP may still be suitable to

the region. The forage has few disease or nematode problems (Prine et al., 1981;

Baltensperger et al., 1986), is palatable to a wide range of livestock (French et al., 1987),

and is persistent under grazing (Sollenberger et al., 1987).

An array of clipping regimes has been used to study the effects of defoliation on

nutritive value of RP. In a two-year study, Beltranena et al. (1981) examined the effects

of 2-, 4-, 6-, 8-, 10-, or 12-wk cutting intervals on yield, % CP, and % IVOMD. As

clipping interval increased, concentration of CP and IVOMD declined. Crude protein

percentage ranged from 21.9 to 14.7% and IVOMD from 74.3 to 64.8%. Saldivar et al.

(1990) also found decreases in concentrations of CP and IVOMD with increased interval

between clippings. Their results implicated leaf/stem ratio and its rate of change as

important factors influencing nutritive value.

Romero et al. (1987) investigated the effects of season and of increasing week of

regrowth on nutrient composition and digestibility of RP. They reported greater NDF






65

and ADF and lower CP concentrations for leaves of RP grown in summer vs. fall.

Response to regrowth intervals between leaf and stem fractions was variable, but

investigation of combined leaf and stem fractions showed increasing fiber and decreasing

CP concentrations with increasing maturity.

The concentration of CP in RP was less than that in alfalfa, while concentrations

of neutral and acid detergent fiber were greater (Romero et al., 1987; Terrill et al., 1996).

In situ experiments showed RP to have slower rates of DM disappearance than alfalfa

(Romero et al., 1987) but similar concentrations of highly soluble DM (24 vs. 27%) and

less potentially digestible (43 vs. 45%) DM (Romero et al., 1987). Although alfalfa had

greater disappearance of CP after 24 h (85 vs. 72%), the authors noted that even with less

CP, RP "may potentially contribute more protein post-ruminally than alfalfa" due to its

less ruminally soluble and potentially degradable protein.

In the study by Beltranena et al. (1981), yields of DM were 6.6 and 10.0 t/ha at

the 4- and 6-wk clipping intervals, respectively. Clipping intervals greater than 6 wk did

not increase DM yield. Forage had greater concentrations of CP and IVOMD at 4 wk

(20.1 and 72.9%) than at 6 wk (17.9 and 70.4%), and the authors suggested a 4 wk

defoliation interval might be a suitable compromise between quantity and nutritive value

for intensive grazing systems.

Ortega-S. et al. (1992) studied the effects of different grazing frequencies and

intensities by beef heifers on performance of RP pastures. With a 42-d grazing cycle, a

stand of 80% RP could be maintained if residual DM was 1700 kg/ha or greater. With a

21-d grazing cycle, the residual DM needed to maintain an 80% stand was 2300 kg/ha.

The study underscores the importance of proper grazing management of RP pastures.






66

Sollenberger et al. (1987) compared performance of stockers grazing either RP or

bahiagrass (Paspalum notatum Fliigge) pastures in a rotational stocking system without

supplement. Animals grazing RP had greater ADG than animals grazing bahiagrass (0.98

vs. 0.37 kg/d, respectively). Although bahiagrass pastures supported more animals (4.3

vs. 3.0 head/d) for a greater number of days (157 vs. 119 d), total gain/ha over the

growing season was greater for animals grazing RP (316 vs. 232 kg/ha).

Trials with growing goats also indicate that RP is a high quality forage. When fed

RP or alfalfa hays, growing goats eating RP always had numerically greater voluntary

intake, and significantly greater (P < 0.07) intakes for 9 wk of the 20-wk study (Gelaye et

al., 1990). Concentrations of NDF (45.3 vs. 45.8%), ADF (34.4 vs. 33.3%), and ADL

(8.9 vs. 8.0%) were similar for alfalfa and RP, respectively. Organic matter (OM)

concentration was 2 percentage units greater for RP. Apparent digestibility of OM and

fiber fractions was greater for RP. Goats consuming RP had both greater gain in BW and

feed conversion efficiency but less (P < 0.08) retained nitrogen and less ruminal

propionate concentration. Numerically less N retention, less (P < 0.09) ruminal

propionate concentration, and greater acetate:propionate ratio were also observed by

Gelaye and Amoah (1991).

Gelaye and Amoah (1991) fed growing goats complete diets containing either

10.5% (as-fed basis) ground RP or ground alfalfa hay. Diets containing RP had about

10% more NDF than those containing alfalfa, mostly due to a greater hemicellulose

concentration. Feed intake and ADG were numerically less but not significantly different

for animals consuming the RP diet. Apparent digestion coefficients for CP, NDF, and






67

hemicellulose tended to be greater (P < 0.07) when goats ate the diet containing RP.

Though not stated, this may have been due to slower rate of passage.

Staples et al. (1997) showed that RP silage is suitable for lactating dairy cows.

The researchers fed 50:50 forage:concentrate diets, substituting RP for corn silage at 0,

40, 70, and 100% of the forage source (0, 20, 35, and 50% of dietary DM). Milk yield

was greatest when cows ate diets with 20% RP silage, following the same pattern as

DMI. Linear decreases (P < 0.10) of both total VFA concentrations and body weight

gain (P < 0.05) were observed with increasing RP silage. This likely reflects lesser

concentrations of energy in RP silage as compared with corn silage.

Use of RP in grazing systems for lactating dairy cows has not been reported

previously. Questions needing research include effects of SR and supplementation rate

for animals grazing RP. Economic costs must particularly be considered because "slow

establishment, vegetative propagation, and the need for chemical weed control... [make]

rhizoma peanut...a high-input, management-intensive forage crop ... [requiring]

appropriate attention to all production needs and inputs" (Mooso et al., 1995). Such

requirement "costs" may be prohibitive despite its excellent pest resistance and nutritive

value characteristics.

Some Management Strategies for the Improvement of Milk Production in
Subtropical Environments

Bovine Somatotropin (bST)

Some of the original investigations of the efficacy of exogenous bST were

conducted with animals on pasture (Brumby and Hancock, 1955; Brumby, 1956), but the

majority of the related literature investigates its effects on the performance of cows in

confinement. Further, investigations of the use of bST with pastured cows primarily have






68

been limited to temperate climates (Brumby, 1956; Peel et al., 1985; Hoogendoom et al.,

1990; Chilliard et al., 1991).

Generally, bST injections increase milk production of cows on pasture. Results

from Chilliard et al. (1991) indicated no effect of bST on milk production, but the results

were confounded by a greater amount of concentrate feeding to control cows. Treated

cows tended to lose more weight, which was attributed to medium quality available

pasture and low amounts of concentrate supplementation.

Peel et al. (1985) tested the effects of growth hormone with five pairs of

monozygotic twins. One twin from each pair received a daily injection of 50 mg of

growth hormone for 22 wk. The animals grazed ryegrass-white clover pastures, and the

SR was intentionally kept low so as not to limit the animals' genetic potential. Milk

production increased nearly 18% with bST injection (19.8 vs. 23.3 kg of milk/d) but milk

composition was unchanged. Pasture intake, measured twice, was numerically greater

(8%) at the eighth week of the trial and significantly greater (14%) by the 22nd wk. Feed

conversion efficiency and BW were not changed, but the treatment group appeared to

have greater body condition loss during the first 4 wk of the trial.

A 10% increase in milk production due to bST was reported by Hoogendoorn et

al. (1990). Cows grazed ryegrass-white clover pastures and were injected bi-weekly with

a controlled release formulation that delivered 25-mg of bST/d. Milk yields totaled 2360

and 2600 kg/cow for the control and bST-treated cows over the 26-wk trial, with similar

increases in milk fat and protein production. Milk yield was greater when pasture was

not limiting. A period of warm, dry weather resulted in a decline in herbage production

and a concomitant convergence of group milk yields. Differences due to treatment





69

returned with provision of supplemental greenchop corn and increased pasture herbage.

Although the authors were unable to discern measurable differences in DMI, the changes

in production with changes in feed supply indicated that cows treated with bST likely had

greater intakes.

Intake differences were shown by Michel et al. (1990), who fed cut pasture

(ryegrass-white clover) to lactating dairy cows and found significant increases in DMI

within 4 wk of treatment with bST. Means of milk response were not reported, but cows

of low genetic merit had greater response to bST than did cows of high genetic merit.

Little difference in BW was observed over the course of the 50-d trial, but body condition

score was generally less for bST treated cows than for controls. This indicates the

necessity of providing adequate feed to meet the energy requirements of cows treated

with bST.

Valentine et al. (1990) reported that bST injections increased milk production

from cows grazing ryegrass-subterranean clover pastures and supplemented with a

barley-faba bean (Viciafaba) concentrate. Injections of 320 mg of a sustained release

formulation every 28, 21, or 14 d resulted in average dosages of 11.4, 15.2, or 22.8 mg/d.

Milk production was 17.6, 18.1, and 18.8 kg/d vs. 15.9 kg/d for control cows,

corresponding to 10.7, 13.8, and 18.2% increase in milk production with increased dose.

Live weights were also increased, and the authors attributed this to greater gut fill due to

greater pasture intake, although intake was not measured

Hartnell et al. (1991) explored dose responses within parities with much greater

levels ofbST administered (biweekly doses of 250, 500, or 750 mg ofbST) to cows in

confinement in four different geographic regions within the U.S.A. Averaged over






70

parities, production ranged from 25.2 to 31.5 kg of milk/cow per d, and increases above

control were 12.3, 15.9, and 25.3% for the three treatments, respectively.

Effects of Heat on Milk Production, and Cooling Strategies for Pastured Cows

Cool, comfortable cows produce more milk. Milk production and tolerance to

heat stress are likely inversely related (Smith and Mathewman, 1986) due to the high rate

of metabolism associated with milk synthesis (Marai and Forbes, 1989). Generally, feed

intake begins to decline when mean daily environmental temperatures reach 25 to 270C,

though this is modulated by climatic and nutritional factors (Beede et al., 1985; Beede

and Collier, 1986). Reductions in DMI occur due to decreased grazing activity, increased

water consumption and increased respiration, benefiting the heat-stressed ruminant by

reducing heat load via lessened heat of fermentation and gut metabolism (Roman Ponce

et al., 1978; Mallon6e et al., 1985). Ruminal contraction rates and ingesta passage rates

also decrease with elevated temperatures (Attebery and Johnson, 1969; Warren et al.,

1974).

Typically, the greater concentration of dietary roughage, the greater the reduction

in DMI with elevated ambient temperature (Beede and Collier, 1986). Thus, the negative

effects of high ambient temperature on animal production are generally greater for

grazing animals because reduction in feed intake is due mainly to reduced forage

consumption (Beede and Collier, 1986).

Technologies for heat stress abatement in confined-housing production systems

have made great advances in the past decade but are limited for animals on pasture.

Typical cooling methods for pasture systems include cooling ponds, fixed or mobile

shade structures, trees, and permanent structures such as barns. Immobile structures are






71

likely less suitable because of the potential for continued camping and concomitant

fouling in those areas of prolonged congregation. Increases in pests (flies and other

parasites) and infection (primarily mastitis) are possible. Generally, any mechanical

methods of cooling such as fans and misters are likely to be difficult to apply to large-

scale grazing systems and would be of limited suitability due to increased costs and the

potential for fouling the pastures. Some use of shades and misters with mobile irrigation

units have been attempted in Florida (J. Trout, personal communication), but no research

as to their efficacy has been reported.

Work by Missouri researchers indicates that the pattern of cooling is more

beneficial to improving production than provision of cooling in a general sense (Spain

and Spiers, 1999; Spiers et al., 1999). Cows had better performance responses when kept

at cooler environmental temperatures during the night. Cooling fans were more effective

at improving performance when used at night rather than in the daytime. Thus, cows

grazing in environments where differences between day and night temperatures are great

may not suffer the effects of heat stress as severely as cows in environments with little

change between day- and nighttime temperatures.

This cooling opportunity can be diminished, however, if the nighttime relative

humidity is high because moist air reduces the efficiency of evaporative cooling (West,

1994). Thus, a more appropriate measure of heat stress would be some combination of

temperature and humidity, such as a temperature humidity index (THI), as the one

referred to by West (1994). The THI is calculated as the dry bulb temperature - (0.55 -

0.55 * relative humidity) * (dry bulb temperature * 58), and mean THI greater than 72

reduce milk production (Johnson, 1987, cited by West, 1994).






72

bST in Hot Environments

Because of the increase in body temperatures associated with the use of bST,

concerns have been raised about its use on heat-stressed cattle (Kronfeld, 1988). In a

study by Mollett et al. (1985) milk production was not increased with bST administration,

and the authors suggested that a period of high heat and humidity affected the response to

treatment.

In a study of bST and shade effects, Zoa-Mboe et al. (1989) reported no increases

in milk production due to bST though milk production was increased with shade.

However, on a 3.5% fat-corrected basis, both shade and bST treatments increased milk

production to approximately 24 kg/d vs. 22 kg/d for control cows. Several positive

responses to bST when used in hot climates have been reported across Bos taurus breeds,

Bos species, and ruminant genera (Amiel et al. unpublished data; Ludri et al., 1989;

Phipps et al., 1991; West et al., 1990). Generally, provided sufficient quantities of a

balanced diet are available, bST is effective in hot conditions.

Amiel et al. (unpublished data) tested the effects of bST in several herds in

Jamaica. Milk production responses were similar across a variety of management

conditions, increasing approximately 17% with bST (9.9 vs. 11.6 kg of milk/d).

Performance responses from eight herds of Jamaican Hope cattle ranged from 16 to 30%

whereas 6 and 14% increases were observed for Holstein and Holstein cross cattle

injected with bST, respectively. Conditions were hot and humid, pasture forages were

generally inadequate due to a period of drought, and extra concentrate typically was not

fed to compensate for lack of sufficient pasture.





73

Johnson et al. (1991) tested the effects of bST in a 30-d farm trial in Florida, and

in a 10-d trial with cows in an environmental chamber in Missouri. Injections of bST

increased milk production by 21% (28.8 vs. 34.9 kg of 3.5% FCM/d) and 35% (21.0 vs.

28.3 kg of 3.5% FCM/d) for the farm and chamber studies, respectively. While the THI

in the farm trial generally remained above 72, and was maintained above 75 in the

chamber study, cows appeared capable of dissipating additional heat due to increased

production, likely by increased respiration rates. Elvinger et al. (1992) found that cows

treated with bST increased milk yield in both cool and hot environments. However, in

both environments, the bST treated cows had greater rectal temperatures, contrary to the

findings of Johnson et al. (1991).

Though administration of bST may or may not increase rectal temperatures

(Mohammed and Johnson, 1985; Zoa-Mboe et al., 1989; Elvinger et al. 1992) it often

causes increased respiration rates for cows in hot environments (Mohammed and

Johnson, 1985; Staples et al., 1988; Zoa-Mboe et al., et al., 1989). Mohammed and

Johnson (1985) and Staples et al. (1988) reported increased respiration rates with no

increases in rectal temperature, but increased temperatures were reported by Zoa-Mboe et

al. (1989) and West et al. (1990).

During a 10-d injection period in the study by Staples et al. (1988), respiration

rates tended (P = 0.084) to increase (78.2 vs. 84.1 breaths/min) with bST administration,

but body temperatures were not different (39.6 vs. 39.7 OC). Zoa-Mboe et al. (1989)

reported increases in respiration rates (107 vs. 113 breaths/min) and rectal temperatures

(39.8 vs. 40.0 �C) with bST treatments.






74

West et al. (1990) indicated that bST is efficacious under hot and humid

conditions, for both Jersey and Holstein cows. Milk production increased 21% with bST

administration, though the increase was greater for cows at one standard deviation below

pretreatment mean milk production. Response to bST for cows one standard deviation

above pretreatment mean milk production was non-significant. Both a.m. and p.m. body

temperatures were increased in cows administered bST. Treatment by breed interactions

were observed for both production and body temperature increases. Compared to

Jerseys, Holsteins had greater milk production increases in response to bST but lower

body temperature increases. The authors hypothesized that the increased body

temperatures partially explain the lower production responses of Jerseys. If this is

correct, then increases in temperature with bST cannot be explained solely by increases in

metabolism due to increased milk production, an idea supported by the work of Cole and

Hansen (1993).

While management strategies such as designed shading and bST improve animal

performance, few have investigated their use with lactating dairy cows grazing pasture

under hot conditions. More generally, grazing systems management for intensive dairy

production in hot climates has received little attention in the United States. While

utilization of grazing represents a potentially viable method of production in the

Southeast, the limited information for producers regarding recently released forages

adapted to the region, as well as responses to various management strategies prompted

the research that follows.














CHAPTER 3
PASTURE-BASED DAIRY PRODUCTION SYSTEMS: INFLUENCE OF FORAGE,
STOCKING RATE, AND SUPPLEMENTATION RATE ON ANIMAL
PERFORMANCE

Introduction

The economics of dairying in the United States has encouraged farmers to search

for new ways to reduce costs. While increasing herd size is a common option, many

smaller producers have begun using intensive rotational stocking systems to reduce

inputs. However, for producers using grazing in the Southeast, the climate presents

unique challenges to production. The ability to grow superior quality forages is of

particular concern for graziers (producers using grazing systems). Perennial, warm-

season forages typically are of lower nutritive value than either cool-season perennials or

warm-season annuals, but they do have the agronomic advantage of being adapted to the

region. Thus, despite their lower quality, forages such as bahiagrass (Paspalum notatum)

and bermudagrass (Cynodon dactylon (L.) Pers.) are the foundation of forage production

systems for grazing animals in the Southeast.

Recent literature regarding grazing dairy systems in the southeastern United

States is limited. The majority of data pertaining to dairy cow grazing in North America

has been published by researchers in the Northeast and Midwest under very different

environmental conditions. Some research from Australia and other tropical areas may be

applicable to the southeastern environment, but the forages grown are typically of

different genera and the amounts of concentrate fed are less than the amounts provided by



75






76

U.S. producers. Thus, our first objective was to investigate animal and pasture

productivity when two recently released forages were used as a grazing base for lactating

dairy cows.

Supplemental concentrate feeds typically are fed to lactating dairy cattle in the

U.S. The availability of inexpensive concentrates makes this possible and desirable,

especially since wholly forage-based diets cannot meet the energy requirements of high-

producing, lactating dairy cows. However, supplement can have a large effect on DMI

and rumen function, and thus production responses to supplement are inconsistent.

Providing supplement may not be profitable, and factors such as pasture and animal

management should be included when considering the efficacy of supplementation.

Thus, our second objective was to test animal and pasture production responses to two

rates of supplementation within each forage base.

The response to forage and supplement may depend upon stocking rate. Most

models describing the effect of stocking rate on production indicate that while production

per animal decreases with increasing stocking rate, production per land area increases.

Optimum pasture utilization typically requires stocking rates at which forage

consumption is limited, but excessively high stocking rates may limit production per land

area if pasture productivity is compromised. With high stocking rates, however, the

response to forage type or supplement may be greater than in situations in which forage is

not limiting. Because information about the effect of stocking rate and its interactions

with forage type and supplement level on the productivity of grazing, lactating dairy

cattle was not available, our third objective was to determine animal and pasture






77

production responses to two stocking rates within each forage-supplementation rate

combination

Materials and Methods

Cows, Design, and Treatments

Year one. On 10 July 1995, primiparous (n = 22) and multiparous (n = 22, mean

parity = 2.5) Holstein cows (mean DIM = 106 � 32) at the University of Florida Dairy

Research Unit, (29043' N latitude) were assigned to one of eight management treatments

arranged in a 2 X 2 X 2 factorial in two replicates. The main treatment factors were 1)

forage species grazed: bermudagrass (Cynodon dactylon XC. nlemfuensis cv. 'Tifton

85') (BG) or rhizoma peanut (Arachis glabrata cv. 'Florigraze') (RP), 2)

supplementation rate (SUP): 0.33 or 0.5 kg of supplement (as-is)/kg of daily milk

production, and 3) stocking rate (SR): 5 or 7.5 cows/ha for cows grazing BG pastures and

2.5 or 5 cows/ha for cows grazing RP pastures. All cows received 500 mg of

sometribove zinc (Posilac�; Monsanto, St. Louis, IL.) subcutaneously every 2 wk.

Each of the three experimental periods were 28 d in duration, with the first 14 d of

each period used for adjustment to a newly assigned treatment, and the last 14 d for

collection of data. In period 2, storm damage during the adjustment period caused a 10-d

delay. During this time, cows were kept on non-experimental pastures of their respective

forage assignment for period 2, and all cows were fed supplement at the greater rate.

Cows were assigned randomly to treatment for each period with the restriction that no

cow received the same treatment more than once, and the number of changes from a

given treatment to another treatment was balanced.






78

Soils were primarily of the Tavares (hyperthermic, uncoated Typic

Quartzipsamments) and Chipley (thermic, coated Aquic Quartzipsaments) series with

average P, K, and Mg concentrations of 99, 26, and 50 mg/kg, respectively.

Bermudagrass pastures were fertilized with 67 kg of N/ha on 22 May, 30 June,

and 1 September. Nitrogen was applied as NH4NO3 at the latter dates and as a

combination of NH4NO3 and (NH4)2SO4 on 22 May. All pastures received a total of 33

kg of S/ha on 22 May, with sulfur applied to RP pastures in the form of CaS04. In

addition, all pastures were fertilized with 67 kg of K20/ha in May.

In order to stage the forage growth, Holstein heifers (approximately 400 kg of

body weight (BW)) grazed both forages from 7 June to 1 July 1995. Stocking rates were

10 and 5 heifers/ha for BG and RP pastures, respectively, and animals were fed no

supplement. Experimental cows went onto pastures on 6 July, 4 d before the official start

of the trial.

Bermudagrass and RP pastures were divided into 22 and 29 paddocks

respectively, allowing for 21- and 28-d rest periods between grazing events. Cows were

kept in the bounds of individual paddocks with polywire fencing and paddocks were

back-fenced. Cows were provided shade structures and water tubs that were moved with

the cows to a fresh paddock each morning. Shade structures were 3-m tall, constructed of

galvanized metal pipe, stretched with 80 % shade cloth, and designed to provide a

minimum of 4.65 m2 of shade/cow.

Cows walked 0.4 to 1.2 km from pasture to the parlor for milking and back to

pastures twice daily. Cows were milked at approximately 0700 and 1800 h. Supplement

was a 4:1 mixture (as-fed) of high energy pellets:whole cottonseed (Table 3.1)






79

TABLE 3.1. Ingredient and chemical composition of supplements fed to lactating
Holstein cows on pasture.
--------Year--------
Item 1995 1996
Ingredients (% of DM)
Corn meal 40.2 --
Hominy -- 35.3
Soybean hulls 24.0 23.9
Soybean meal (48%) 7.2 9.6
Whole cottonseed 20.0 19.8
Dried cane molasses 4.0 5.0
Mineral mix' 1.0 --
Mineral mix2 -- 2.5
Calcium carbonate 1.0 1.3
Mono-Dical phosphate 0.4 --
Salt 0.4 --
Trace mineralized salt3 -- 1.3
Diabond 0.8 --
Sodium bicarbonate 1.0 1.3
Chemical composition
Dry matter, % 90.4 91.4
Ash, % 9.5 7.5
NEL, Mcal/kg ofDM4 1.90 1.89
NDF, % of DM 32.6 42.5
ADF, % of DM 23.3 27.7
CP, % of DM 15.6 18.0
Ca, % of DM 1.16 0.91
P, % of DM 0.43 0.61
Mg, % of DM 0.34 0.34
K,% of DM 1.13 1.33
Na, % of DM 0.64 0.93
S, % ofDM 0.19 0.20
Cl, % of DM 0.26 0.82
Fe, ppm, of DM 537 355
Zn, ppm, of DM 121 159
Cu, ppm, of DM 29.8 33
Mn, ppm, of DM 65.4 66
'Composition: > 55% Dyna-Mate, > 0.7% 1% Se, > 0.4% CoSO4, > 1.9% CuSO4,
> 2.6% ZnSO4, 0.7% MnSO4, 36.9% MgO, > 0.001% Cal, 1200 IU/g of vitamin A, > 700
IU/g of vitamin D3, > 300 IU/g of vitamin E.
2Composition: 3.8% N, 10.5% Ca, 3% P, 4.5% K, 2% Mg, 7.4% Na, 1.1% S, 5.4% Cl,
1525 ppm Mn, 1750 ppm Fe, 425 ppm Cu, 1500 ppm Zn, 12.8 ppm I, 49 ppm Co, 24.2
IU of vitamin A/g, 35.2 IU of vitamin D/g, and 0.88 IU of vitamin E/g.
Composition (g/100 g): NaC1, 92 to 97; Mn, > 0.25; Fe, > 0.2; Cu, > 0.033; I, > 0.007;
Zn, > 0.005; Co, > 0.0025.
4Calculated using 1989 NRC values for whole cottonseed.






80

Cows were divided into their respective SUP treatment groups (n = 2) post

milking and fed on a concrete feedbunk line. Amount of supplement offered was based

on the average milk production for each group, with feed amounts adjusted twice weekly.

This method of feeding potentially confounded the effects of SUP with effects of SR and

forage treatments but was considered a typical management practice of commercial

farms.

Year two. Holstein cows (n = 62) were evenly divided between one and > 1

parity. Mean parity for multiparous cows was 3.1 lactations and mean DIM for all cows

was 126 � 38.

Experimental design and choice of treatments were as in Year 1. However, based

on results from 1995, some modifications to protocol were implemented. Cows were not

treated with Posilac�. In 1995 pastures were deemed underutilized, so stocking rate

treatments were increased to 7.5 and 10 cows/ha for BG and 5 and 7.5 cows/ha for RP

pastures. During Year 2, NH4NO3 fertilizer was applied more frequently to BG pastures,

but the total quantity applied was slightly less than in 1995. Bermudagrass pastures

received 45 kg of N/ha as NH4NO3 on 21 May, 8 June, and 7 August. A fourth

application of 56 kg ofN/ha occurred on 11 September. Potassium was applied at 40 kg

of K20/ha on 7 June. Pastures were irrigated from 15 May to 12 June at a rate of 25

mm/wk for a total of 100 mm of water. Due to the loss of BG stand, one replicate pasture

assigned the low SR and low SUP treatments was removed from the study. Pastures were

staged with animals as previously described from 10 June to 6 July. The trial was from 9

July through 2 October 1996.






81

Cows were milked at approximately 0600 and 1800 h. An unpelleted supplement

(Table 3.1) was fed after each milking in troughs located in each paddock. The amount

of supplement fed was recalculated twice weekly. Feed troughs were moved with the

shade and water tubs each day.

Experimental Procedures

Animal measures. Milk weights were recorded at each milking. Milk samples

were collected at six consecutive milkings during each of the last 2 wk of each period.

Samples were analyzed by Southeast Dairy Labs (McDonough, GA) for fat and protein

concentrations and somatic cell count (SCC). Samples were analyzed for milk urea

nitrogen (MUN) in 1996.

Cows were weighed on three consecutive days at the initiation of the trial and at

the end of each period. Body weights were recorded after the a.m. milking and prior to

feeding of supplement. Body condition scores (BCS) were recorded on one of the weigh

days within each period (Wildman et al., 1982).

Respiration rates were recorded on 1 d of each period. Movement of the flank or

bobbing of the head was monitored over 1-min intervals. Measures took place while cows

were on pasture during the time of greatest potential ambient temperature (approximately

1400 to 1600 h). In 1996, rectal temperatures were measured with small, digital

thermometers (MedlineTM, Medline Industries, Inc., Mundelein, IL) after the p.m.

milking.

Blood was obtained from the coccygeal vessels on d 27 of periods 1 and 2 and d

19 in period 3 in 1995. Samples were collected on d 22 or 23 of each period in 1996.

Samples were collected into 9 ml Na-heparinized syringes (Luer Monovette,� LH,






82

Sarstedt, Inc., Newton, NC) after the p.m. milking and placed on ice. Blood was

centrifuged (2000 x g for 30 min) and plasma was collected and frozen at -20 �C on the

same day. Plasma from 1995 was analyzed for urea N (PUN) and glucose at the

USDA/ARS Subtropical Agriculture Research Station (Brooksville, FL) following the

procedures of Marsh et al. (1965) and Gochman and Schmitz (1972), respectively. In

1996, PUN was determined by kit (Kit 535-A, Sigma�, St. Louis, MO) and read on a

plate reader at 540 nm.

Chromium-mordanted fiber was used as an inert marker to determine organic

matter intake (OMI). Each period, forage was collected across all pastures and

composited for each species. Efforts were made to gather forage of quality similar to that

consumed. Forages were dried at 55 �C and ground with a stainless steel Thomas-Wiley

Laboratory Mill (Thomas ScientificTM, Philadelphia, PA) using a 2-mm screen. Fiber

from the forage was chromium mordanted according to the method of Ud6n et al. (1980).

The dried, ground forages (approximately 100 g/L H20) were boiled approximately 2 h in

a mixture of water and liquid laundry detergent (approximately 50 mL). After boiling,

the fibers were washed repeatedly with tap water to remove all soap, rinsed with acetone,

dried at 105 OC, and weighed. The dried forage (500 to 700 g) was placed in a metal

container, and sodium dichromate (100 to 140 g) dissolved in four volumes

(approximately 4 L) of water was added to the forage. Addition of Cr (as sodium

dichromate) equaled 7% of the fiber DM. This slurry was sealed with aluminum foil and

heated in a forced-air drying oven at 105 oC for 24 h. The liquid was then poured off and

the fiber was gently rinsed with tap water to remove excess and unbound Cr. Ascorbic

acid (Aldrich�, Milwaukee, WI) at half the dry fiber weight was mixed with water, added






83

to the fiber, and allowed to stand for 1 to 1.5 h. The fiber was rinsed thoroughly with tap

water and dried at 105 OC. Three � 0.02 g (air dry) ofmordanted fiber were weighed into

28-g gelatin capsules (Jorgenson Laboratories, Loveland, CO). Across the three periods,

average Cr concentration was 42,000 and 46,000 ppm (OM basis) for BG fiber, and

51,000 and 53,000 ppm for RP fiber for 1995 and 1996, respectively.

In all periods of both years, 32 cows were orally-dosed with nine gelatin capsules

containing Cr-mordanted fiber (27 g, as-fed) from their respective forage assignments.

Capsules were administered with a multiple dose balling gun (NASCO, Ft. Atkinson,

WI). In 1995, average dosing time was 1130 h on d 23 of each period. Fecal samples

were collected at approximately 0, 7.5, 19.5, 23, 27, 31, 44.5, 55.5, 68.5, 79.5, 92.5, and

103.5 h post-dosing. Samples at 23, 27, and 31 h post-dosing were collected on pasture at

the cows' leisure, while the remainder were grab samples taken in holding pens at the

milking parlor.

In 1996, cows were dosed after the evening milking on d 25, and fecal samples

were collected at approximately 0, 12, 15, 18, 21, 24, 27, 36, 42, 48, 60, 72, and 84 h

post-dosing. Collections were made on pasture at h 15, 18, 21, 27, and 42.

Fecal samples were refrigerated or frozen immediately after collection. In 1995,

samples from period 1 were dried at 55 �C and samples from periods 2 and 3 were freeze-

dried. In 1996, all samples were dried at 55 �C for at least 48 h. All fecal samples were

ground through a 1-mm screen with a Wiley mill. Samples (2 g, as-is) were dried at 105

�C and ashed at 550 �C for determination of DM and OM according to AOAC (1990)

procedures. Ash was digested in a solution of H2P04 (with added MnSO4) and KBrO3

using heat on a hot plate and analyzed for Cr by atomic absorption spectrophotometry






84

(Atomic Absorption Spectrophotometer 5000, Perkin Elmer, Norwalk, Conn.) following

the methods of Williams et al. (1962). For calculating DM intake, results from the fecal

sample analysis were evaluated with PROC NLIN following the method described by

Pond et al. (1987; Appendix 1). The parameters generated by this program then were

used to estimate fecal output for each cow.

To calculate the intake of pasture, the following assumptions were made:

1) intake of supplement was the same for all cows within a pasture replicate,

2) digestibility of supplement OM was equivalent to calculated TDN from NRC

(1989), and

3) digestibility of forage was affected by the level of supplement intake, as

determined by the equation of Moore et al. (1999; Appendix 2).

The measure of forage in vitro organic matter digestibility (IVOMD) for each

paddock was used to calculate forage intake by cows grazing that paddock (Pond et al.,

1987). Fecal output (kg/d) should equal total intake (kg/d) multiplied by the indigestible

fraction of a feed. Thus, estimates of fecal output are dependent upon accurate

determination of diet digestibility.

The fecal output observed based on the mordanted-fiber methodology did not

equal the fecal output predicted based on estimated forage and supplement digestibilities.

For this reason, an iterative SAS (1991) program (developed by J. E. Moore) was

employed to adjust the forage intake until the difference between fecal output observed

and fecal output predicted differed by less than 0.01 kg/d (Appendix 2).

Expected diet digestibility (% of OM) = [(forage intake, kg of OM * forage

digestibility, %) + (supplement intake, kg of OM* supplement digestibility, %)]/total






85

intake, kg of OM. Because feeding concentrate supplements often alters forage

digestibility (Arriaga-Jordan and Holmes, 1986; Berzaghi et al., 1996), the iterative

program also employed the equation of Moore et al. (1999; Appendix 2) to adjust total

diet digestibility.

Pasture measures. A double sampling technique was used to quantify pre- and

post-graze forage mass (Meijs et al., 1982). Every 2 wk of each period, 25 measures of

forage height were taken using a 0.25-m2, aluminum disk meter. Pre-graze measures

were recorded in paddocks to be grazed the following d, and post-graze measures were

made 1 or 2 d after the cows had grazed the paddock. At one sampling event in each

period, two or three samples were collected pre- and post-graze from one paddock per

pasture to establish a relationship between herbage mass (HM) and the recorded disk

heights. After dropping the plate of the disk meter on the forage, a metal ring was used to

mark the outline of the disk meter, and the forage within the ring was clipped at ground

level. The forage was dried at 55 OC for a minimum of 48 h to a constant weight.

Equations to predict pre- and post-graze forage mass were calculated by

regressing mass on disk height measured at double sampling sites. Regression equations

were assessed for the following data: all samples within a forage species, all pre- or all

post-graze samples within a forage, and pre- or post-graze samples within a period and

within a forage. After review of the data, HM equations for both years were derived from

pre- and post-graze measurements within periods within a forage.

Feed sampling. Once per period, forage was collected for characterization of

chemical composition and digestibility. Attempts were made to collect forage of quality

similar to that consumed after first inspecting an adjacent, grazed paddock. Twenty to 30






86

grab samples were taken from the next paddock to be grazed in each pasture, dried at

least 48 h at 55 �C, and ground through a 1-mm screen with a stainless steel Thomas-

Wiley Laboratory mill. Samples were analyzed by the University of Florida Forage

Evaluation Support Laboratory, Gainesville. For determination of organic matter (OM),

dried samples were ashed for at least 4 h at 5000C. The modified aluminum block

procedure of Gallaher et al. (1975) was used to digest samples prior to analysis for N by

the method of Hambleton (1977). Crude protein (CP) was then calculated as N * 6.25.

Determination of neutral detergent fiber (NDF) and IVOMD concentrations were made

using the procedures of Golding et al. (1985) and Moore and Mott (1974), respectively.

A single pelleted supplement sample and no whole cottonseed samples were

collected in 1995. In 1996, supplement (including whole cottonseed) samples were

collected three times in each period. Equal amounts of sample within periods were

composited, ground through a 1-mm screen, and submitted to the DHIA Forage Testing

Laboratory (Ithaca, NY) for analysis.

Statistical Analysis

Animals. Two cows from the 1995 trial were used in 1996 but were treated as

different animals for purpose of analysis. Data were analyzed using the GLM procedure

of SAS (1991) with the following model:

Yijklmnop = 1 + Ti + Pj + (Tp)ij + K(Tp)k(ij) +

al + Pm + (ap)lm + Yn + (ay)ln + (PY)mn + (aPY)lmn +

(pa)ji + (PP)jm + (Pap)jlm + (py)jn + (PaY)jln + (pPY)jmn + (PaPY)jlmn +

(T1)il + (TP)im + (Tap)ilm + (TY)in + (ray)iln + (tPY)imn + (TapY)ilmn +

(Tpa)il + (TPP)im + (TpaP)ilm + (Tpy)in + (TpaC)iln + (pPY)im +






87

(Tpapy)ilmn +

Vo +

5p(apY)imn +

Eijklmnop,

where

p = overall mean

Ti = effect of year

pj = effect of parity

K(TP)k(ij) = effect of cow within year and within parity

al = effect of forage

pm = effect of SUP

Yn = effect of SR

Vo = effect of period

6p = effect of pasture replicate within forage, SUP and SR treatments

Eijklmnop = effect of residual error.

Single degree of freedom orthogonal contrasts were made to test for treatment

effects. Treatments were considered different at P levels < 0.05 and trends are reported

for P < 0.10. Cow, parity, and their interactions were removed from the model for the

analysis of herbage data.

Results and Discussion

Forage Composition

Averaged across all pastures within forage treatments, estimates of digestibility

and nutritive value of RP were greater than for BG (Table 3.2). The RP pastures




Full Text
196
Hoover, W. H., and S. R. Stokes. 1991. Symposium: Carbohydrate methodology.
Balancing carbohydrates and proteins for optimum rumen microbial yield. J. Dairy Sci.
74:3630-3644.
Huber, J. T., G. C. Graf, and R. W. Engel. 1964. Effect of supplemental feeding of cows
on pasture on milk composition and yield. J. Dairy Sci. 47:63-67.
Hughes, G. P., and D. Reid. 1951. Studies on the behaviour of cattle and sheep in
relation to the utilisation of grass. J. Agrie. Sci. (Camb.) 41:350-366.
Huhtanen, P. 1987. The effects of barley, unmolassed sugar beet pulp and molasses on
milk production, digestibility and digesta passage in dairy cows given silage based diet.
J. Agrie. Sci. Finland. 59:101-120.
Huhtanen, P. 1988. The effects of barley, unmolassed beet pulp and molasses
supplements on organic matter, nitrogen and fibre digestion in the rumen of cattle given
silage diet. Anim. Feed Sci. Technol. 20:259-278.
Huhtanen, P. 1992. The effects of barley vs. barley fibre with or without distillers
solubles on site and extent of nutrient digestion in cattle fed grass-silage-based diet.
Anim. Feed Sci. Technol. 36:319-337.
Huhtanen. P. 1993. The effects of concentrate energy source and protein content on milk
production in cows given grass silage ad libitum. Grass Forage Sci. 48:347-355.
Hunter, R. A., and B. D. Siebert. 1986. The effects of genotype, age, pregnancy,
lactation and rumen characteristics on voluntary intake of roughage diets by cattle. Aust.
J. Agrie. Res. 37:549-560.
Hussey, M. A, and B. W. Pinkerton. 1990. Performance of bermudagrass and stargrass
under irrigated subtropical conditions. J. Prod. Agrie. 3:425-428.
Itoh, F. Y. Obara, M. T. Rose, and H. Fuse. 1998. Heat influences on plasma insulin and
glucagon in response to secretogogues in non-lactating dairy cows. Domest. Anim.
Endo. 15:499-510.
Jenkins, T. C. 1993. Symposium: Advances in Ruminant Lipid Metabolism. Lipid
metabolism in the rumen. J. Dairy Sci. 76:3851-3861.
Jennings, P. G. and W. Holmes. 1984a. Supplementary feeding of dairy cows on
continuously stocked pasture. J. Agrie. Sci. (Camb.) 103:161-170.
Jennings, P. G. and W. Holmes. 1984b. Supplementary feeding to dairy cows: a review.
Tropic Agrie. (Trinidad) 62:266-272.


158
temperature on plasma insulin concentrations in lactating cows, but Itoh et al. (1998)
reported decreased insulin concentrations in non-lactating cows exposed to heat. Calves
exposed to heat had decreased insulin concentrations within 0.5 h post-exposure and
differences were maintained through 24 h of observation (Takahashi et al., 1986).
Amounts of supplement fed do not explain the differences in insulin
concentrations because supplement provision was not different between housing
treatments. One explanation may be related to sampling time. Cows kept in bams did
not eat from approximately 0830 to 1800 h. Blood samples, collected at approximately
1700 h, would have been taken near the time of greatest nutrient depletion. These
changes are corroborated by the fact that plasma insulin concentrations of cows fed silage
in bam were similar to those of cows on pasture. In sheep infused with glucose, insulin
concentrations increased to a greater degree during heat stress (Achmadi et al., 1993).
Thus, the difference in plasma insulin concentrations between housing treatments may
reflect both greater sensitivity to available nutrients in cows on pasture and a decrease in
available nutrients for cows kept in the bam.
Effect of bST. Use of bST increased (P < 0.001) concentrations of plasma IGF-1
over controls nearly 70% (84.5 vs. 143 ng/ml of plasma). The bST treatment likely
affected IGF-1 both directly and indirectly via increased concentrate provision. McGuire
et al. (1992) reported that response to bST increased with increasing plane of nutrition.
The IGF-1 concentrations in bST-treated cows were similar to those reported by Staples
et al. (1988), but IGF-1 concentrations of untreated cows were about twice the
concentration reported for controls in that study.


150
to adjust forage digestibility due to associative effects of supplement feeding and thus
forage intake estimates, no additional adjustments to forage digestibility were made for
cows consuming com silage. If feeding com silage resulted in a greater depression of
forage digestibility, OMI was over-predicted.
Milk Production and Composition
Effect of housing. Daytime housing with fans and sprinklers did not affect milk
production (P < 0.11) of cows. Numerically, however, housed cows produced nearly 5%
more milk than unhoused cows (17.8 vs. 17.0 kg/cow per d, respectively) (Table 4.4).
Housing cows during the day tended (P <0.10) to increase production of 4% FCM by
5.5% (17.2 vs. 16.3 kg/d).
That differences between housing regimes did not significantly affect raw milk
production in this study is surprising given the greater energy expenditure of cows kept
on pasture. Maintenance costs for heat stressed cows increase above thermoneutral, but
intake typically declines with increasing temperature; thus milk production decreases
(Collier and Badenga, 1985). The greater milk production from housed cows despite
having similar OMI to those of pastured cows indicates a greater efficiency of nutrient
utilization for housed cows. It is certain that housed cows expended less energy for
maintenance because they walked less and experienced less heat stress.
Using cows of low milk production may have limited the ability to detect
treatment differences. Comparisons of shade vs. evaporative cooling using cows
producing much greater quantities of milk have been made (Chan et al., 1997; Chen et
al., 1993). Chan et al. (1997) reported a tendency of increased milk production with


11
requirements because of increased walking and grazing activities (NRC, 1989). The
increased energy requirements of these activities may lower energy balance, putting
downward pressure on voluntary DMI.
Some have suggested that intake capacity is in part a function of the energy
required for production. For example, increased rumen volume has been attributed to the
increased energy demand of lactation (Tulloh et al., 1965), and Redmond (1988, cited by
Allen, 1996) reported that weight of reticulorumen contents increased more than 40% in
the first 2 months of lactation in dairy cows. In a comparison of rumen load and
clearance between lactating and non-lactating sheep, Weston and Cantle (1982) showed
that both were increased by lactation.
Goetsch et al. (1991, p. 2635) reviewed 18 Latin-square experiments to
determine effects of various feedstuffs ... on intake and digestion by Holstein steer
calves ingesting bermudagrass hay ad libitum. The authors reported that fiber fractions
in the feeds were of negligible importance and the coincident absence of strong
relationships between bermudagrass composition and digestion ... implies that variation
in chemically fractionated fiber components of bermudagrass had little impact on nutrient
status and (or) gut fill regulation of DMI (p. 2639) further noting that growth and energy
utilization may have been involved with regulating DMI.
This remains a subject of debate, however. Friggens et al. (1998) fed constraining
or non-constraining diets over a lactation, switching the diets of half the dairy cows in
each test group at 153 days in milk. Diets were composed of grass silage and a barley-
based concentrate. The NDF concentrations of the diets were approximately 37 and 43%
and the ADF concentrations were approximately 21 and 26% for the low- and high-fill


CHAPTER 3
PASTURE-BASED DAIRY PRODUCTION SYSTEMS: INFLUENCE OF FORAGE,
STOCKING RATE, AND SUPPLEMENTATION RATE ON ANIMAL
PERFORMANCE
Introduction
The economics of dairying in the United States has encouraged farmers to search
for new ways to reduce costs. While increasing herd size is a common option, many
smaller producers have begun using intensive rotational stocking systems to reduce
inputs. However, for producers using grazing in the Southeast, the climate presents
unique challenges to production. The ability to grow superior quality forages is of
particular concern for graziers (producers using grazing systems). Perennial, warm-
season forages typically are of lower nutritive value than either cool-season perennials or
warm-season annuals, but they do have the agronomic advantage of being adapted to the
region. Thus, despite their lower quality, forages such as bahiagrass (Paspalum notatum)
and bermudagrass (Cynodon dactylon (L.) Pers.) are the foundation of forage production
systems for grazing animals in the Southeast.
Recent literature regarding grazing dairy systems in the southeastern United
States is limited. The majority of data pertaining to dairy cow grazing in North America
has been published by researchers in the Northeast and Midwest under very different
environmental conditions. Some research from Australia and other tropical areas may be
applicable to the southeastern environment, but the forages grown are typically of
different genera and the amounts of concentrate fed are less than the amounts provided by
75


107
Forage effects. Cows grazing RP pastures were more heat stressed, having
greater (P < 0.05) body temperature (39.4 vs. 39.1C) and greater (P < 0.05) RR (96 vs.
92 breaths/min) than cows grazing BG (Table 3.4). These measures, indicative of greater
energy expenditure, agree with the milk production and BW change responses.
Concentrations of PUN were also greater (P <0.01) for cows grazing RP pastures
(15.3 vs. 12.8 mg%). Though slight, the increased PUN concentration may represent an
additional energetic cost to detoxify ammonia for animals grazing RP.
From 1995 to 1996, PUN concentrations increased approximately 68% (from 9.6
to 16.1 mg%) for cows grazing BG pastures, compared with a 17% increase in PUN
concentrations (from 14.1 to 16.5 mg %) for cows grazing RP (year by forage interaction,
P < 0.001). Plasma urea N concentration reflects dietary CP status (Staples and Thatcher,
1999). The low concentration of PUN for cows grazing BG in 1995 may indicate that
dietary protein was limiting for cows grazing BG that year. Therefore, the CP
concentration of the supplement was increased in 1996.
Forage had no effect on plasma glucose concentrations. Primiparous cows had
greater plasma glucose concentrations than multiparous cows when grazing BG (59.8 vs.
57.8 mg %) but their plasma glucose concentrations were less than those of multiparous
cows when RP was consumed (57.4 vs. 58.6 mg %; parity by forage interaction, P <
0.01). This interaction likely reflects a greater tendency of increased substitution of
supplement for forage for multiparous cows grazing RP. The greater glucose
concentrations for primiparous cows grazing BG is less easily explained unless
primiparous cows were more aggressive at the feed bunk and more selective at grazing
greater quality forage. Little difference was observed in plasma glucose concentrations


56
differences in digestibility were unrelated to age at harvest, and that changes in IVDMD
apparently are related to environmental conditions not clearly understood under field
conditions Adjei et al. (1989) also reported that forage nutritive value typically was
greater in fall than in summer and differences between cultivars within seasons were
observed as well. Animal performance often mirrors these changes (Greene et al., 1990).
Holt and Conrad (1986) investigated decreasing leaf proportion as a source of
decline in forage digestibility because leaves are usually more digestible than stems.
Leafiness decreased with age but, though the decline in leaf proportion was a significant
factor, it explained less than 50% of the decline in forage digestibility (r2 = 0.44). The
authors noted that stem digestibility was a likely factor in cultivar digestibility
differences, but this was not explored. Genotype and seasonal effects on [IVDMD]
were greater than and largely independent of leaf effects when plant material was all the
same chronological age (p. 435). Similar results with respect to leaf proportion were
observed by Mathews et al. (1994a). They investigated IVOMD and nutrient
concentration of Callie bermudagrass in response to four methods of harvest. Pastures
were stocked continuously, rotationally stocked in short and long rotations, or cut for hay.
Leaf lamina as a percentage of the plant material sampled was least with continuous
stocking (33.5% across years) and averaged 47% with the other three methods. However,
the weighted mean of IVOMD was relatively stable (56.5%), not differing by more than
3.2 percentage units.
Location also determines the productivity and quality of bermudagrass in as much
as it combines such factors as rainfall or soil moisture, ambient temperature, soil
characteristics, and incident light. For example, though Adjei et al. (1989) did not


113
could be increased in proportion to the decrease in forage consumption, and based on
average SR across years, SR for BG could be increased from 7.5 to 8.25 cows/ha and SR
for RP could be increased from 5.0 to 6.0 cows/ha when feeding the greater amount of
supplement.
Year by supplement and parity by supplement interactions (P < 0.05) also were
observed for supplement OMIPBW. The data have little meaning, however, due to the
differences in BW across years and parities (data not shown).
Calculations of nutrient intake within forage and SUP treatment combinations
indicated that 4% FCM production likely was not limited by nutritional deficiency with
the exception of cows grazing BG and fed low amounts of supplement (Table 3.6). Cows
fed the lesser amount of supplement when grazing BG were likely deficient in daily
intake of DM, energy, and CP and had marginal intake of Ca and P. With BG managed
as in these experiments, large amounts of supplement must be fed or the supplement
nutrient concentrations must be adjusted to ensure adequate nutrient intake.
Conversely, supplement intakes were likely excessive for cows grazing RP. With
either SUP, cows grazing RP consumed excess CP (Table 3.6) that likely increased
maintenance costs due to the need for increased N excretion. Assuming all N in excess
of requirement was lost as urea, and using the NRC (1989) estimate of 7 kcal of ME/g of
N excreted, N excretion cost cows 1.2 or 1.7 Meal of ME/d with the low and high SUP
treatments, respectively. Only S intake appeared marginal regardless of SUP.
Comparison of our intake data with NRC estimates of nutrient requirements was
made as well (Table 3.7). The data represent only cows used in the intake estimate study.


TABLE 3.6. Calculated daily intake of nutrients1 by cows grazing Tifton 85 bermudagrass (BG) or Florigraze rhizoma peanut (RP)
pastures. Cows received supplement (SUP) at either 0.33 kg (Low) or 0.5 kg (High) (as-fed) per kg of daily milk production.
Ingredient
NEL1
DM
NDF
ADF
CP
Ca
P
Mg
K
Na
S
Cl
Fe
Zn
Cu
Mn
Mcal/d
- - kg/d -
g/d -
mg/d
Low SUP
BG
10.6
8.3
6.7
3.4
1.1
35
25
20
156
3
23
42
481
364
37
624
Supplement
8.8
4.6
1.7
1.2
0.8
48
24
16
57
36
9
25
2058
646
145
303
Total
19.3
12.9
8.5
4.6
1.9
82
49
36
212
39
39
32
2540
1010
182
927
High SUP
BG
9.8
7.7
6.2
3.2
1.0
32
23
19
144
2
21
38
445
336
35
576
Supplement
15.7
8.2
3.1
2.1
1.4
85
43
28
101
65
16
45
3676
1154
259
541
Total
25.4
15.9
9.3
5.3
2.4
117
66
47
245
67
37
83
4120
1490
293
1118
Low SUP
RP
18.7
13.3
5.9
4.3
2.4
221
35
56
218
1
21
58
492
524
36
477
Supplement
9.6
5.1
1.9
1.3
0.8
52
26
17
62
40
10
27
2255
708
159
332
Total
28.3
18.3
7.8
5.6
3.2
274
61
73
280
40
31
85
2746
1231
195
810
High SUP
RP
15.9
11.3
5.0
3.7
2.0
189
30
47
186
1
18
49
419
447
31
407
Supplement
16.9
8.9
3.3
2.3
1.5
92
46
30
109
70
17
48
3970
1246
279
585
Total
32.9
20.2
8.4
6.0
3.5
281
76
78
295
71
35
98
4389
1693
311
992
Requirement2
23.3
16.0
4.5
3.4
2.2
84
54
32
144
29
32
40
800
640
160
640
Calculated from the average of estimates presented in Tables 3.1 and 3.2.
Calculations based on NRC requirements for a 500 kg cow producing 20 kg of 4.0% FCM and gaining 0.275 kg/d. Intake was
assumed to be 3.2% of BW.


41
at the expense of fiber digestion. Similar results were found by England and Gill (1985)
who added sucrose to grass silage diets at 50, 75, 100, and 150 g/kg of silage DM. Silage
DMI was reduced, but not total DMI. With increasing proportions of dietary sucrose, a
corresponding decrease in cellulose digestion was observed. The results indicated that
the benefits of N utilization were offset by the decrease in diet digestibility, perhaps due
to the rapid solubility of the sucrose.
Phillips (1988) suggested com silage would be a suitable nutritional
complement to herbage of variable energy and high CP concentrations. An experiment
by Holden et al. (1995) indicated that supplemental silage fed to cows grazing pasture
might have altered ruminal fermentation and reduced N load because silage supplement
also reduced concentrations of plasma urea N from 29.6 to 27.3 mg/dL. This could not
be determined by the authors, however, because the change in plasma urea N
concentration with silage treatment could have resulted from better N utilization or
decreased intake of ruminally degradable protein. Production responses were unaffected
by supplemental silage.
In some experiments, microbial utilization of forage N was not markedly
improved by supplementation with barley (Thomas et al., 1980; Rooke et al., 1985).
Greater intraruminal N recycling due to increased ruminal protozoal number has been
implicated in the lack of N utilization by microbes (Chamberlain et al., 1985).
Substitution with fibrous concentrates such as beet pulp and distillers solubles for barley
has resulted in increased duodenal NAN primarily due to increased feed N flow
(Huhtanen, 1988, 1992) with concomitant increase in milk production and milk protein
yield (Huhtanen, 1987; Ala-Seppala et al., 1988).


GRAZING SYSTEMS AND MANAGEMENT STRATEGIES FOR LACTATING
HOLSTEIN COWS IN FLORIDA
By
JOHN HERSCHEL FIKE
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1999

ACKNOWLEDGMENTS
This work could not have been completed without the assistance of several
people. Thanks first go to my wife, Wonae, without whose patience, assistance and
understanding this work could not have been completed. The support and encouragement
of the authors parents and family also were instrumental in making this dissertation
possible.
The author wishes to express his gratitude for the teaching, direction and patience
received from his advisors Dr. Charles R. Staples and Dr. Lynn E. Sollenberger. The
Churchillian words of encouragement from Dr. Staples that came during some dark hours
will not be forgotten.
Thanks also go to Dr. John E. Moore for encouragement, mentoring, and excellent
teaching. Drs. Mary Beth Hall and Peter J. Hansen also were instrumental to this work
by providing excellent teaching and assistance whether in or out of the classroom.
To my plastic-sleeved compatriots, Bisoondat Maccoon and Renato Fontanelli,
the wish is extended that though you have adequate sample, your fecal-sample cups will
never runneth over.
Others to be recognized for their help include D. Hissem, J. Lindsay, and M.
Russell for farm support, Drs. R. E. Littell and C. R. Wilcox for statistical assistance, and
Dr. H. H. Head for assistance with immunoassays. Thanks to O. A. Carrijo, Jr., J. Hayen,
E. M. Hirchert, and J. P. Jennings for assistance in the laboratory, at the farm, or both.
li

Thanks for the generous financial assistance given by the Dean for Academic
Programs for the first year and the Department of Dairy and Poultry Sciences for the
remaining years. Thanks also go to American Farm Bureau, CBAG, and Monsanto for
their financial assistance of the research.
in

TABLE OF CONTENTS
page
ACKNOWLEDGMENTS ii
LIST OF TABLES vii
LIST OF FIGURES ix
KEY TO ABBREVIATIONS xi
ABSTRACT xii
CHAPTER 1. INTRODUCTION 1
CHAPTER 2. LITERATURE REVIEW 3
Climatic Challenges to Southeastern Dairies 4
Climatic Animals 6
Energy Considerations for the Grazing Ruminant 7
Some Animal and Nutritional Factors Influencing Feed Intake 9
Some Non-Nutritional Factors Affecting Behavior and Forage Intake of Grazing
Ruminants 13
Mechanistic Components of Forage Intake 13
Daylight and Temperature 17
Measurement of Forage Intake in Grazing Ruminants 18
Herbage Allowance and Stocking Rate Effects on Forage Intake and Performance
of Ruminants 21
Supplement Effects on Animal Performance with Particular Emphasis on
Lactating Cows in Pasture-Based Dairy Systems 25
Supplement Effects on Production 26
Supplement Effects on Intake 29
Supplement Effects on Forage Digestibility 33
Synchronizing Nitrogen and Carbohydrate Supplements to Increase Microbial
Protein Synthesis in the Rumen 37
Loss of Feed Nitrogen in Ruminants 37
Responses to Supplemental Carbohydrate 39
Effects of Supplement Feeding Frequency 42
Effects of Timing of Supplement Provision Relative to Forage Intake 44
Additional Energy and Protein Supplements for Animals on Pasture 45
Fats 45
Escape Proteins 46
IV

Effect of Supplements on Grazing Behavior 47
Interactions of Supplement and Herbage Allowance on Performance of Lactating
Cows in Pasture-Based Dairy Systems 49
Two Perennial Forages for Lactating Cows in Pasture-Based Dairy Systems in the
Southeast 51
Bermudagrass 51
Comparisons of Grasses and Legumes 60
Rhizoma Peanut 63
Some Management Strategies for the Improvement of Milk Production in
Subtropical Environments Systems 67
Bovine Somatotropin (bST) 67
Effects of Heat on Milk Production and Cooling Strategies for Pastured Cows 70
bST in Hot Environments 72
CHAPTER 3. PASTURE-BASED DAIRY PRODUCTION SYSTEMS:
INFLUENCE OF FORAGE, STOCKING RATE, AND
SUPPLEMENTATION RATE ON ANIMAL PERFORMANCE 75
Introduction 75
Materials and Methods 77
Cows, Design, and Treatments 77
Experimental Procedures 81
Statisitical Analyses 86
Results and Discussion 87
Forage Composition 87
Milk Production and Composition per Cow 89
Milk Production per Land Area 100
Body Weight and Condition 101
Respiration, Temperature, and Blood Metabolites 105
Intake of Organic Matter and Nutrients 109
Treatment Effects on Forage Nutritive Value Estimates 117
Treatment Effects on Herbage Mass, Availability, and Intake Estimates as
Determined by Pasture Sampling 120
Simple Economic Assessment of Supplementation 125
Conclusions 127
CHAPTER 4. PASTURE-BASED DAIRY PRODUCTION SYSTEMS:
INFLUENCE OF HOUSING, bST, AND FEEDING STRATEGY ON
ANIMAL PERFORMANCE 130
Introduction 130
Materials and Methods 131
Cows, Design, and Treatments 131
Experimental Measurements 134
Statistical Analysis 142
Results and Discussion 145
Grazing Time and Intake of Organic Matter 145
Milk Production and Composition 150
v

Body Weight and Composition 155
Plasma IGF-1 and Insulin 157
Respiration Rates and Body Temperatures 159
Conclusions 163
CHAPTER 5. FINAL SUMMARY AND CONCLUSIONS 167
APPENDIX 1. SAS PROGRAM OF POND ET AL. (1987) FOR THE
ESTIMATION OF FECAL OUTPUT 181
APPENDIX 2. SAS PROGRAM TO ADJUST FORAGE INTAKE UNTIL
FECAL OUTPUT OBSERVED AND FECAL OUTPUT PREDICTED
DIFFER BY LESS THAN ONE-HUNDREDTH OF A KILOGRAM PER
DAY 182
APPENDIX 3. RAINFALL AND TEMPERATURE DATA FOR GRAZING
TRIALS IN 1995, 1996, AND 1997 183
LIST OF REFERENCES 184
BIOGRAPHICAL SKETCH 214
vi

LIST OF TABLES
Table page
3.1 Ingredient and chemical composition of supplements fed to lactating Holstein cows
on pasture 79
3.2 Nutritive value characteristics, chemical composition, and calculated net energy of
lactation (NEl) and total digestible nutrients (TDN) of Tifton 85 bermudagrass and
Florigraze rhizoma peanut pastures. Samples were hand-plucked once each period,
based on visual appraisal of forage consumed by grazing cows.
88
3.3 Effect of forage, stocking rate (SR), and supplementation rate (SUP) on milk
production and composition of Holstein cows grazing Tifton 85 bermudagrass and
Florigraze rhizoma peanut during the summers of 1995 and 1996 90
3.4 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on
body weight (BW) and body condition score change (ABCS), respiration rate (RR),
body temperature (TEMP), and plasma urea nitrogen (PUN) and plasma glucose of
Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut
during the summers of 1995 and 1996 102
3.5 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on
forage, supplement and total organic matter intake (OMI), and on forage,
supplement, and total organic matter intake as a percent of bodyweight (OMIPBW)
of Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut
during the summers of 1995 and 1996 110
3.6 Calculated daily intake of nutrients by cows grazing Tifton 85 bermudagrass (BG)
or Florigraze rhizoma peanut (RP) pastures. Cows received supplement (SUP) at
either 0.33 kg (Low) or 0.5 kg (High) (as-fed) per kg of daily milk production 114
3.7 Effect of forage, stocking rate (SR), and supplementation rate (SUP) on bodyweight
(BW) change, 4% fat corrected milk (FCM) production, and measures of energy (E)
status of Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma
peanut during the summers of 1995 and 1996 115
3.8 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on
forage, supplement and crude protein (CP), in vitro organic matter digestibility
(IVOMD), and neutral detergent fiber (NDF) concentrations in Tifton 85
Vll

bermudagrass and Florigraze rhizoma peanut during the summers of 1995 and 1996.
Samples were hand-plucked once each period based on visual appraisal of forage
consumed by grazing cows 118
3.9 Regression groupings and regression coefficients for predicting 1995 and 1996 pre-
and post-graze herbage mass of Tifton 85 bermudagrass and Florigraze rhizoma
peanut pastures 121
3.10 Disk meter estimates of the effect of forage species, stocking rate (SR), and
supplementation rate (SUP) on forage pre- and post-graze herbage mass (HM),
herbage allowance (HA), and dry matter intake (DMI) of grazing, lactating Holstein
cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut during the
summers of 1995 and 1996 122
3.11 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on milk
income minus supplement costs (MIMSC), assuming supplement intake
proportionate to LS means of milk production within a given SUP treatment and
calculated on both per cow and per land area bases 126
4.1 Supplement ingredients 133
4.2 Chemical composition, and nutritive value of supplement, com silage and
bermudagrass pasture 133
4.3 Influence of housing (0800 to 1500 h on pasture or in bams with fans and
sprinklers), bST, and bST with supplemental silage on organic matter intake (OMI)
of Holstein cows grazing Tifton 85 bermudagrass pastures 146
4.4 Influence of housing (0800 to 1500 h on pasture or in bams with fans and
sprinklers), bST, and bST with supplemental silage on milk production and
composition of Holstein cows grazing Tifton 85 bermudagrass pastures 151
4.5 Calculated daily intake of nutrients by cows grazing Tifton 85 bermudagrass (BG)
pastures and not treated (-bST) or treated (+bST) with exogenous growth hormone.
An additional treatment tested the effect of feeding com silage (Silage) to cows
treated with bST 153
4.6 Influence of housing (0800 to 1500 h on pasture or in bams with fans and
sprinklers), bST, and bST with supplemental silage on body weight (BW), body
condition score (BCS), respiration rates (RR), and concentrations of plasma insulin
and insulin-like growth factor-1 (IGF-1) of Holstein cows grazing Tifton 85
bermudagrass pastures 156
vm

LIST OF FIGURES
Figure page
3.1 Interaction of forage [Tifton 85 bermudagrass (BG) or Florigraze rhizoma peanut
(RP)] and year (1995 or 1996) on production of milk, 4% fat corrected milk (FCM),
and milk fat and milk fat percent 92
3.2 Interaction of forage, stocking rate (SR), and year on milk and 4% fat corrected milk
(FCM) yields and body weight change (DBW). Forages were Tifton 85
bermudagrass and Florigraze rhizoma peanut. Low and high SR for BG were 5.0
and 7.5 cows/ha in 1995 and 7.5 and 10.0 cows/ha in 1996. Low and high SR for
RP were 2.5 and 5.0 cows/ha in 1995 and 5.0 and 7.5 cows/ha in 1996 93
3.3 Interaction of supplementation rate and forage species on production of milk, 4% fat
corrected milk (FCM), milk fat, and protein. Supplementation rates were 0.33 (Lo)
and 0.5 (Hi) kg of supplement per kg of daily milk production. Forage species were
Tifton 85 bermudagrass and Florigraze rhizoma peanut 95
3.4 Interaction of supplementation rate and year on production of 4% fat corrected milk
and milk fat, and percentages of milk fat and protein. Low (Lo) and high (Hi)
supplementation rates were 0.33 and 0.5 kg of supplement per 1 kg of daily milk
production, respectively 98
3.5 Interaction of parity, year, and supplementation rate on production of milk, 4% fat
corrected milk (FCM), and milk fat and milk fat percent. Low (Lo) and high (Hi)
supplementation rates were 0.33 kg and 0.5 kg of supplement per kg of daily milk
production. Supplementation rates did not differ by year (1995 or 1996) 99
3.6 Interaction of parity, forage, and stocking rate on body weight change (ABW).
Average low (Lo) and high (Hi) stocking rates were 6.25 and 8.75 cows/ha for
Tifton 85 bermudagrass (BG) and 3.75 and 6.25 cows/ha for Florigraze rhizoma
peanut (RP) pastures. Stocking rates were the same across parities 104
3.7 Interaction of supplementation rate and year on changes of body condition score
(ABCS 5 point scale) and body weight (ABW). Low (Lo) and high (Hi)
supplementation rates were 0.33 and 0.5 kg of supplement per kg of daily milk
production 104
IX

3.8 Interaction of forage, supplementation rate, and year on body weight change (ABW).
Forages were Tifton 85 bermudagrass and Florgraze rhizoma peanut. Low (Lo) and
high (Hi) supplementation rates were 0.33 and 0.5 kg of supplement per 1 kg of
daily milk production. Supplementation rates did not differ by year (1995 or
1996) 106
3.9 Interactions of parity, forage, and stocking rate (SR) on forage and total organic
matter intake (OMI) and forage and total OMI as a percent of body weight
(OMIPBW)- Forages were Tifton 85 bermudagrass (BG) or Florigraze rhizoma
peanut (RP). Average low and high SR for BG pastures were 6.25 and 8.75
cows/ha. Average low and high SR for RP pastures were 3.75 and 6.25 cows/ha.
112
4.1 Vibracorder charts for cows treated with bST and housed in bams from 0800 to
1500 h (A) and for cows housed on pasture (B). Note the greater grazing intensity
for cows housed in the bam during the day 147
4.2 Effect of housing on body temperatures of cows measured over a 24-h period and
averaged over bST treatment regimes 160
4.3 Effect of bST on body temperatures of cows measured over a 24-h period and
averaged over daytime bam and daytime housing regimes 162
4.4 Regression equation estimates of body temperatures of cows measured over a 24-h
period and showing interaction of bST (+ or -) and housing treatments 164
4.5 Effect of bam plus bST (B+) vs. bam plus bST plus silage (B+S) treatment on body
temperatures of cows measured over a 24-h period 165
x

KEY TO ABBREVIATIONS
ADF acid detergent fiber
ADG average daily gain
BCS body condition score
BG Tifton 85 bermudagrass
bST bovine somatotropin
BW body weight
CP crude protein
DE digestible energy
DM dry matter
DMI dry matter intake
FCM fat corrected milk
FI forage intake
GT grazing time
HA herbage allowance
HM herbage mass
IB intake per bite
IGF-1 insulin-like growth factor 1
IVDMD in vitro dry matter digestibility
IVOMD in vitro organic matter digestibility
ME metabolizable energy
MUN milk urea nitrogen
MY milk yield
N nitrogen
NAN non-ammonia nitrogen
NDF neutral detergent fiber
NEl net energy of lactation
NEFA non-esterified fatty acid
NRC National Research Council
NSC non-structural carbohydrate
OM organic matter
OMI organic matter intake
PUN plasma urea nitrogen
RB rate of biting
RP Florigraze rhizoma peanut
SCC somatic cell count
SR stocking rate
SUP supplementation rate
THI temperature-humidity index
TMR totally mixed ration
TT temperature transponder
xi

Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
GRAZING SYSTEMS AND MANAGEMENT STRATEGIES FOR
LACTATING HOLSTEIN COWS IN FLORIDA
By
John Herschel Fike
December, 1999
Chairman: Charles R. Staples
Major Department: Dairy and Poultry Sciences
Two experiments tested effects of two pasture forage species, the legume rhizoma
peanut (RP; Arachis glabrata) or bermudagrass (BG; Cynodon spp. cv. Tifton 85), two
supplementation rates (SUP; 0.33 or 0.5 kg/kg of milk), and two stocking rates (SR) on
performance of mid-lactation Holstein cows.
The RP supported more milk per cow (17.3 vs. 16.3 kg/d), but less milk per
hectare than BG pastures. With each additional kg of supplement fed above the low SUP,
cows produced an additional 0.87 kg of milk/d if grazing BG vs. an additional 0.43 kg of
milk/d if grazing RP.
Respiration rates and body weight (BW) losses generally were greater when
treatments stimulated milk production. Optimum SR for BG and RP pastures were
approximately 10 and 5 cows/ha. Cows grazing RP had greater forage (11.3 vs. 7.6 kg/d;
Xll

2.26 vs. 1.52% of BW) and total (17.7 vs. 13.5 kg/d; 3.54 vs. 2.70% of BW) organic
matter intakes (OMI). Increased supplement provision increased daily OMI, but
decreased forage intake. Substitution of forage with supplement (kg/kg) was 0.51 for RP
and 0.18 for BG.
A third experiment tested the effects of housing pasture-based cows in bams or on
pasture from 0800 to 1530 h. Within housing treatments, cows did or did not receive
bST. A fifth treatment tested the effect of feeding silage to barn-housed cows injected
with bST.
Intake of pasture and milk production were similar for both housing managements
although cows housed in bams spent less time grazing. Treatment with bST increased
milk production (18.1 vs. 16.6 kg/d). Production was unaffected by silage intake.
Housed cows and bST-treated cows maintained or gained BW. Respiration rates
and body temperatures were greater for pastured cows, and body temperatures were
greater in cows given bST.
Improved grasses in combination with large amounts of supplemental feeds are
likely most suited for pasture-based dairy production systems in Florida. Providing fans
and sprinklers to relieve heat stress and injecting with bST was only moderately effective
to stimulate milk production of midlactation cows in a pasture-based system.
xiii

CHAPTER 1
INTRODUCTION
While use of pasture-based production systems is the norm for beef production in
the U.S., pasture use for dairy production was all but abandoned until the mid- to late
1980s when management of pastures using intensive rotational stocking began to be
adopted. During a time of financial duress, pasture systems garnered renewed interest,
primarily due to perceptions that they have reduced production costs, require less initial
investment, have less demanding labor requirements, and are more environmentally
sound than production with confined-housing.
Information regarding their use is limited, however, particularly for producers in
the Southeast. Regardless of the production system, producers in the Southeast must
overcome several challenges to be successful. The lesser quality of perennial forages
adapted to the region and the negative effects of high heat and humidity on animal
performance are the primary limitations to production. Thus, information in this arena is
vital because the challenges to production likely are more formidable for pasture-based
dairies.
Forages adapted to the region typically are of less quality than cool-season species
due to greater concentrations of fiber and lower concentrations of digestible nutrients.
Other potential limitations of pasture-based systems include variability in forage supply
and nutritive value, both of which are highly dependent upon climatological conditions.
1

2
Pasture-based production systems are energetically demanding of the animal.
Cows face greater energy requirements for walking and foraging in addition to energy
demands for dissipation of heat load during periods of high ambient temperature and high
humidity. Such requirements may limit severely the nutrients available for production.
Production potential of pasture-based dairies may also be affected by numerous
management practices. Issues of particular concern include suitability of available forage
species, types and amounts of supplement to feed, appropriate stocking rates, effects of
management strategies upon animal production and physiology, and the interactions of
these factors.
The studies described herein were conducted to test the effects of forage species,
supplementation rate, stocking rate, and some potential management practices on animal
intake and performance. Some simple estimates of income are also reported along with
concluding statements regarding the viability of such systems.

CHAPTER 2
LITERATURE REVIEW
Since the 1980s, the economics of dairying in the United States has put farmers in
a severe cost-price squeeze (Muller et al., 1995). Reducing feed costs has become critical
because these costs are estimated to account for 50 to 60% of operating costs (Elbehri
and Ford, 1995). To cope with this economic reality, many dairies using confined
housing have increased herd size. Technological advances have helped drive this change
(Lanyon, 1995), and typically are most profitable when employed on a large scale
(Thomas et al., 1994). Increasing herd size can help farmers reduce feed costs per cow
by increasing purchasing power with larger commodity purchases (Lanyon, 1995).
Further, fixed costs can be reduced by increased use of farm equipment and greater
throughput of cows through the milking parlor. These management changes rely upon
increased efficiencies and greater milk production to increase profit but both increased
herd size and increased technological sophistication have resulted in dairy production
becoming an even more capital-intensive agribusiness (Thomas et al., 1994, p. 1).
Facing the same economic and environmental pressures as other dairies but
without the ability or desire to expand the size of their herd and facilities, some producers
have opted for another way to improve profitability. Their strategy relies on reduced
levels of inputs and lower cost structures (Parker et al., 1993). This is attempted by use
of alternative forage feeding systems, particularly, intensive grazing (Elbehri and Ford,
1995). Smaller farms have been subjected to greater financial stress than properties
3

4
supporting large herds (Parker et al., 1992, p. 2587, citing Hallberg and Partenhiemer,
1991, and citing Kaffka, 1987), thus it is understandable that most interest in grazing
systems has been shown by dairy producers with herds of fewer than 100 cows (Parker
et al., 1992, p. 2587).
Milk production per cow or farm may decrease in grazing herds as producers
change from management of confined housing to management of grazing systems, but
graziers assume that the decrease in production costs is greater than the cost of lost milk
production, thus gamering greater net profit. Some studies (Emmick and Toomer, 1991;
Parker et al., 1992) have indicated returns per cow can increase from $85 to $165 with
the use of pasture (Muller and Holden, 1994). Other reasons cited for choosing pasture-
based production systems include reduced labor, best land use, improved cow health, and
reduced manure handling, as well as improved quality of lifestyle for the owner/manager
(Loeffler et al., 1996). One survey indicated that total hours of labor were not decreased
in grazing-based systems, but that time devoted to various tasks changed as that activitys
importance in the system changed (Loeffler et al., 1996).
Climatic Challenges to southeastern Dairies
Regardless of the production system, the climate of the Southeast presents unique
challenges for producers in the region. Of particular concern is the effect of heat and
humidity on both plants and livestock. The effect of the climate may be more adverse for
animals on pasture.
Climatic Effects on Forages
The perennial, warm-season forages adapted to the Southeast are typically of
lower nutritive value than either cool-season perennials or warm-season annuals

5
[National Research Council (NRC), 1989], Even at similar NDF and lignin
concentrations, warm-season grasses are less digestible than cool-season grasses (Barton
et al., 1976; Mertens and Lofton, 1980). Minson and McLeod (1970) reported that the
mean DM digestibility coefficient for tropical grasses was 13 percentage units less than
that of temperate grasses. When grown at warmer temperatures, forages have greater
concentrations of fiber and are less digestible than those grown under more temperate
conditions (Deinum and Dirven, 1976; Fales, 1986). Greater humidity also creates
potential for additional plant stresses via increased phytopathogen load.
For southeastern producers using confined-housing systems, growing high quality
forages may be of limited concern. Despite the climatological challenges, acceptable
quality maize (Zea mays L.) silage can be grown locally and high quality alfalfa
(Medicago sativa L.) hay is available for purchase from growers in western states.
Moreover, producers in the region using confined-housing frequently use by-product
feeds such as brewers and distillers grains, whole cottonseed, and cottonseed hulls.
These feeds may supply substantial portions of the diets roughage, potentially reducing
the need for homegrown forages.
The ability to grow superior quality forages is of particular concern for graziers
(producers using grazing systems). Perennial, warm-season forages typically are of
lower quality than cool-season forages as measured by comparisons of animal
performance (Galloway et al., 1993b). Stobbs (1976, cited by Ruiz, 1983) showed that
Jersey cows grazing immature tropical pastures produced approximately 60% as much
milk as those grazing temperate pastures. Cool season species generally are considered
to be of greater quality due to greater digestibility because of differences in the relative

6
amount and arrangement of tissues (Akin, 1986a,b, p. 194). However, warm-season
species do have the agronomic advantage of being adapted to the region. Thus, despite
their lower quality, forages such as bahiagrass (Paspalum notation) and bermudagrass
(Cynodon dactylon (L.) Pers.) are the foundation of forage production systems for
grazing animals in the Southeast.
Other forage quality concerns for graziers may include pasture variability in
supply and nutritive value over the course of the growing season (Holt and Conrad,
1983). Changes may correspond with changes in climatic conditions, such as
temperature, soil moisture, leaf/stem ratio and the proportions of dead leaves in the sward
(Beaty et al., 1982; Henderson and Robinson, 1982). Grazing dairies, reliant upon locally
grown perennial forages, thus are likely more susceptible to changing forage quality than
many dairy farms using confined housing.
Climatic Effects on Animals
Higher environmental heat and humidity affect dairy cows negatively by limiting
their ability to dissipate body heat. In such circumstances, cows are likely to decrease
DMI, and in more severe conditions may also suffer from heat-related disorders such as
respiratory alkalosis/metabolic acidosis, ketosis related to excessive decrease of DMI,
and laminitis associated with feeding diets of large concentrations of grain (Sanchez et
al., 1994; Nocek, 1997; 0rskov, 1999). Heat stress also impairs the cows reproductive
performance and embryo survival (Thatcher and Collier, 1986; Wolfenson et al., 1988;
Ealy et al., 1993).
Heat stress can be mitigated with cooling technologies. The technological
advances in confined-housing systems include well-ventilated bams with high roofs and

7
high-speed fans with wetting mechanisms (Flamenbaum et al., 1986; Chen et ah, 1993;
Chan et ah, 1997). Such facilities increase shade and evaporative cooling, providing
relief from excessive ambient temperatures.
Ways to cool cows on pasture are limited, however. Fixed and mobile shade
structures, trees, cooling ponds, and strategic movement (e.g. allowing cows access to
cooling bams during times of high ambient temperature) represent the major methods
used to reduce heat stress of pastured animals. In addition, pastured cows face additional
heat stress from the heat of activity caused by grazing and walking to and from the parlor.
Thus, the effect of heat stress is likely of greater concern for graziers.
Recent literature regarding grazing dairy systems in the southeastern United
States is limited, although results with beef steers on pasture may have application. The
majority of data pertaining to dairy cow grazing in North America has been published by
researchers working in the Northeast and Midwest under very different environmental
conditions. Some research from Australia and other tropical areas may be applicable to
the southeastern environment, but the forages grown are typically of different genera and
the amounts of concentrate fed are less than the amounts provided by U.S. producers.
Thus, while pasture-based dairies may be a viable alternative to confined housing
systems in the Southeast, more information on factors affecting their viability is needed.
Energy Considerations for the Grazing Ruminant
Energy requirements for grazing cattle are likely greater than requirements for
cattle housed in confinement (Van Es, 1974; NRC, 1989). For lactating cows housed in
confinement, the NRC (1989) estimates that the maintenance requirement is 80 kcal of
NEi7kg of BW 075 (Moe et al., 1972) which includes an activity requirement of 10%.

8
Based on work by Brody (1945), the NRC (1989) recommends an additional allowance
of 3%/km walked per day and an added 10% maintenance allowance/d for cows grazing
good pasture. Brody (1945) estimated that standing (vs. lying down) increases energy
expenditure by 9%, but research that is more recent suggests this is an underestimate
(Clark et al., 1972; Vercoe, 1973). Robbins (1993) suggested that a better estimate of the
cost of standing versus lying (including small position changes) would be 20%. This
does not mean to suggest that the grazing animal necessarily stands more than an animal
in confined housing, but it does emphasize the point that energy needs for grazing
ruminants are likely underestimated by some current energy system recommendations.
Depending on the pasture or environmental conditions, the requirements might be
expected to be much greater (Osuji, 1974; DiMarco and Aello, 1996; Noller, 1997, cited
by Reis, 1998). Noller (1997, cited by Reis, 1998) estimated that increasing the energy
requirements by 10 to 20% is probably not enough for cattle grazing tropical forages
under tropical conditions. DiMarco and Aello (1996, cited by Reis, 1998) indicated that
for grazing cattle, maintenance energy might need to be increased 27 to 30%.
The energy requirements of grazing animals may be expected to increase if
animals require more time for foraging, if topography is hilly, or if environmental
conditions compromise thermoregulation (Robbins, 1993). Additionally, the efficiency
associated with consuming the diet is likely reduced. Osuji (1974) reported that sheep
fed fresh grass required approximately 12% more metabolizable energy than those fed an
equivalent amount of dry matter as dried grass. The increase was due primarily to the
additional time required to achieve equal DMI.

9
Grazing is energetically expensive for the cow, and any improvement in
performance will hinge upon increasing energy intake or increasing the efficiency with
which ingested energy is utilized (McCollum and Horn, 1990, p. 1). Even with
relatively high quality cool-season pastures, animal performance is often less than might
be expected given the chemical composition and nutritive value of the forage. This may
be due to the lower efficiency of utilization of fresh forage (Osuji, 1974) or to differences
in energy intake (Kolver and Muller, 1998). Kolver and Muller (1998) examined the
reason behind performance differences of cows consuming high quality pasture and those
eating a totally mixed ration (TMR) primarily composed of com and legume silages,
high moisture shelled com, whole cottonseed, soybean meal, legume hay and wheat
middlings. The concentration of NEl of the diets was similar (1.63 and 1.65 Mcal/kg of
DM for pasture and TMR), but NEl intake was less (32.4 vs. 40.2 Mcal/d) for cows
grazing pasture. The apparent DM digestibility of the diets was approximately equal (77
and 76% for pasture and TMR, respectively), but dietary NDF and ADF concentrations
were 40 and 20% greater for the pasture diets. The authors reported that differences in
intake rather than differences in energy between pasture and TMR limited energy intake
by pastured cows.
Some Animal and Nutritional Factors Influencing Feed Intake
Understanding the mechanisms regulating feed intake historically has been a key
research objective, because the amount of forage consumed is the major determinant of
production by animals fed forage-based diets (Buxton et al., 1995, p. 10). As much as
60 to 90% of the variation in digestible energy intake may be due to animal variability,
with 10 to 40% due to diet digestibility (Crampton et ah, 1960; Reid, 1961). Though

10
intake and digestibility may be strongly correlated (Anderson et al., 1973), intake of
digestible nutrients is affected more by differences in intake than by differences in
digestibility (Waldo, 1986, p. 618).
Much effort has been made to determine whether voluntary intake was limited
primarily through physical or physiological control mechanisms. Conrad et al. (1964)
examined results from 114 trials with lactating cows and reported the relative importance
of physical and physiological factors regulating feed intake changes as diet digestibility
increases. Intake of diets having between 50 and approximately 67% digestibility was
thought to be limited by physical factors such as digestibility of a feed and its rate of
passage through the digestive tract. Intake of diets having a digestibility greater than
67% was limited primarily by physiological control mechanisms. This breakpoint
[67%] is likely a convenient mathematical simplification (Allen, 1996, p. 3064) because
voluntary intake is likely regulated by numerous, integrated signals from the intestinal
tract and digestive organs (Forbes, 1996). Regardless of the breakpoint or precise
mechanisms of intake control, research supports the theory that intake often is restricted
by rumen distention, i.e. physical constraint (Balch and Campling, 1962; Grovum and
Phillips, 1978; Friggens et al., 1998).
Constraints on feed intake by physical mechanisms are, in part, a function of
digestive tract capacity and are related to energy balance (Allen, 1996). Voluntary DMI
of cows in negative or slightly positive energy balance decreased in response to inert fill
added to the reticulorumen but was unaffected in cows having greater positive energy
balance (Johnson and Combs, 1991, 1992; Dado and Allen, 1995). This is of particular
relevance for the grazing dairy cow which has increased maintenance energy

11
requirements because of increased walking and grazing activities (NRC, 1989). The
increased energy requirements of these activities may lower energy balance, putting
downward pressure on voluntary DMI.
Some have suggested that intake capacity is in part a function of the energy
required for production. For example, increased rumen volume has been attributed to the
increased energy demand of lactation (Tulloh et al., 1965), and Redmond (1988, cited by
Allen, 1996) reported that weight of reticulorumen contents increased more than 40% in
the first 2 months of lactation in dairy cows. In a comparison of rumen load and
clearance between lactating and non-lactating sheep, Weston and Cantle (1982) showed
that both were increased by lactation.
Goetsch et al. (1991, p. 2635) reviewed 18 Latin-square experiments to
determine effects of various feedstuffs ... on intake and digestion by Holstein steer
calves ingesting bermudagrass hay ad libitum. The authors reported that fiber fractions
in the feeds were of negligible importance and the coincident absence of strong
relationships between bermudagrass composition and digestion ... implies that variation
in chemically fractionated fiber components of bermudagrass had little impact on nutrient
status and (or) gut fill regulation of DMI (p. 2639) further noting that growth and energy
utilization may have been involved with regulating DMI.
This remains a subject of debate, however. Friggens et al. (1998) fed constraining
or non-constraining diets over a lactation, switching the diets of half the dairy cows in
each test group at 153 days in milk. Diets were composed of grass silage and a barley-
based concentrate. The NDF concentrations of the diets were approximately 37 and 43%
and the ADF concentrations were approximately 21 and 26% for the low- and high-fill

12
diets, respectively. Milk production was greatest from cows initially fed the non
constraining diet, but when switched to a constraining diet, intake declined rapidly even
though, immediately prior to the changeover, cows on [the non-constraining] diet had a
much greater milk yield and thus a much greater presumed energy requirement, (p.
2236). The authors concluded that milk yield had no effect on the capacity of the cow to
consume a constraining diet... [and] intake capacity is independent of cow
performance (p. 2237). The authors noted that intake capacity might be expected to
change during very early and very late phases of lactation as others have shown (Hunter
and Siebert, 1986; Stanley et al., 1993).
The results of Friggens et al. (1998) underscore the importance of dietary factors
that affect gut fill. Of a forages intrinsic characteristics, fiber is thought to be the main
component limiting voluntary intake due to its filling properties (Jung and Allen,
1995). In 1965, Van Soest reported large negative correlation between percent of plant
cell wall constituents (NDF) and voluntary intake. Neutral detergent fiber represents the
total cell wall fraction of a feedstuff, and is considered a mechanism controlling forage
intake by ruminants (Waldo, 1986; Jung and Allen, 1995).
Intake of perennial, warm-season grasses in the Southeast typically is considered
limited by physical (fill) effects due to their high fiber concentrations and low
digestibilities. The National Research Council recommends dietary NDF concentrations
of 25 to 28% in rations for lactating cows (NRC, 1989), but the majority of summer,
perennial grasses common to the region generally have concentrations of NDF in excess
of 70% (DM basis). If warm-season perennial grasses are the sole forage source in the
diet, their large NDF concentrations might represent a steep hurdle for producers trying to

13
maintain adequate intake for high-producing dairy cows. However, the strength of the
negative relationship between fiber and intake (or digestion) for animals consuming
bermudagrass has been questioned (Golding et al., 1976a; Jones et al., 1988; Goetsch et
al., 1991) and bears further investigation.
Some Non-Nutritional Factors Affecting Behavior and Forage Intake Of Grazing
Ruminants
Mechanistic Components of Forage Intake
A mechanistic or mathematical model of forage intake by the grazing ruminant
was first put forth by Allden and Whittaker (1970) following the work of Allden (1962).
The model reduces forage intake (FI; kilograms) to the product of the main components
of grazing behavior; that is time spent grazing (GT; minutes or hours), rate of biting
during grazing (RB; bites per minute), and the intake of forage per bite (IB; grams).
Hence the equation: FI = (IB*RB*GT)/1000.
Research indicates that if herbage mass is maintained above amounts which
restrain intake, animals can maintain fairly constant amounts of intake by adjusting IB,
RB, and GT (Willoughby, 1959; Allden and Whittaker, 1970). Of these three variables,
IB is the most affected by sward conditions (Hodgson, 1985). Intake per bite normally
falls sharply as herbage mass or sward height declines (Hodgson, 1985, p. 340, citing
Allden and Whittaker, 1970 and Hodgson, 1981). Negative correlations between IB and
herbage on offer (r = -0.61) and sward bulk density (r = -0.70) have been shown with
tropical pastures (Stobbs, 1973). Sward height may be positively related to intake of
warm-season species (Flores et al., 1993), though universality is unlikely when one
considers the range in morphologies of tropical forages.

14
Leaf distribution in the canopy has the greatest influence on IB, (Stobbs, 1973;
Hodgson, 1985) because IB is the product of bite volume (depth x area) and the bulk
density (weight per unit volume) of herbage within the sward horizons encompassed in a
bite (Hodgson, 1985, p. 342-343). Other factors that influence IB include sward height,
presence of stem and pseudostem horizons, and the height of these horizons relative to
total sward height, all of which affect ease of prehension and depth of biting into the
canopy (Flores et al., 1993).
Sward maturity has strong effects on efficiency of the grazing activity due to its
effect on leaf distribution in the canopy (Stobbs, 1973; 1974a). Stobbs (1973) studied IB
in dairy cows grazing tropical swards at 2, 4, 6, or 8 wk of regrowth. The IB was limited
by the low yield and density of herbage at 2 wk of age even though pastures contained
82% leaf. Intake per bite increased at 4 wk with increasing available herbage, but
decreased with increasing maturity (6 and 8 wk) primarily due to decreasing leaflstem
ratio. Mean IB at 2, 4, 6, and 8 wk were approximately 0.23, 0.27, 0.17, and 0.15 g
OM/bite. This research also compared responses between species (Setaria anceps and
Chloris gayana) that showed that sward maturity affected IB differently between species
(Stobbs, 1973). Mayne et al. (1997) reported intakes of 0.4 to 1.1 g of DM/bite for cows
grazing ryegrass pastures. These values are quite high, but their estimates were made
indirectly. Pulido and Leaver (1997) did not report IB but reported rates of intake of
perennial ryegrass of 20 to 30 g of OM/min. Assuming a bite rate of 55 bites/min, IB
ranged from 0.36to0.55gof OM/bite.
Research into the effect of progressive defoliation on intake of tropical pastures
showed that cows selected more than 80% leaf from the upper layers of the sward in the

15
early stages of defoliation (Chacon and Stobbs, 1976). Work by Roth et al. (1990)
showed that cattle continued to select large proportions of leaf even as leaf percentage of
the canopy decreased. As the quantity of leaf decreases, animals increased GT, RB, and
total number of eating bites, but these activities were not sustained as pastures became
severely defoliated (Chacon and Stobbs, 1976). Chacon and Stobbs (1976) suggested
that leaf yield would give a better expression of forage on offer than the more commonly
used grazing pressure.
Biting rates between 51 and 63 bites/min were reported by Chacon and Stobbs
(1976) when cows grazed warm-season forages. Rates as great as 90 bites/min on
temperate pasture were reported by Hodgson (1985) but this likely represents total jaw
movements. Rates of biting declined linearly with increasing length of grazing period
when forage was not limiting (Stobbs, 1974b). Greenwood and Demment (1988)
compared intake behavior of unfasted steers or those fasted for 36 h. They reported that
ingestive bites increased approximately 30% (38.9 vs. 29.7 bites/min) due to fasting, but
this response was seen during the morning only.
Under forage-limiting conditions with temperate pastures, RB increases as IB
decreases, but RB rarely increases enough to maintain herbage intake (Allden and
Whittaker, 1970; Hodgson, 1981). Moreover, the changes in RB likely are due to the
manipulative jaw movements required to harvest the forage (Stobbs, 1974b; Chambers et
al., 1981). With temperate pastures, RB may increase when forage is limited due to a
reduction in manipulative jaw movements (Hodgson, 1985), but low availability of
herbage would likely decrease ingestive RB with most tropical pastures, as animals
would spend more time selecting leaf material.

16
In a comparison of grazing of cool- and warm-season grasses, Stobbs (1974b)
reported that RB was much less with Abyssinian barley (Hordeum vulgare) than with S.
anceps, and the decline in RB over time was less with the tropical grass. Cows grazing
barley were observed grasping large mouthfuls of forage with their tongues and chewing
the forage several times before swallowing, whereas cows grazing S. anceps took small
amounts of herbage and their mastication bites accounted for less than 5% of total
grazing bites.
A more apparent behavioral response to decreasing IB is an increase in GT, but
the degree of this compensatory mechanism is also limited, such that daily FI variations
may reflect closely the observed variations in IB (Hodgson, 1985). Stobbs (1974a)
reported that cows rarely take more than 36,000 prehension bites in a day. Based on this
value and the biting rates reported by Chacon and Stobbs (1976), the upper limit to daily
grazing time would be 10 to 12 h, though the latter authors reported 39,600 prehension
bites/d in one study, and GT as great as 800 min/d with cattle grazing tropical legumes
have been reported (Smith, 1959; Stobbs, 1970). In the study by Chacon and Stobbs
(1976), average maximum GT reported was 10.75 h/day, and GT patterns were
curvilinear. Cows grazed approximately 9 h during the first few days on a new pasture.
Grazing time increased to a maximum between days 3 through 6 then subsequently
declined despite a reduction in the quantity of herbage on offer in the later stages of
defoliation (Chacon and Stobbs, 1976, p. 714).
Work by Pulido and Leaver (1997) has shown that level of performance affects
intake. The authors measured intake of cows having initial milk yields of 21 or 35 kg/d.

17
On average, cows grazed an additional 2.45 min for each additional kg of daily milk
produced.
Grazing time also may be dependent upon the system of grazing management
utilized. Le Du et al. (1979) reported that with rotational stocking, cows did not
compensate for decreased herbage availability with increased GT. Rapid defoliation with
strip-grazed pastures would be expected to make large alterations in canopy structure,
requiring animals to increase manipulative jaw movements (Hodgson, 1981) in order to
consume a large proportion of leaf material.
Daylight and Temperature
In general, cows graze primarily during daylight hours, exhibiting strong
periodicity in grazing behavior (Hughes and Reid, 1951; Stobbs, 1970). Adams (1985)
noted that most grazing behavior studies show that cows typically have a major grazing
period occurring early in the morning and one later in the afternoon. Additional
intermittent grazing bouts occur throughout other periods of the day and night.
Phillips (1989) reported marked reluctance of cattle to eat at night (Phillips and
Denne, 1988) even in hot climates (Alhassan and Kabuga, 1988), but this may be true
more for steers than for lactating animals which likely are under greater heat strain.
Stobbs (1970, p. 242) reported that during the night cows grazing tropical pastures
behave more as individuals and that high yielding cows can spend a considerable
length of time grazing during this period. While Stobbs (1970) indicated that night
grazing might be limited to 30% of grazing time, work by Seath and Miller (1947)
indicated that in hot, humid environments (Louisiana), cows would graze more during
night time. Part of the differences in these studies may be in the designation of night,

18
however, and Stobbs (1970) noted that greater than 50% of grazing would often occur
between a.m. and p.m. milkings which occurred after dawn and before dusk, respectively.
Measurement of Forage Intake in Grazing Ruminants
Several methods of intake estimation for animals on pasture have been explored.
Each method employs different assumptions which must be met if the estimates are to be
valid (Moore, 1996).
Early attempts to estimate intake from individual animals included use of fecal
collection bags for total fecal collection. In addition to the potential for loss or urine
contamination due to poor design or lack of fit, the bags also have the potential to stress
the animal and to alter intake by changing grazing behavior.
To avoid such problems, other researchers cut and carried green pasture to
animals kept in confinement. Though this approach affords a great degree of precision, it
may be highly inaccurate because it reduces both the opportunity for selection and the
work required to harvest the forage. Experimental results are likely most affected when
swards are highly heterogeneous or when environmental factors or sward density would
have large effects on grazing behavior.
Marker technologies for the estimate of FI of grazing animals have been used
extensively. Markers are reference compounds used to investigate both chemical
(hydrolysis and synthesis) and physical (flow) digestive processes (Owens and Hanson,
1992). Fecal output (flow) is the measure of interest in the grazing animal because it can
be used to calculate intake using the following equation: FI (kg) = Fecal output (kg)/(100
- diet digestibility (%)).

19
Characteristics of an ideal marker were outlined by Owens and Hanson (1992)
and include the following traits: 1) it should be unabsorbable, 2) it should not affect or be
affected by animal or microbial digestive processes, 3) its flow should closely mimic that
of the material it marks, and 4) it must be analyzable with a specific and sensitive
methodology. No single marker currently meets all these criteria.
Both internal (a dietary fraction such as lignin or plant alkanes) and external (e.g.,
colored plastic chips or rare earth metals) markers have been employed. Use of either
type of marker relies upon an accurate estimate of its intake. This is controlled by the
researcher using external markers, but calculation of internal marker intake depends upon
accurate estimates of what the animal consumes. This may be a particular problem in
grazing situations where herbage consumed may not be the same as selected by the
researcher.
The external marker, CT2O3, has been used extensively but its suitability has been
questioned (Ellis et al., 1980). The CT2O3 does not associate with a particular liquid or
feed fraction and thus may settle out of the rumen contents and flow with large
variability, particularly when animals consume forage diets. Holden et al. (1995, p. 158)
worked with CT2O3 and noted that significant daily variation in DMI indicates that
analysis of composited samples of forages and feces for intake determination may not be
adequate for estimation of intake under grazing conditions. Another disadvantage of
using Cr23 is the multiple doses required over several days in order for Cr to reach
equilibrium concentrations in the digestive tract. Additional handling of animals is
undesirable, particularly when it has potential to disturb established patterns of grazing
behavior

20
More recently, use of pulse-dosed markers has gained acceptance. Animals are
dosed once with labeled feed fractions, and numerous fecal samples are collected over a
period of time long enough for the label source to have cleared the animal (typically 96 or
more hours). A nonlinear equation relating time after dosing to fecal [Cr] is used to
generate parameters for the estimation of fecal output (Pond et al., 1987). This method
has advantages in that the animals observed need only be handled once for dosing.
Fiber mordants, especially Cr-mordanted fiber, have been used as markers due to
the tenacity with which heavy metals bind the fiber particles. Disadvantages to this
method include the amount of effort involved in preparing mordanted fiber and the
potential negative effects of mordanting upon passage characteristics of the fiber particles
(Ellis et ah, 1980).
Estimation of intake using external markers also requires an accurate estimate of
diet digestibility. Pasture samples may be obtained with surgically altered animals
(esophogeally- or ruminally-fistulated) or by hand plucking. Estimates of diet
digestibility are then obtained with in vitro techniques. Either method can be inaccurate
because potential exists for the sampling animal or for the researcher to select plant
material that is different from the plant material chosen by the animals being studied. If
supplements are fed, they may further alter diet digestibility, thwarting accuracy of
estimation.
With each of these methods, care must be taken during the laboratory analysis,
since feces must go through several preparation steps prior to the Cr analysis. An
additional difficulty with marker methodologies is the large number of samples which
must be collected and processed to make reasonable estimates of intake.

21
Herbage intake for individual animals also can be estimated with measurements
of grazing behavior, where FI = GT*RB*IB. This method may be beneficial in
overcoming any effects that supplemental feeds may have on estimates of diet
digestibility. However, all three measures for the estimate are quite variable over time,
especially with changes in sward conditions (Stobbs, 1973; Chacon and Stobbs, 1976;
Hodgson, 1985). Further, it is unlikely that a researcher would have access to more than
a few esophogeally-fistulated animals, limiting the number of estimates of IB, and the
fistulated animals may not be representative of the population of interest.
Another common method of estimating intake is by disappearance of herbage
mass (HM). On rotationally stocked pastures with short (1 to 3 d) grazing periods, HM is
estimated both pre- and post-graze with devices such as sward sticks, rising plate meters
or capacitance meters that allow rapid collection of numerous measurements. The
difference between pre- and post-graze HM (disappearance) is the herbage assumed eaten
by the grazing animal(s). Such estimates are more suitable when measuring group
intakes and are advantageous with respect to eliminating effects of supplement on forage
digestibility (Milne et al., 1981). However, their usefulness is limited to conditions
where pastures are uniform.
Herbage Allowance or Stocking Rate Effects on Forage Intake and Performance of
Ruminants
Due to the complexity of plant-animal interactions and the difficulty of obtaining
such information, most research regarding these relationships considers only the gross
effects of herbage allowance (HA; kg of forage DM/kg of animal live weight), grazing
pressure, or stocking rate (SR) on animal performance. Several models have been
proposed to describe these effects (Mott, 1960; Jones and Sandland, 1974; Mott and

22
Moore, 1985). In all the models, as SR increases, animal gain decreases but gain per land
area increases. A variant model by Jones (1981) suggested that at very low SR,
gain/animal also might be compromised, and Stuth et al. (1981) reported that at high
amounts of daily HA of bermudagrass pastures, defoliation efficiency is reduced.
Much of the debate among researchers appears to center on the nature of the
animal responses at the extremes of HA. Hart (1972) stated that animal gain decreases
linearly in response to increasing SR (animals/land area), and thus gain to land area is
necessarily curvilinear. Matches and Mott (1975, p. 205) noted that the exact form of
trends reported in the literature have differences depending on the researcher and
circumstances of experimentation. The rapid declines in output (per animal or land
area) proposed by Mott (1960) are likely most applicable to limited-input, extensive
grazing systems (Pearson and Ison, 1997) unsuited for intensive milk production.
Contention also has arisen over the nature of DMI in response to HA. Hodgson
(1975, cited by Stockdale, 1985) reported that intake followed HA in a linear fashion.
Others have reported asymptotic intake responses to HA (Allden and Whittaker, 1970;
Stuth et al., 1981). Stockdale (1985) reviewed eight experiments under Australian
conditions and noted that though DMI of grazing dairy cows was reduced with
decreasing HA, the relationship was not always curvilinear. He noted that combining the
data from all the experiments resulted in a significant quadratic term. The intake
response to increasing HA reported by Le Du et al. (1979) was positive and asymptotic
and similar responses were reported in a review by Phillips (1989). However, the nature
of the response likely is linear over the range of SR typically used (Jones and Sandland,
1974).

23
As HA increases, forage intake increases, primarily due to increased opportunities
for diet selection (Le Du et al., 1979). Thus the nutritive value of forage consumed also
increases, though nutritive value of the total sward may decrease due to accumulation of
senescing or senescent leaves and stems (Hamilton et al., 1973; Hodgson, 1985).
Piaggio and Prates (1997) noted good correlation between steer gains and HA
within season on range pastures. The nature of the response was quadratic, but a
regression equation explaining the relationships between intake and HA or between gain
and HA over an entire year could not be fitted. Thus, the authors created a new variable,
corrected energy pressure. The product of HA and metabolizable energy (ME) of
herbage, corrected energy pressure was scaled for availability and possibility of selection
which was simplified to the proportion of green material in the sward. The relationships
y
between intake or gain and corrected energy pressure were strong (R >0.82) and
curvilinear.
Phillips (1989) reviewed studies of lactating cows grazing temperate pastures and
producing approximately 15 to 18 kg of milk/d. He reported that to prevent a decline in
individual performance, minimum HA should allow for DMI of at least 40 g of OM/kg of
liveweight per day. This is in contrast with a value of 60 g of OM/kg of liveweight per
day suggested by Minson and Wilson (1994). Studies of cool-season pasture grasses
suggest that maximum intake occurs when HA is approximately twice intake (Le Du et
al., 1979), but HA required for maximum yield/cow may be greater with tropical pastures
(Stobbs, 1977). Cowan and OGrady (1976) indicated that DMI was depressed due to
decreased grazing time when HM was less than 2000 kg/ha in tropical grass-legume
pastures.

24
The response of DMI to HA appears to vary depending upon length of the
experiment. Stockdale (1985) reported that average DMI was 2.9 kg/d greater with long
term experiments than short-term experiments, regardless of the HA. The author
suggested that greater intake in long-term experiments was due to adaptation.
Stocking rate may have both short and long-term consequences for both pasture
and animal production, particularly for forage species that exhibit seasonal growth habits.
Intense grazing bouts during initial periods of growth may reduce reproductive tillering
and the deleterious effects of accumulated dead material in the sward later in the grazing
season (Michell and Fulkerson, 1987). Michell and Fulkerson (1987) observed that the
quantities of available green herbage were the same in pastures that had been subjected to
low or high SR (1.9 or 3.4 cows/ha) on ryegrass (Loliumperenne L.)-white clover
(Trifolium repens) pastures. However, quantities of dead herbage were greater in the low
SR pastures over most of the grazing season. Diet digestibilities between treatments were
similar, but production from cows on the low SR appeared compromised due to a
reduction of DMI.
Grazing intensity also affects botanical composition and herbage yield of grasses,
legumes, and weeds (Brougham, 1960; Michell and Fulkerson, 1987). Composition and
yield changes in response to SR are variable depending upon grazing events through the
season and emphasize the importance of management in maintaining high quality
pastures (Brougham, 1960). Because dead plant tissue (Hodgson, 1985) and fecal matter
(Phillips and Leaver, 1985) negatively affect intake and are more prevalent in the fall
than in the spring, Phillips (1989) suggested managing pastures for greater sward height
as the grazing season progresses.

25
Fales et al. (1995, p. 88) reported that SR was a key management variable in
determining productivity and profitability of grazing systems but it has not been
adequately researched in the USA with high producing dairy cows. Castle et al. (1968)
reported that by increasing SR with lactating dairy cows on mixed temperate pastures
(primarily ryegrass, timothy, and white clover), herbage utilization was increased; output
per land area was increased approximately 28%, though at the expense of individual
animal performance. Stockdale et al. (1987, p. 927, citing Stockdale, 1985) stated that it
is not possible to feed cows well on pasture alone if the herbage is to be adequately
utilized, and thus SR must of necessity be high. In order to maintain milk production
while optimizing pasture utilization, supplements must be fed.
Supplement Effects on Animal Performance with Particular Emphasis on Lactating
Cows in Pasture-Based Dairy Systems
Mott (1959) proposed that comparisons of forage quality are best expressed in
terms of differences in animal performance and gave guidelines for these comparisons,
including (but not limited to) no provision of supplemental energy or protein. However,
cows consuming only well-managed temperate pasture had intakes capable of supporting
as much as 28 kg of milk/d (Muller et al., 1995), yet the genetic potential of dairy cows
for milk production is much greater than this amount (NRC, 1989). Maximizing milk
production per animal has been the goal of most of the U.S. dairy industry, and this has
been facilitated by the availability of relatively inexpensive concentrate feeds. Thus,
forage quality for lactating dairy cows is rarely evaluated by Motts (1959) guidelines.
The energy requirements of high producing dairy cows cannot be met by forages
alone (Galyean and Goetsch, 1993; NRC, 1989). Several studies have shown energy to
be the first dietary limitation to optimum performance of cows grazing N-fertilized

26
pastures (Royal and Jeffrey, 1972; Delgado and Randel, 1989; Davison et al., 1991;
Reeves et al., 1996).
To maximize the performance of animals on pasture, supplemental feeds
(primarily energy feeds) are required to balance or increase the nutrient supply (Leaver,
1985a,b; NRC, 1989; Muller et al., 1995). Without supplemental energy, milk
production may be maintained by excessive mobilization of fat stores. This may have
potentially negative consequences in that it may result in metabolic disorders such as
ketosis or fatty liver syndrome.
Although milk yield is the typical performance variable measured, reproduction
has been shown to be compromised in beef cattle when energy intake is limited
(Wiltbank et al., 1964). Muller et al. (1995) noted that reproductive performance of dairy
cows also may be compromised without supplemental energy if pastures are high in CP
due to the negative relationship between high rumen degradable protein and fertility in
the lactating cow (Ferguson and Chalupa, 1989).
Supplement Effects on Production
Though the feeding of supplements is a common practice, production responses to
supplement are inconsistent and may not be profitable. Citing Leaver et al. (1968) and
Joumet and Demarquilly (1979), Meijs and Hoekstra (1984) reported that typical
responses were approximately 0.3 to 0.4 kg of milk per kg of supplement fed to cows
grazing adequate temperate pasture. In a summary of 12 papers, Combellas et al. (1979)
reported similar responses (0.34 kg of milk per kg of supplement) when cows grazed
tropical pastures. Davison et al. (1991) reported similar results but speculated that cows

27
were not adapted to high amounts of supplement (8 kg of DM/d) and that abundant
available herbage resulted in greater than normal substitution effects.
Ruiz (1983) suggested that one reason for poor response to supplementation of
grazing cows [in some experiments] is the stage of lactation at which comparisons were
made. Ruiz noted that cows on research trials were often beyond peak of lactation and,
as cows approached the end of lactation, nutrients may have been more readily
partitioned to replenishment of body reserves rather than milk synthesis.
Studies by Jennings and Holmes (1984a) and Stockdale et al. (1987) confirmed
the theory of Ruiz (1983). Jennings and Holmes (1984a) found increased total intake and
increased milk production with supplement, but a concomitant decrease in milk fat
concentration resulted in no difference in FCM production. Cow BW increased with
supplement, indicating that the nutritional benefit of concentrate nutrients was not
reduced per se, but that nutrients were partitioned toward body reserve repletion.
Stockdale et al. (1987, p. 936) reported that marginal return from feeding [concentrate
supplement] decreased as lactation progressed whereas increases in BW due to
supplement were greatest for cows in the latter stage of lactation.
Feeding supplement to cows in the early lactation period may have strong,
positive residual effects on milk production in later lactation (Cowan et al., 1975;
Martinez et al., 1980). A comparison of supplement provision during the first 10 wk of
lactation vs. the whole lactation period showed that when given the same rate of
supplement through the whole lactation, cows produced only an additional 181 L of milk
in response to an extra 754 kg of concentrate (Martinez et al., 1980, cited by Jennings and
Holmes, 1984b). Lack of residual effect (Martinez et al., 1980) may have resulted from

28
ample HA that provided intake adequate for lower milk production found later in
lactation, a response also reported by others (Le Du et al., 1979; Poole, 1987).
Length of study may also be an important consideration for proper interpretation
of response to supplement when cows grazed tropical grasses. Jennings and Holmes
(1984b) found that in short-term studies (n = 18, average duration = 80 d), the average
response to supplements was 0.46 kg of milk/kg of supplement though they noted no
consistent association between level of response to supplementary feeding and stage of
lactation, (p. 270). A review by Cowan et al. (1977) suggested responses of 0.3 to 0.6
kg of FCM/kg of supplement were common for studies of less than 60 d in duration.
In studies conducted over most or all of the lactating period, responses to
supplement were typically between 0.9 to 1.2 kg of FCM/kg of supplement (Cowan et al.,
1977; Cowan, 1985, cited by Davison et al., 1991; McLachlan et al., 1994). However, a
review by Jennings and Holmes (1984b) indicates greater variability of response should
be expected with complete lactation studies. The authors found the range of response to
supplement was 0.10 to 1.80 kg of milk/kg of supplement, with an average response of
0.82 kg of milk/kg of supplement. Jennings and Holmes (1984b) further noted that mean
SR was 4.2 cows/ha and average milk yield of unsupplemented cows was 2,560 kg of
milk /lactation. Such information serves as a reminder that factors such as pasture and
animal management and animal genetic capacity should be included in consideration of
response to supplement. For example, a review by Moran and Trigg (1989) comparing
response to concentrate feeding between U.S. and Australian cattle indicated that both
groups of cows responded well to concentrate up to 2 metric ton per lactation. However,
U.S. cattle were able to respond to concentrate up to 3.5 metric ton per year.

29
Several long-term studies (>250 d) have shown linear MY increases in response
to an increasing supplement rate (Cowan et al., 1977; Davison et ah, 1991; McLachlan et
ah, 1994). Others have reported a curvilinear response (Balch, 1967; Coulon and
Remond, 1991, Delaby and Peyraud, 1997).
Other factors which may affect the response to supplement include quality of
pasture and supplement, amount of pasture and supplement fed, and the degree to which
supplemental feeds replace pasture intake (Stockdale et ah, 1987). Although feeding
supplement can cause numerous production responses (form and magnitude), the
variability of response is associated primarily with the effect of supplement on DMI.
Supplement Effects on Intake
Provision of supplement may increase, decrease or have no effect on forage or
total DMI (Moore, 1980). Forage intake may increase if a nutrient imbalance is
corrected, leading to increased passage rate due to greater microbial degradation of the
forage or stimulation of appetite. Generally, forage intake depressions occur when
supplements are fed with forages which have greater nutritive value (Blaxter and Wilson,
1963; Holmes and Jones, 1964; Leaver, 1973; Golding et ah, 1976b; Arriaga-Jordan and
Holmes, 1986). Large differences in substitution rates have been reported and the effects
have greater relation to differences among forages rather than to differences among
concentrates (Waldo, 1986).
Golding et ah (1976b) tested the effects of grain supplement on forage intake
depression when the supplement was fed at approximately 50% of total digestible energy
(DE) intake. Bermudagrass harvested at four maturities (4, 6, 8, or 10 wk) was fed as
hay to wethers with or without supplement. With increased forage maturity, DE intake

30
decreased, without or with supplement. Feeding supplement reduced DE intake from hay
at all maturities but had the greatest depressing effect on DE intake of wethers fed the
highest quality (4-wk maturity) hay. When fed supplement, wethers fed the 4-wk
maturity hay decreased hay DE intake by 80 kcal/BW0 7:1 per day, while those fed the 10-
wk maturity hay had decreased hay DE intake by 1 kcal/BW0 75 per day. The increase in
DE intake due to supplement for the 4-wk maturity hay was approximately half that of
the 10-wk maturity hay (26 vs. 51 kcal/BW per day for 4- and 10-wk maturities,
respectively). Intermediate decreases in hay DE intake with concomitant increases in
total DE intake occurred when supplements were fed in combination with hays of
intermediate maturity.
Concentrates had limited effects on forage intake in a study by Galloway et al.
(1993a). The researchers compared five supplement combinations fed to Holstein steers
eating bermudagrass hay in confinement. The hay was of moderate quality, averaging
11.4% CP, 75% NDF, and 52% digestibility. Supplements, fed at 0.75% of BW, were
ground com, dried whey, dried molasses product, or a combination of com and whey or
com and molasses. Although intake of bermudagrass as a percent of BW was
numerically less for all of the three corn-based supplements, only the com plus molasses
treatment significantly decreased bermudagrass intake.
Several researchers have reported forage intake depressions that varied with the
amount of supplement fed (Campling and Murdoch, 1966; Tayler and Wilkinson, 1972;
Sarker and Holmes, 1974; Cowan et al., 1977; Combellas et al., 1979). Though forage
quality may affect the response of intake to supplement, Waldo (1986) noted that total

31
dietary DMI is affected very little by forage quality when diets contain very large (>
80% of DM) levels of concentrate.
Sarker and Holmes (1974) fed supplement in increments of 2, 4, 6, or 8 kg OM/d
to non-lactating cows grazing ryegrass. Though total OM intake (OMI) increased with
increasing amount of supplement, the average increase in intake was 0.46 kg of OM/kg of
concentrate OM fed.
Combellas et al. (1979) fed 0, 3, or 6 kg of concentrates to lactating heifers
grazing Cenchrus ciliaris pastures. Across rainy and dry seasons, herbage intake
decreased approximately 0.52 kg with each kg of concentrate fed, and the authors noted
that this agreed with the range of 0.41 to 0.60 kg estimated from the equations of Holmes
and Jones (1964) and Holmes (1976) for a forage of 65% digestibility.
Supplements frequently are fed to animals consuming bermudagrass, and
Galloway et al. (1993a, p. 173, citing Galloway et al., 1992) stated that moderate dietary
levels of supplemental grain (e.g., 20 to 30%) can improve nutrient intake and
performance by cattle consuming bermudagrass. At greater amounts, nutrient digestion,
intake, or both, of the forage portion of the diet can be affected negatively.
Type of supplement fed also is an important factor with respect to substitution
effects. Mould and 0rskov (1983) reported that feeding large amounts of rapidly
fermentable starch led to decreased intake. Meijs (1986) fed high-starch supplements
(containing com and cassava) or high fiber supplements (containing beet pulp, palm
kernel expeller, soybean hulls, and com gluten feed) to cows grazing predominantly
perennial ryegrass swards. Supplement intakes were 5.5 and 5.3 kg of OM/d with forage
intakes of 11.5 and 12.6 kg of OM/d for high and low starch treatments, respectively.

32
Average forage substitution rate for animals receiving the starchy supplement was 0.45
kg of herbage/kg concentrate vs. 0.21 kg of herbage/kg of concentrate for animals
receiving the more fibrous supplement. Milk and FCM yields were greater for animals
receiving the fibrous supplement, but feeding the starch-based supplement resulted in
0.17 kg greater ADG vs. fibrous supplement.
Similar responses to type of supplement have been found with cows consuming
com silage as the base forage (Huhtanen, 1993). Supplements were crushed barley alone
or mixed grain (40%) and pelleted fibrous by-products (60%). Cows eating the fibrous
supplement consumed 0.43 kg/d more (P <0.10) silage and more total DM, but lower
ME (212.7 vs. 218.0 MJ/d). Milk production increased 1.5 kg/d when animals consumed
the fibrous supplement. The author suggested that positive associative effects from the
combination of different carbohydrate sources or the greater CP intake (0.20 kg/d) due to
the fibrous supplement may help explain greater milk yields. Though liveweight did not
change due to supplement and insulin concentrations were not reported, greater plasma
insulin concentration for barley supplement have been reported by Miettinen and
Huhtanen (1989). This hormonal change would suggest greater partitioning of nutrients
to body tissues and may explain the results of Meijs (1986).
Gordon et al. (1993) compared the effects of fibrous or starchy supplements on
milk production and energetic efficiency. Fibrous supplements included sugar beet and
citrus pulp as well as cottonseed while starchy concentrates contained barley and wheat.
Cows were fed the supplements with high- or low-digestibility grass silage. The authors
reported greater milk production (23.5 vs. 21.6 kg/d) by cows fed the fibrous supplement.
Milk protein percentage was greater with the starch supplement, potentially indicative of

33
greater microbial synthesis, but milk protein production did not differ due to milk
production differences. Partial efficiency of milk production was unaffected by
supplement type.
Galloway et al. (1993b) compared provision of soy hulls, com, or a combination
of the two at equal digestible energies (differing amounts in kg/d) to steers consuming
bermudagrass hay. Providing hulls resulted in a greater decrease in bermudagrass intake
relative to com or com plus soy hull supplementation, but total DMI were similar for
steers fed the supplemented diets and greater than for steers fed bermudagrass alone.
Supplement increased particulate rate of passage from the rumen (avg. 4.71 vs. 4.18%/h),
which could have negative effects on digestibility of bermudagrass. However, the overall
supplement effect was an increased diet digestibility.
A comparison of a TMR or grain concentrate as a supplement for pasture-fed
dairy cattle indicated that a TMR supplement may not be an improvement over
concentrate feeds. Welch and Palmer (1997) fed 1) no supplement, 2) 7.3 kg of
concentrate/d, or 3) an equal quantity of TMR balanced for 38.5 kg of daily milk to cows
grazing unspecified cool-season pastures. Milk production was greatest for concentrate
fed cows and least for unsupplemented cows, but milk fat concentration followed an
opposite pattern. The researchers speculated that pasture intake fiber in the TMR
probably reduced pasture DM intake (p. 222).
Supplement Effects on Forage Digestibility
Energy supplements often affect forage digestibility and DMI in a similar manner.
Milne et al. (1981) fed sheep increasing amounts of grain concentrate and found a linear
decrease in digestibility of ingested herbage. A 9.6 percentage unit decrease (64.3 vs.

34
54.7%) in true ruminal digestion of cool-season forage DM was reported when lactating
dairy cows were fed supplemental corn at 6.4 kg/d. Total tract digestibility of DM was
less affected (71.9 vs. 69.9%), however (Berzaghi et al., 1996).
Research with steers (Vadiveloo and Holmes, 1979; Galloway et al., 1993a,b) and
sheep (Chenost et al., 1981, cited by Arriaga-Jordan and Holmes, 1986) has shown that
when forages are of low to moderate digestibility, supplement often improves overall
total diet digestibility, likely due to the greater digestibility of the supplement (Galloway
et al., 1993a). Diet digestibility is often unimproved when supplements are fed with high
quality forages, however. Arriaga-Jordan and Holmes (1986) studied the effects of
concentrate supplementation on herbage digestibility in dairy cattle. Feeding a grain-
based supplement to cows eating high quality pasture increased total intake, but reduced
herbage intake and depressed digestibility of the herbage consumed, thus reducing the
potential nutritional benefit of the concentrates.
Supplements also affect diet digestibility by affecting rates of passage of digesta
through the digestive tract. Waldo et al. (1972) were the first to model the relationship
between rates of digestion and passage on total digestion: k]/(ki +k2), where ki and k2 are
rates of digestion and passage, respectively. In theory, if passage is 0 then digestion will
equal 100% of potential extent of digestion (ki/ki = 1). Conversely, if passage is rapid, it
will have a large, depressive effect on diet digestion. For example, Tyrrell and Moe
(1972) fed increasing amounts of com grain as a supplement to cows fed com silage
diets. Although intakes increased with supplementation, the decreased digestibility of the
diet due to increased passage resulted in decreased concentration of dietary ME.

35
Forage intake and digestibility in response to supplement feeding also is related to
supplement effects on ruminal microbes. Growth of ruminal microbes is reduced in vitro
with decreased ruminal pH (Russell and Dombrowski, 1980). Low rates of starch
supplementation may increase numbers of cellulolytic microbes, but feeding diets with
large concentrations of rapidly fermentable starch may lead to a cascade of events
including decreased ruminal pH, reduced cellulolytic microbes, and ultimately, decreased
intake (Mould and 0rskov, 1983).
Cellulolysis is decreased not only by reduced pH but also by preferential starch
digestion by the microbes (Mould et al., 1983; Hoover, 1986). Mould et al. (1983) fed
increasing amounts of barley to sheep, with or without additional bicarbonate salt to
buffer ruminal pH. Diets were fed at a fixed rate, just below maximum voluntary intake,
so passage should not have confounded the findings. Even when pH was maintained at
approximately 6.7, DM digestibility decreased with increasing concentration of barley in
the diet, and the depression in apparent DM digestion was greater in sheep fed the more
processed barley, suggesting that fiber-digesting microbes preferentially selected starch.
Moreover, reduction in cellulolysis in response to starch supplementation was greater
when roughages were of lower DM degradability (Mould et al., 1983), which has
implications for cows grazing warm-season pastures.
Caird and Holmes (1986, p. 53, citing Jennings and Holmes, 1984a) stated that
the response in intake to concentrates depends on the influence of the concentrate on
herbage digestibility. Others have reported that extensively fermented, fiber-based
supplements have less negative effects on forage intake and digestion. For example,
when soybean hulls were used as a supplement for beef cattle, reductions in forage

36
consumption were not as evident as when starch-based supplements were fed (Martin and
Hibberd, 1990). Klopfenstein and Owen (1987) reported that supplementation with
soybean hulls had less effect on ruminal pH compared with supplementation with cereal
grains. The lack of starch in soybean hulls may prevent the decreases in fibrolytic
activity caused by preferential starch utilization by fiber-digesting microbes (Hoover,
1986).
Other supplement sources such as beet pulp and by-product feeds have also been
considered with varying results. Thus, Galloway et al. (1993b) noted that the optimum
supplement composition might vary with the forage source with which it is fed.
Though the characteristics of a forage affect both ruminal conditions and
absorption of nutrients (Minson, 1990), it should be noted again that the effects of
[forage] quality differences may decrease and even disappear if enough grain is fed. In
such a case there would be no effect of forage quality on animal performance (Golding
et al., 1976b). However, extent of production may confound the effect and interpretation
of responses to supplement. From work with steers, Joanning et al. (1981) reported that
at intake below twice maintenance, associative effects between forage and concentrate
might not occur, though this suggestion was based on extrapolations. Ultimately, with
high-performance dairy cows, optimizing use of feed supplements will require a balance
between improvements in intake and concomitant decreases in digestion.
Besides the changes in digestibility, additional concerns with feeding large
amounts of high-starch concentrate may include reduced milk fat concentrations (Huber
et al., 1964; Jennings and Holmes, 1984a; Polan et al., 1986; Sutton et al., 1986) and

37
negative effects due to slug feeding of supplements such as periodic reductions in intake
and ruminal acidosis.
Synchronizing Nitrogen And Carbohydrate Supplements To Increase Microbial
Protein Synthesis in the Rumen
Loss of Feed Nitrogen in Ruminants
Proteins in pasture forages can be degraded rapidly and extensively by ruminal
microbes (Beever et al., 1986a, b; Van Vuuren et al., 1991) and considerable N losses
have been reported for animals grazing pasture. For example, steers grazing ryegrass or
white clover pastures consumed approximately 0.61 and 1.18 g of N/kg of live weight,
and non-NH3-N (NAN) flow to the small intestine was greater with clover diets (0.60 vs.
0.76 g of NAN/kg of live weight for ryegrass and clover, respectively; Beever et al.,
1986b). However, the differential between intake N and NAN flow represented a 35%
loss of N prior to the duodenum for cows grazing clover pastures and little loss of N for
cows grazing ryegrass. Ruminal NH3 concentrations typically ranged between 20 and
100 mg of NH3-N/L of ruminal fluid for grass diets, but ranged from 250 to 300 mg of
NH3-N/L of rumen fluid for clover diets.
Similar ruminal N losses (37%) were reported for non-lactating cows consuming
unfertilized fresh cool-season pasture grasses (Holden et al., 1994b). Cows were fed
fresh pasture, silage, or hay and consumed similar quantities (13.0 to 13.7 kg of DM/d) of
the mixed-grass forage. The CP concentration of the forage was approximately 17% in
each forage form with the OM:CP ratio ranging from 4.5 to 5.1. Ruminal NH3
concentrations were greater for cows consuming pasture. The authors, citing work by
Ushida et al. (1986), suggested that the greater ruminal NH3 concentrations might have
been related to greater protozoal counts they observed in the pasture-fed cows. Though

38
bacterial N as a percentage of N flowing to the small intestine was greatest for cows
grazing pasture, N flow to the small intestine relative to N intake was least for cows
grazing pasture, indicative of the greater N losses. Flows of certain essential amino acids
also tended to be less with pasture-fed cows. Holden et al. (1994b) also suggested that
diet selection over time may affect fermentation patterns because intake of CP and
ruminally degradable protein likely decline with time spent grazing (Chacon and Stobbs,
1976).
Loss of N from the rumen is costly due to significant energetic expenditure
associated with urea synthesis and excretion. Urea synthesis and excretion cost
approximately 5 kcal/g of N excreted (NRC, 1989). Greaney et al. (1996) estimated that
25% or more of liver oxygen consumption was for the detoxification of ammonia to urea
when diets were pelleted alfalfa (2.7% N) or fresh white clover (4.4% N). The authors
noted that these energetic costs of N loss were likely underestimated because increased
ammonia loading would likely result in increased amino acid catabolism, sodium pump
activity and oxidative phosphorylation. In addition to the greater energetic expenditure,
additional N costs are incurred with hepatic removal of NH3 due to amino acid
catabolism (Lobley et al., 1995; Greaney et al., 1996). This may further limit animal
performance if supplies of essential amino acids are limited.
Though microbial protein is the primary protein source for lactating dairy cows
(Glenn, 1994), Leng and Nolan (1984) noted that it alone cannot provide an adequate
supply of amino acids to the small intestine for maximum growth and production by the
host, as reported by Holden et al. (1994b). This might in part account for reduced
persistency observed with grazing dairy cows (Hoffman et al., 1993). To offset these

39
limitations, some have fed rumen escape proteins, but performance responses to
ruminally undegradable intake proteins have been inconsistent, both for cows in
confinement and on pasture (Davison et al., 1991; Aldrich et al., 1993; Petit and
Tremblay, 1995a,b; Jones-Endsley et al., 1997). Such responses highlight the need for
first optimizing ruminal fermentation to maximize microbial protein synthesis (Aldrich et
al., 1993; Glenn, 1994).
To maximize microbial cell yields per unit of nutrient input (e.g., feed materials)
the rate of ATP production from fermentation reactions must equal the usage rate by
biosynthetic reactions at all times (Hespell and Bryant, 1979). With adequate ATP
(derived primarily from carbohydrate fermentation), rumen microbes can incorporate
amino acids into microbial protein (Nocek and Russell, 1988). Thus, providing
supplemental energy (typically grains high in carbohydrates) may be an effective way to
increase microbial yield and reduce excess N excretion.
Responses to Supplemental Carbohydrate
Responses to providing carbohydrate energy sources are mixed, however. With
continuous culture studies, Hoover and Stokes (1991) reported a high correlation (r =
0.99) between percent carbohydrate digestion and nonstructural carbohydrate (NSC) as a
percentage of dietary carbohydrate. However, the correlation of microbial efficiency to
NSC as a percentage of dietary carbohydrate was much lower (r = 0.33). These results
have been confirmed using cows on pasture by Carruthers et al. (1996) who found that
increasing the proportion of NSC in pasture without increasing energy intake did not
increase ruminal microbial protein synthesis or increase milk solids production in early
lactation.

40
Nocek and Russell (1988) noted that even seemingly appropriate amounts of
dietary CP and carbohydrate may not provide an ideal balance of protein and
carbohydrate to the rumen microorganisms. The authors compared four theoretical diets
that were isonitrogenous and isocaloric but which had variable concentration of ruminally
available CP and carbohydrate. Theoretical bacterial synthesis and amino acid supply to
the small intestine were markedly different among the diets and demonstrated the
potential difficulty inherent in formulating diets for maximum microbial production.
This challenge may be even greater when forage and concentrates are consumed as
individual components such as occurs in grazing systems.
A batch culture study more similar to pasture feeding conditions was conducted to
test the effects of asynchronous nitrogen and energy supplies on microbial growth
(Newbold and Rust, 1992). Cultures were supplied glucose and urea or com and soybean
meal processed for slow or rapid microbial digestion, respectively. Regardless of
substrate, only transient effects of nutrient imbalance on cell yield were reported.
Though the mean bacterial population was greater from 5 to 8 h of incubation,
populations were similar at 12 h. However, the authors could not rule out end-product
inhibition as a reason for similar bacterial mass at the end of the experiments.
Rooke et al. (1987) studied the effects of constant-rate infusions of urea, casein,
glucose syrup, or casein and glucose syrup into the rumens of cows consuming ryegrass
silage. Infusions did not affect ruminal pH or VFA concentrations, but glucose and the
casein-glucose mixture reduced the rumen NH3-N concentration. Glucose and the casein-
glucose mixture also increased the quantities of OM, ADF, NAN, amino acid N, and
microbial N entering the small intestine, indicating that microbial yield was increased but

41
at the expense of fiber digestion. Similar results were found by England and Gill (1985)
who added sucrose to grass silage diets at 50, 75, 100, and 150 g/kg of silage DM. Silage
DMI was reduced, but not total DMI. With increasing proportions of dietary sucrose, a
corresponding decrease in cellulose digestion was observed. The results indicated that
the benefits of N utilization were offset by the decrease in diet digestibility, perhaps due
to the rapid solubility of the sucrose.
Phillips (1988) suggested com silage would be a suitable nutritional
complement to herbage of variable energy and high CP concentrations. An experiment
by Holden et al. (1995) indicated that supplemental silage fed to cows grazing pasture
might have altered ruminal fermentation and reduced N load because silage supplement
also reduced concentrations of plasma urea N from 29.6 to 27.3 mg/dL. This could not
be determined by the authors, however, because the change in plasma urea N
concentration with silage treatment could have resulted from better N utilization or
decreased intake of ruminally degradable protein. Production responses were unaffected
by supplemental silage.
In some experiments, microbial utilization of forage N was not markedly
improved by supplementation with barley (Thomas et al., 1980; Rooke et al., 1985).
Greater intraruminal N recycling due to increased ruminal protozoal number has been
implicated in the lack of N utilization by microbes (Chamberlain et al., 1985).
Substitution with fibrous concentrates such as beet pulp and distillers solubles for barley
has resulted in increased duodenal NAN primarily due to increased feed N flow
(Huhtanen, 1988, 1992) with concomitant increase in milk production and milk protein
yield (Huhtanen, 1987; Ala-Seppala et al., 1988).

42
The effects of com supplementation on intake and digestion characteristics in
lactating cows consuming primarily orchardgrass (Dactylis glomerata L.) and white
clover were studied by Berzaghi et al. (1996). Provision of supplement decreased
ruminal NH3 (17 vs. 22 mg/dl) and increased N recovery at the duodenum (86.7 vs.
75.3% of N intake), though total tract N recovery was reduced with supplementation
(71.9 vs. 78.8%). Digestibility ofNDF also was reduced with supplementation,
suggesting that com had negative effects on fiber digestion. Differences in microbial
flow to the duodenum were not significant.
Effects of Supplement Feeding Frequency
Feeding frequency may also alter ruminal fermentation patterns, improve nutrient
synchrony, and enhance microbial growth. Gustafsson et al. (1993) studied more than
38,000 records of Swedish cows and found that feeding concentrates 4 or more times per
day resulted in 3 and 7% (by year) increases in milk production compared with feeding
twice per day. Their study indicated that feeding frequency positively affected milk
production of primiparous cows with low ME intakes but that this was less of a factor as
ME intake increased. Increasing feeding frequency from 1 to 2 times per day for dairy
cows grazing tropical pastures was shown to increase milk production approximately
11% (McLachlan et al., 1994), but no milk production responses were observed in a
comparison of providing supplement 2 or 4 times per day to cows grazing cool-season
pastures (Hongerholt et al., 1997).
McLachlan et al. (1994) fed 0, 2, 4, 6, or 8 kg of a cracked-com, meat-meal
supplement and reported that the FCM response was greatest with 6 kg of supplement/d
and pasture substitution rates were less when the supplement was provided twice daily.

43
From these results the authors inferred that more frequent feeding resulted in more stable
ruminal fermentation patterns, and that cellulolytic activity was closer to optimum.
However, increased milk protein percentage and greater milk fat concentrations (which
could support the hypothesis of increased microbial growth and cellulolytic activity with
increased feeding frequency) were not observed.
Kolver et al. (1995) fed a supplement either with the base forage (a cool-season
pasture grass) or four hours after forage feeding. With synchronous feeding they found
less diurnal variation in ruminal pH, but average pH was lower (6.06 vs. 6.17).
Synchronous feeding reduced concentrations of ruminal NH3 at 3 and 5 h post-feeding,
but N retention for milk and growth were unaffected.
In a review, Robinson (1989, p. 1199) noted that although improved efficiency
of rumen fermentation in frequently fed cows seems unlikely to result in increased milk
yield in research studies, it can result in increased milk energy output due to increased fat
yield in situations where the combination of infrequent feeding and high inclusion of
rapidly fermentable dietary components results in perturbation of rumen fermentation
sufficient to depress milk fat output. In addition, some evidence suggests that
maintenance of body condition, often a critical problem in high producing herds may be
better maintained with more frequent feeding. Production benefits due to improved
ruminal fermentation efficiency are likely to be quantitatively small when compared with
production gains due to the increased intake associated with greater feeding frequency
(Robinson, 1989).

44
Though McLachlan et al. (1994) did not report changes in body condition, their
results of increased FCM and reduced forage substitution with increased feeding
frequency support the observations of Robinson (1989).
Hongerholt et al. (1997) fed a supplement 2 or 4 times per day and reported that
BW change and non-esterified fatty acids (NEFA) concentrations were unaffected when
grain intakes were similar across treatments. In contrast, feeding 6 rather than 2 times
per day resulted in greater milk fat concentrations and decreased concentrations of
plasma NEFA (Sutton et al., 1986), indicative of enhanced cellulolytic activity and
energy availability from the diet.
Effects of Timing of Supplement Provision Relative to Forage Intake
Timing of forage and concentrate provision relative to each other may affect
intake and performance. Morita et al. (1991; cited by Morita et al., 1996) reported that
steers ate more roughage when concentrate was fed after roughage provision. Work from
Germany (Voigt et al., 1978, cited by Robinson, 1989, p. 1205) indicated that providing
grain supplements before feeding roughage (chopped ryegrass) had different effects upon
ruminal pH and digestion of cellulose depending upon the fermentability of the grain.
Barley, a rapidly fermented grain, caused a greater depression in ruminal pH than com, a
more slowly grain. Feeding the ryegrass before the grains caused a greater increase in
forestomach whole-diet cellulose digestion if barley was the grain supplement (63.6 vs.
75.0%) rather than com (72.1 vs. 78.3%). Differences in ruminal cellulose digestion
were unaffected by feeding sequence if the ryegrass was pelleted and total diet digestion
was reduced. Morita et al. (1996) also noted that roughage consumption and fiber

45
digestibility in the rumen were greater when cows ate roughage before concentrate rather
than in the reverse order.
Timing might also be important relative to ruminal heat production. Russell
(1986) reported that adding pulses of glucose to glucose-limited cultures immediately
doubled heat production with little increase in cell protein. In addition to reduced
efficiency of microbial protein production, consumption of primarily soluble
carbohydrate-based supplements in asynchrony with dietary protein might increase
ruminal heat. Heat in the rumen negatively affects intake of DM and water and alters
ruminal fermentation patterns (Gengler et al., 1970). A 3 C increase in rumen
temperature (from 38.0 to 41.3 C) resulted in a 14% decrease in feed intake (13.2 vs.
11.4 kg/d for control and treatment cows, respectively) in the study by Gengler et al.
(1970).
Additional Energy and Protein Supplements for Animals on Pasture
Fats
Fat feeding may improve milk production but has potential for negative side
effects with respect to microbial fermentation, growth, and feed digestion (Emery and
Herdt, 1991). Fat feeding to lactating cows typically has been limited to mixed rations,
and information on feeding fats to cows on pasture is limited.
King et al. (1990) compared production from cows grazing ryegrass pastures and
receiving no supplement, 3.5 kg of a grain-based pelleted concentrate, or 3.8 kg of pellets
containing 0.5 kg of added fatty acids (primarily palmitic, stearic, and linoleic acids).
Diets were not isocaloric. Forage intakes were similar and were estimated at 17.0, 16.3,
and 15.6 kg of DM/d for control, concentrate, and concentrate plus fatty acid treatments.

46
Total intake was an average of 2.5 kg/d greater for supplemented cows. Production of
milk, 4% FCM, and milk protein were not different between concentrate treatments but
were greater than for the unsupplemented treatment. Cows fed fatty acids produced
greater quantities of milk fat. Volatile fatty acids in ruminal fluid were essentially
unchanged between concentrate treatments, indicating that the fatty acids used did not
affect microbial function. However the low amount of added dietary fat and the small
percentage of which was unsaturated fatty acid would not be expected to significantly
hinder microbial function (Jenkins, 1993).
Escape proteins
In a review, Oldham (1984) noted that supplemental proteins might directly affect
control of food intake in ways not directly related to improvements in digestibility. This
has been shown by Froetschel et al. (1997) who reported that ruminal undegradable
proteins contain peptide sequences that may increase gut motility.
Because of the rapid and extensive degradation of proteins in lush pastures
(Beever et al., 1986a,b), some researchers have explored the utility of supplementing
cows with less ruminally degradable sources of protein. Jones-Endsley et al. (1997)
compared amounts (6.4 vs. 9.6 kg/d) and concentrations (12 and 16% CP) of protein
supplements for lactating dairy cows. The 16% supplement appeared designed to provide
additional ruminally undegradable protein, but this was not made clear by the presented
feed analysis. Amount of supplement did not affect forage intake, but animals
consuming the 16% CP concentrate tended to consume more forage (1.6 kg/d) than did
those fed the 12% CP supplement.

47
Hongerholt and Muller (1998) also found no response of grazing, lactating cows
to increased dietary ruminally undegradable protein, but Stobbs et al. (1977) reported that
escape protein from protected casein stimulated intake. When Davison et al. (1991)
provided meat and bone meal to lactating cows, they were not able to measure forage
intake changes. However, by calculations of energy requirements for observed milk
production and weight changes, the authors determined that forage intake was likely
increased. Consumption of meat and bone meal did not result in greater milk yield, but
did result in less (P = 0.068) BW loss over the first 100 d of the trial and greater (P =
0.054) gain over the entire lactation. The authors concluded that responses to protein
supplements ... vary with the type of pasture, the level of grain or energy supplement fed
and the level of pasture on offer (Davison et al., 1991, p. 162).
Effect of Supplements on Grazing Behavior
Several researchers have reported reduced grazing time with supplementation.
Sarker and Holmes (1974) fed 2, 4, 6, or 8 kg of concentrate supplement/d. They
reported large decreases in GT (an average of 28 min/kg of supplement) with
supplementation. Although total OM intake increased 2 kg from the low to the high
supplementation rate (11.5 vs. 13.6 kg of OM/d), herbage OM intake decreased from 9.9
to 7.4 kg of OM/d.
Cowan et al. (1977) fed a 4:1 cormsoybean meal concentrate at 0, 2, 4, or 6 kg/d
to cows grazing green panic (Panicum maximum var. trichoglume) and glycine (Glycine
wightii cv. Tinaroo) pastures. They reported decreased grazing time with increased
supplement (23 min/d per kg of supplement fed) during autumn and winter months (time
of reduced HA), but not during summer. Available pasture increased with increasing

48
amount of supplement fed. Estimates of forage mass excluded dead material. Average
mass of DM harvested increased 188 kg/ha for each kg increase in concentrate fed,
indicative of reduced forage intake. Herbage on offer ranged from 4000 to 6000 kg of
green DM/ha in summer to 500 to 1500 kg of green DM/ha in winter (below the forage
not limiting intake level). Average length of lactation was greater for supplemented
cows (275 d) compared to those of 0 (222 d) or 2 kg/d (252 d) supplement groups. Cows
assigned to 0 or 2 kg/d treatments had to be removed from treatment early due to
excessive weight loss.
A study of heifers grazing Cenchrus ciliaris pastures showed that grazing time
decreased 11 min/kg of supplement fed (Combellas et al., 1979). Heifers received a high
energy, high protein concentrate at 0, 3, or 6 kg/d. Rate of biting, total bites, and intake
per bite were also decreased. Though not significant, the number of grazing periods was
numerically greater with increased rate of supplementation.
Pulido and Leaver (1997) reported decreased GT of 11 min/kg of concentrate,
though effects were much more dramatic when concentrate fed was greater than 6 kg/d.
For 0, 6, or ad lib kg of daily concentrate intake, GT were 531, 526, and 381 min/d and
rates of forage intake were 31.4, 25.8, and 20.7 g/min. Forage intake decreased 0.69 kg/d
for each kg of concentrate consumed.
A study with beef steers (Adams, 1985) indicated that timing of supplement
feeding affects grazing behavior and forage intake. Steers grazing Russian wild ryegrass
(Elymus junceus) in Montana received forage only (control) or morning or afternoon
feedings of com supplement (0.3 kg of supplement/100 kg of BW). Though
supplemented steers ate less forage than steers on the control treatment, comparison

49
between morning and afternoon feedings indicated greater forage intake with afternoon
feeding (2.6 and 2.9 percent of BW for morning and afternoon feedings, respectively).
Total intakes were not different among the three treatment groups, but forage intake and
total intake were greater for afternoon-supplemented steers in comparison with morning
supplemented animals. Feeding supplement to steers in the morning resulted in a 24%
decrease in forage intake/h of grazing time in comparison with control and afternoon
feeding treatments (Adams, 1985).
Reid (1951) noted that DMI and grazing time are not necessarily correlated.
Similarly, Krysl and Hess (1993) noted that a decrease in grazing time does not
necessarily mean a decrease in forage intake because harvest efficiency (defined as g of
forage OMI/kg of BW per min spent grazing) may change. Work of Barton et al. (1992)
confirmed these ideas. The authors observed grazing behavior of dairy steers fed
supplemental cottonseed meal at 0 or 2.5% of BW in the AM or PM. The steers reduced
grazing time on intermediate wheatgrass (Thinopyrum intermedium Host) pastures by
approximately 1.5 h when provided cottonseed meal supplement, but forage intakes were
not different across treatments. Steers receiving cottonseed meal had numerically greater
forage intake.
Interactions of Supplement and Herbage Allowance on Performance of Lactating
Cows in Pasture-Based Dairy Systems
The two main factors considered to cause the variable responses to supplement
are forage availability and forage nutritive value. Work by Blaser et al. (1960)
demonstrated that concentrate supplements were used more efficiently when herbage was
limited.

50
To investigate the interactions of herbage availability and level of concentrate
supplementation on OMI, Meijs and Hoekstra (1984) stocked lactating Friesians on
perennial ryegrass pastures at 16.3 or 24.8 kg of pasture OM/cow per d. Values for HA
are 2-yr averages within treatments. Three rates of concentrate (1, 3, or 5 kg/cow per d in
1981 and 1, 4, or 7 kg/cow per d in 1982) were fed. Greater herbage intake was reported
at the greater HA (13.6 vs. 11.3 kg of OM/cow per d for the greater and lesser HA,
respectively). Increasing concentrate intake negatively affected forage OMI. This was
primarily due to the decrease in forage intake by cows on the greater HA treatment
(forage by concentrate interaction). Forage OMI of 14.9, 13.6, and 12.3 kg/cow per d
were reported for cows fed the low, medium and high concentrate rates, respectively, for
cows on the greater HA treatment, whereas forage OMI decreased only from 11.4 to 11.0
kg/cow per d with increasing concentrate for cows on the lesser HA treatment.
Relatively few experiments have been conducted on tropical pastures to
determine objectively the relationship between herbage availability and the performance
of dairy cattle. There is therefore little evidence on which to determine the pasture
conditions under which supplementary feeding might be most efficiently employed
(Jennings and Holmes, 1984b, p. 270). Little research has been published on this topic in
the last 15 years.
Cowan and Davison (1978) investigated effects of supplementing maize (0 or 3
kg/d) to cows grazing tropical pastures of mixed forage species at 1800 or 3300 kg of
DM/ha. Milk production was increased from 6.5 to 9.3 kg/cow per day with supplement
offered to cows assigned to the lower level of HM but was unaffected by supplement
(13.0 kg/d) offered at the greater level of HM.

51
Two Perennial Forages for Lactating Cows in Pasture-Based Dairy Systems
in the Southeast
Bermudagrass
Bermudagrass is one of the most extensively grown improved, perennial, warm-
season forages for the Southeast. According to G. W. Burton, bermudagrasses occupy
more than half the pasture acreage in the southern United States (cited in Adams, 1992,
p. 19). First introduced to the U.S. in 1751 (Burton and Hanna, 1995, citing the diary of
Thomas Spalding), bermudagrass has been the subject of much research. Numerous
improved cultivars of the grass have been released since the 1940s (Burton and Hanna,
1995), and a review of the literature reveals improvements in both yield and digestibility
(Monson and Burton, 1982). Today, more than 5 million hectares in the Southeast have
been sprigged with improved bermudagrasses, with many more supporting common
bermudagrass (Burton and Hanna, 1995).
Though well adapted to much of the region, bermudagrasses typically have high
concentrations of NDF and low concentrations of NEl and digestible nutrients (West et
al., 1997). A compilation of 18 experiments in which bermudagrass hay harvested at
vegetative to mature growth stages, obtained from local producers and grown with a
variety of management practices was reported by Goetsch et al. (1991, p. 2635). Mean
NDF concentration was 74.5% with a range of 65.6 to 86.7% (DM basis). Though mean
OM digestion was 54.9 %, the range of OM digestion was quite wide, from 27.5 to
75.4%.
Bermudagrass yield responses and nutritive value characteristics are affected by
numerous factors, including frequency of defoliation (grazing or clipping), fertility,
temperature, season, and location, and responses vary by cultivar (Wilkinson et al., 1970;

52
Jolliff et al., 1979; Henderson and Robinson, 1982; Holt and Conrad, 1986; Adjei et al.,
1989). Soil moisture also has been implicated as a factor affecting quality of warm-
season grasses (Henderson and Robinson, 1982; Pitman and Holt, 1982).
Yield typically increased with decreased frequency of defoliation (Decker et al.,
1971; Holt and Conrad, 1986; Adjei et al., 1989) though this was not reported by
Ethridge et al. (1973). Conversely, in vitro digestibility decreased with decreased
defoliation frequency (Decker et al., 1971; Holt and Conrad, 1986; Jolliff et al., 1979),
but the magnitude of change in digestibility has been inconsistent (Hussey and Pinkerton,
1990). Data from Holt and Conrad (1986, p. 435) indicated that both yield and dry
matter digestibility cannot be maximized by manipulating harvest or utilization
frequency, necessitating a compromise in one or both in any management situation.
In pasture systems, both digestibility and availability of forage influence animal
performance. As digestibility decreases, more forage must be consumed to maintain
animal gain, and the upper limit of productivity will be reduced (Dubl et al., 1971).
Forage quality, as determined by intake, nutritive value and efficiency of utilization, is
well demonstrated by work of Greene et al. (1990). Stocker performance was compared
using four different bermudagrass cultivars. Though the cultivar Grazer did not
produce the greatest forage DM yields, animal output per unit land area with Grazer was
approximately 18% greater than the average production with the other cultivars
(Brazos, Coastal, and Tifton 44).
The varying nature of cultivar responses makes finding an appropriate
compromise between maximum yield and greatest nutritive value more difficult.
Optimum will likely depend on production aims. For example, Adjei et al. (1989)

53
investigated the response of three bermudagrass cultivars to grazing at 2, 4, 6, and 8 wk
frequencies within seasons (Winter/Spring and Summer/Fall). Yield response of Callie
35-3 (now cv. Florakirk) to grazing frequency was quadratic in nature. Maximum
yields for both Callie 35-3 and Tifton 78 occurred at the 6-wk grazing interval, with
yields of 2.6 and 3.6 t/ha for the respective cultivars. A linear response to grazing was
observed for Tifton 79, with a maximum yield of 3.5 t/ha occurring at the 8-wk grazing
frequency. Conversely, as grazing frequency decreased, in vitro organic matter
digestibility (IVOMD) declined in a linear fashion for Callie 35-3 and exhibited both
linear and quadratic characteristics for Tifton 78 and 79 depending on season. For the
Tifton cultivars, greatest digestibility occurred at the 4-wk grazing frequency.
Concentration of CP also decreased with decreased grazing frequency for all cultivars
with the nature of the responses dependent on season and cultivar.
Holt and Conrad (1986) investigated yield and digestibility responses to
frequency of harvest among several varieties of bermudagrass and one stargrass (C.
nlemfuensis Vanderyst) cultivar (Tifton 68). Although Coastal bermudagrass had the
greatest seasonal yield at all clipping frequencies (average of 15.8 metric T/ha), its
IVDMD was least at all clipping frequencies (average of 54.8% IVDMD). The stargrass
cultivar had intermediate yield (average of 13.8 t/ha) and greatest digestibility (average of
65.4% IVDMD) at all clipping frequencies. The greater IVDMD for Tifton 68 resulted in
that cultivar producing the greatest quantity of digestible OM. The best compromise
between yield and digestibility for all cultivars was at approximately 4 wk of regrowth.
Many studies of the effect of fertilization on bermudagrass yield and nutritive
value have been conducted. Typically, increased CP concentrations were reported with

54
increasing N application (Monson et al., 1971; Monson and Burton, 1982; Thom et al.,
1990). Good fertilization is essential to production of quality bermudagrass. Stallcup et
al. (1986) fertilized bermudagrass pastures at 0 to 200 kg of N/ha in 50 kg increments and
reported that CP concentrations in bermudagrass fertilized with 0 and 50 kg of N/ha were
11.4 to 14.3%, respectively. Although apparent DM digestibility increased slightly (61.3
to 62.0%), CP digestibility increased from 54.2 to 63.6%. When the hays were fed to
steers, the difference in N retention (measured as a percent of N fed) was quite large (2.8
vs. 21%, respectively). Increasing the rate of N application above 50 kg of N/ha had
more modest positive effects on the variables measured. Monson and Burton (1982)
investigated the effect of two levels of N fertilization (336 or 672 kg/ha) and cutting
frequency (1,2,4, or 8 wk) on yield, quality, and persistence of eight bermudagrass
cultivars. Digestibility increased with increased N application with weekly harvests.
Significant interactions between harvest frequency and genotype in response to N also
were noted. Besides increasing CP and yield, N fertilization also has been shown to
increase carotene and xanthophyll concentrations in bermudagrass (Monson et al., 1971).
Ocumpaugh (1990) noted that if legumes are used, chemical N sources are not a
necessity for bermudagrass production. He reported that when Coastal bermudagrass
pastures were overseeded with sub-clover (71 subterraneum) or arrowleaf clover (71
vesiculosum) they produced as well as similar pastures receiving two applications of 56
kg of N/ha. In years of plentiful rainfall grass-legume pastures out-yielded grass-N
pastures.
Singular use of N fertilizer may not be effective for bermudagrass production.
Welch et al. (1981, cited by Pratt and Darst, 1986) reported that yields with N

55
fertilization were 50% of those when both N and K were applied. Pratt and Darst (1986)
also indicated that response to K fertilization was not always immediate. In their work, K
deficiency was seen (vis-a-vis large decline in yield) in the third year of study, and they
emphasized the need for long-term observation.
Effects of other fertilizers on animal responses have been investigated. Mathews
et al. (1994b) fed non-lactating cows chopped Tifton 78-common bermudagrass hays
which had or had not been fertilized with S (gypsum). The authors reported a 30.4
percentage unit increase in the apparent digestibility of S (vs. unfertilized control) and a
10.6 percentage unit increase in the apparent digestibility of lignin. Apparent N
digestibility slightly increased with S fertilization. Digestibility of ADF and NDF tended
(P = 0.18) to be increased by 1.5 percentage units, and DMI also tended (P = 0.14) to be
increased with S supplementation.
Henderson and Robinson (1982) grew bermudagrass in chambers to study the
effects of differing light intensity, moisture, and temperature on bermudagrass harvested
at 14 or 21 d. Yield increased with increased temperature and with increased photon flux
density, and in vitro digestibility decreased with increased temperature. When soil
moisture was low, light level did not affect forage digestibility across the array of
temperatures. Similarly, increased age reduced digestibility to a lesser degree under
moisture-limited conditions.
Seasonal effects on digestibility have been observed. Forage digestibility
typically is greatest in spring, declines in summer and increases in late summer or early
fall (Carver et al., 1978; Holt and Conrad, 1986), though this pattern is not always
observed (Guerrero et al., 1984). Holt and Conrad (1986, p. 435-436) noted that

56
differences in digestibility were unrelated to age at harvest, and that changes in IVDMD
apparently are related to environmental conditions not clearly understood under field
conditions Adjei et al. (1989) also reported that forage nutritive value typically was
greater in fall than in summer and differences between cultivars within seasons were
observed as well. Animal performance often mirrors these changes (Greene et al., 1990).
Holt and Conrad (1986) investigated decreasing leaf proportion as a source of
decline in forage digestibility because leaves are usually more digestible than stems.
Leafiness decreased with age but, though the decline in leaf proportion was a significant
factor, it explained less than 50% of the decline in forage digestibility (r2 = 0.44). The
authors noted that stem digestibility was a likely factor in cultivar digestibility
differences, but this was not explored. Genotype and seasonal effects on [IVDMD]
were greater than and largely independent of leaf effects when plant material was all the
same chronological age (p. 435). Similar results with respect to leaf proportion were
observed by Mathews et al. (1994a). They investigated IVOMD and nutrient
concentration of Callie bermudagrass in response to four methods of harvest. Pastures
were stocked continuously, rotationally stocked in short and long rotations, or cut for hay.
Leaf lamina as a percentage of the plant material sampled was least with continuous
stocking (33.5% across years) and averaged 47% with the other three methods. However,
the weighted mean of IVOMD was relatively stable (56.5%), not differing by more than
3.2 percentage units.
Location also determines the productivity and quality of bermudagrass in as much
as it combines such factors as rainfall or soil moisture, ambient temperature, soil
characteristics, and incident light. For example, though Adjei et al. (1989) did not

57
specifically test genotype by location, their research indicated that Tifton 78 was
unsuitable for central Florida conditions even though it had been released and was
finding some use in Georgia.
Numerous investigators have studied the suitability of use of bermudagrass as an
animal feed. Typically, the grass is used more in extensive feeding systems such as
pasture for beef cattle or dry dairy stock.
Stocking rates on bermudagrass may have a large influence on animal
performance once some critical level is reached. Working with a biophysical model,
Parsch et al. (1997) simulated forage production responses to a range of beef cattle SR.
According to the model, with improved bermudagrass pastures weight gain per head is
essentially unaffected by grazing intensity until a critical SR (6 head/ha) is reached.
Bransby et al. (1988, p. 278) also reported that grazing systems on bermudagrass appear
to be well buffered against changes in grazing intensity across a wide range of stocking
rates and available herbage.
The interaction of forage and SR with continuously stocked bermudagrass
pastures was investigated by Guerrero et al. (1984). Forages were Callie, Coastal, and
three experimental hybrids. Stocking rates varied by cultivar but the range averaged from
4.6 to 11.0 steers/ha. Forage digestibility was increased with increasing SR, and greater
digestibility occurred primarily at medium and heavy SR. However, ADG decreased as
available herbage declined, and cultivar differences in digestibility and yield were
observed.
Roth et al. (1984, 1990) studied bermudagrass growth, morphology, and
compositional responses at four different HA under continuous stocking management.

58
Decreased HA affected leaf chemical characteristics and the proportion of leaf in the HM.
Leaf NDF decreased from 75.2 to 71.3% from high to low HA, and the average
proportion of leaf in the HM decreased by 51.6 and 39.7% for low and high HA
treatments, respectively.
Leaf proportion in the diet was unaffected across grazing pressures (82.7% for
low and 78.5% for high pressures), however, demonstrating diet selectivity of the grazing
animal. Animals also showed selectivity for leaves of greater quality as the concentration
of NDF in leaves selected was less than that in leaves in the standing herbage. With the
lower HA treatments, the proportion of dead material increased as leaf declined during
the hotter months. The dead material consisted primarily of uprooted stolons and dead
stems, and their disappearance later in the grazing season was due to consumption.
Although dead herbage is not high quality, the concentration of NDF in the dead
herbage of the low HA treatment was approximately 9.0 percentage units less than that of
the other treatments. As HA decreased, NDF concentration of the herbage was reduced
in the two pastures with the lowest HA compared with the two pastures with the greatest
HA. Moreover, reductions in NDF concentrations with decreased HA were observed in
all herbage components, and particularly in the senesced herbage.
Other studies (Arnold, 1960; Hamilton et al., 1973; Adjei et al., 1980) have not
shown the positive relationship between HA and NDF concentration of the herbage or the
diet found by Roth et al. (1990). The latter noted that the previous studies were
conducted using greater HA, however.
In 1993, a new cultivar, Tifton 85, was released (Burton et al., 1993). The grass is
actually an interspecific hybrid between bermudagrass and stargrass (Tifton 68), and it

59
produces an abundance of stems and leaves in spring, followed by more vegetative
growth later in the season (Hill et al., 1993, p. 3222). The authors reported greater NDF
concentrations in the forage earlier in the grazing season and suggested that this might be
due to the cultivars growth habit.
Tifton 85 has [rjapid growth rate and high IVDMD values relative to other
bermudagrass hybrids (Hill et ah, 1993 p. 3219). Hill et ah (1993) tested Tifton 85
grown in small plots and found that it produced greater quantities of DM with greater
digestibility than all other cultivars in the comparison. In comparison with Coastal
bermudagrass, [at one time the predominant cultivar in the Southeast (Holt and Conrad,
1983)], Tifton 85 produced more than 25% more DM (16.7 vs. 13.3 t of DM/ha) the and
forage was more than 12% more digestible (58.8 vs. 52.3% IVDMD).
Hill et ah (1993) also compared Tifton 85 with Tifton 78 in a grazing study.
Tifton 78 is a cultivar widely used because of its relatively high digestibility and yield.
The researchers maintained HM of both forages at approximately 2500 kg of DM/ha over
2 yr and sampled esophageally fistulated steers to estimate forage nutritive value
characteristics. Tester steers and variable SR also were used to determine ADG and to
calculate grazing d/ha. Steers grazed 169 d each year, and though the ADG with the two
forages were similar (0.67 vs. 0.65 kg/ for Tifton 85 and 78, respectively) Tifton 85
supported in excess of 500 more grazing days over the 3 yr of the study. The BW gain/ha
was 46% greater for steers grazing Tifton 85 as a consequence (1160 vs. 790 kg/ha). Hill
et ah (1993, p. 3224) noted a strong tendency for Tifton 85 to remain more productive
later in the grazing season than Tifton 78 did. This translated into slightly greater rates
of BW gain in August and September.

60
Mandebvu et al. (1998) compared DM and NDF digestibilities of first and second
cuttings (3.5 wk of growth) of Tifton 85 hay with that of Coastal bermudagrass hay of 4
wk growth. The IVDMD was reported as 63.6, 59.9, and 52.0% for the first and second
cuttings of Tifton 85 and the Coastal bermudagrass hay, respectively. The NDF
digestibilities were 61.4, 58.5, and 47.5%. First-cut Tifton 85 had a greater potentially
digestible NDF fraction in whole forage (77.9 vs. 67.1%) and in extracted NDF (81.5 vs.
70.7) than did Coastal bermudagrass.
Much literature details performance of beef animals grazing bermudagrass
pastures, with some information released comparing Tifton 85 with Tifton 78 (Hill et al.,
1993), but information regarding use of bermudagrass for grazing dairy animals is
limited. A study by Martinez et al. (1980, cited by Jennings and Holmes, 1984b) may
have overpredicted the potential use of bermudagrass as a pasture forage for dairy cows.
The authors reported that cows grazing Coast-cross I bermudagrass produced 4125 kg of
milk/cow per yr without supplementation.
West et al. (1997) indicated that Tifton 85 may be suitable for confinement
dairies, but no information is presently available regarding use of Tifton 85 by lactating
cows in grazing systems without or with supplemental feeds. In the study by West et al.
(1997), 3.5% FCM yields were not different for cows fed diets of either 15 or 30%
bermudagrass or alfalfa hays. Results suggested that the NDF digestion of Tifton 85 was
more rapid and more extensive than that of alfalfa or com silage components of the diets.
Comparisons of Grasses and Legumes
The high concentrations of NDF and low concentrations of digestible nutrients
associated with warm-season perennial grasses limit their desirability for use in animal

61
production systems. Many have looked to forage legumes for suitable alternatives to
grasses because animal performance is often greater when legumes are fed (Rattray and
Joyce, 1974; Thomas et al., 1985; Beever et ah, 1986b; Hoffman et ah, 1998). The
following discussion primarily will consider cool-season perennial legumes, because few
warm-season perennial legumes have proven suitable for intensive grazing systems.
Regarding chemical composition, legumes typically have greater concentrations
of protein than grasses, with a larger percentage of the protein being ruminally
degradable (Beever et ah, 1986a; Glenn, 1994). The soluble portion of legume CP also is
different, having more amino acids and peptides than that of grasses (Glenn et ah, 1989).
Legumes generally have less NDF than grasses, and the composition of NDF in legumes
is markedly different. Legumes have less hemicellulose, typically less cellulose, more
lignin and more pectic substances (Van Soest, 1965) than grasses.
In vitro digestibility studies indicate that legumes typically have a greater rate but
lesser extent of digestion in comparison with grasses (Smith et ah, 1972). Glenn (1994)
noted that, relative to alfalfa, proportionately more grass NDF typically is digested in the
rumen. A review of several comparisons of alfalfa and orchardgrass fed to growing
animals indicated that total tract digestibility of orchardgrass was 94% that of alfalfa
(Glenn, 1994). In comparisons of alfalfa with ryegrass or orchardgrass, researchers
typically have found greater true fiber and DM digestibility for the grasses (Holden et ah,
1994a; Hoffman et ah, 1998), but the greater DM digestibility may in part be related to
the lower intakes of cows on the grass-based diets.
Holden et ah (1994a) fed diets of 55 or 66% forage (orchardgrass and alfalfa hays,
respectively) which were formulated to have equivalent NDF concentrations. Lactating

62
cows consumed 17.5 and 15.1 kg of OM/d for the alfalfa and orchardgrass diets,
respectively, and total tract digestions of NDF, ADF, and DM were greater for cows fed
the grass diets. In the study by Hoffman et al. (1998), lactating cows were fed diets based
on 70% inclusion of alfalfa or perennial ryegrass silage. Intake of DM was greater when
cows ate alfalfa silage (22.5 vs. 20.3 kg of DM/d), though true digestibility of NDF and
DM was greater for the ryegrass silage-based diet. In both studies, milk production was
greater with the alfalfa-based diet.
In a comparison of steers grazing pure stands of ryegrass or white clover, Beever
et al. (1986b) reported a nearly 25% greater DMI of the clover pasture (26.0 vs. 20.9 g/kg
of LW). Although intakes are generally greater with legumes, the better performance
typically associated with their consumption may not be only an intake effect. Glenn
(1994, citing Tyrrell et al. 1992 and Varga et al., 1990) noted that the large differences in
digestible OM composition must have some effect on the composition of absorbed
nutrients.
Differences in digestible OM composition likely contribute to the greater
efficiency of ME use associated with legume consumption (Armstrong, 1982). Greater
energetic efficiency of lactating cows fed alfalfa in comparison with orchardgrass was
reported by Casper et al. (1993). The authors fed ensiled forages (direct-cut and treated
with formaldehyde and formic acid) with two high-starch concentrate sources (barley or
com grain). Intakes of DM and ME and the digestibility of the DM were all greater for
the alfalfa-based diets. Although heat production was greater when cows consumed
alfalfa, heat production per unit of ME intake was greater for the orchardgrass diets. The

63
greater heat production/ME likely indicated an increased energy cost associated with
digestion of orchardgrass.
Although the greater DMI and efficiency of utilization reported with legumes is
desirable, legume use in pasture systems in warm climates often has been limited. Few
perennial legumes have been satisfactorily productive or persistent in forage systems in
subtropical regions of the humid Southeast, and some researchers have argued that
legumes have little place in production systems in the region (Rouquette et al., 1993). To
date, insects, nematodes, phytopathogens and poor persistence under grazing conditions
have relegated tropical legumes to limited roles in forage production systems in the
tropics (Maraschin et al., 1983).
Rhizoma Peanut
One legume with promise for the region, however, is rhizoma peanut (Arachis
glabrata Benth.). The legume is fine-stemmed and leafy, with potential for use in
grazing or stored-forage production systems (Prine et al., 1981). Introduced to Florida
from Brazil in 1936 and first distributed to commercial growers in 1978 (Prine et al.,
1986), most acreage expansion has occurred since 1980 (French, 1988). In 1990, an
estimated 1200 ha of rhizoma peanut (RP) had been planted in Florida (Niles et al.,
1990), with plantings increasing to 8100 ha by 1999 (E. C. French, personal
communication). The plant is being tried in other Deep South states as well (Prine et al.,
1986; Ocumpaugh, 1990; Mooso et al., 1995). Factors slowing its use by producers
include farmer unfamiliarity with the crop and high establishment costs (Prine et al.,
1986).

64
Another reason for RPs limited use may be its slow rate of establishment. In
studies by Valentim et al. (1987) and Terrill et al. (1996), RP was slower to establish than
alfalfa. In the study by Terrill et al. (1996), RP produced less DM than did alfalfa (cv.
Pioneer 526) in the first 2 yr (11.9 vs. 6.1 Mg/ha). In the third year of the study,
however, DM production did not differ between RP and alfalfa (10.6 vs. 11.4 t/ha), and
leaf yield was greater for RP (6.2 vs. 5.4 metric t/ha). Similarly, Valentim et al. (1987)
found that RP outyielded alfalfa (cv. Florida 77) in the fourth year of their trial. Florida
77 has poor stand longevity, however, and over time this may affect comparison of yield
for the two forages.
Despite its establishment and propagation difficulties, RP may still be suitable to
the region. The forage has few disease or nematode problems (Prine et al., 1981;
Baltensperger et al., 1986), is palatable to a wide range of livestock (French et al., 1987),
and is persistent under grazing (Sollenberger et al., 1987).
An array of clipping regimes has been used to study the effects of defoliation on
nutritive value of RP. In a two-year study, Beltranena et al. (1981) examined the effects
of 2-, 4-, 6-, 8-, 10-, or 12-wk cutting intervals on yield, % CP, and % IVOMD. As
clipping interval increased, concentration of CP and IVOMD declined. Crude protein
percentage ranged from 21.9 to 14.7% and IVOMD from 74.3 to 64.8%. Saldivar et al.
(1990) also found decreases in concentrations of CP and IVOMD with increased interval
between clippings. Their results implicated leaf/stem ratio and its rate of change as
important factors influencing nutritive value.
Romero et al. (1987) investigated the effects of season and of increasing week of
regrowth on nutrient composition and digestibility of RP. They reported greater NDF

65
and ADF and lower CP concentrations for leaves of RP grown in summer vs. fall.
Response to regrowth intervals between leaf and stem fractions was variable, but
investigation of combined leaf and stem fractions showed increasing fiber and decreasing
CP concentrations with increasing maturity.
The concentration of CP in RP was less than that in alfalfa, while concentrations
of neutral and acid detergent fiber were greater (Romero et al., 1987; Terrill et ah, 1996).
In situ experiments showed RP to have slower rates of DM disappearance than alfalfa
(Romero et ah, 1987) but similar concentrations of highly soluble DM (24 vs. 27%) and
less potentially digestible (43 vs. 45%) DM (Romero et ah, 1987). Although alfalfa had
greater disappearance of CP after 24 h (85 vs. 72%), the authors noted that even with less
CP, RP may potentially contribute more protein post-ruminally than alfalfa due to its
less ruminally soluble and potentially degradable protein.
In the study by Beltranena et ah (1981), yields of DM were 6.6 and 10.0 t/ha at
the 4- and 6-wk clipping intervals, respectively. Clipping intervals greater than 6 wk did
not increase DM yield. Forage had greater concentrations of CP and IVOMD at 4 wk
(20.1 and 72.9%) than at 6 wk (17.9 and 70.4%), and the authors suggested a 4 wk
defoliation interval might be a suitable compromise between quantity and nutritive value
for intensive grazing systems.
Ortega-S. et ah (1992) studied the effects of different grazing frequencies and
intensities by beef heifers on performance of RP pastures. With a 42-d grazing cycle, a
stand of 80% RP could be maintained if residual DM was 1700 kg/ha or greater. With a
21-d grazing cycle, the residual DM needed to maintain an 80% stand was 2300 kg/ha.
The study underscores the importance of proper grazing management of RP pastures.

66
Sollenberger et al. (1987) compared performance of Stockers grazing either RP or
bahiagrass (Paspalum notation Fliigge) pastures in a rotational stocking system without
supplement. Animals grazing RP had greater ADG than animals grazing bahiagrass (0.98
vs. 0.37 kg/d, respectively). Although bahiagrass pastures supported more animals (4.3
vs. 3.0 head/d) for a greater number of days (157 vs. 119 d), total gain/ha over the
growing season was greater for animals grazing RP (316 vs. 232 kg/ha).
Trials with growing goats also indicate that RP is a high quality forage. When fed
RP or alfalfa hays, growing goats eating RP always had numerically greater voluntary
intake, and significantly greater (P < 0.07) intakes for 9 wk of the 20-wk study (Gelaye et
al., 1990). Concentrations of NDF (45.3 vs. 45.8%), ADF (34.4 vs. 33.3%), and ADL
(8.9 vs. 8.0%) were similar for alfalfa and RP, respectively. Organic matter (OM)
concentration was 2 percentage units greater for RP. Apparent digestibility of OM and
fiber fractions was greater for RP. Goats consuming RP had both greater gain in BW and
feed conversion efficiency but less (P < 0.08) retained nitrogen and less ruminal
propionate concentration. Numerically less N retention, less (P < 0.09) ruminal
propionate concentration, and greater acetate:propionate ratio were also observed by
Gelaye and Amoah (1991).
Gelaye and Amoah (1991) fed growing goats complete diets containing either
10.5% (as-fed basis) ground RP or ground alfalfa hay. Diets containing RP had about
10% more NDF than those containing alfalfa, mostly due to a greater hemicellulose
concentration. Feed intake and ADG were numerically less but not significantly different
for animals consuming the RP diet. Apparent digestion coefficients for CP, NDF, and

67
hemicellulose tended to be greater (P < 0.07) when goats ate the diet containing RP.
Though not stated, this may have been due to slower rate of passage.
Staples et al. (1997) showed that RP silage is suitable for lactating dairy cows.
The researchers fed 50:50 forage:concentrate diets, substituting RP for com silage at 0,
40, 70, and 100% of the forage source (0, 20, 35, and 50% of dietary DM). Milk yield
was greatest when cows ate diets with 20% RP silage, following the same pattern as
DMI. Linear decreases (P < 0.10) of both total VFA concentrations and body weight
gain (P < 0.05) were observed with increasing RP silage. This likely reflects lesser
concentrations of energy in RP silage as compared with com silage.
Use of RP in grazing systems for lactating dairy cows has not been reported
previously. Questions needing research include effects of SR and supplementation rate
for animals grazing RP. Economic costs must particularly be considered because slow
establishment, vegetative propagation, and the need for chemical weed control... [make]
rhizoma peanut...a high-input, management-intensive forage crop ... [requiring]
appropriate attention to all production needs and inputs (Mooso et al., 1995). Such
requirement costs may be prohibitive despite its excellent pest resistance and nutritive
value characteristics.
Some Management Strategies for the Improvement of Milk Production in
Subtropical Environments
Bovine Somatotropin (bST)
Some of the original investigations of the efficacy of exogenous bST were
conducted with animals on pasture (Brumby and Hancock, 1955; Brumby, 1956), but the
majority of the related literature investigates its effects on the performance of cows in
confinement. Further, investigations of the use of bST with pastured cows primarily have

68
been limited to temperate climates (Brumby, 1956; Peel et al., 1985; Hoogendoom et al.,
1990; Chilliard et al., 1991).
Generally, bST injections increase milk production of cows on pasture. Results
from Chilliard et al. (1991) indicated no effect of bST on milk production, but the results
were confounded by a greater amount of concentrate feeding to control cows. Treated
cows tended to lose more weight, which was attributed to medium quality available
pasture and low amounts of concentrate supplementation.
Peel et al. (1985) tested the effects of growth hormone with five pairs of
monozygotic twins. One twin from each pair received a daily injection of 50 mg of
growth hormone for 22 wk. The animals grazed ryegrass-white clover pastures, and the
SR was intentionally kept low so as not to limit the animals genetic potential. Milk
production increased nearly 18% with bST injection (19.8 vs. 23.3 kg of milk/d) but milk
composition was unchanged. Pasture intake, measured twice, was numerically greater
(8%) at the eighth week of the trial and significantly greater (14%) by the 22nd wk. Feed
conversion efficiency and BW were not changed, but the treatment group appeared to
have greater body condition loss during the first 4 wk of the trial.
A 10% increase in milk production due to bST was reported by Hoogendoom et
al. (1990). Cows grazed ryegrass-white clover pastures and were injected bi-weekly with
a controlled release formulation that delivered 25-mg of bST/d. Milk yields totaled 2360
and 2600 kg/cow for the control and bST-treated cows over the 26-wk trial, with similar
increases in milk fat and protein production. Milk yield was greater when pasture was
not limiting. A period of warm, dry weather resulted in a decline in herbage production
and a concomitant convergence of group milk yields. Differences due to treatment

69
returned with provision of supplemental greenchop com and increased pasture herbage.
Although the authors were unable to discern measurable differences in DMI, the changes
in production with changes in feed supply indicated that cows treated with bST likely had
greater intakes.
Intake differences were shown by Michel et al. (1990), who fed cut pasture
(ryegrass-white clover) to lactating dairy cows and found significant increases in DMI
within 4 wk of treatment with bST. Means of milk response were not reported, but cows
of low genetic merit had greater response to bST than did cows of high genetic merit.
Little difference in BW was observed over the course of the 50-d trial, but body condition
score was generally less for bST treated cows than for controls. This indicates the
necessity of providing adequate feed to meet the energy requirements of cows treated
with bST.
Valentine et al. (1990) reported that bST injections increased milk production
from cows grazing ryegrass-subterranean clover pastures and supplemented with a
barley-faba bean (Vicia faba) concentrate. Injections of 320 mg of a sustained release
formulation every 28, 21, or 14 d resulted in average dosages of 11.4, 15.2, or 22.8 mg/d.
Milk production was 17.6, 18.1, and 18.8 kg/d vs. 15.9 kg/d for control cows,
corresponding to 10.7, 13.8, and 18.2% increase in milk production with increased dose.
Live weights were also increased, and the authors attributed this to greater gut fill due to
greater pasture intake, although intake was not measured
Hartnell et al. (1991) explored dose responses within parities with much greater
levels of bST administered (biweekly doses of 250, 500, or 750 mg of bST) to cows in
confinement in four different geographic regions within the U.S.A. Averaged over

70
parities, production ranged from 25.2 to 31.5 kg of milk/cow per d, and increases above
control were 12.3, 15.9, and 25.3% for the three treatments, respectively.
Effects of Heat on Milk Production, and Cooling Strategies for Pastured Cows
Cool, comfortable cows produce more milk. Milk production and tolerance to
heat stress are likely inversely related (Smith and Mathewman, 1986) due to the high rate
of metabolism associated with milk synthesis (Marai and Forbes, 1989). Generally, feed
intake begins to decline when mean daily environmental temperatures reach 25 to 27C,
though this is modulated by climatic and nutritional factors (Beede et al., 1985; Beede
and Collier, 1986). Reductions in DMI occur due to decreased grazing activity, increased
water consumption and increased respiration, benefiting the heat-stressed ruminant by
reducing heat load via lessened heat of fermentation and gut metabolism (Roman Ponce
et al., 1978; Mallone et al., 1985). Ruminal contraction rates and ingesta passage rates
also decrease with elevated temperatures (Attebery and Johnson, 1969; Warren et al.,
1974).
Typically, the greater concentration of dietary roughage, the greater the reduction
in DMI with elevated ambient temperature (Beede and Collier, 1986). Thus, the negative
effects of high ambient temperature on animal production are generally greater for
grazing animals because reduction in feed intake is due mainly to reduced forage
consumption (Beede and Collier, 1986).
Technologies for heat stress abatement in confined-housing production systems
have made great advances in the past decade but are limited for animals on pasture.
Typical cooling methods for pasture systems include cooling ponds, fixed or mobile
shade structures, trees, and permanent structures such as barns. Immobile structures are

71
likely less suitable because of the potential for continued camping and concomitant
fouling in those areas of prolonged congregation. Increases in pests (flies and other
parasites) and infection (primarily mastitis) are possible. Generally, any mechanical
methods of cooling such as fans and misters are likely to be difficult to apply to large-
scale grazing systems and would be of limited suitability due to increased costs and the
potential for fouling the pastures. Some use of shades and misters with mobile irrigation
units have been attempted in Florida (J. Trout, personal communication), but no research
as to their efficacy has been reported.
Work by Missouri researchers indicates that the pattern of cooling is more
beneficial to improving production than provision of cooling in a general sense (Spain
and Spiers, 1999; Spiers et al., 1999). Cows had better performance responses when kept
at cooler environmental temperatures during the night. Cooling fans were more effective
at improving performance when used at night rather than in the daytime. Thus, cows
grazing in environments where differences between day and night temperatures are great
may not suffer the effects of heat stress as severely as cows in environments with little
change between day- and nighttime temperatures.
This cooling opportunity can be diminished, however, if the nighttime relative
humidity is high because moist air reduces the efficiency of evaporative cooling (West,
1994). Thus, a more appropriate measure of heat stress would be some combination of
temperature and humidity, such as a temperature humidity index (THI), as the one
referred to by West (1994). The THI is calculated as the dry bulb temperature (0.55 -
0.55 relative humidity) (dry bulb temperature 58), and mean THI greater than 72
reduce milk production (Johnson, 1987, cited by West, 1994).

72
bST in Hot Environments
Because of the increase in body temperatures associated with the use of bST,
concerns have been raised about its use on heat-stressed cattle (Kronfeld, 1988). In a
study by Mollett et al. (1985) milk production was not increased with bST administration,
and the authors suggested that a period of high heat and humidity affected the response to
treatment.
In a study of bST and shade effects, Zoa-Mboe et al. (1989) reported no increases
in milk production due to bST though milk production was increased with shade.
However, on a 3.5% fat-corrected basis, both shade and bST treatments increased milk
production to approximately 24 kg/d vs. 22 kg/d for control cows. Several positive
responses to bST when used in hot climates have been reported across Bos taurus breeds,
Bos species, and ruminant genera (Amiel et al. unpublished data; Ludri et al., 1989;
Phipps et al., 1991; West et al., 1990). Generally, provided sufficient quantities of a
balanced diet are available, bST is effective in hot conditions.
Amiel et al. (unpublished data) tested the effects of bST in several herds in
Jamaica. Milk production responses were similar across a variety of management
conditions, increasing approximately 17% with bST (9.9 vs. 11.6 kg of milk/d).
Performance responses from eight herds of Jamaican Hope cattle ranged from 16 to 30%
whereas 6 and 14% increases were observed for Holstein and Holstein cross cattle
injected with bST, respectively. Conditions were hot and humid, pasture forages were
generally inadequate due to a period of drought, and extra concentrate typically was not
fed to compensate for lack of sufficient pasture.

73
Johnson et al. (1991) tested the effects of bST in a 30-d farm trial in Florida, and
in a 10-d trial with cows in an environmental chamber in Missouri. Injections of bST
increased milk production by 21% (28.8 vs. 34.9 kg of 3.5% FCM/d) and 35% (21.0 vs.
28.3 kg of 3.5% FCM/d) for the farm and chamber studies, respectively. While the THI
in the farm trial generally remained above 72, and was maintained above 75 in the
chamber study, cows appeared capable of dissipating additional heat due to increased
production, likely by increased respiration rates. Elvinger et al. (1992) found that cows
treated with bST increased milk yield in both cool and hot environments. However, in
both environments, the bST treated cows had greater rectal temperatures, contrary to the
findings of Johnson et al. (1991).
Though administration of bST may or may not increase rectal temperatures
(Mohammed and Johnson, 1985; Zoa-Mboe et al., 1989; Elvinger et al. 1992) it often
causes increased respiration rates for cows in hot environments (Mohammed and
Johnson, 1985; Staples et al., 1988; Zoa-Mboe et al., et al., 1989). Mohammed and
Johnson (1985) and Staples et al. (1988) reported increased respiration rates with no
increases in rectal temperature, but increased temperatures were reported by Zoa-Mboe et
al. (1989) and West et al. (1990).
During a 10-d injection period in the study by Staples et al. (1988), respiration
rates tended (P = 0.084) to increase (78.2 vs. 84.1 breaths/min) with bST administration,
but body temperatures were not different (39.6 vs. 39.7 C). Zoa-Mboe et al. (1989)
reported increases in respiration rates (107 vs. 113 breaths/min) and rectal temperatures
(39.8 vs. 40.0 C) with bST treatments.

74
West et al. (1990) indicated that bST is efficacious under hot and humid
conditions, for both Jersey and Holstein cows. Milk production increased 21% with bST
administration, though the increase was greater for cows at one standard deviation below
pretreatment mean milk production. Response to bST for cows one standard deviation
above pretreatment mean milk production was non-significant. Both a.m. and p.m. body
temperatures were increased in cows administered bST. Treatment by breed interactions
were observed for both production and body temperature increases. Compared to
Jerseys, Holsteins had greater milk production increases in response to bST but lower
body temperature increases. The authors hypothesized that the increased body
temperatures partially explain the lower production responses of Jerseys. If this is
correct, then increases in temperature with bST cannot be explained solely by increases in
metabolism due to increased milk production, an idea supported by the work of Cole and
Hansen (1993).
While management strategies such as designed shading and bST improve animal
performance, few have investigated their use with lactating dairy cows grazing pasture
under hot conditions. More generally, grazing systems management for intensive dairy
production in hot climates has received little attention in the United States. While
utilization of grazing represents a potentially viable method of production in the
Southeast, the limited information for producers regarding recently released forages
adapted to the region, as well as responses to various management strategies prompted
the research that follows.

CHAPTER 3
PASTURE-BASED DAIRY PRODUCTION SYSTEMS: INFLUENCE OF FORAGE,
STOCKING RATE, AND SUPPLEMENTATION RATE ON ANIMAL
PERFORMANCE
Introduction
The economics of dairying in the United States has encouraged farmers to search
for new ways to reduce costs. While increasing herd size is a common option, many
smaller producers have begun using intensive rotational stocking systems to reduce
inputs. However, for producers using grazing in the Southeast, the climate presents
unique challenges to production. The ability to grow superior quality forages is of
particular concern for graziers (producers using grazing systems). Perennial, warm-
season forages typically are of lower nutritive value than either cool-season perennials or
warm-season annuals, but they do have the agronomic advantage of being adapted to the
region. Thus, despite their lower quality, forages such as bahiagrass (Paspalum notatum)
and bermudagrass (Cynodon dactylon (L.) Pers.) are the foundation of forage production
systems for grazing animals in the Southeast.
Recent literature regarding grazing dairy systems in the southeastern United
States is limited. The majority of data pertaining to dairy cow grazing in North America
has been published by researchers in the Northeast and Midwest under very different
environmental conditions. Some research from Australia and other tropical areas may be
applicable to the southeastern environment, but the forages grown are typically of
different genera and the amounts of concentrate fed are less than the amounts provided by
75

76
U.S. producers. Thus, our first objective was to investigate animal and pasture
productivity when two recently released forages were used as a grazing base for lactating
dairy cows.
Supplemental concentrate feeds typically are fed to lactating dairy cattle in the
U.S. The availability of inexpensive concentrates makes this possible and desirable,
especially since wholly forage-based diets cannot meet the energy requirements of high-
producing, lactating dairy cows. However, supplement can have a large effect on DMI
and rumen function, and thus production responses to supplement are inconsistent.
Providing supplement may not be profitable, and factors such as pasture and animal
management should be included when considering the efficacy of supplementation.
Thus, our second objective was to test animal and pasture production responses to two
rates of supplementation within each forage base.
The response to forage and supplement may depend upon stocking rate. Most
models describing the effect of stocking rate on production indicate that while production
per animal decreases with increasing stocking rate, production per land area increases.
Optimum pasture utilization typically requires stocking rates at which forage
consumption is limited, but excessively high stocking rates may limit production per land
area if pasture productivity is compromised. With high stocking rates, however, the
response to forage type or supplement may be greater than in situations in which forage is
not limiting. Because information about the effect of stocking rate and its interactions
with forage type and supplement level on the productivity of grazing, lactating dairy
cattle was not available, our third objective was to determine animal and pasture

77
production responses to two stocking rates within each forage-supplementation rate
combination
Materials and Methods
Cows, Design, and Treatments
Year one. On 10 July 1995, primiparous (n = 22) and multiparous (n = 22, mean
parity = 2.5) Holstein cows (mean DIM = 106 32) at the University of Florida Dairy
Research Unit, (2943 N latitude) were assigned to one of eight management treatments
arranged in a 2 X 2 X 2 factorial in two replicates. The main treatment factors were 1)
forage species grazed: bermudagrass (Cynodon dactylon XC. nlemfuensis cv. Tifton
85) (BG) or rhizoma peanut (Arachis glabrata cv. Florigraze) (RP), 2)
supplementation rate (SUP): 0.33 or 0.5 kg of supplement (as-is)/kg of daily milk
production, and 3) stocking rate (SR): 5 or 7.5 cows/ha for cows grazing BG pastures and
2.5 or 5 cows/ha for cows grazing RP pastures. All cows received 500 mg of
sometribove zinc (Posilac ; Monsanto, St. Louis, IL.) subcutaneously every 2 wk.
Each of the three experimental periods were 28 d in duration, with the first 14 d of
each period used for adjustment to a newly assigned treatment, and the last 14 d for
collection of data. In period 2, storm damage during the adjustment period caused a 10-d
delay. During this time, cows were kept on non-experimental pastures of their respective
forage assignment for period 2, and all cows were fed supplement at the greater rate.
Cows were assigned randomly to treatment for each period with the restriction that no
cow received the same treatment more than once, and the number of changes from a
given treatment to another treatment was balanced.

78
Soils were primarily of the Tavares (hyperthermic, uncoated Typic
Quartzipsamments) and Chipley (thermic, coated Aquic Quartzipsaments) series with
average P, K, and Mg concentrations of 99, 26, and 50 mg/kg, respectively.
Bermudagrass pastures were fertilized with 67 kg of N/ha on 22 May, 30 June,
and 1 September. Nitrogen was applied as NH4NO3 at the latter dates and as a
combination of NH4NO3 and (NP^StTt on 22 May. All pastures received a total of 33
kg of S/ha on 22 May, with sulfur applied to RP pastures in the form of CaSC>4. In
addition, all pastures were fertilized with 67 kg of K20/ha in May.
In order to stage the forage growth, Holstein heifers (approximately 400 kg of
body weight (BW)) grazed both forages from 7 June to 1 July 1995. Stocking rates were
10 and 5 heifers/ha for BG and RP pastures, respectively, and animals were fed no
supplement. Experimental cows went onto pastures on 6 July, 4 d before the official start
of the trial.
Bermudagrass and RP pastures were divided into 22 and 29 paddocks
respectively, allowing for 21 and 28-d rest periods between grazing events. Cows were
kept in the bounds of individual paddocks with poly wire fencing and paddocks were
back-fenced. Cows were provided shade structures and water tubs that were moved with
the cows to a fresh paddock each morning. Shade structures were 3-m tall, constructed of
galvanized metal pipe, stretched with 80 % shade cloth, and designed to provide a
minimum of 4.65 m2 of shade/cow.
Cows walked 0.4 to 1.2 km from pasture to the parlor for milking and back to
pastures twice daily. Cows were milked at approximately 0700 and 1800 h. Supplement
was a 4:1 mixture (as-fed) of high energy pellets:whole cottonseed (Table 3.1)

79
TABLE 3.1. Ingredient and chemical composition of supplements fed to lactating
Holstein cows on pasture.
Item
1995
- Year -
1996
Ingredients (% of DM)
Com meal
40.2

Hominy

35.3
Soybean hulls
24.0
23.9
Soybean meal (48%)
7.2
9.6
Whole cottonseed
20.0
19.8
Dried cane molasses
4.0
5.0
Mineral mix'
1.0

Mineral mix2

2.5
Calcium carbonate
1.0
1.3
Mono-Dical phosphate
0.4

Salt
0.4

Trace mineralized salt3

1.3
Diabond
0.8

Sodium bicarbonate
1.0
1.3
Chemical composition
Dry matter, %
90.4
91.4
Ash, %
9.5
7.5
NEL, Mcal/kg of DM4
1.90
1.89
NDF, % of DM
32.6
42.5
ADF, % of DM
23.3
27.7
CP, % of DM
15.6
18.0
Ca, % of DM
1.16
0.91
P, % of DM
0.43
0.61
Mg, % of DM
0.34
0.34
K, % of DM
1.13
1.33
Na, % of DM
0.64
0.93
S, % of DM
0.19
0.20
Cl, % of DM
0.26
0.82
Fe, ppm, of DM
537
355
Zn, ppm, of DM
121
159
Cu, ppm, of DM
29.8
33
Mn, ppm, of DM
1^ ^ .
65.4
66
'Composition: > 55% Dyna-Mate, > 0.7% 1% Se, > 0.4% C0SO4, > 1.9% CuS04,
> 2.6% ZnS04, 0.7% MnS04, 36.9% MgO, > 0.001% Cal, 1200 IU/g of vitamin A, > 700
IU/g of vitamin D3, > 300 IU/g of vitamin E.
"Composition: 3.8% N, 10.5% Ca, 3% P, 4.5% K, 2% Mg, 7.4% Na, 1.1% S, 5.4% Cl,
1525 ppm Mn, 1750 ppm Fe, 425 ppm Cu, 1500 ppm Zn, 12.8 ppm I, 49 ppm Co, 24.2
IU of vitamin A/g, 35.2 IU of vitamin D/g, and 0.88 IU of vitamin E/g.
"Composition (g/100 g): NaCl, 92 to 97; Mn, > 0.25; Fe, > 0.2; Cu, > 0.033; I, > 0.007;
Zn, > 0.005; Co, > 0.0025.
Calculated using 1989 NRC values for whole cottonseed.

80
Cows were divided into their respective SUP treatment groups (n = 2) post
milking and fed on a concrete feedbunk line. Amount of supplement offered was based
on the average milk production for each group, with feed amounts adjusted twice weekly.
This method of feeding potentially confounded the effects of SUP with effects of SR and
forage treatments but was considered a typical management practice of commercial
farms.
Year two. Holstein cows (n = 62) were evenly divided between one and > 1
parity. Mean parity for multiparous cows was 3.1 lactations and mean DIM for all cows
was 126 38.
Experimental design and choice of treatments were as in Year 1. However, based
on results from 1995, some modifications to protocol were implemented. Cows were not
/R\
treated with Posilac In 1995 pastures were deemed underutilized, so stocking rate
treatments were increased to 7.5 and 10 cows/ha for BG and 5 and 7.5 cows/ha for RP
pastures. During Year 2, NH4NO3 fertilizer was applied more frequently to BG pastures,
but the total quantity applied was slightly less than in 1995. Bermudagrass pastures
received 45 kg of N/ha as NH4NO3 on 21 May, 8 June, and 7 August. A fourth
application of 56 kg of N/ha occurred on 11 September. Potassium was applied at 40 kg
of K^O/ha on 7 June. Pastures were irrigated from 15 May to 12 June at a rate of 25
mm/wk for a total of 100 mm of water. Due to the loss of BG stand, one replicate pasture
assigned the low SR and low SUP treatments was removed from the study. Pastures were
staged with animals as previously described from 10 June to 6 July. The trial was from 9
July through 2 October 1996.

81
Cows were milked at approximately 0600 and 1800 h. An unpelleted supplement
(Table 3.1) was fed after each milking in troughs located in each paddock. The amount
of supplement fed was recalculated twice weekly. Feed troughs were moved with the
shade and water tubs each day.
Experimental Procedures
Animal measures. Milk weights were recorded at each milking. Milk samples
were collected at six consecutive milkings during each of the last 2 wk of each period.
Samples were analyzed by Southeast Dairy Labs (McDonough, GA) for fat and protein
concentrations and somatic cell count (SCC). Samples were analyzed for milk urea
nitrogen (MUN) in 1996.
Cows were weighed on three consecutive days at the initiation of the trial and at
the end of each period. Body weights were recorded after the a.m. milking and prior to
feeding of supplement. Body condition scores (BCS) were recorded on one of the weigh
days within each period (Wildman et al., 1982).
Respiration rates were recorded on 1 d of each period. Movement of the flank or
bobbing of the head was monitored over 1 -min intervals. Measures took place while cows
were on pasture during the time of greatest potential ambient temperature (approximately
1400 to 1600 h). In 1996, rectal temperatures were measured with small, digital
thermometers (Medline, Medline Industries, Inc., Mundelein, IL) after the p.m.
milking.
Blood was obtained from the coccygeal vessels on d 27 of periods 1 and 2 and d
19 in period 3 in 1995. Samples were collected on d 22 or 23 of each period in 1996.
Samples were collected into 9 ml Na-heparinized syringes (Luer Monovette, LH,

82
Sarstedt, Inc., Newton, NC) after the p.m. milking and placed on ice. Blood was
centrifuged (2000 x g for 30 min) and plasma was collected and frozen at -20 C on the
same day. Plasma from 1995 was analyzed for urea N (PUN) and glucose at the
USDA/ARS Subtropical Agriculture Research Station (Brooksville, FL) following the
procedures of Marsh et al. (1965) and Gochman and Schmitz (1972), respectively. In
1996, PUN was determined by kit (Kit 535-A, Sigma, St. Louis, MO) and read on a
plate reader at 540 nm.
Chromium-mordanted fiber was used as an inert marker to determine organic
matter intake (OMI). Each period, forage was collected across all pastures and
composited for each species. Efforts were made to gather forage of quality similar to that
consumed. Forages were dried at 55 C and ground with a stainless steel Thomas-Wiley
Laboratory Mill (Thomas Scientific, Philadelphia, PA) using a 2-mm screen. Fiber
from the forage was chromium mordanted according to the method of Udn et al. (1980).
The dried, ground forages (approximately 100 g/L FLO) were boiled approximately 2 h in
a mixture of water and liquid laundry detergent (approximately 50 mL). After boiling,
the fibers were washed repeatedly with tap water to remove all soap, rinsed with acetone,
dried at 105 C, and weighed. The dried forage (500 to 700 g) was placed in a metal
container, and sodium dichromate (100 to 140 g) dissolved in four volumes
(approximately 4 L) of water was added to the forage. Addition of Cr (as sodium
dichromate) equaled 7% of the fiber DM. This slurry was sealed with aluminum foil and
heated in a forced-air drying oven at 105 C for 24 h. The liquid was then poured off and
the fiber was gently rinsed with tap water to remove excess and unbound Cr. Ascorbic
acid (Aldrich, Milwaukee, WI) at half the dry fiber weight was mixed with water, added

83
to the fiber, and allowed to stand for 1 to 1.5 h. The fiber was rinsed thoroughly with tap
water and dried at 105 C. Three 0.02 g (air dry) of mordanted fiber were weighed into
28-g gelatin capsules (Jorgenson Laboratories, Loveland, CO). Across the three periods,
average Cr concentration was 42,000 and 46,000 ppm (OM basis) for BG fiber, and
51,000 and 53,000 ppm for RP fiber for 1995 and 1996, respectively.
In all periods of both years, 32 cows were orally-dosed with nine gelatin capsules
containing Cr-mordanted fiber (27 g, as-fed) from their respective forage assignments.
Capsules were administered with a multiple dose balling gun (NASCO, Ft. Atkinson,
WI). In 1995, average dosing time was 1130 h on d 23 of each period. Fecal samples
were collected at approximately 0, 7.5, 19.5, 23, 27, 31, 44.5, 55.5, 68.5, 79.5, 92.5, and
103.5 h post-dosing. Samples at 23, 27, and 31 h post-dosing were collected on pasture at
the cows leisure, while the remainder were grab samples taken in holding pens at the
milking parlor.
In 1996, cows were dosed after the evening milking on d 25, and fecal samples
were collected at approximately 0, 12, 15, 18, 21, 24, 27, 36, 42, 48, 60, 72, and 84 h
post-dosing. Collections were made on pasture at h 15, 18, 21,27, and 42.
Fecal samples were refrigerated or frozen immediately after collection. In 1995,
samples from period 1 were dried at 55 C and samples from periods 2 and 3 were freeze-
dried. In 1996, all samples were dried at 55 C for at least 48 h. All fecal samples were
ground through a 1-mm screen with a Wiley mill. Samples (2 g, as-is) were dried at 105
C and ashed at 550 C for determination of DM and OM according to AO AC (1990)
procedures. Ash was digested in a solution of H2PO4 (with added MnS04) and KBr03
using heat on a hot plate and analyzed for Cr by atomic absorption spectrophotometry

84
(Atomic Absorption Spectrophotometer 5000, Perkin Elmer, Norwalk, Conn.) following
the methods of Williams et al. (1962). For calculating DM intake, results from the fecal
sample analysis were evaluated with PROC NLIN following the method described by
Pond et al. (1987; Appendix 1). The parameters generated by this program then were
used to estimate fecal output for each cow.
To calculate the intake of pasture, the following assumptions were made:
1) intake of supplement was the same for all cows within a pasture replicate,
2) digestibility of supplement OM was equivalent to calculated TDN from NRC
(1989), and
3) digestibility of forage was affected by the level of supplement intake, as
determined by the equation of Moore et al. (1999; Appendix 2).
The measure of forage in vitro organic matter digestibility (IVOMD) for each
paddock was used to calculate forage intake by cows grazing that paddock (Pond et al.,
1987). Fecal output (kg/d) should equal total intake (kg/d) multiplied by the indigestible
fraction of a feed. Thus, estimates of fecal output are dependent upon accurate
determination of diet digestibility.
The fecal output observed based on the mordanted-fiber methodology did not
equal the fecal output predicted based on estimated forage and supplement digestibilities.
For this reason, an iterative SAS (1991) program (developed by J. E. Moore) was
employed to adjust the forage intake until the difference between fecal output observed
and fecal output predicted differed by less than 0.01 kg/d (Appendix 2).
Expected diet digestibility (% of OM) = [(forage intake, kg of OM forage
digestibility, %) + (supplement intake, kg of OM* supplement digestibility, %)]/total

85
intake, kg of OM. Because feeding concentrate supplements often alters forage
digestibility (Arriaga-Jordan and Holmes, 1986; Berzaghi et al., 1996), the iterative
program also employed the equation of Moore et al. (1999; Appendix 2) to adjust total
diet digestibility.
Pasture measures. A double sampling technique was used to quantify pre- and
post-graze forage mass (Meijs et al., 1982). Every 2 wk of each period, 25 measures of
forage height were taken using a 0.25-m aluminum disk meter. Pre-graze measures
were recorded in paddocks to be grazed the following d, and post-graze measures were
made 1 or 2 d after the cows had grazed the paddock. At one sampling event in each
period, two or three samples were collected pre- and post-graze from one paddock per
pasture to establish a relationship between herbage mass (HM) and the recorded disk
heights. After dropping the plate of the disk meter on the forage, a metal ring was used to
mark the outline of the disk meter, and the forage within the ring was clipped at ground
level. The forage was dried at 55 C for a minimum of 48 h to a constant weight.
Equations to predict pre- and post-graze forage mass were calculated by
regressing mass on disk height measured at double sampling sites. Regression equations
were assessed for the following data: all samples within a forage species, all pre- or all
post-graze samples within a forage, and pre- or post-graze samples within a period and
within a forage. After review of the data, HM equations for both years were derived from
pre- and post-graze measurements within periods within a forage.
Feed sampling. Once per period, forage was collected for characterization of
chemical composition and digestibility. Attempts were made to collect forage of quality
similar to that consumed after first inspecting an adjacent, grazed paddock. Twenty to 30

86
grab samples were taken from the next paddock to be grazed in each pasture, dried at
least 48 h at 55 C, and ground through a 1-mm screen with a stainless steel Thomas-
Wiley Laboratory mill. Samples were analyzed by the University of Florida Forage
Evaluation Support Laboratory, Gainesville. For determination of organic matter (OM),
dried samples were ashed for at least 4 h at 500C. The modified aluminum block
procedure of Gallaher et al. (1975) was used to digest samples prior to analysis for N by
the method of Hambleton (1977). Crude protein (CP) was then calculated as N 6.25.
Determination of neutral detergent fiber (NDF) and IVOMD concentrations were made
using the procedures of Golding et al. (1985) and Moore and Mott (1974), respectively.
A single pelleted supplement sample and no whole cottonseed samples were
collected in 1995. In 1996, supplement (including whole cottonseed) samples were
collected three times in each period. Equal amounts of sample within periods were
composited, ground through a 1-mm screen, and submitted to the DHIA Forage Testing
Laboratory (Ithaca, NY) for analysis.
Statistical Analysis
Animals. Two cows from the 1995 trial were used in 1996 but were treated as
different animals for purpose of analysis. Data were analyzed using the GLM procedure
of SAS (1991) with the following model:
Yyicimnop U X¡ + Pj + (xp)y + K(xp)k(¡j) +
a, + pm + (aP)im + Yn + (ay)ln + (pY)mn + (OCpY)lmn +
(pa)j| + (pp)jm + (pap)j,m + (pY)jn + (p (xa)n + (xP)im + (xap)iim + (xY)in + (xaY)iln + (xpY)imn + (xaPY)ilmn +
(xpa)ii + (xpp)im + (xpap)iim + (xpY)in + (xpaY)iln + (xppY)imn +

87
(TpaPY)jimn +
V0 +
5p(ttPy)lmn
Gjklmnopi
where
p = overall mean
Tj = effect of year
Pj = effect of parity
K(xp)k(ij) = effect of cow within year and within parity
oci = effect of forage
pm = effect of SUP
yn = effect of SR
v0 = effect of period
6P = effect of pasture replicate within forage, SUP and SR treatments
cykimnop = effect of residual error.
Single degree of freedom orthogonal contrasts were made to test for treatment
effects. Treatments were considered different at P levels < 0.05 and trends are reported
for P < 0.10. Cow, parity, and their interactions were removed from the model for the
analysis of herbage data.
Results and Discussion
Forage Composition
Averaged across all pastures within forage treatments, estimates of digestibility
and nutritive value of RP were greater than for BG (Table 3.2). The RP pastures

88
TABLE 3.2. Nutritive value characteristics, chemical composition, and calculated net
energy of lactation (NEl) and total digestible nutrients (TDN) of Tifton 85 bermudagrass
and Florigraze rhizoma peanut pastures. Samples were hand-plucked once each period,
based on visual appraisal of forage consumed by grazing cows.
Item
Bermudagrass Rhizoma peanut
Year
1995 1996 1995 1996
CP, % of DM1
13.5
13.1
19.0
16.6
ADF, % of DM
45.5
36.5
32.7
32.5
NDF, % of DM 1
81.9
80.4
43.5
45.5
IVOMD12, % of OM
55.5
62.1
71.2
71.2
TDN3, %
55.2
58.2
62.1
62.1
NEl4, Mcal/kg of DM
1.23
1.31
1.41
1.41
Ash, % of DM
5.64
5.13
8.67
8.48
Ca, % of DM
0.41
0.42
1.64
1.70
P, % of DM
0.33
0.27
0.27
0.26
Mg, % of DM
0.24
0.25
0.39
0.45
K, % of DM
1.97
1.77
1.71
1.58
Na, % of DM
0.018
0.045
0.004
0.008
S, % of DM
0.30
0.24
0.16
0.15
Cl, % of DM
0.57
0.43
0.46
0.41
Fe, ppm of DM
51
65
32
42
Zn, ppm of DM
44.5
43
42
37
Cu ppm of DM
5
4
3.5
2
Mn, ppm of DM
49
101
47
25
Mo, ppm of DM
1.2
1.4
1.2
1.3
Least squares mean from two samples within each treatment combination collected over
three periods within each experimental year.
2In vitro organic matter digestibility
Calculated using the equation % TDN = [(%IVOMD*0.49) + 32.2]*OM concentration
(J. E. Moore, personal communication).
Calculated using NRC (1989) equations: NEL = [0.0245 TDN(% of DM) 0.12].

89
averaged 4.5 percentage units more CP (17.8 vs. 13.3 %) and contained less NDF (44.5
vs. 81.2%) and ADF (32.6 vs. 41.0%) on a DM basis. Rhizoma peanut had greater
average IVOMD (71.2 vs. 58.8%) also. These estimates of nutritive value are similar to
values reported by others (Beltranena et al., 1981; Gelaye et al., 1990; Hill et al., 1993;
Mandebvu et al., 1998).
Milk Production and Composition Per Cow
Parity and year effects. No main effects of parity were observed, and year
effects occurred only for SCC. In 1995, milk contained fewer (P < 0.001) somatic cells
(286 vs. 596 thousands of cells).
Forage effects. Cows grazing RP pastures produced more (P < 0.001) milk than
cows grazing BG (17.3 vs. 16.2 kg/d), but milk was of lower fat concentration (P <0.01;
3.42 vs. 3.54 %; Table 3.3). Milk fat production is stimulated by more fibrous diets, and
the differences in fiber concentration between the two forages likely explains the
difference in milk fat concentration. Greater milk production by cows grazing RP
pastures offset the reduced milk fat concentration, as shown by the greater (P <0.01)
production of 4% FCM (15.7 vs. 15.0 kg/d) and greater (P < 0.05) amount of milk fat
produced (0.58 vs. 0.56 kg/d) by cows eating RP. Forage type had no effect on milk
protein percent, but greater (P < 0.001) quantities of milk protein were produced by cows
grazing RP (0.52 vs. 0.48 kg/d). Measured only in 1996, MUN concentrations tended (P
< 0.052) to be greater when cows grazed RP (17.7 vs. 17.1 mg%). Compared with
multiparous cows, primiparous cows had greater SCC when grazing RP (500 vs. 350
thousands of somatic cells) but lower SCC when grazing BG (420 vs. 480 thousands of
somatic cells; parity by forage interaction, P < 0.01).

TABLE 3.3. Effect of forage, stocking rate (SR), and supplementation rate (SUP) on milk production and composition of Holstein
cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut during the summers of 1995 and 1996.
Tifton 85 bermudagrass Florigraze rhizoma peanut
Stocking Rate1 Stocking Rate2 Probability3
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage SR x SR
Item 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 SEM Forage SR SUP x SR x SUP x SUP x SUP
Milk, kg/d
17.9
14.9
17.4
14.6
18.1
16.6
18.2
16.7
0.3
***
NS
***
NS
*
NS
NS
FCM, kg/d
16.3
13.9
16.0
13.7
16.1
15.1
16.2
15.3
0.3
**
NS
***
NS
**
NS
NS
Fat, %
3.44
3.6
3.48
3.6
3.38
3.4
3.3
3.50
0.0
**
NS
***
NS
NS
NS
NS
Fat, kg/d
0.61
0.5
0.60
0.5
0.59
0.5
0.6
0.58
0.0
*
NS
***
NS
***
NS
NS
Protein, %
2.99
2.9
3.01
2.9
3.01
2.9
3.0
2.98
0.0
NS
t
**
NS
NS
NS
NS
Protein, kg/d
0.53
0.4
0.52
0.4
0.54
0.4
0.5
0.49
0.0
***
NS
***
NS
t
NS
NS
see4
375
530
447
490
374
413
478
423
41
NS
NS
NS
NS
NS
NS
NS
MUN5, mg %
17.2
18.2
16.0
17.0
17.0
18.8
17.0
18.2
0.4
t
*
**
NS
NS
NS
NS
'High and low stocking rates for Tifton 85 bermudagrass were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates for Florigraze rhizoma peanut were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and +, respectively.
4Somatic cell count, xlOOO.
5Milk urea nitrogen.

91
Interactions of forage and year with respect to milk production, 4% FCM
production, milk fat percentage, and milk fat production (Figure 3.1) reveal greater
reductions in performance in 1996 for animals grazing BG. For cows grazing RP
pastures, the 0.26 percentage-unit increase in milk fat concentration from 1995 to 1996
offset the 1-kg decrease in daily milk production. This resulted in the same amount of
4% FCM production over the two years. A smaller increase in milk fat percentage did
not offset the decreased milk production in 1996 for cows grazing BG, however.
Stocking rate effects. Stocking rate did not influence milk production, but cows
grazing at lower SR tended (P < 0.053) to produce milk with greater concentrations of
protein (3.00 vs. 2.97%). These responses may be indicative of greater concentrations of
degradable protein and digestible OM in the diet and may reflect opportunity to select
plant parts of greater nutritive value. Likewise, MUN was lower (P < 0.05) when cows
were stocked at the lower rate (17.1 vs. 17.8 mg %) suggesting more efficient use of
dietary CP for milk protein.
In 1995, greater SR resulted in greater milk and 4% FCM production for cows
grazing RP but reduced milk and 4% FCM production for cows grazing BG. Results for
1996 were opposite, with the greater SR causing decreased milk and 4% FCM production
for cows grazing RP but increased production for cows grazing BG (year by forage by
SR interaction, P < 0.05; Figure 3.2). Based on the visual appraisal of the BG pastures at
the high SR in 1996 (10 cows/ha), herbage allowance and forage nutritive value were
near optimum. Intake of digestible OM may have been greater and thus stimulated milk
production. However the RP pastures at the high SR in 1996 (7.5 cows/ha) appeared to
lack sufficient high quality forage which likely resulted in a reduction in milk production.

92
"O
"Sb
S
u
Uh
ox
n
ox
1
1
1995 1996
Year
Figure 3.1. Interaction of forage [Tifton 85 bermudagrass (BG) or Florigraze rhizoma
peanut (RP)] and year (1995 or 1996) on production of milk, 4% fat corrected milk
(FCM), and milk fat and milk fat percent.

ABW, kg/28d 4% FCM, kg/d Milk yield, kg/d
93
Forage
Figure 3.2. Interaction of forage, stocking rate (SR), and year on milk and 4% fat cor
rected milk (FCM) yields and body weight change (ABW). Forages were Tifton 85
bermudagrass and Florigraze rhizoma peanut. Low and high SR for BG were 5.0 and
7.5 cows/ha in 1995 and 7.5 and 10.0 cows/ha in 1996. Low and high SR for RP were
2.5 and 5.0 cows/ha in 1995 and 5.0 and 7.5 cows/ha in 1996.

94
Supplementation rate effects. Supplementation rate affected all milk production
and milk component responses except SCC. Cows receiving the greater SUP produced
2.1 kg/d more (P < 0.001) milk and 1.6 kg/d more (P < 0.001) 4% FCM. The smaller
FCM response to SUP was due to reduced (P < 0.001) milk fat concentration (3.41 vs.
3.55 %) with increased SUP. Diets with additional supplement were likely more
glucogenic. Greater milk production in response to increased SUP outweighed the
decline in milk fat concentration, thus total fat production was greater (P < 0.001) by
cows fed the greater amount of supplement (0.59 vs. 0.54 kg/d). Supplement likely
increased growth of ruminal microbes as was shown by others (Rooke et al., 1987;
Berzaghi et al., 1996). This would explain the increased (P <0.01) milk protein
percentage with the greater SUP (3.01 vs. 2.96%), resulting in greater (P < 0.001) daily
milk protein production (0.54 vs. 0.46 kg/d). Providing additional supplement also
reduced (P <0.01) MUN concentrations (16.8 vs. 18.1 mg%). The MUN data indicate
that providing additional supplement resulted in greater ruminal NH3 capture by rumen
bacteria.
When cows grazed BG, the percent increase in milk production in response to
additional supplement was double (19.6 vs. 9.0%) that of cows grazing RP pastures
(forage by SUP interaction, P < 0.05; Figure 3.3). The greater production response with
additional supplement for cows grazing BG is indicative of a lower substitution rate with
the lower quality forage (Blaxter and Wilson, 1963; Golding et al., 1976b; Arriaga-
Jordan and Holmes, 1986). With each additional kg of supplement fed above the low
SUP, cows produced an additional 0.87 kg of milk/d if grazing BG vs. an additional 0.43
kg of milk/d if grazing RP.

95
"O
'Sb
2
a>
i4
>
T3
'Sb
u
tu
n
ox
^1-
20.0
10.0
-
16.1
15.2
16.1
SE = 0.2
P<0.01
13.8
-
Lo
Hi
Lo
Hi
Figure 3.3. Interaction of supplementation rate and forage species on production of milk,
4% fat corrected milk (FCM), milk fat, and protein. Supplementation rates were 0.33
(Lo) and 0.5 (Hi) kg of supplement per kg of daily milk production. Forage species were
Tifton 85 bermudagrass and Florigraze rhizoma peanut.

96
Increasing supplement had similar depressing effects on milk fat percentage
across forages. Thus, FCM responses to forage and SUP treatments were similar to that
of milk production (forage by SUP interaction, P < 0.01; Figure 3.3). For cows grazing
BG, the increase in FCM produced with additional supplement (2.3 kg/d) was double the
response (0.9 kg/d) of cows grazing RP. Response of daily fat production to SUP
followed the same trend (forage by SUP interaction, P < 0.01; Figure 3.3). Total protein
produced tended to be greater in response to additional supplement when cows grazed
BG (forage by SUP interaction, P < 0.10; Figure 3.3).
Multiparous cows produced more milk, 4% FCM, and milk fat in response to
increased SUP than primiparous cows (parity by SUP interaction, P < 0.05). When fed
the greater SUP treatment, primiparous cows produced an additional 1.7 kg of milk (18.1
vs. 16.4 kg of milk/d), compared with 2.7 additional kg of milk for multiparous cows
(17.7 vs. 15.0 kg/d). Increases of 1.2 and 2.0 kg of 4% FCM due to additional
supplement were observed for primiparous and multiparous cows, respectively. Milk fat
production within high and low SUP treatments were 0.61 and 0.57 kg/d for primiparous
cows compared to 0.59 and 0.52 kg/d for multiparous cows, following the milk
production responses to supplement. Milk fat concentrations in response to SUP were
not different between parities.
Primiparous cows had lesser SCC when provided additional supplement,
compared with greater SCC at the greater SUP rate for multiparous cows (parity by
supplement interaction, P < 0.01). With the low and high SUP treatments, SCC (in
thousands of cells) were 483 and 422 for primiparous cows vs. 360 and 499 for
multiparous cows.

97
Greater 4% FCM (P < 0.05) and milk fat production (P <0.01) and greater milk
protein concentration (P <0.10) in response to additional supplement were observed in
1996 compared with 1995 (year by SUP interaction; Figure 3.4). Production responses to
supplement are greater when forage is limiting (Phillips, 1988) and this would seem a
plausible explanation for the increased 4% FCM response to supplement in 1996.
However, based on estimates of intake to be presented subsequently, forage intake was
not limited by increasing SR in 1996. Opposite the effects of supplement and year on
milk protein concentration, the depression in milk fat concentration in response to
additional supplement was greater in 1995 than in 1996 (year by SUP interaction, P <
0.05; Figure 3.4). That the greatest changes in protein and fat concentrations did not
occur in the same year is surprising: milk fat concentrations often decrease with greater
supplement feeding with a concomitant increase in milk protein concentrations due to
increased microbial growth. Milk protein concentrations essentially did not change due
to SUP in 1995 (2.96 and 2.98%) but increased from 2.97 to 3.05% with increasing SUP
in 1996. This suggests improved N capture by rumen microbes when cows were fed the
greater amount of supplement in 1996.
In 1996, increased supplementation resulted in milk, 4% FCM, and fat production
increases between 14 and 20% across parities. In 1995, a similar response was observed
for multiparous cows but not for primiparous cows (year by parity by SUP interaction, P
< 0.05; Figure 3.5). Likewise, milk fat percent was not similarly affected by SUP across
parity and years. Reduction in milk fat concentration was similar in 1995 and 1996 for
primiparous cows fed the greater SUP. However, milk fat concentration of multiparous
cows was more dramatically decreased by greater supplementation in 1995 but was

98
3.75 -
N
ox
.0$
3.55 -
s
3.35 -
3.15 -
vO
3.10 -
o'
e\
C
S
3.00 -
o
a,
2.90 -
1
2.80 -
2.96
2.98
3.05
1995 1996
Year
SE 0.03
P < 0.05
3.51
Lo
3.54
Lo
3.29
Hi
Hi
SE = 0.01
P<0.10
Figure 3.4. Interaction of supplementation rate and year on production of 4% fat corrected
milk and milk fat, and percentages of milk fat and protein. Low (Lo) and high (Hi) sup
plementation rates were 0.33 and 0.5 kg of supplment per 1 kg of daily milk production,
respectively.

99
T3
M
c\
2
"3
4
T3
'5b
2
U
Uh
V?
ox
"3-
Figure 3.5. Interaction of parity, year, and supplementation rate on production of milk, 4%
fat corrected milk (FCM), and milk fat and milk fat percent. Low (Lo) and high (Hi) sup
plementation rates were 0.33 kg and 0.5 kg of supplement per kg of daily milk production.
Supplementation rates did not differ by year (1995 or 1996).

100
unaffected in 1996 (year by parity by SUP interaction; P < 0.05; Figure 3.5). With
primiparous cows, milk protein production was less affected by supplementation rate in
1995 than in 1996, while multiparous cows had similar improved responses to
supplement in both years (year by parity by SUP interaction, P < 0.05). Primiparous
cows produced 0.52 and 0.55 kg of protein/d at the low and high SUP in 1995 vs. 0.42
and 0.52 kg of protein/d in 1996. Multiparous cows produced 0.46 and 0.53 kg of milk
protein/d in 1995 and 0.43 and 0.51 kg of milk protein/d in 1996 for low and high SUP
treatments, respectively.
Milk Production per Land Area
Because production per land area may be a more appropriate measure of
profitability for dairies using grazing systems this measure also was calculated. Milk
production/cow was multiplied by cow/ha (SR), and the resultant yields per land area
were analyzed without cow effects in the model.
The average SR for BG pastures over the 2 years was 7.5 cows/ha vs. 5 cows/ha
for RP. As a result milk production from BG far exceeded (P < 0.001) production from
cows grazing RP (118 vs. 87 kg of milk/ha per day). This represents a nearly forty
percent difference in favor of BG.
Stocking rate had a greater effect on milk production/ha than did supplementation
rate. Increasing SUP from 0.33 kg of supplement: 1 kg of daily milk to 0.5 kg of
supplements kg of daily milk increased (P < 0.001) milk production 14% on a land area
basis (97 vs. Ill kg of milk/ha per d), but increasing SR resulted in a 51% increase (P <
0.001) in milk production per land area (83 vs. 125 kg of milk/ha per d).

101
The response to supplement on a land-area basis was greater when cows grazed
BG than RP (132 and 110 kg of milk/ha per day at high and low SUP for BG vs. 90 and
83 kg of milk/ha per day at high and low SUP for RP; forage by supplement interaction,
P < 0.001). In this case, both the lesser substitution of forage by supplement for cows on
BG and the potential to carry more cows on BG pastures overwhelmed RPs greater
production per cow.
Production per land area response to increased supplement feeding was greater at
the high SR (SUP by SR interaction, P < 0.01). Milk production of cows fed the high and
low SUP treatments was 135 and 115 kg/ha per day at the greater SR vs. 88 and 78 kg of
milk/ha per day with the high and low SUP treatments at the lesser SR. Others (Blaser et
al., 1960; Phillips, 1988) have reported a greater response to supplement when forage is
limiting, but forage was likely only limiting for RP at the high SR.
Body Weight and Condition
Parity and year effects. Over the two years, multiparous cows weighed an
average of 65 kg more (P < 0. 001) than their primiparous counterparts (537 vs. 472 kg)
but had less (P < 0.01) body condition (2.49 vs. 2.78). Multiparous cows lost more (P <
0.05) weight than did primiparous cows (-9 vs. -6 kg/28-d period), but this difference
was not reflected in BCS change. Cow BCS was greater (P <0.01) in 1995 than 1996
(2.78 vs. 2.48), but changes in BCS were less (P < 0.05) in 1995 than in 1996 (-0.07 vs.
-0.16).
Forage effects. Cows grazing RP lost approximately 5 kg more (P < 0.05) BW
per 28-d period (-10 vs. -5 kg) than cows grazing BG (Table 3.4). Though the RP was
of greater nutritive value and would be expected to support greater weight gain, weight

TABLE 3.4. Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on body weight (BW) and body condition
score change (ABCS), respiration rate (RR), body temperature (TEMP), and plasma urea nitrogen (PUN) and plasma glucose of
Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut during the summers of 1995 and 1996.
Tifton 85 bermudagrass Florigraze rhizoma peanut
Stocking Rate1 Stocking Rate2 Probability3
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage SR x SR
Item 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 SEM Forage SR SUP x SR X SUP x SUP x SUP
Average BW, kg
507
506
508
507
498
500
504
508
2
*
*
NS
t
NS
NS
NS
ABW, kg/28-d period
-6
-4
-4
-5
-16
-11
-9
-4
3
*
t
NS
NS
NS
NS
NS
BCS
2.67
2.68
2.63
2.63
2.60
2.65
2.59
2.61
0.04
NS
NS
NS
NS
NS
NS
NS
ABCS/28-d period
0.01
-0.11
-0.20
-0.12
-0.04
-0.10
-0.12
-0.24
0.08
NS
f
NS
NS
NS
NS
NS
RR, breaths/min
93
85
100
89
100
90
102
95
2
*
*
***
NS
NS
NS
NS
TEMP, C
39.2
39.1
39.2
38.9
39.4
39.3
39.4
39.5
0.1
*
NS
NS
NS
NS
NS
NS
PUN, mg %
13.0
13.4
12.9
12.0
14.9
16.2
14.6
15.3
0.5
***
t
NS
NS
t
NS
NS
Plasma glucose, mg %
59.6
57.4
59.9
57.4
59.9
56.4
59.0
57.6
0.6
NS
NS
***
NS
NS
NS
NS
'High and low stocking rates were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.

103
losses on RP pastures may be attributable to greater energy expenditure associated with
greater milk production, or due to less gut fill due to greater intake and faster passage of
forage OM, or both.
Stocking rate effects. Cows stocked at the greater SR were slightly lighter, on
average, (approximately 4 kg; P < 0.05) than cows at the lesser SR. Likewise, BW loss
tended (P < 0.070) to be greater for cows stocked at the greater rate (-9 vs. -5 kg/28-d
period).
Cows assigned to the greater SR lost 7 to 8 kg/28-d period more than cows
assigned to the lower SR across years and forages with one exception (Figure 3.2). In
1996, cows grazing BG lost 7 kg less when grazing at the greater vs. lesser SR (year by
forage by SR interaction P < 0.10).
Primiparous cows lost 6 to 8 kg of BW/28-d period across forage species and SR
except when assigned to BG pastures at the low SR on which BW loss was zero (Figure
3.6). Conversely, the BW loss of multiparous cows was similar (4 to 9 kg of BW/28-d
period) except when grazing RP at the high SR, in which multiparous cows lost 19 kg of
BW/28-d period (parity by forage by SR interaction, P < 0.05).
Supplementation rate effects. Strikingly, SUP had no effect on changes in BCS
or BW, nor were SUP by treatment interactions detected. In 1995, the greater SUP
resulted in a loss of BW and body condition, likely due to greater milk production, but in
1996, providing additional supplement had little effect on BW and helped maintain body
condition (year by SUP interaction, P < 0.05; Figure 3.7). The year by SUP interaction
patterns for change of BW and BCS are dissimilar in 1996, with the decrease in BCS at

104
Parity
Figure 3.6. Interaction of parity, forage, and stocking rate on body weight change (ABW).
Average low (Lo) and high (Hi) stocking rates were 6.25 and 8.75 cows/ha for Tifton 85
bermudagrass (BG) and 3.75 and 6.25 cows/ha for Florigraze rhizoma peanut (RP) pastures.
Stocking rates were the same across parities.
T3
00
c/5
U
03
<
"O
oo
(N
'So
r\
£
CQ
<
0.00
Lo Hi
Lo
Hi
-5 -
10 -
-15
-12
1995
-0.28
Lo
Hi
Lo
Hi
-4
-7
1996
Year
SE = 0.07
P < 0.05
SE = 2
P < 0.05
Figure 3.7. Interaction of supplementation rate and year on changes of body condition
score (ABCS 5 point scale) and body weight (ABW). Low (Lo) and high (Hi) supple
mentation rates were 0.33 and 0.5 kg of supplement per kg of daily milk production.

105
the low supplementation rate (-0.28 points) being much greater than would be expected
given the change in BW (-7 kg/28-d period).
Cows fed the greater SUP lost more BW than those fed the lesser SUP, regardless
of forage, with the exception of cows grazing BG in 1996 which lost the most weight
when offered the least amount of supplement (year by forage by SUP interaction, P <
0.05; Figure 3.8). Increasing the amount of supplement fed frequently results in greater
forage substitution (Davison et al., 1991; Reeves et al., 1996) so that total intake may not
change. This may influence BW changes. This effect of grain feeding on forage intake
will be discussed subsequently.
A year by SR by SUP interaction (P < 0.05) for change of BCS was observed but
will not be discussed due to the complexity of explanation given the changes in SR made
from Year 1 to Year 2 of the experiment.
Respiration, Temperature, and Blood Metabolites
Parity and year effects. Primiparous cows had greater (P < 0.001)
concentrations of PUN than multiparous cows (14.8 vs. 13.3 mg %), and the
concentration of PUN was greater (P < 0.001) in 1996 than 1995 (16.3 vs. 11.8 mg %),
reflecting the increased CP concentration of the supplement in 1996.
Respiration rate and temperature were unaffected by parity or year, indicating
similar levels of heat stress across years. However, primiparous cows had greater RR in
1995 (99 vs. 92 breaths/min) and similar RR in 1996 (92 vs. 94 breaths/min; parity by
year interaction, P < 0.05). Glucose in plasma averaged 58.4 mg% and was unaffected
by parity or year.

106
Forage
Figure 3.8. Interaction of forage, supplementation rate, and year on body weight change
(ABW). Forages were Tifton 85 bermudagrass and Florgraze rhizoma peanut. Low (Lo)
and high (Hi) supplementation rates were 0.33 and 0.5 kg of supplement per 1 kg of daily
milk production. Supplementation rates did not differ by year (1995 or 1996).

107
Forage effects. Cows grazing RP pastures were more heat stressed, having
greater (P < 0.05) body temperature (39.4 vs. 39.1C) and greater (P < 0.05) RR (96 vs.
92 breaths/min) than cows grazing BG (Table 3.4). These measures, indicative of greater
energy expenditure, agree with the milk production and BW change responses.
Concentrations of PUN were also greater (P <0.01) for cows grazing RP pastures
(15.3 vs. 12.8 mg%). Though slight, the increased PUN concentration may represent an
additional energetic cost to detoxify ammonia for animals grazing RP.
From 1995 to 1996, PUN concentrations increased approximately 68% (from 9.6
to 16.1 mg%) for cows grazing BG pastures, compared with a 17% increase in PUN
concentrations (from 14.1 to 16.5 mg %) for cows grazing RP (year by forage interaction,
P < 0.001). Plasma urea N concentration reflects dietary CP status (Staples and Thatcher,
1999). The low concentration of PUN for cows grazing BG in 1995 may indicate that
dietary protein was limiting for cows grazing BG that year. Therefore, the CP
concentration of the supplement was increased in 1996.
Forage had no effect on plasma glucose concentrations. Primiparous cows had
greater plasma glucose concentrations than multiparous cows when grazing BG (59.8 vs.
57.8 mg %) but their plasma glucose concentrations were less than those of multiparous
cows when RP was consumed (57.4 vs. 58.6 mg %; parity by forage interaction, P <
0.01). This interaction likely reflects a greater tendency of increased substitution of
supplement for forage for multiparous cows grazing RP. The greater glucose
concentrations for primiparous cows grazing BG is less easily explained unless
primiparous cows were more aggressive at the feed bunk and more selective at grazing
greater quality forage. Little difference was observed in plasma glucose concentrations

108
between parities or forages in 1996, but large differences in 1995 resulted in a year by
parity by forage interaction (P < 0.01). This does not follow the milk yield data and may
be a reflection of the different methods of feeding between the two years.
Stocking rate effects. Respiration rates were inexplicably greater (P < 0.05) for
cows stocked at the lower rate (96 vs. 92 breaths/min). Although forage intakes were
greater at the lower stocking rate, total intakes were not different between SR, and SR
had no effect on body temperatures.
Cows on the lower SR tended to have lower PUN. However, the lower PUN were
likely the result of greater supplement OMI for cows on the low SR treatment.
Supplementation rate effects. Supplement rate had no effect on body
temperature, but the greater amount of SUP feeding caused a 10% increase (P < 0.001) in
RR (99 vs. 90 breaths/min). The greater SUP also increased (P <0.01) plasma glucose
concentrations (59.5 vs. 57.2 mg%) but did not affect PUN.
While not significant for milk yield, a year by SR by SUP interaction (P < 0.05)
was observed for plasma glucose. Glucose concentrations followed the pattern of milk
yield and reflect the different amounts of supplement fed during the two years.
Glucose concentrations decreased as SUP fed decreased. This occurred to a
greater degree with multiparous than primiparous cows in 1995 but to a greater degree
with primiparous cows than multiparous cows in 1996 (year by parity by SUP interaction,
P < 0.01). In 1995, glucose concentrations in plasma at the high and low SUP were 59.7
and 58.7 mg% for primiparous cows vs. 60.8 and 55.9 mg% for multiparous cows. In
1996, plasma glucose concentrations were 59.8 and 56.9 mg% for primiparous cows vs.
58.0 and 57.3 mg% for multiparous cows at the high and low SUP, respectively.

109
Intake of OM and Nutrients
Parity and year effects. Expressed in terms of daily amount, intake of forage
OM, supplement OM, and total OM were not different between parities. It was assumed
that cows of all parities ate equal amounts of supplement within a treatment. Therefore
supplement OMI as a percentage of BW (OMIPBW) was necessarily greater (P < 0.001)
for the lighter, primiparous cows. Because forage OMI was not different by parity, total
OMIPBW also was greater (P <0.01) for primiparous cows as a consequence of our
assumptions. Forage, supplement, and total OMI was 1.96, 1.30, and 3.26% of BW/d for
primiparous cows compared to 1.79, 1.14, and 2.94% of BW/d for multiparous cows.
Forage effects. Cows grazing RP pastures consumed 49% more (P < 0.001)
forage OM than cows grazing BG pastures (11.3 vs. 7.6 kg of OM/d; Table 3.5). Cows
grazing RP pastures were fed more (P < 0.01) supplement because they produced more
milk, thus supplement intakes were 6.4 and 5.9 kg of OM/d for RP and BG pastures,
respectively (P < 0.01). Total OMI were 31% greater (P < 0.001) for cows grazing RP in
comparison with cows grazing BG pastures (17.7 vs. 13.5 kg/d. The measures of
OMIPBW followed the same patterns as OMI. Cows grazing RP pastures consumed
more (P < 0.001) forage (2.26 vs. 1.51% of BW), more (P < 0.01) supplement (1.28 vs.
1.18% of BW) and more (P < 0.001) total OM (3.54 vs. 2.70% of BW) than cows grazing
BG pastures.
Stocking rate effects. Greater SR reduced (P < 0.05) both forage OMI and
forage OMIPBW. Cows consumed 9.0 and 9.9 kg of forage OM/d (1.82 and 1.95% of
BW), when assigned to the high and low SR, respectively. However, cows stocked at the
higher rate consumed slightly more (P < 0.05) supplement (6.2 vs. 6.0 kg of OM/d; 1.26

TABLE 3.5. Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on forage, supplement (suppl.) and total
organic matter intake (OMI) of Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut during the summers of
1995 and 1996.
Tifton 85 bermudagrass Florigraze rhizoma peanut
Stocking Rate1 Stocking Rate2 Probability3 -
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage SR x SR
Item 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 SEM Forage SR SUP x SR x SUP x SUP x SUP
Forage OMI, kg/d
6.7
8.1
7.9
7.7
9.4
11.9
11.4
12.5
0.5
***
*
*
NS
NS
NS
NS
Suppl. OMI, kg/d
7.7
4.1
7.4
4.3
8.4
4.7
7.8
4.5
0.1
***
*
***
NS
NS
t
NS
Total OMI, kg/d
14.4
12.2
15.3
12.0
17.8
16.6
19.2
17.1
0.5
***
NS
***
NS
NS
NS
NS
Forage OMI,%ofBW
1.35
1.61
1.57
1.54
1.93
2.42
2.25
2.46
0.11
***
NS
*
NS
NS
NS
NS
Suppl. OMI, % of BW
1.56
0.82
1.48
0.86
1.70
0.95
1.56
0.91
0.03
**
*
***
NS
NS
t
NS
Total OMI, % of BW
2.91
2.43
3.05
2.40
3.63
3.37
3.81
3.37
0.11
***
NS
***
NS
NS
NS
NS
'High and low stocking rates were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.

Ill
vs. 1.20% of BW). Thus, total OMI and OMIPBW were not different due to SR (15.3
and 15.9 kg of OM/d and 3.08 and 3.16% of BW/d).
At the high SR, primiparous cows ate less BG whereas multiparous cows ate more
BG (parity by forage by SR interaction, P < 0.05; Figure 3.9). Conversely, SR had little
effect on forage consumption when primiparous cows grazed RP but multiparous cows
decreased RP OMI more than 2.5 kg/d with increasing SR (13.0 vs. 10.4 kg of OMI/d for
low and high SR, respectively). Similar interactions were observed for total OMI as well
as forage and total OMIPBW (Figure 3.9).
Supplementation rate effects. Providing additional supplement led to reduced
(P < 0.05) forage OMI (10.1 vs. 8.8 kg/d for high and low SUP treatments, respectively).
Total OMI was 2.2 kg/d greater (P <0.001) for cows on the high SUP treatment (16.7 vs.
14.5 kg/d). Results for OMIPBW followed the same pattern.
Cows grazing RP pastures experienced a greater decrease in forage consumption
when fed more supplement compared to those grazing BG pastures. The substitution of
forage OM by supplement OM (kg/kg) was 0.51 for RP and 0.18 for BG. Though the
forage by SUP interaction was not significant for forage OMI, cows grazing BG pastures
and provided greater amounts of supplement increased total OMI by 22 % vs. a 10 %
increase in total OMI with additional supplement for cows grazing RP. Greater
substitution rates of supplement for forage have been reported for greater quality forages
(Golding et al., 1976b). The forage by supplement interaction for milk production
(Figure 3.3) further supports the conclusion of greater substitution rates of grain for
forage for cows grazing RP because cows were better able to maintain milk production at
the low SUP when grazing RP compared with cows grazing BG. Assuming that SR

Total OMI, kg/d Forage OMI, kg/d
Parity Parity
Figure 3.9. Interactions of parity, forage, and stocking rate (SR) on forage and total organic matter intake (OMI) and forage and total
OMI as a percent of body weight (OMIPBW). Forages were Tifton 85 bermudagrass (BG) or Florigraze rhizoma peanut (RP). Average
low and high SR for BG pastures were 6.25 and 8.75 cows/ha. Average low and high SR for RP pastures were 3.75 and 6.25 cows/ha.

113
could be increased in proportion to the decrease in forage consumption, and based on
average SR across years, SR for BG could be increased from 7.5 to 8.25 cows/ha and SR
for RP could be increased from 5.0 to 6.0 cows/ha when feeding the greater amount of
supplement.
Year by supplement and parity by supplement interactions (P < 0.05) also were
observed for supplement OMIPBW. The data have little meaning, however, due to the
differences in BW across years and parities (data not shown).
Calculations of nutrient intake within forage and SUP treatment combinations
indicated that 4% FCM production likely was not limited by nutritional deficiency with
the exception of cows grazing BG and fed low amounts of supplement (Table 3.6). Cows
fed the lesser amount of supplement when grazing BG were likely deficient in daily
intake of DM, energy, and CP and had marginal intake of Ca and P. With BG managed
as in these experiments, large amounts of supplement must be fed or the supplement
nutrient concentrations must be adjusted to ensure adequate nutrient intake.
Conversely, supplement intakes were likely excessive for cows grazing RP. With
either SUP, cows grazing RP consumed excess CP (Table 3.6) that likely increased
maintenance costs due to the need for increased N excretion. Assuming all N in excess
of requirement was lost as urea, and using the NRC (1989) estimate of 7 kcal of ME/g of
N excreted, N excretion cost cows 1.2 or 1.7 Meal of ME/d with the low and high SUP
treatments, respectively. Only S intake appeared marginal regardless of SUP.
Comparison of our intake data with NRC estimates of nutrient requirements was
made as well (Table 3.7). The data represent only cows used in the intake estimate study.

TABLE 3.6. Calculated daily intake of nutrients1 by cows grazing Tifton 85 bermudagrass (BG) or Florigraze rhizoma peanut (RP)
pastures. Cows received supplement (SUP) at either 0.33 kg (Low) or 0.5 kg (High) (as-fed) per kg of daily milk production.
Ingredient
NEL1
DM
NDF
ADF
CP
Ca
P
Mg
K
Na
S
Cl
Fe
Zn
Cu
Mn
Mcal/d
- - kg/d -
g/d -
mg/d
Low SUP
BG
10.6
8.3
6.7
3.4
1.1
35
25
20
156
3
23
42
481
364
37
624
Supplement
8.8
4.6
1.7
1.2
0.8
48
24
16
57
36
9
25
2058
646
145
303
Total
19.3
12.9
8.5
4.6
1.9
82
49
36
212
39
39
32
2540
1010
182
927
High SUP
BG
9.8
7.7
6.2
3.2
1.0
32
23
19
144
2
21
38
445
336
35
576
Supplement
15.7
8.2
3.1
2.1
1.4
85
43
28
101
65
16
45
3676
1154
259
541
Total
25.4
15.9
9.3
5.3
2.4
117
66
47
245
67
37
83
4120
1490
293
1118
Low SUP
RP
18.7
13.3
5.9
4.3
2.4
221
35
56
218
1
21
58
492
524
36
477
Supplement
9.6
5.1
1.9
1.3
0.8
52
26
17
62
40
10
27
2255
708
159
332
Total
28.3
18.3
7.8
5.6
3.2
274
61
73
280
40
31
85
2746
1231
195
810
High SUP
RP
15.9
11.3
5.0
3.7
2.0
189
30
47
186
1
18
49
419
447
31
407
Supplement
16.9
8.9
3.3
2.3
1.5
92
46
30
109
70
17
48
3970
1246
279
585
Total
32.9
20.2
8.4
6.0
3.5
281
76
78
295
71
35
98
4389
1693
311
992
Requirement2
23.3
16.0
4.5
3.4
2.2
84
54
32
144
29
32
40
800
640
160
640
Calculated from the average of estimates presented in Tables 3.1 and 3.2.
Calculations based on NRC requirements for a 500 kg cow producing 20 kg of 4.0% FCM and gaining 0.275 kg/d. Intake was
assumed to be 3.2% of BW.

TABLE 3.7. Effect of forage, stocking rate (SR), and supplementation rate (SUP) on bodyweight (BW) change, 4% fat corrected milk
(FCM) production, and measures of energy (E) status of Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut
during the summers of 1995 and 1996
Tifton 85 bermudagrass Florigraze rhizoma peanut
Stocking Rate1 Stocking Rate2 Probability3
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage SR x SR
Item 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 SEM Forage SR SUP x SR x SUP x SUP x SUP
Average BW, kg
507
504
508
507
497
500
504
513
3.0
NS
*
NS
NS
NS
NS
NS
FCM, kg/d
16.5
14.2
16.6
13.8
15.8
15.7
16.5
15.5
0.4
t
NS
***
NS
**
NS
NS
Maintenance E, Mcal/d4
10.1
10.1
10.1
10.1
10.0
10.0
10.1
10.2
0.3
NS
NS
NS
NS
NS
NS
NS
FCM E, MCal/d5
12.2
10.5
12.3
10.2
11.7
11.6
12.2
11.5
0.3
t
NS
***
NS
**
NS
NS
Total E output, Mcal/d6
22.4
20.6
22.4
20.3
21.7
21.6
22.3
21.7
0.4
NS
NS
**
NS
*
NS
NS
BW change, kg/d
-0.2
-0.3
-0.1
-0.1
-0.5
-0.3
-0.2
-0.1
0.1
NS
*
NS
NS
NS
NS
NS
Tissue E, Mcal/d7
0.9
1.3
0.5
0.6
2.3
1.5
1.1
0.4
0.5
NS
*
NS
NS
NS
NS
NS
Forage E intake, Mcal/d8
9.3
10.9
10.9
9.4
14.3
18.2
17.7
19.2
0.8
***
t
*
f
t
*
NS
Suppl. E intake, Mcal/d9
14.3
7.7
13.8
8.0
15.7
8.9
14.5
8.4
0.3
* *
t
***
t
*
t
NS
Dietary intake E, Mcal/d
23.5
18.6
24.7
17.5
29.9
27.1
32.2
27.7
0.7
***
NS
***
NS
*
t
NS
Total E input, Mcal/d
24.5
19.9
25.2
18.1
32.2
28.6
33.3
28.1
0.8
***
NS
***
NS
NS
NS
NS
E status, Mcal/d10
2.1
-0.7
2.7
-2.2
10.6
7.0
11.0
6.4
0.9
***
NS
***
NS
NS
NS
NS
'High and low stocking rates for Tifton 85 bermudagrass were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates for Florigraze rhizoma peanut were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.
4Calculated using NRC equations for maintenance and activity, maintenance E = 0.073*BW75. Requirement was also increased 25% for energy of activity and
increased an additional 10% above maintenance for primiparous cows.
Calculated using NRC equations, milk energy = 0.74Mcal/kg*FCM, kg/d.
6Total E output = Maintenance E + FCM E, Mcal/d.
Calculated using NRC (1989) equations. Tissue E = +4.92 Mcal/kg BW loss and -5.12 Mcal/kg BW gain.
Calculated using the NRC (1989) conversion of TDN to NEL, where NEL = [0.0245*TDN(% of DM)-0.12]. Calculation of TDN was based on the equation for
estimation of TDN in warm-season grasses used by the University of Florida Forage Evaluation Support Laboratory (J. E. Moore, personal communication), where %
TDN = [(IVOMD, % 0.49) + 32.2] OM concentration.
Calculated using estimated supplement digestibility of 86%. TDN was calculated using tabular values, and NEL was calculated from estimated TDN using NRC
(1989) equations.
'"Energy status = Energy input energy output.

116
Predicted energy inputs were greater than outputs by an average of 4.8 Mcal/d (23% of
estimated energy requirement) and quite variable. The standard deviation of all energy
difference estimates was 7.0 Mcal/d, 32.4% above estimated requirements. The results
indicate that either energy intake was overestimated or maintenance energy requirements
were underestimated, although maintenance energy requirement was increased from 10%
to 25%. Estimates of energy status (energy intake minus energy output) for cows grazing
RP pastures were particularly poor, especially for cows fed the greater SUP. Energy
states were over-estimated (P < 0.001) by 8.8 Mcal/d for cows grazing RP, compared
with -0.5 Mcal/d for cows grazing BG. The over-estimate (P < 0.001) of energy status
was 2.5-fold greater with additional supplementation (2.6 vs. 6.6 Mcal/d for low and high
SUP rates, respectively). Some of the variability may be attributed to the method of
feeding in 1995. When cows were fed at the feedbunk (1995), intakes would likely vary
to a greater degree than when cows were fed from troughs in their individual pastures
(1996). However, comparison of energy status predictions between years indicated no
improvement, and energy status difference was less in 1995 than in 1996.
These data are subject to several sources of error. Overestimates of intake,
underestimates of maintenance requirements, and overestimates of diet digestibility (due
to predictions of associative effects) all may have limited the accuracy of prediction.
Regardless, the differences between energy inputs and outputs suggest that nutrients of
RP were poorly utilized, and that different feeding strategies with respect to supplements
are likely necessary to optimally utilize RPs better nutritive characteristics.

117
Treatment Effects on Forage Nutritive Value Estimates
Analysis values in Table 3.8 represent the least squares means of hand-plucked
samples from individual pastures, rather than an average across all pastures within a
given forage.
Year effects. Of the nutritive value measures, only NDF was unaffected by year.
Decreased (P < 0.001) CP (16.3 vs. 14.8% for 1995 and 1996, respectively) would
suggest that samples containing lesser concentrations of CP likely included more plant
stems, dead leaf, or both. This is contradicted, however, by increased (P < 0.001)
IVOMD (63.3 vs. 66.7%) and the lack of change in forage NDF concentration (62.7 vs.
62.9%) between years.
Forage effects. The IVOMD and CP concentration of RP exceeded (P < 0.001)
those of BG pastures by 21 and 33%, respectively, while NDF concentrations of RP were
approximately 55% less (P < 0.001) than those of BG. Concentrations of in vitro
digestible OM, CP, and NDF were 71.2, 17.8, and 44.5% for RP and 58.8, 13.3, and
81.8% for BG, agreeing with the findings of others (Beltranena et al., 1981; Hill et al.,
1993).
The IVOMD of sampled BG increased from 1995 to 1996 (55.5 vs. 62.1%) which
may indicate that the greater SR increased the quality of BG, while the digestibility of
sampled RP pastures was unchanged by year (71.2%; year by forage interaction, P <
0.001). Concentrations of CP in BG remained essentially unchanged across years (13.5
vs. 13.1% for 1995 and 1996, respectively), while CP in RP sampled decreased from
1995 to 1996 (19.0 vs. 16.6%; year by forage interaction, P < 0.01). Concentration of

TABLE 3.8. Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on forage, supplement and crude protein
(CP), in vitro organic matter digestibility (IVOMD), and neutral detergent fiber (NDF) concentrations in Tifton 85 bermudagrass and
Florigraze rhizoma peanut during the summers of 1995 and 1996. Samples were hand-plucked once each period based on visual
appraisal of forage consumed by grazing cows.
Tifton 85 bermudagrass Florigraze rhizoma peanut
Stocking Rate1 Stocking Rate2 Probability3
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage SR x SR
Item 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 SEM Forage SR SUP x SR X SUP x SUP x SUP
CP, %
14.3
13.1
13.2
12.4
17.7
18.2
17.9
14.5
0.4 ***
t
NS
NS
t
NS
NS
IVOMD, %
60.2
58.3
60.0
56.8
70.8
71.4
71.2
71.5
0.9 ***
NS
NS
NS
*
NS
NS
NDF, %
80.7
81.6
81.3
81.0
45.8
44.4
44.5
43.4
0.8 ***
NS
NS
NS
NS
NS
NS
'High and low stocking rates were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.

119
NDF in BG decreased from 1995 to 1996 (81.9 vs. 80.4%) while that in RP increased
(43.5 vs. 45.5%; year by forage interaction, P < 0.05).
Stocking rate effects. Increased SR had no effect on IVOMD or concentration of
NDF but did tend (P < 0.10) to increase CP concentrations (15.3 vs. 15.8% for low and
high SR, respectively) as evidenced by the tendency (P <0.10) of greater MUN
concentrations of cows kept at the greater SR. Year by SR interactions would indicate
forage rather than SR effects, and their absence in these data represents the confounding
effect of averaging the results over both forages. Although year by forage by SR
interactions were not observed for any nutritive value measure, the numeric patterns were
consistent with such interactions but masked by large standard error.
Supplementation rate effects. Supplementation rate had no effect on any
nutritive value measures. Increasing SUP had little effect on IVOMD of RP pastures
(71.0 vs. 71.5% for low and high SUP treatments, respectively) while IVOMD of BG
pastures increased with increasing SUP (57.5 vs. 60.1%; forage by SUP interaction, P <
0.05). Similarly, greater SUP resulted in no change in CP concentration (17.8%) of RP,
whereas CP concentration of BG tended to increase at the greater SUP (12.8 vs. 13.8;
forage by SUP interaction, P < 0.10).
These results do not imply that increasing SUP improved forage nutritive value,
but rather those cows fed more supplement consumed forage of greater nutritive value as
well. Forage OMI data (Table 3.6) support this idea, since greater supplement intake
decreased forage intake, which would have allowed for greater selection.

120
Treatment Effects on Herbage Mass, Availability, and Intake Estimates as
Determined by Pasture Sampling
Unless stated otherwise, the HM values presented represent the average of the
pre- and post-graze HM values. Herbage allowance (HA) represents kg of herbage
DM/kg of animal BW. Estimates of HA were calculated as 0.5 (pre-graze + post-graze
HM, kg/ha)/(average BW, kg/cow cows/ha). The DMI estimates (kg/cow) were
calculated as [(pre-graze post-graze HM, kg/ha) paddock size,
ha/paddock]/(cows/paddock).
Coefficients of determination for the regression equations used to estimate HM
typically were greater at the initial pre- and post-graze sampling events within both year
and forage type (Table 3.9). Initial estimates of HM appeared to have been better with
BG, but the relative change in r2 from one period to another was less with RP. The larger
relative change in r2 from one period to another with BG is indicative of the
accumulation of large quantities of herbage in the BG pastures which made difficult
accurate HM estimates.
Year effects. The HM and HA of pastures were less (P < 0.001) in 1996,
reflecting the effects of both the greater SR and greater (P < 0.001) DMI observed in that
year (Table 3.10). For 1995 and 1996, HM averaged 6250 and 4250 kg of DM/ha, HA
averaged and 2.2 and 1.2 kg of DM/kg of BW, and DMI averaged 12.5 and 19.4 kg of
DM/cow per d.
Forage effects. Across periods over the 2 yr, pre-graze HM of BG pastures
averaged approximately 2600 more (P < 0.001) kg of DM/ha than RP pastures (7270 vs.
4650 kg of DM/ha). This difference carried over to post-graze HM (6250 vs. 3650 kg of
DM/ha) measures for forages as well.

121
TABLE 3.9. Regression1 groupings and regression coefficients for predicting 1995 and
1996 pre- and post-graze herbage mass of Tifton 85 bermudagrass and Florigraze
rhizoma peanut pastures.
1995
Period
- Year
1996
Period -
Item 1
2
3
1
2
3
Bermudagrass
regression grouping
Pregraze estimates
Measurements, n
16
13
16
13
13
14
Intercept
21.81
51.73
75.70
23.17
124.59
96.24
Slope
6.797
9.902
10.245
8.989
4.972
5.444
r2
0.896
0.528
0.421
0.784
0.562
0.344
Postgraze estimates
Measurements, n
14
15
15
14
13
16
Intercept
40.24
77.13
109.37
27.87
83.74
55.28
Slope
5.597
8.053
8.503
7.227
7.449
7.230
r2
0.937
0.719
0.579
0.646
0.619
0.872
Rhizoma peanut
regression grouping
Pregraze estimates
Measurements, n
15
16
15
16
16
16
Intercept
32.68
61.80
46.98
1.186
-0.303
8.836
Slope
7.798
7.927
12.506
10.21
12.14
9.75
r2
0.700
0.495
0.595
0.730
0.722
0.580
Postgraze estimates
Measurements, n
13
12
14
16
16
16
Intercept
40.08
73.28
72.67
-18.624
-10.517
-8.791
Slope
7.674
7.046
10.547
14.39
15.24
12.31
r2
Itt i r
0.735
0.675
0.540
0.693
0.776
0.889
'Herbage mass = Intercept + Slope Disk meter height, cm.

TABLE 3.10. Disk meter estimates of the effect of forage species, stocking rate (SR), and supplementation rate (SUP) on forage pre-
and post-graze herbage mass (HM), herbage allowance (HA), and dry matter intake (DMI) of grazing, lactating Holstein cows grazing
Tifton 85 bermudagrass and Florigraze rhizoma peanut during the summers of 1995 and 1996.
Tifton 85 bermudagrass Florigraze rhizoma peanut
- Stocking Rate1 Stocking Rate2 Probability3
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage x SR x SR
Item
0.5:1
0.33:1
0.5:1
0.33:1
0.5:1
0.33:1
0.5:1
0.33:1 SEM Forage
SR
SUP
x SR
x SUP x SUP x SUP
Pre-graze HM,
7220
6980
7320
7540
4460
4460
4890
4780 110
***
**
NS
NS
NS
NS
NS
kg/ha
Post-graze HM,
6290
5960
6460
6310
3380
3120
4140
3960 100
***
***
*
**
NS
NS
NS
kg/ha
Average HM, kg/ha
6760
6470
6890
6920
3920
3790
4510
4370 100
***
***
t
t
NS
NS
NS
HA, kg of forage/kg
1.6
1.5
2.3
2.3
1.1
1.1
2.0
1.9 0.0
***
***
NS
NS
NS
NS
NS
of BW
Forage DMI4, kg/d
12.0
13.0
15.0
22.3
14.3
17.3
16.3
17.7 1.8
NS
*
*
t
NS
NS
NS
'High and low stocking rates were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.
4DMI calculated as [(pre-graze post-graze HM, kg/ha) paddock size, ha/paddock]/(cows/paddock).

123
A year by forage interaction (P <0.01) for HM was observed, and as with the
nutritive value estimates, the interaction more likely indicates the effect of increased SR
from 1995 to 1996 rather than changes in the forages or their growing conditions.
Increasing SR from 1995 to 1996 had less effect on BG, decreasing BG HM by 17%
(7390 vs. 6130 kg of DM/ha), but the increased SR decreased RP HM by 38% (5120 vs.
3180 kg of DM/ha).
As with HM, HA was greater (P < 0.001) for BG than for RP pastures (1.9 vs. 1.5
kg of pasture DM/kg of animal BW) despite the lower SR used with RP. Because the
change in HM due to SR was similar across years, increasing the SR from 1995 to 1996
had less effect on HA in 1996 (year by forage interaction, P < 0.001). Thus, the ratios of
the HA values were a mathematical consequence of, and very nearly reflect the ratios of
the low and high SR within years. Effect of forage was not significant with respect to
forage DMI. Average estimated DMI across forages was 16.0 kg of DM/cow per d.
Stocking rate effects. Greater SR reduced (P <0.01) pre-graze HM (5780 vs.
6130 kg of DM/ha (Table 3.10). This was likely due to carry-over effects from previous
grazing events within each grazing season as reflected in differences in post-graze HM.
The difference (P < 0.001) between SR treatments for post-graze HM (4690 vs. 5210 kg
of DM/ha for greater and lesser SR, respectively) was approximately 65% larger than the
difference between SR treatments for pre-graze HM. Post-graze HM for RP pastures
decreased by 800 kg of DM/ha as SR increased (4050 vs. 3250 kg of DM/ha) compared
with a 260 kg/ha decline in BG pastures (6380 vs. 6120 kg of DM/ha; forage by SR
interaction, P < 0.01).

124
Greater SR resulted in decreased (P< 0.001) HA by nearly 40% (1.3 vs. 2.1 kg of
pasture DM/kg BW). In 1995, HA at the high and low SR were 1.7 and 2.8 kg of DM/kg
of BW vs. HA of 1.0 and 1.5 kg of DM/kg of BW in 1996 (year by SR interaction, P <
0.001).
Estimates of DMI were less (P < 0.05) for cows assigned to the greater SR
treatment (14.1 vs. 17.8 kg DMI/d for high and low SR treatments, respectively). Forage
DMI for cows grazing RP pastures differed slightly between SR treatments (15.8 and
17.0 kg of DM/cow per d) while forage DMI was markedly less at the high SR when
cows grazed BG (12.5 vs. 18.7 kg of DM/cow per; forage by SR interaction, P < 0.10).
Supplementation rate effects. No carry-over effects of SUP treatment were
observed in pre-graze HM, but post-graze HM was greater (P < 0.05) when cows were
fed greater amounts of supplement (5060 vs. 4840 kg of DM/ha). The effect of SUP
treatment on HA was not significant. Estimated forage DMI decreased (P < 0.05) with
the greater SUP treatment (14.4 vs. 17.6 kg of DM/cow per d).
Minson and Wilson (1994) suggested that the lower limit of HA which would not
limit individual animal performance is 60 g of OM/kg of BW. The smallest HA observed
during the study was 0.75 kg of DM/kg of BW, occurring in 1996 in RP pastures stocked
at the greater rate with the low SUP. Based on these estimates, HA was not limiting for
any treatment. However, taking samples from ground level inflated the HA values,
particularly for BG, due to the inclusion of large amounts of dead herbage. The estimate
also has limits due to inclusion of standing dead and stemmy herbage which cows
avoided grazing. Thus, a more suitable estimate would have been HA adjusted for the
proportion of green material in the sward (Piaggio and Prates, 1997).

125
Intake may be limited when HM in tropical grass-legume pastures is less than
2000 kg/ha (Cowan and OGrady, 1976). All pre-graze estimates of HM were greater
than 2000 kg/ha, but as with HA, the inclusion of large amounts of dead material may
limit the value of the estimate, particularly for BG. Also, the post-graze HM of RP
pastures combined with high SR and low SUP treatments in 1996 was 1770 kg of DM/ha,
suggesting that forage may have been limiting with that treatment.
All intake estimates via disk meter were quite large relative to the estimates of
intake using the marker technique. The effect of supplement on the substitution of forage
reported earlier was not observed. The use of a disk meter to estimate DMI is thought
best limited to situations where pasture swards are uniform.
Simple Economic Assessment of Supplementation
Using only the milk production data, a simple assessment of income per cow or
income per land area was performed (Table 3.11). Milk income was calculated as
$0.33/kg of milk, and supplement costs were calculated as $0.22/kg of supplement.
Supplement intake was estimated as one third or one half of milk production, depending
upon the supplement treatment. Supplement cost was subtracted from milk production to
provide a simple economic assessment of supplementation.
Cows grazing RP returned equal or greater income on a per cow per day basis
than cows grazing BG ($4.13 vs. $3.85/cow per day) illustrating the higher digestibility
and intake potential of RP. This advantage of RP over BG pastures was greatest when
the amount of supplement fed was lowest ($4.27 vs. $3.80/cow per day, compared to
$3.99 vs. $3.90/cow per day for the low and high SUP respectively). Feeding additional
supplement was more profitable only when BG was grazed. Milk income minus
supplement costs (MIMSC) was $0.10/cow per day greater for cows eating more

TABLE 3.11. Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on milk income1 minus supplement costs2
(MIMSC), assuming supplement intake proportionate to LS means of milk production within a given SUP treatment and calculated on
both per cow and per land area bases.
Tifton 85 bermudagrass
Stocking Rate3
Florigraze rhizoma peanut
Stocking Rate4
High Low High Low
Supplementation rate (kg/kg of milk per d)
0.5:1
0.33:1
0.5:1
0.33:1
0.5:1
0.33:1
0.5:1
0.33:1
MIMSC, $/cow per d
3.97
3.85
3.83
3.75
3.98
4.26
4.00
4.29
MIMSC, $/ha per d
34.7
33.7
23.9
23.4
24.9
26.6
15.0
16.1
'Estimated milk income = US $0.33/kg of milk.
Estimated supplement cost = US $0.22/kg of supplement.
3High and low stocking rates were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
4High and low stocking rates were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.

127
supplement on BG but was $0.29/cow per day lower for cows eating more supplement on
RP. These responses reflect the effects of substitution. One aspect of substitution not
accounted for in this analysis is the potential for greater SR when feeding more
supplement to cows grazing RP pastures.
The greater dollar return on a per cow basis for RP pastures is dwarfed by the
greater income per unit land area capable with BG pastures. By these calculations, use of
BG resulted in a 40% greater dollar retum/ha. Average income/ha for BG was $28.95 vs.
$20.65 for cows grazing RP.
Conclusions
Successful utilization of pasture-based forage systems in Florida is likely to
depend upon a variety of factors. Along with forage type, SR, supplement type and
feeding regime, pasture and animal management factors such as fertilization, forage
components for other seasons, types of supplement provided, exogenous growth hormone
(bST), cooling systems for cows (trees, shades, ponds, bams with misters and fans), breed
differences, and reproductive management must be considered. Further, despite its
potential for reduced costs, the rather low production per cow in this study suggests that
use of pasture for lactating dairy cows in Florida may limit its consideration by most
producers.
For producers using grazing, RP is likely to be of limited use in Florida dairy
grazing systems until N fertilizers become prohibitively expensive. The greater milk
production/cow associated with RP cannot compensate for the forages limited ability to
support large numbers of lactating cows/ha. Tifton 85 bermudagrass, however, appears

128
to be an excellent forage for dairy grazing given its relatively high nutritive value
characteristics and great yields.
Ability to optimize SR for both animal and forage production will be critical for
producer success with grazing. Results from this study indicated that increasing SR on
productive forages such as BG might improve forage quality. Stocking rates of 10
cows/ha may not be great enough in conditions of rapid growth of Tifton 85, but this
depends upon factors such as rainfall and fertilization practices. At SR of 7.5 cows/ha on
RP pastures, HA may limit animal production. Although estimates of OMI suggest that
the high SR, low SUP treatment within RP pastures did not limit forage OMI, such high
SR may have negative consequences in terms of maintenance and productivity of stand,
and would only be advisable under excellent growing conditions.
Providing supplement is a cost-effective way to improve performance of cows on
pasture, particularly forages of moderate quality and of more limited availability. The
positive milk production and MIMSC responses to additional supplement when cows
grazed BG pastures indicate the value of providing supplement to cows grazing this
moderate quality forage. However, the limited production response and negative
MIMSC response to supplement when cows grazed RP indicates the potential for
substitution with high quality forage. Further, the over-prediction of energy input with
RP pastures indicates that the supplementation treatments in this study were not effective
in combination with RP.
Although several studies have indicated greater response to supplement when
forage availability was limited, forage availability likely was not limited in these studies,
and no such responses were observed.

129
Concerns about pasture-based production systems include the losses of BW and
body condition, and the poor reproductive performance associated with their use. Cows
in these studies were moved directly from bams to pastures in the heat of the summer.
No time was given for adaptation to either the heat or the new system of forage
consumption, and BW losses were greatest in the first treatment period. In year-round
pasture-based systems, however, losses of BW might be reduced due to better adaptation.
Further, strategies such as winter calving might limit the losses associated with the heat
of summer and allow for greater reproductive success. However, changing the season of
production may strain the graziers ability to utilize rapidly growing summer pastures and
may require large supplemental forage inputs during the winter grazing season. Other
options for graziers in Florida may include the use of cows better adapted to Floridas
climate and improved heat abatement strategies.

CHAPTER 4
PASTURE BASED DAIRY PRODUCTION SYSTEMS: INFLUENCE OF HOUSING,
bST, AND FEEDING STRATEGIES ON ANIMAL PERFORMANCE
Introduction
For dairy farmers in the Southeast considering pasture-based production systems
for lactating dairy cows, environmental stress is a particular concern. Cool, comfortable
cows produce more milk, and in areas where the climate is typically hot and humid, milk
production is likely to be compromised due to the inverse relationship between milk
production and heat stress tolerance. This situation is exacerbated for pasture dairies by
at least three factors. First, as temperature increases, DMI typically decreases to a greater
degree with increasing concentration of roughage in the diet. Secondly, more direct
exposure to solar radiation results in greater heat load for cows on pasture with limited
shelter. Thirdly, grazing cows have larger heats of maintenance due to greater activity
(walking and grazing).
Typical cooling methods for pasture systems include cooling ponds, fixed or
mobile shade structures, and trees. Technologies for heat stress abatement in confined-
housing production systems have seen great advances in the past decade but remain
limited for animals on pasture. However, such structures may be available for producers
switching to grazing systems, and their efficacy for pasture-based dairy systems have not
been tested.
Another possible way to improve production of cows in grazing systems is with
the use of bST. Few studies using bST have been conducted with cows grazing pastures
130

131
in hot climates. Because of the increase in body temperatures associated with the use of
bST, concerns have been raised about its use on heat-stressed cattle. However, review of
the literature indicates that cattle may be able to dissipate additional heat production due
to bST treatment.
While management strategies such as designed shading and bST improve animal
performance, few have investigated their use with lactating dairy cows grazing pasture
under hot conditions. This lack of information was the impetus for the study that follows.
Materials and Methods
Cows, Design, and Treatments
On 28 July 1997, 32 multiparous cows (average parity = 2.9; average DIM = 196
38) at the University of Florida Dairy Research Unit were assigned randomly to one of
five treatments arranged in two replicates. Treatments were 1) cows maintained on
pasture continuously, 2) Treatment 1 plus Posilac (Monsanto, St. Lousi, MO; bST), 3)
cows maintained on pasture from approximately 1800 to 0530 h, then in free-stall
housing with fans and misters from 0730 to 1530 h, 4) Treatment 3 plus bST, and 5)
Treatment 4 plus com silage fed at 0.5% of body weight (DM basis) in the bam. The
bST was injected on d 1 and 13 in Periods 1 and 2. In Period 3, the second dose of bST
was delayed to d 15 due to oversight. Cows were assigned to a new treatment for each of
the three periods. No cow received the same treatment more than once and the number of
changes from a given treatment to another was balanced. Periods 1 and 2 lasted 24 d, and
Period 3 lasted 26 d. The first 12 d of each period served to adjust cows to a new
treatment. The remaining days of each period were used for data collection.

132
Pastures (Cynodon dactylon XC. nlemfuensis cv. Tifton 85) were fertilized with
NH4NO3 at a rate of 67 kg of N/ha on 18 July and 4 September. Pastures were divided
into 16 paddocks, allowing a 15-d rotation. The integrity of bermudagrass (BG)
paddocks was maintained with energized poly wire fencing. Fencing prevented cows
from grazing the next days forage allotment as well as BG in its regrowth phase. Cows
were provided shade structures (80% sun-block shade cloths stretched over metal pipe
frames) and water tubs that were moved to a fresh paddock each morning. Shade
structures were designed to provide 4.6 m2 of shade/cow. Stocking rates were 13.3 and
10 cows/ha for cows fed or not fed silage, respectively.
Cows were milked at 0530 and 1630 h. After the morning milking, cows assigned
to Treatments 1 and 2 were returned to pastures. Cows assigned to Treatments 3, 4, and 5
were taken to a freestall bam where they were housed within their respective treatment
groups. After the p.m. milking all cows were moved to pasture where they remained
until the a.m. milking.
Supplement was fed at a rate of 0.50 kg (as-fed)/kg of milk produced per day. Averages
of 3- or 4-d milk weights were reviewed twice weekly and the amount of supplement
provided was adjusted accordingly. Fifty percent of this daily amount was fed after each
milking in the pastures or in the bam, according to treatment assignment. When housed,
cows were fed in the bam by treatment group. When cows were on pasture, supplement
was fed to each replicate within treatment. Supplement ingredients are listed in Table
4.1. Average nutritive value characteristics of the supplement and forages are reported in
Table 4.2.

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Table 4.1. Supplement ingredients.
Item
(%, DM basis)
Hominy
35.8
Soybean hulls
23.9
Soybean meal
9.5
Whole cottonseed
20.1
Mineral mix'
2.7
Limestone
1.3
Trace mineral salt2
1.3
Molasses
4.0
Sodium bicarbonate
1.3
'Composition: > 55% Dyna-Mate, > 0.7% 1% Se, > 0.4% C0SO4, > 1.9% Q1SO4,
> 2.6% ZnS04, 0.7% MnS04, 36.9% MgO, > 0.001% Cal, 1200 IU/g of vitamin A, > 700
IU/g of vitamin D3, > 300 IU/g of vitamin E.
Composition (g/100 g): NaCl, 92 to 97; Mn, > 0.25; Fe, > 0.2; Cu, > 0.033; I, > 0.007;
Zn, > 0.005; Co, > 0.0025.
Table 4.2. Chemical composition, and nutritive value of supplement, com silage and
bermudagrass pasture.
Item
Maize Silage'
- Feedstuff
Supplement Bermudagrass2"5
Dry matter, %
26.2
92.5

IVOMD, %
65.6

60.3
TDN, %
62.0
76.0
57.4
NEL, Mcal/kg
1.38
1.83
1.29
NDF, %
57.2
38.0
77.6
ADF, %
33.4
23.0
35.1
CP, %
7.97
17.35
14.7
Ash, %
3.4
9.1
5.1
Ca, %
0.25
1.16
0.41
P,%
0.27
0.52
0.31
Mg, %
0.18
0.33
0.26
K, %
1.11
1.35
1.70
Na, %
0.013
1.27
0.038
S,%
0.11
0.20
0.29
Cl, %
0.3
1.24
0.53
Fe, ppm
51
503
55
Zn, ppm
26
194
38
Cu, ppm
4
48
5
Mn, ppm
22
93
42
Mo, ppm
<1
<1.4
1.3
'Estimate of TDN and NEL from NRC (1989) for com silage, few ears.
2Estimate of TDN calculated with the following equation: % TDN = [(%IVOMD*0.59)
+ 32.2] OM concentration (J. E. Moore, personal communication).
3NEL calculated from the estimate of TDN described in Footnote 2, using NRC (1989)
equations: NEL = [0.0245*TDN(% of DM) 0.12],

134
Five days prior to the experiments start, all cows were moved into the freestall
bam for adaptation. At this time, cows were fed a diet consisting of a mixture of the
farms high-herd TMR, com silage, and the experimental supplement. The high-herd
TMR portion of the diet was phased out over 5 d with an increasing percentage of
supplement and com silage being fed.
Experimental Measurements
Milk production, body weight, and body condition score. Milk weights were
recorded at each milking. Milk samples were collected at six consecutive milkings
within the last 12 d of each period. Samples were analyzed by Southeast Dairy Labs
(McDonough, GA) for milk fat and protein percentages, somatic cell count (SCC), and
milk urea nitrogen (MUN).
Cows were weighed after the a.m. milking on three consecutive days at the
initiation of the trial and at the end of each period. Body condition scores were recorded
on one of the weigh days within each period (Wildman et al., 1982).
Respiration rates and body temperatures. Respiration rates were measured by
monitoring the movement of the flank or bobbing of the head over a 1-min interval.
Measures took place during the afternoon before the p.m. milking during a time of
greatest potential ambient temperature.
Body temperatures were not measured in Period 1 because the units for measuring
body temperatures were unavailable. In Periods 2 and 3, fifteen cows (three per
treatment) were used to determine the effect of treatment on body temperature. Intra-
vaginal telemetric temperature transponders (Telonics, Mesa, AZ) were used to record
body temperatures. Since only five temperature transponders (TT) were available, one

135
cow per treatment was fitted with a TT and temperatures measured for 48 h. This was
repeated for a second and third group of five cows each. The TT were taped to
progesterone-free Eazi Breed, controlled intravaginal drug releasing devices (InterAg,
Hamilton, NZ) and inserted into the vagina.
Each TT broadcast a signal at its own frequency, and the frequencies were preset
into a radio scanner. The scanner moved sequentially through the preset TT frequencies,
recording three signals per given TT in approximately 1 min. Thus, a set of three
readings for all treatments was obtained approximately every 5 min.
Factoring out 2 h for set-up, installation and TT adaptation, the theoretical
maximum number of readings per treatment was approximately 10,000 (36 readings/h per
cow times 46 h times 3 cows per treatment-period times 2 periods). Differences in TT
signal strength, distance from TT to the scanner (0.75 km maximum), computer shut
down, and environmental and atmospheric conditions often resulted in loss of signals, or
signals which did not represent physiological temperatures. Across the two periods, an
average of 4400 readings were taken for cows on pasture and 5400 readings for cows in
the bam.
Plasma metabolites. Blood samples were collected from the coccygeal vessels
thrice at 2- to 4-d intervals within the last week of each period. Vacutainors (Becton
Dickinson, Franklin Lakes, NJ) containing EDTA were used for the first sample taken.
At the remaining 8 dates, blood was collected into 9-ml Na-heparinized (Luer
Monovette LH, Sarstedt, Inc., Newton, NC,) syringes. Blood was sampled after the
p.m. milking and placed on ice. Blood was then centrifuged for 0.5 hr (2000 x g), plasma
collected, and plasma frozen at -20C for future analyses.

136
Glucose in plasma was analyzed following the colorimetric procedure of
Gochman and Schmitz (1972). Plasma was filtered with 16 X 174 mm standard model
serum filters (Fisherbrand, Fisher Scientific, Pittsburgh, PA) and analyzed directly with
an automated analyzer (Bran+Luebbe, Model II, Bran+Luebbe Analyzing Technologies,
Elmsford, NY).
Plasma hormones. Double antibody radioimmunoassay was performed for
determination of insulin and insulin-like growth factor-1 (IGF-1) following the
procedures of Abribat et al. (1990). Second antibodies for use in the assays were
prepared in Florida native sheep maintained at the University of Florida Dairy Research
Unit. Sheep were injected subcutaneously with guinea pig and rabbit gamma globulins
and reinjected 2 wk later. Sheep were bled at 2 and 6 wk after the second injection and
the serum obtained was pooled and frozen. Second antibodies of sheep anti-guinea pig
and sheep anti-rabbit in the pooled plasma were used in the assays. For a complete
description of the antibody collection, preparation, and iodination methods, see Garcia-
Gavidia (1998).
Plasma insulin concentration was determined following procedures described by
Soeldner and Sloane (1965) as modified by Malven et al. (1987). Approximately 100 pg
of highly purified insulin (Sigma Immunochemicals, St. Louis, MO) was dissolved in 30
mM of HC1 (pH = 2.5) in an ultrasonic water bath. This stock insulin was diluted in an
assay buffer of 0.33 M borate, 0.01% merthiolate, and 0.5% BSA to give a final
concentration of 100 ng/ml. Standards of 0, 0.3, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10, 15,20, 25,
and 30 ng insulin/ml were prepared from the solution of insulin in the BSA buffer. First
antibody (guinea pig anti-bovine insulin, Sigma Chemical, Co., St. Louis, MO) was

137
dissolved in assay buffer with BSA at 1:20,000, and sheep anti-guinea pig second
antibody was diluted in borate/EDTA assay buffer.
Plasma samples (100 pi) were pipetted into 12 x 75 mm borosilicate tubes (in
duplicate) to which 100 to 200 pi of assay buffer with BSA then was added. Immediately
afterward, 100 pi of primary antiserum were added to all but the total count and non
specific binding tubes, and all tubes received 100 pi of iodinated (I125) insulin. Samples
were vortexed 60 s on a plate vortexer and incubated for 24 h at 4C. After incubation,
100 pi of sheep anti-guinea pig second antibody and 100 pi of normal guinea pig serum
(1:100) were added to all but the total count tubes. After incubating for 10 min, 0.75 ml
of 15% polyethylene glycol in borate buffer were added to all tubes except total count
tubes. Tubes then were vortexed, incubated for 10 min, centrifuged (2000 x g) in a
refrigerated (4C ) centrifuge (RC-2B, refrigerated centrifuge, Sorvall Instruments,
Newtown, CT) for 30 min, decanted, and inverted on absorbent paper till dry. Bound
radioactivity in dry tubes was measured with a Packard auto gamma counter (model B-
5005) and results were calculated by the spline radioimmunoassay data processing
procedure.
IGF-1 was extracted from its binding proteins following the procedure of Enright
et al. (1989). The extract solution was a 60:30:10 mixture (by volume) of ethanol,
acetone, and acetic acid. The extraction mixture (400 pi) was added to 100 pi of well-
mixed plasma in 12 x 75 mm borosilicate tubes and the two were mixed thoroughly for
15 sec on a vortexer and then allowed to stand for 30 min. Tubes then were centrifuged
(2000 x g) in a refrigerated (4C ) centrifuge for 30 min (RC-2B). Supernatant (250 pi)
was transferred to 12 x 75 mm polystyrene tubes. To neutralize the extraction mixture,

138
100 pi of 0.855 M Trizma base were added. A final 1:14 dilution was made by adding
350 pi of assay buffer.
The IGF-1 (highly purified Human IGF-1 from Upstate Biotechnology, Inc.,
Richmond, CA) for iodination was dissolved (0.5 pg/pl) in 0.1-M acetic acid (pH = 2.5).
Highly purified bovine IGF-1 supplied by Monsanto Company (St. Louis, MO) was
dissolved in 0.1-M acetic acid (10 pg/100 pi) to prepare Stock 0. Stock solutions 1 and 2
were made by adding 10 pi of Stock 0 to 490 and 990 pi of assay buffer, respectively.
Using Stock 2, standards containing 0, 50, 100, 200, 300, 400, 500, 600, 800, 1000, 1200,
1500, and 1500 pg of IGF-l/ml were prepared.
First antibody, rabbit anti-bovine IGF-1 was provided by Drs. Louis Underwood
and Judson J. Van Wyk, Division of Pediatric Endocrinology, University of North
Carolina, Chapel Hill, NC. The first antibody was dissolved in assay buffer [200 mg of
protamine/1, 4.4 g/L of sodium monobasic phosphate, 10 ml of 2% sodium azide, 3.72
g/L of EDTA (0.013 M), and 2.5 g/L of BSA] at a 1:4000 ratio. Second antibody (sheep
anti-rabbit) was diluted in EDTA-PBS for use.
Ten microliters of plasma extract were combined with 190 pi of assay buffer in
duplicate. One hundred pi of diluted primary antiserum and iodinated IGF-1 were both
added to all tubes immediately thereafter. Tubes were vortexed on a plate vortexer and
allowed to incubate for 20 to 30 h at 4C. Diluted sheep anti-rabbit antibody (100 pi) and
50 pi normal rabbit serum (1:50) were added to all but total count tubes and allowed to
stand for 30 min. Assay buffer with 6% polyethylene glycol (1 ml) then was added to all
but total count tubes. Tubes were vortexed, allowed to stand for 15 min, centrifuged for
30 min (2000 x g) at 4C (RC-3B, refrigerated centrifuge, Sorvall Instruments), and then

139
decanted. After draining and drying on absorbent paper, bound radioactivity in tubes was
measured using a Packard auto gamma counter (model B-5005) and results were
calculated by the spline radioimmunoassay data processing procedure.
Grazing time and organic matter intake. Grazing time was measured in
periods 1 and 2 using vibracorders (Kienzle Co., Germany). Each cows grazing activity
was recorded for 24 h in Period land for 48 h in Period 2. The vibracorders were
fastened to metal yokes that were hung over the neck of the cows and fastened with cloth
belts and metal buckles. A freely swinging pendulum with an attached stylus inside the
vibracorders marked waxed charts. At the end of each measurement period the charts
were collected. A planimeter was used to measure the markings on the chart to estimate
grazing time.
Chromium-mordanted fiber was used as an inert marker to determine dry matter
intake. In Periods 1 and 2, 10 to 15 forage samples were collected across all pastures and
composited. Efforts were made to gather forage of quality similar to that estimated to be
consumed. Fiber from the forage was chromium mordanted according to the method of
Udn et al. (1980). Forages were dried at 55C and ground with a stainless steel 2-mm
screen (Thomas-Wiley Laboratory Mill, Thomas Scientific, Philadelphia, PA). The
dried, ground forage was boiled approximately 2 h in a mixture of water and liquid
laundry detergent (approximately 100 g of forage/L of solution) to isolate the cell wall
fraction. After boiling, the fiber was washed repeatedly with water to remove all soap,
rinsed with acetone, dried at 105C, and weighed. The dried forage (500 to700 g) was
placed in an 8-L metal container. Sodium dichromate (100 to 140 g) was dissolved in
approximately 4 1 of water and added to the forage. Addition of chromium (as sodium

140
dichromate) equaled 7% of the fiber DM. This slurry was sealed with aluminum foil and
heated at 105C for 24 h in a drying oven. The liquid was poured off and the fiber was
rinsed gently to remove unbound Cr. Ascorbic acid (Aldrich, Milwaukee, WI) at half
the dry fiber weight was mixed with water, added to the fiber, and allowed to stand for 1
to 1.5 h. The fiber was rinsed thoroughly with tap water and dried at 105C. Three 0.02
g of mordanted fiber were weighed into 28-g gelatin capsules (Jorgenson Laboratories,
Loveland, CO). Excess mordanted fiber prepared for use in Periods 1 and 2 were
combined for use in Period 3. Average Cr concentration in the mordanted fiber for
dosing was 62,700 ppm (OM basis).
In each period, all cows on trial were dosed orally with nine gelatin capsules
containing Cr-mordanted fiber (27 g, as-fed). Capsules were administered with a
multiple dose balling gun (NASCO, Ft. Atkinson, WI). Cows were dosed after the
evening milking 3 d prior to the end of each period. Samples of feces were collected via
rectum at 0, 12, 15, 18, 21, 24, 27, 36, 42, 48, 60, 72, and 84 h post-dosing. Collections
were made on pasture at approximately h 15, 18, 21, 27, and 42 as volunteered by the
cow.
Fecal samples were refrigerated (maximum time of 96 h) until they could be dried
(55C for a minimum of 48 h). Dry samples were ground through a 1-mm screen
(Thomas-Wiley Laboratory mill, Philadelphia, PA). Ground samples (2 g) were dried at
105C and ashed at 550C for determination of DM and OM according to AO AC (1990)
procedures. Ash was digested on a hot plate in a solution containing H2PO4 (with added
MnS04) and KBr03 and analyzed for Cr by atomic absorption spectrophotometry

141
(Atomic Absorption Spectrophotometer, Model 5000, Perkin Elmer, Norwalk, Conn.)
following the methods of Williams et al. (1962).
Results from the intake study were evaluated with PROC NLIN using the method
of Pond et al. (1987; Appendix 1). Parameters generated by this program were used to
estimate fecal output for each cow. Estimates were based on the following assumptions:
1) supplement intake was the same for all cows within a pasture replicate,
2) supplement digestibility was constant regardless of forage intake,
3) digestibility of forage was affected by the level of supplement intake, as
determined by the equation of Moore et al. (1999; Appendix 2).
Theoretically, fecal output should equal total intake multiplied by the indigestible
fraction of a feed. Because fecal output observed, based on the mordanted-fiber
methodology, was not equal to the fecal output predicted based on forage and supplement
digestibilities, an iterative SAS (1991) program (developed by Dr. J. E. Moore) was
employed to adjust the estimate of bermudagrass intake until the difference between fecal
output observed and predicted differed by less than 0.01 kg/d (Appendix 2).
Expected diet digestibility (%) = [(bermudagrass intake, kg bermudagrass
digestibility, %) + (silage intake, kg silage digestibility, %) + (supplement intake, kg *
supplement digestibility, %)]/total intake, kg. Because feeding concentrate supplements
often alters forage digestibility (Arriaga-Jordan and Holmes, 1986; Berzaghi et al., 1996),
the iterative program also employed the equation of Moore et al. (1999; Appendix 2 to
adjust total diet digestibility.
Feed sampling. Forage was collected once each period to characterize forage
nutritive value (Table 4.2). Forage was collected in a manner similar to that used for

142
chromium mordanting as previously described. Samples taken from a fresh paddock in
each pasture were dried at least 48 h at 55C, and ground through a 1-mm screen
(Thomas-Wiley Laboratory mill, Philadelphia, PA). Samples within pasture within
period were analyzed by the University of Florida Forage Evaluation Support Laboratory,
Gainesville. For determination of organic matter (OM), dried samples were ashed for at
least 4 h at 500C. The modified aluminum block procedure of Gallaher et al. (1975)
was used to digest samples prior to analysis for N by the method of Hambleton (1977).
Crude protein (CP) was then calculated as N 6.25. Determination of neutral detergent
fiber (NDF) and IVOMD concentrations were made using the procedures of Golding et
al. (1985) and Moore and Mott (1974), respectively.
Silage and supplement samples were collected three times in each period
(approximately every 8 d) and frozen till future analysis. Silage samples were dried at
55C for 48 h for determination of % DM. Dried silage was ground, and an equal weight
of sample within period was composited and submitted to the DHI Forage Testing
Laboratory, Ithaca, NY, for analysis. Equal weights (as-fed basis) of supplement were
composited by period and submitted to the above lab for analysis.
Statistical Analysis
Animal measures. One cow was removed from the trial during Period 2 due to a
health problem unrelated to treatment. A replacement cow was used in Period 3 to
maintain the stocking rate, but her data were not used in the analyses.
Most data were analyzed using the GLM procedure of SAS (1991) with the
following model:

143
Y¡jk= u + a¡ + Pj + Y k(j) + Al + e¡jki,
where
]i = overall mean
cq = effect of cow
Pj = effect of treatment
yk(j) = effect of pasture(trt)
A| = effect of period
¡jki = effect of residual error.
Single degree of freedom contrasts for treatment were housing (1+2) vs. (3 + 4),
bST (1 + 3) vs. (2 + 4), interaction (1 + 4) vs. (2 + 3), and silage supplement (4 vs. 5).
Treatment effects were considered significant at P levels < 0.05 and trends at P < 0.10.
Temperature measures. Plots of the temperature data were evaluated visually
and readings exhibiting spontaneous spiking and readings outside of 38 to 40C were
deleted. Greater signal variability for cows on pasture resulted in an average of 13.7% of
readings being deleted vs. an average of 8.5% of readings deleted for cows in the bam.
Visual evaluation showed three general trends in the data. First, an increase in
body temperature was observed through the daylight hours until the p.m. milking.
Secondly, a parabolic decrease and subsequent increase in temperature was observed as
cows went onto showers for cleaning, were milked, and returned to pasture. Thirdly, a
decrease in temperature was observed through the night until after the a.m. milking.
To evaluate the curves, the data were divided into these respective segments on
the horizontal (time) axis. Because bam and pasture cows did not arrive at the shower at
the same time and because time on the showers and time back to pasture varied slightly
for each group, further adjustments on the horizontal axis were necessary. For Segment

144
1, all data were shifted so that peak temperature for all cows occurred at 1624 h, just
before milking. For Segment 2, the time from peak pre- to peak post-shower
temperatures was adjusted to equal 2 h 42 min. This adjustment allowed the minimum
temperature for all cows in section 2 to occur at 1745 h, during the time of showering,
milking, and drinking. Segment 3 data were shifted so that all cows had near-peak or
peak temperature at 1906 h, when cows returned to pasture.
After adjustments, data were modeled by segment using PROC MIXED
procedure of SAS (Littell et al., 1996). Because our interest was in plotting the effect of
treatment over time without individual cow effects, cow was not included in the model.
Regression coefficients generated from the analysis were used to plot the data.
The resultant curves were evaluated visually for congruity of temperature between
segments. Since the generated curves were not always congruent from one section to the
next, algebraic operands using dummy variables were applied to the original data set to
force the joining of sections within each curve (Draper and Smith, 1981). Both PROC
MIXED and PROC GLM were used to evaluate the adjusted curves. The curves were
modeled using PROC GLM since the PROC MIXED method partitioned out only very
little variability due to cow within treatment and period. (After partitioning, overall
residual error was greater than residual error due to Cow(treatment by period) by a factor
greater than 106.)
Several different points in time (hour) were substituted into the model equation
and the ESTIMATE procedure of GLM was then used to calculate differences in
temperature between treatments. After taking the derivative of the model equation with

145
respect to hour (dy/dhour), the ESTIMATE procedure was used to determine differences
among the slopes of the treatments.
Results and Discussion
Grazing Time and Intake of Organic Matter
Effect of housing. Per design, keeping cows in the bam limited their opportunity
to graze (Table 4.3). Cows on pasture spent more time (P < 0.001) in grazing activities as
measured by vibracorder than did cows kept in the bam from 0800 to 1500 h (6.9 vs. 5.3
h of grazing time/cow per d). The estimates of grazing time for cows grazing pastures
through the day in this study are less than those reported by Stobbs (1970), who tested a
variety of forage species and fed little supplement. Results are similar to those of
Combellas et al. (1979) who reported 6.6 hours of grazing/d for heifers receiving 6 kg/d
of supplement. However, direct comparison of grazing times is difficult due to
differences in milk production, BW, environment, forage species, and pasture
management.
Though grazing time was greater for cows on pasture, grazing intensity appeared
greater for cows housed in bams (Figure 4.1), and the estimates of forage OMI indicate
that grazing time did not affect forage intake (Table 4.3). Average forage OMI of BG,
excluding cows on the silage treatment, was 9.2 kg/d, or 1.58% of BW. Because forage
OMI was unaffected by grazing time, housed cows must have grazed with greater
harvesting efficiency [defined as intake over time (Barton et al., 1992; Krysl and Hess,
1993)]. This might have occurred as a result of an increased bite rate due to temporary
deprivation from pastures as has been reported by Greenwood and Demment (1988).

Table 4.3. Influence of housing (0800 to 1500 h on pasture or in bams with fans and sprinklers), bST, and bST with supplemental
silage on organic matter intake (OMI) of Holstein cows grazing Tifton 85 bermudagrass pastures.
Item
Pasture
-bST +bST
-bST
- Bam -
+bST
+silage
+bST
SEM
Housing
Probability
Housing
bST x bST
Silage
Grazing time, h/d
6.5
7.2
5.0
5.6
4.0
0.4
***
*
NS
***
BG2 OMI, kg/d
9.5
9.4
8.9
9.0
7.4
0.6
NS
NS
NS
***
Sup.3 OMI, kg/d
6.7
8.0
7.3
7.9
7.8
0.2
NS
***
*
NS
Silage OMI, kg/d
-
-
-
-
3.0
-
-
-
-
-
Total4 OMI, kg/d
16.2
17.4
16.2
16.9
18.2
0.5
NS
**
NS
**
BG OMI, %BW5
1.65
1.61
1.52
1.54
1.25
0.10
NS
NS
NS
***
Sup. OMI, %BW
1.16
1.37
1.26
1.35
1.32
0.04
NS
***
*
NS
Silage OMI, %BW
-
-
-
-
0.53
-
-
-
-
-
Total OMI, %BW
2.81
2.98
2.78
2.89
3.10
0.09
NS
*
NS
*
'p < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.
2Tifton 85 bermudagrass.
3 Supplement.
4Total OMI (BG OMI + Sup. OMI) = silage OMI of cows receiving the bam + silage + bST treatment.
5Body weight.

147
Figure 4.1 Vibracorder charts for cows treated with bST and
housed in bams from 0800 to 1500 h (A) and for cows housed
on pasture (B). Note the greater grazing intensity for cows
housed in the bam during the day.

148
Housing had no effect on supplement intake (7.4 vs. 7.6 kg of OM/d for unhoused
and housed cows, respectively), corresponding with milk production responses. Total
OMI/d also were unaffected by housing treatment with OMI of 16.8 and 16.6 kg/d (2.90
and 2.84% of BW) for unhoused and housed cows, respectively.
Effect of bST. Cows treated with bST grazed approximately 45 min more (P <
0.05) than untreated cows (6.3 vs. 5.6 h of grazing/d) each day, however, forage OMI
was unaffected by bST treatment. Given the conditions imposed, cows treated with bST
would not be expected to increase intake of forage OM since supplement provided was
increased with increasing milk production.
For bST-treated cows consuming only pasture, forage intakes likely will increase
given adequate amounts of available herbage (Hoogendoom et al., 1990). While intake
responses to bST treatment for cows grazing pasture may not be observed directly
(Hoogendoom et al., 1990) or only slowly discemable (e.g., after 22 wk; Peel et al.,
1985), Michel et al. (1990) reported increases in pasture intake within 4 wk of initial bST
administration. DUrso et al. (1998) reported that ewes increased intake due to bST
treatment, particularly at greater SR. The authors reported that hormone-treated animals
grazed less selectively and ate faster.
The OMI from supplement increased for bST-treated cows because of the
management strategy of feeding the amount of supplement based on milk production.
Cows injected with bST averaged 8.0 kg of supplement OMI/d vs. 7.0 kg/d for untreated
cows. Based on the supplementation strategy of feeding 0.5 kg of supplement (as-fed
basis)/kg of daily milk production, it appears that cows on pasture and treated with bST
received excess supplement. However, this may be an artifact of using least squares

149
means because supplement OMI matched the raw means for milk production of each
treatment.
Increased supplement OMI in response to bST treatment was greater for cows
kept on pasture than for cows kept in bams during the day (housing by bST treatment
interaction, P < 0.05), matching raw means of milk production.
Across all treatments, total OMI averaged 17.0 kg/d (2.87% of BW) and were
greater than those reported for TMR-fed cows in a similar stage of a lactation and milk
production under heat stress conditions (Staples et al., 1988). Housing had no effect on
total OMI/d, contradictory to the results of Zoa-Mboe et al. (1989).
Effect of supplemental silage. Feeding silage curtailed grazing time by more (P
< 0.001) than 25% (5.6 vs. 4.0 h of grazing/d). Phillips and Leaver (1986) noted that the
effect of supplemental forage provision on grazing time depended on whether the
supplemental forage was a substitute for or a supplement to the grazed forage. With
decreased grazing time came a concomitant decrease (P < 0.001) in BG OMI of about
18% (from 9.0 to 7.4 kg/d, respectively). However, total forage OMI was increased
approximately 17% with supplemental silage (from 9.0 to 10.5 kg of forage OMI/d).
Moran and Stockdale (1992) also compared intake and milk production of cows fed
pasture alone or pasture with supplemental com silage. They reported no effect of silage
on pasture DMI, but pasture intake was numerically less than that for unsupplemented
cows.
As feeding silage did not affect milk production, supplement OMI was not
different between the two silage treatments. Cows fed silage consumed more (P <0.01)
total OMI per day by nearly 8%. Whereas the equation of Moore et al. (1999) was used

150
to adjust forage digestibility due to associative effects of supplement feeding and thus
forage intake estimates, no additional adjustments to forage digestibility were made for
cows consuming com silage. If feeding com silage resulted in a greater depression of
forage digestibility, OMI was over-predicted.
Milk Production and Composition
Effect of housing. Daytime housing with fans and sprinklers did not affect milk
production (P < 0.11) of cows. Numerically, however, housed cows produced nearly 5%
more milk than unhoused cows (17.8 vs. 17.0 kg/cow per d, respectively) (Table 4.4).
Housing cows during the day tended (P <0.10) to increase production of 4% FCM by
5.5% (17.2 vs. 16.3 kg/d).
That differences between housing regimes did not significantly affect raw milk
production in this study is surprising given the greater energy expenditure of cows kept
on pasture. Maintenance costs for heat stressed cows increase above thermoneutral, but
intake typically declines with increasing temperature; thus milk production decreases
(Collier and Badenga, 1985). The greater milk production from housed cows despite
having similar OMI to those of pastured cows indicates a greater efficiency of nutrient
utilization for housed cows. It is certain that housed cows expended less energy for
maintenance because they walked less and experienced less heat stress.
Using cows of low milk production may have limited the ability to detect
treatment differences. Comparisons of shade vs. evaporative cooling using cows
producing much greater quantities of milk have been made (Chan et al., 1997; Chen et
al., 1993). Chan et al. (1997) reported a tendency of increased milk production with

4.4. Influence of housing (0800 to 1500 h on pasture or in bams with fans and sprinklers), bST, and bST with supplemental silage on
milk production and composition of Holstein cows grazing Tifton 85 bermudagrass pastures.
Pasture Bam Probability
+silage Housing
Item
-bST
+bST
-bST
+bST
+bST
SEM
Housing
bST
x bST
Silage
Milk yield, kg/d
16.2
17.7
17.0
18.5
17.9
0.6
NS
* *
NS
NS
4% FCM1, kg/d
15.3
17.3
16.3
18.0
17.6
0.6
t
***
NS
NS
Milk fat, %
3.65
3.80
3.76
3.85
3.90
0.04
NS
NS
NS
NS
Milk fat, kg/d
0.59
0.68
0.64
0.70
0.69
0.03
NS
***
NS
NS
Milk protein, %
3.22
3.23
3.23
3.27
3.26
0.03
NS
NS
NS
NS
Milk protein, kg/d
0.52
0.57
0.54
0.60
0.58
0.02
t
***
NS
NS
MUN2, mg%
18.0
18.5
18.1
18.0
15.5
0.3
NS
NS
NS
***
SCC3, x 1000 cells
747
610
443
834
545
236
NS
NS
NS
NS
'P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.
2Fat corrected milk.
3Milk urea nitrogen.
4Somatic cell count.

152
evaporative cooling similar to the increases found in this study, while Chen et al. (1993)
noted a 9% increase in milk production with evaporative cooling over shade alone.
Milk fat percentage was unaffected by treatment, but housed cows tended to have
numerically greater (P <0.12) milk fat production. Cows kept in the bam during the day
tended (P <0.10) to produce greater quantities of milk protein (0.57 vs. 0.55 kg/d) than
cows on pasture, largely due to milk production.
Effect of bST. Injections of bST increased (P <0.01) milk production
approximately 9% (18.1 vs. 16.6 kg/d) (Table 4.4). Use of bST increased (P < 0.001)
production of 4% FCM approximately 12% (17.7 vs. 15.8 kg/d).
In a review, West (1994) reported that responses to bST treatment by cows in hot
environments ranged from 3.4 to 48.6%, and response to bST typically decreased with
increasing amount of pre-treatment milk production (Lotan et al., 1993; West et al.,
1990). Thus, given the relatively low amount of pretreatment milk production, greater
responses to bST might have been expected. However, the percentage increase in
production in response to bST was similar to that found by Staples et al. (1988) whose
cows produced similar quantities of milk in a 30-d trial.
Estimates of nutrient intake based on NRC recommendations suggest that nutrient
intake did not prevent cows on this trial from producing 20 kg of 4% fat corrected milk/d
(Table 4.5). This suggests that either maintenance costs were greater than NRC (1989)
estimates, or nutrient intake, particularly energy, was overestimated.
Although bST treatment did not affect milk fat concentration, the greater
percentage increase in 4% FCM production compared to the percentage increase in milk
production (12 vs. 9%) partially resulted from numerically greater concentrations of milk

TABLE 4.5. Calculated daily intake of nutrients by cows grazing Tifton 85 bermudagrass (BG) pastures and not treated (-bST) or
treated (+bST) with exogenous growth hormone. An additional treatment tested the effect of feeding com silage (Silage) to cows
treated with bST.
Ingredient
Item
NEL
DM
NDF
ADF
CP
Ca
P
Mg
K
Na
S
Cl
Fe
Zn Cu
Mn
Mcal/d
- kg/d -
- - g/d
mg/d
-bST
BG
12.5
9.7
7.5
3.4
1.4
40
30
25
164
4
28
51
530
365
49
411
Supplement
14.1
7.7
2.9
1.8
1.3
89
40
25
104
97
15
95
3869
1490
331
716
Silage
















Total
26.6
17.4
10.5
5.2
2.8
129
70
50
268
101
43
146
4400
1855
380
1127
+bST
BG
12.5
9.7
7.5
3.4
1.4
40
30
25
164
4
28
51
530
365
49
411
Supplement
15.9
8.7
3.3
2.0
1.5
100
45
28
117
110
17
107
4372
1683
374
809
Silage
















Total
28.4
18.4
10.8
5.4
2.9
141
75
53
281
114
45
159
4902
2049
423
1220
+bST + Silage
BG
10.1
7.8
6.1
2.8
1.1
33
24
20
132
9
23
41
426
294
39
330
Supplement
15.7
8.6
3.3
2.0
1.5
99
45
28
116
109
17
106
4322
1664
370
800
Silage
4.4
3.2
1.8
1.1
0.3
8
9
6
36
0
3
10
162
84
13
69
Total
30.2
19.6
11.2
5.8
2.9
140
77
54
284
112
43
157
4910
2042
422
1199
Requirement1
23.3
16.0
4.5
3.4
2.2
84
54
32
144
29
32
40
800
640
160
640
'Calculations based on NRC requirements for a 500 kg cow producing 20 kg of 4.5% FCM and gaining 0.275 kg/d. Intake was
assumed to be 3.2% of BW.

154
fat from cows treated with bST. The numerical increases in milk fat concentration are
consistent with reports of increased milk fat concentration due to bST treatment in short
term trials and especially when cows are in negative energy balance (Chalupa and
Galligan, 1989; Hoogendoom et al., 1990). This suggests that the increased feed
provided to cows treated with bST (due to increased milk production) did not completely
compensate for the increased energy associated with increased milk production.
However, calculation of energy balance using NRC (1989) equations and feed intake
estimates did not confirm differences in energy balance due to bST treatment (data not
shown).
Increased (P < 0.001) daily production of milk fat and milk protein occurred
primarily because of the increase in milk production due to bST (Table 4.4).
Effect of supplemental silage. Feeding supplemental silage in the bam had no
effect on milk production, 4% FCM production, nor milk fat and protein concentrations
or quantities. Similar results have been reported by Australian researchers utilizing
mixed warm- and cool-season pastures (Moran and Stockdale, 1992) and by researchers
studying use of com silage with temperate pastures (Holden et al., 1995).
When pasture was limited or when supplemental forage was of greater quality
than the grazed forage, milk yield typically increased with silage inclusion (Huber et al.,
1964; Phillips, 1988). No difference in herbage disappearance due to any treatment was
observed (data not shown). The lack of influence of silage supplementation indicates that
forage availability did not limit production of cows fed silage and also implies that the
increased stocking rate used for that treatment was appropriate.

155
The equation used to predict NEl of BG and silage indicates the BG to be of
much lesser energy concentration, but this likely underestimates the quality of the BG.
West et al. (1997) reported that Tifton 85 can make up a substantial portion of dairy cow
rations with limited effect on intake and production. The authors reported that the NDF
of BG underwent greater and more rapid in vitro digestion than NDF of com silage and
rates of passage were not different between the cows fed a com silage-based control diet
and diets having 30% BG hay, despite the fact that the BG diet was nearly 40% greater in
NDF concentrations.
Body Weight and Condition
Effect of housing. Housing cows during the day promoted weight gain. Cows
kept on pasture lost (P < 0.001) approximately 11 kg of BW/24-d period, but cows kept
in the bam gained approximately 6 kg of BW/24-d period (about 1% of BW/month)
(Table 4.6). These differences in BW changes further highlight the lower maintenance
costs for housed cows due to reductions in activity and heat stress.
Effect of bST. On average, cows treated with bST gained small amounts of BW
(2.5 kg/24-d period), but cows not given bST lost about 7 kg of BW/24 d period (Table
4.6). The BW gain response was likely a result of the increased supplement provided to
bST-treated cows.
Effect of supplemental silage. Cows receiving silage tended (P <0.10) to not
gain as much as those not fed additional roughage in the bam. Because OMI was
increased for cows fed silage with no change in milk production, partitioning of nutrients
to BW gain might be expected. However, changes in BW do not necessarily reflect
changes in body reserves, particularly in trials with a change-over design and involving
feeds with different physical characteristics (Combellas et al., 1979, p. 308). Cows not

Table 4.6. Influence of housing (0800 to 1500 h on pasture or in bams with fans and sprinklers), bST, and bST with supplemental
silage on body weight (BW), body condition score (BCS), respiration rates (RR), and concentrations of plasma insulin and insulin-like
growth factor-1 (IGF-1) of Holstein cows grazing Tifton 85 bermudagrass pastures.
Item
Pasture
-bST +bST
-bST
- Bam -
+bST
+silage
+bST
SEM
Housing
Probability
Housing
bST x bST
Silage
ABW", kg/24-d
-12.9
-8.8
-1.3
13.8
5.4
5
***
**
NS
t
ABCS3/24-d
-0.17
-0.29
-0.24
-0.04
-0.29
0.14
NS
NS
NS
NS
RR, breaths/min
89
88
69
70
68
2
***
NS
NS
NS
IGF-1, ng/ml
88
141
91
144
146
7
NS
***
NS
NS
Insulin, ng/ml
0.58
0.61
0.52
0.57
0.61
0.01
*
t
NS
NS
'P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.
Change in body weight.
3Change in body condition score.

157
fed supplemental silage could have had greater gut fill because they consumed more BG
which contained greater concentrations of fiber and indigestible OM. Because neither
milk production nor weight gain increased with the increased OMI, efficiency of nutrient
utilization may have decreased with supplemental com silage, or intake of metabolizable
energy may not have been increased. All cows lost body condition and the losses were
typical for cows on pasture in the summer. Feeding silage tended (P < 0.11) to lower
body condition score, but numerical changes indicated greater tissue losses for cows
receiving the additional forage (Table 4.6). Others (Moran and Stockdale, 1992; Holden
et al., 1995) reported numeric increases in BW gain or condition score with similar levels
of supplemental silage, but the trials were 8 to 10 wk in duration. Our results may be a
consequence of the postulated difference in gut fill between the two treatments and if so
indicates that condition score measurements were based upon more than changes in fat
depot size.
Plasma IGF-1 and Insulin
Effect of housing. Housing had no effect on IGF-1 at any sampling date.
McGuire et al. (1995) reported 50% reductions in circulating IGF-1 concentrations 48 h
after the initiation of feed deprivation, but differences due to short-term deprivation were
undetectable.
Greater (P < 0.05) insulin concentrations were detected for cows kept on pasture
continually. Average concentrations were 59.5 and 54.5 ng of insulin/mL for pasture and
bam cows, respectively. Others have reported decreased plasma insulin concentrations
during the summer (Denbow et al., 1986), but results from work with cows in
environmental chamber studies are mixed. Johnson et al. (1991) reported no effect of

158
temperature on plasma insulin concentrations in lactating cows, but Itoh et al. (1998)
reported decreased insulin concentrations in non-lactating cows exposed to heat. Calves
exposed to heat had decreased insulin concentrations within 0.5 h post-exposure and
differences were maintained through 24 h of observation (Takahashi et al., 1986).
Amounts of supplement fed do not explain the differences in insulin
concentrations because supplement provision was not different between housing
treatments. One explanation may be related to sampling time. Cows kept in bams did
not eat from approximately 0830 to 1800 h. Blood samples, collected at approximately
1700 h, would have been taken near the time of greatest nutrient depletion. These
changes are corroborated by the fact that plasma insulin concentrations of cows fed silage
in bam were similar to those of cows on pasture. In sheep infused with glucose, insulin
concentrations increased to a greater degree during heat stress (Achmadi et al., 1993).
Thus, the difference in plasma insulin concentrations between housing treatments may
reflect both greater sensitivity to available nutrients in cows on pasture and a decrease in
available nutrients for cows kept in the bam.
Effect of bST. Use of bST increased (P < 0.001) concentrations of plasma IGF-1
over controls nearly 70% (84.5 vs. 143 ng/ml of plasma). The bST treatment likely
affected IGF-1 both directly and indirectly via increased concentrate provision. McGuire
et al. (1992) reported that response to bST increased with increasing plane of nutrition.
The IGF-1 concentrations in bST-treated cows were similar to those reported by Staples
et al. (1988), but IGF-1 concentrations of untreated cows were about twice the
concentration reported for controls in that study.

159
Insulin concentrations tended (P <0.10) to increase due to bST at the second
sampling date and as an average of all sampling dates. In a study involving increasing
plane of nutrition and bST administration, plasma insulin concentrations increased with
bST treatment for cows fed diets greater in energy density and crude protein
concentration (diet by bST interaction) (McGuire et al., 1992).
Effect of supplemental silage. Feeding silage increased (P < 0.05) plasma IGF-1
concentrations at the second blood sampling date only. Concentrations of plasma IGF-1
might be expected to increase based on the results of McGuire et al. (1992) if total energy
intake was increased in this group of cows.
Respiration Rates and Body Temperatures
Effect of housing. Cows kept on pasture during the daylight hours took nearly
30% more (P < 0.001) breaths/min than those housed in the bam (89 vs. 69 per min for
bam and pasture cows, respectively). The RR of housed cows were somewhat greater
than those reported for cows maintained in a thermoneutral environment, indicating some
level of heat stress, but RR were somewhatlower than those typical of cows subjected to
heat stress (Manalu et al., 1991; Zoa-Mboe et al., 1989). The RR of cows under shade on
pasture were only 10% less than the RR of shaded cows in dirt lots reported by Zoa-
Mboe et al. (1989), but the cows in this study had much lower levels of milk production.
Further, a report of RR of 120 breaths/min for unshaded lactating cows (Zoa-Mboe et al.,
1989) illustrates the degree of cow discomfort under Southeastern conditions without
some method of reducing heat load.
By 0900 h, cows on pasture were hotter than cows kept in the bam (Figure 4.2).
Temperatures of all cows continued to increase, peaking at approximately 1630 h, the

Temperature,
39.8 -
39.6 -
39.4
39.2
39.0
38.8
38.6
38.4
38.2
Pasture
Bam
Hour
Figure 4.2. Effect of housing on body temperatures of cows measured over a 24-h period a averaged over bSt
treatment regimes.
4:30 AM

161
average time at which cows arrived at the parlor for milking. The temperature increases
were greater for pasture cows, however, as indicated by the greater slope, and at 1630 h,
temperatures were approximately 0.5 C greater for cows coming from pasture (39.5 vs.
39.0 C). Temperatures decreased immediately thereafter due to the cooling effect of the
shower wash system. After milking, temperatures increased for both treatments as cows
returned to pasture. This increase post p.m. milking was greater for bam cows,
suggesting greater grazing activity than cows given access to pasture continually.
Effect of bST. Increased RR with bST treatment have been reported (Zoa-Mboe
et al., 1989) but did not occur in this study, in agreement with Manalu et al. (1991). Cole
and Hansen (1993) also reported no effect of bST on RR, but RR were much greater in
their study and the authors suggested that the lack of difference due to treatment might
have been due to second-phase panting which is associated with respiratory alkalosis
(Bianca and Findlay, 1962).
Cows treated with bST had greater temperatures (p< 0.05) throughout the day,
although temperatures were similar in the early morning (0730 to 0800) after a period of
night cooling (Fig. 4.3). Cows not injected with bST increased body temperature at a
slower rate from approximately 1100 h until 1630 h (Fig. 4.3). Treated cows had a nearly
linear rate of temperature increase from the morning to evening milking. These results
agree with the findings of others (Zoa-Mboe et al., 1989; West et al., 1990, 1991;
Elvinger et al., 1992; Sullivan et al., 1992; Cole and Hansen, 1993) and contradicts early
reports (Mohammed and Johnson, 1985; Manalu et al., 1991) that bST had no effect on
rectal temperatures. Although the greater body temperatures associated with bST have
been associated with increased milk production (West et al., 1990) work of Cole and

Temperature,
Hour
Figure 4.3. Effect of bST on body temperatures of cows measured over a 24-h period and averaged over daytime
bam and daytime pasture housing regimes.

163
Hansen (1993) suggests that bST increases body temperatures of non-lactating cows as
well.
Treatment with bST also affected body temperature patterns once cows returned
to pasture, with treated cows maintaining increased body temperatures far longer than
untreated cows. Though this temperature pattern for bST-treated cows appears to reflect
a greater drive to graze, such a drive was not confirmed with the forage intake data.
Therefore, cows receiving bST may have been more aggressive grazers (greater bite rate)
upon initial return to pastures.
Effect of supplemental silage. Cows fed silage in the bam had a different
temperature pattern than those not receiving silage (Figure 4.4). Body temperatures of
cows on both treatments reached the same temperature within an hour of grazing (1900h),
but temperatures of cows fed silage quickly dropped thereafter, suggesting that they spent
less time grazing. Cows not fed silage but treated with bST had greater drive to graze
than cows fed silage, and their temperatures were sustained until 0130 h, likely due to
increased grazing activity.
From approximately 0930 to 1430 h, cows on pasture did not differ in
temperature, regardless of bST treatment, whereas cows in the bam treated with bST had
greater temperatures than non bST-treated cows (Fig. 4.5). Milk production was greater
by bST-treated cows on pasture as well.
Conclusions
Use of exogenous bST increased milk production (1.5 kg/d; 9%) and 4% FCM
production (1.9 kg/d; 12%) of cows managed in a pasture-based system regardless of type
of heat abatement used. Economic benefit of its use will depend upon its cost vs. milk

Hour
Figure 4.4. Regression equation estimates of body temperatures of cows measured over a 24-h period and showing
interaction of bST (+ or -) and housing treatments.

Temperature,
39.8 -
39.6 -
39.4 -
39.2 -
39.0
38.8
38.6
38.4
38.2
B +
a B + S
Hour
Figure 4.5. Effect of bam plus bST (B +) vs. bam plus bST plus silage (B + S) treatment on body temperatures of
cows measured over a 24-h period.
4:30 AM

166
price. Body temperatures increased in cows treated with bST likely due to increased
metabolism associated with greater milk production and grazing activity. Milk fat and
protein averaged 3.79 and 3.24% respectively and was unaffected by treatments. Intake
of pasture was not affected by bST injections possibly because of greater intake of
supplement. Greater intake of supplement also may have resulted in better management
of body weight and greater concentration of plasma insulin of cows given bST.
Housing cows during the day effectively reduced heat stress as indicated by lower
body temperatures and respiration rate. Production of 4%FCM increased (0.9 kg/d) in
response to daytime housing. Though responses likely were not economical at this stage
of lactation, some form of cooling other than shade alone may have benefit for cows in
earlier stages of lactation. Daily OMI were not affected by housing system suggesting
that cows housed in cooling bams during periods of peak heat stress and deprived of feed
practiced compensatory intake when given access to pasture. Bam housing between
0800 and 1800 h did prevent body weight loss suggesting lower maintenance costs than
cows without access to fans and sprinklers and required to walk greater distance for
milking.
Provision of silage did not enhance milk production nor promote weight gain in this
study. Cows reduced pasture OMI approximately 0.5 kg for each 1 kg of silage OMI,
and the lack of production or gain response to silage indicates reductions in efficiency of
nutrient utilization.

CHAPTER 5
FINAL SUMMARY AND CONCLUSIONS
In the USA, interest in the use of pasture-based forage systems for dairy
production has increased in the past decade. Renewed interest in grazing for dairy cattle
has been driven primarily by tightened economic conditions in which production costs
increased while milk prices dropped. Southern producers wanting to know more about
grazing have had little information upon which to make management decisions. Most
information about dairy grazing in the USA comes from research conducted in temperate
climates and is of limited relevance for producers in the South whose primary forage base
is warm-season pasture. Thus, a series of experiments was conducted to quantify the
responses of lactating Holstein cows to different grazing systems and management
strategies.
The first two experiments tested the effects of grazing systems. Forages were
bermudagrass (BG; Cynodon spp. cv. Tifton 85) and rhizoma peanut (RP; Arachis
glabrata cv. Florigraze), two relatively new forages available to producers. The forages
were tested in combination with two stocking rates (SR) and two supplementation rates
(SUP). The SR differed between forages to account for the different growth rates of the
two species. The BG pastures were stocked at 5.0 or 7.5 cows/ha in 1995 and 7.5 and
10.0 cows/ha in 1996. The RP pastures were stocked at 2.5 and 5.0 cows/ha in 1995 and
5.0 and 7.5 cows/ha in 1996. Supplementation rates were 0.33 and 0.5 kg of supplement
(as-fed basis)/kg of daily milk production.
167

168
Cows grazing RP pastures produced more milk than cows grazing BG (17.3 vs.
16.2 kg/d), but milk was of lower fat concentration. Because production per land area
may be a more appropriate measure of profitability for dairies using grazing systems this
measure also was calculated. Despite lower milk production per cow with BG, milk
production per ha with BG pastures exceeded production per ha with RP pastures (118
vs. 87 kg of milk/ha per day) by nearly forty percent though this took more cows.
Across all treatments, cows lost an average of 6 kg/28-d period, with the majority
of the loss occurring during the first period. Cows grazing RP were more heat stressed,
having greater respiration rates, and they lost more BW (-10 vs. -5 kg/28-d period) than
cows grazing BG. These measures are indicative of greater energy expenditure
associated with greater milk production.
Tifton 85 and RP have both proven of acceptable quality for use in the diets of
high-producing dairy cows kept in confinement housing (Staples et al., 1997; West et al.,
1997), but dietary NDF and ADF concentration in these studies were much greater than
recommended by NRC (1989) and may have limited intake, particularly for BG-based
diets. Cows grazing RP pastures consumed 49% more forage OM than cows grazing BG
pastures (11.3 vs. 7.6 kg of OM/d) and supplement intakes were greater when cows
grazed RP because of their greater milk production.
In comparison with the NRC (1989) recommendation for feeding a reference cow
of 500 kg and producing 20 kg of 4% FCM/d, DMI of the BG-based diets were limiting,
and daily intakes of energy, CP, Ca and P were limiting when cows were fed the low
SUP.

169
Comparison of OMI with NRC estimates of nutrient requirements suggests that
OMI was over-predicted, particularly for RP pastures, but the data are subject to several
sources of error. Overestimates of intake, underestimates of maintenance requirements,
and overestimates of diet digestibility, (related to the prediction of associative effects) all
may have limited the accuracy of prediction.
The estimates of OM and nutrient intakes for cows grazing RP suggest that forage
quality was quite high, but the less than expected production responses obtained when
cows grazed this forage suggest that nutrients of RP were poorly utilized. Increased
maintenance costs, though likely greater due to increased heats of fermentation and milk
synthesis, would be unlikely to account for production amounts less than those predicted.
Thus, different feeding strategies with respect to supplements are likely necessary to
optimally utilize RPs better nutritive characteristics.
Use of RP may be of benefit in mixed swards if a compatible, high quality grass is
available. Poppi and McClennan (1995) reported that the benefit of legumes in pasture
may be due primarily to their effect on intake rather than an improvement in forage
nutritive value. The greater OMI of RP vs. that of BG suggests that the legume could be
useful in stimulating intake if used as a companion with an appropriate graminaceous
species.
Tifton 85 BG, despite large concentrations of fiber and moderate digestibility,
proved to be a desirable forage for milk production on a land area basis. The high
carrying capacity and the good response to supplement of cows grazing this forage are
useful attributes for forages in grazing systems.

170
Herbage mass was never limiting for cows grazing BG, regardless of SR but HM
appeared to be limiting when cows grazed RP at the high (7.5 cows/ha) SR. For BG, the
tendencies of improved production at greater SR suggest that this forage requires greater
management and utilization for optimal animal performance. Conversely, decreases in
production at the greatest SR for cows grazing RP suggest that quantity, rather than
quality, of available forage limited animal performance with this forage.
Cows grazing RP returned equal or greater income (milk income minus
supplement cost) on a per cow per day basis than cows grazing BG ($4.13 vs. $3.85/cow
per day) illustrating the higher digestibility and intake potential of RP. This advantage of
RP over BG pastures was greatest when the amount of supplement fed was lowest ($4.27
vs. $3.80/cow per day, compared to $3.99 vs. $3.90/cow per day for the low and high
SUP respectively). Feeding additional supplement was generated greater milk income
only when BG was grazed. Milk income minus supplement costs were $0.11/cow per
day greater for cows eating more supplement on BG but was $0.28/cow per day lower for
cows eating more supplement on RP. These responses reflect the effects of substitution.
One aspect of substitution not accounted for in this analysis is the potential for greater SR
when feeding more supplement to cows grazing RP pastures.
The greater dollar return on a per cow basis for RP pastures is dwarfed by the
greater income per unit land area capable with BG pastures. By these calculations, use of
BG resulted in a 40% greater dollar retum/ha. Average income/ha for BG was $28.95 vs.
$20.65 for cows grazing RP.
Supplementation rate affected all milk production and milk component responses
except SCC. Cows receiving the greater SUP produced more milk of lesser fat

171
concentration. Supplement likely increased growth of ruminal microbes and this would
explain the increased milk protein percentage with the greater SUP.
Feeding sizeable quantities of supplemental energy feeds can obscure the effects
of forage quality on animal performance (Waldo, 1986). Further, several researchers
(Blaxter and Wilson, 1963; Golding et al., 1976b; Arriaga-Jordan and Holmes, 1986)
have reported greater substitution with better quality forages. That appeared to be a
particular limitation with RP. With each additional kg of supplement fed above the low
SUP, cows produced an additional 0.87 kg of milk/d if grazing BG vs. an additional 0.43
kg of milk/d if grazing RP.
The response to supplement on a land-area basis was greater when cows grazed
BG than RP (132 and 110 kg of milk/ha per day at high and low SUP for BG vs. 90 and
83 kg of milk/ha per day at high and low SUP for RP). Both the lesser substitution of
forage with supplement by cows on BG and the greater carrying capacity of BG pastures
affected this response.
Surprisingly, SUP had no effect on changes in BW, nor were SUP by treatment
interactions detected. However, BW losses were numerically greater with the greater
SUP, in agreement with the observation that treatments supporting greater milk
production promoted BW loss. Feeding additional supplement caused a 10% increase in
RR (99 vs. 90 breaths/min).
Although total OMI increased approximately 2 kg/d with additional supplement,
forage OMI was reduced approximately lkg/d, and cows grazing RP pastures
experienced a greater decrease in forage consumption when fed more supplement
compared to those grazing BG pastures. The substitution of forage OM by supplement

172
OM (kg/kg) was 0.51 for RP and 0.18 for BG. Cows grazing BG pastures and provided
greater amounts of supplement increased total OMI by 22 % vs. a 10 % increase in total
OMI with additional supplement for cows grazing RP.
The limited improvement in production with RP over that with BG suggests that
use of adapted leguminous forages has little merit in these systems (Rouquette et al.,
1993). This likely will remain true as long as inexpensive by-product energy feeds are
available. However, production limits due to forage substitution may be offset by the
ability to increase SR, and to a greater degree with RP than BG.
The calculated nutritional deficiency for cows grazing BG and fed the low SUP
indicates that large amounts of supplement must be fed or the supplement nutrient
concentrations must be adjusted to ensure adequate nutrient intake when BG is managed
as in these experiments. Oppositely, supplement intakes caused RP-based diets to
contain excessive CP, likely increasing maintenance costs due to the need for increased N
excretion. With RP, only S intake appeared marginal regardless of SUP.
Nutrient intake estimates with both forages highlights the need for feeding suitable
amounts of supplement with appropriate nutrient concentrations.
One limitation of the study presented was the use of the same supplement for
animals grazing both forage types. Though this prevented the confounding of forage
effects with supplement effects, the response to supplement likely would be improved by
more appropriately balancing the supply of nutrients available to the cow. Although this
may not affect production, a more economical supplement could be offered (Hoffman et
al., 1993).

173
Stocking rate did not influence milk production, but cows grazing at lower SR
tended to produce milk with greater concentrations of protein which may reflect
opportunity to select plant parts of greater nutritive value. Likewise, in 1996 MUN was
lower when cows were stocked at the lower rate suggesting more efficient use of dietary
CP for milk protein.
On a land area basis, the effect of SR on milk production was greater than the
effect of feeding additional supplement. Increasing SUP from 0.33 kg of supplements
kg of daily milk to 0.5 kg of supplement: 1 kg of daily milk increased (P < 0.001) milk
production 14% on a land area basis (97 vs. Ill kg of milk/ha per d), but increasing SR
resulted in a 51% increase (P < 0.001) in milk production per land area (83 vs. 125 kg of
milk/ha per d).
Cows assigned to the greater SR lost 7 to 8 kg more per 28-d period than cows
assigned to the lower SR across years and forages with one exception. In 1996, cows
grazing BG lost 7 kg less BW when grazing at the greater vs. lesser SR
Increasing SR resulted in reduced forage OMI, but cows stocked at the greater
rate were fed slightly more supplement because of greater milk production. Thus, total
OMI and OMIPBW were not different due to SR (15.3 and 15.9 kg of OM/d and 3.08 and
3.16% of BW/d).
In a third study, the effect of additional management strategies on milk production
was investigated. Cows were housed in bams (with fans and sprinklers) or on pastures
(with shade cloth only) between AM and PM milkings. After PM milking all cows
returned to BG pastures. Within housing treatments, cows did or did not receive bST

174
injection, and a fifth treatment tested the effect of feeding supplemental silage to cows
treated with bST and housed in bams.
Keeping cows in the bam limited their time spent grazing, but despite the reduced
grazing time, forage intake was not compromised by bam housing. Average forage OMI
of BG, excluding cows on the silage treatment, was 9.2 kg/d, or 1.58% of BW. Because
forage OMI was unaffected by grazing time, housed cows must have grazed with greater
harvesting efficiency (defined as intake over time (Barton et al., 1992; Krysl and Hess,
1993). This might have occurred as a result of an increased bite rate due to temporary
deprivation from pastures as has been reported by Greenwood and Demment (1988).
Supplement and total OMI were unaffected by housing treatment. Average
supplement and total OMI were 7.5 and 16.7 kg/d. Daytime housing with fans and
sprinklers increased (P < 0.11) milk production by 5% for housed cows (17.8 vs. 17.0
kg/cow per d, respectively).
That differences between housing regimes were not greater in this study is
surprising given the presumed greater energy expenditure of cows kept on pasture. The
greater milk production from housed cows despite having similar OMI to those of
pastured cows indicates a greater efficiency of nutrient utilization for housed cows. It is
highly likely that housed cows expended less energy for maintenance because they were
required to walk less and experienced less heat stress.
Housing cows during the day did promote weight gain. Cows kept on pasture lost
approximately 11 kg of BW/24-d period vs. an increase of approximately 6 kg of BW/24-
d period for housed cows. These differences in BW changes further highlight the lower
maintenance costs for housed cows due to reductions in activity and heat stress.

175
Housing had no effect on IGF-1 at any sampling date. Greater insulin
concentrations were detected for cows kept on pasture continually
Cows kept on pasture during the daylight hours took nearly 30% more
breaths/min than those housed in the bam (89 vs. 69 per min for bam and pasture cows,
respectively). By 0900 h, cows on pasture were hotter than cows kept in the bam.
Temperatures of all cows peaked at approximately 1630 h when cows were washed for
the evening milking. Body temperatures decreased immediately thereafter due to the
cooling effect of the shower wash system. After milking, temperatures increased for both
housing treatments as cows returned to pasture, but the increase post p.m. milking was
greater for bam cows, suggesting greater grazing activity of the cows denied access to
pasture during the day.
Responses to cooling with fans and misters may be greater with more modem
cooling equipment (fans were an older, box-type with slower wind speed), but such
equipment may be more typical of systems put in place by low-input operators.
Regardless, the effect of cooling likely would be greater for cows in earlier stages of
lactation when milk production and heats of metabolism would be greater. Economic
feasibility of constructing such facilities for a pasture-based startup operation seems
unlikely but must consider the life of the system. Use of such pre-existing facilities
might have financial merit.
Research with other types of cooling may warrant exploration. Some producers
have taken advantage of the shallow subsurface waters common to the state by digging
cooling ponds. In these more limited input systems, use of trees as a resource for both
cooling and harvest may have financial benefit.

176
Treatment with bST encouraged increased grazing activity (6.3 vs. 5.6 h of
grazing/d), but forage OMI was unaffected by bST treatment. Given the conditions
imposed, cows treated with bST would not be expected to increase intake of forage OM
since supplement provided was increased with increasing milk production. If bST-
treated cows consumed only pasture, forage intakes likely would have increased given
adequate amounts of available herbage.
Cows injected with bST increased milk production approximately 9% (18.1 vs.
16.6 kg/d) and thus were fed an average of 8.0 kg of supplement OMI/d vs. 7.0 kg/d for
untreated cows. Although within the range of reported production increases in response
to bST, greater responses to bST might have been expected given the relatively low
amount of pretreatment milk production.
On average, and despite increased milk production, cows treated with bST gained
small amounts of BW (2.5 kg/24-d period), but cows not given bST lost about 7 kg of
BW/24 d period. The BW gain response was likely a result of the increased supplement
provided to bST-treated cows because they produced more milk.
Use of bST increased concentrations of plasma IGF-1 over controls nearly 70%
(143.vs. 84.5 pg/ml of plasma). The bST treatment likely affected IGF-1 both directly
and indirectly via increased concentrate provision. Averaged over all sampling dates,
insulin concentrations tended to increase due to bST treatment. As with IGF-1, bST
likely affected insulin concentrations directly and indirectly via increased
supplementation.
Increased RR with bST treatment has been reported but did not occur in this
study. However, cows treated with bST had greater temperatures throughout the day.

177
The increase in body temperature is in agreement with several other studies and
contradicts popular press and technical reports of Monsanto which suggest that cows are
capable of dissipating additional heat via greater RR and sweating.
Cows not injected with bST increased body temperature at a slower rate from
approximately 1100 h until 1630 h. Treatment with bST also affected body temperature
patterns once cows returned to pasture, with treated cows maintaining increased body
temperatures far longer than untreated cows. Though this temperature pattern for bST-
treated cows appears to reflect a greater drive to graze. Also cows receiving bST may
have been more aggressive grazers (greater bite rate) upon initial return to pastures.
Feeding silage curtailed grazing time by more than 25% (5.6 vs. 4.0 h of
grazing/d). The decreased grazing time resulted in decreased BG OMI of about
18% (from 9.0 to 7.4 kg/d, respectively), but total forage OMI was increased
approximately 17% with supplemental silage (from 9.0 to 10.5 kg of forage OMI/d).
As feeding silage did not affect milk production, supplement OMI was not
different between the plus or minus silage treatments. Cows fed silage consumed more
total OMI per day by nearly 8%. Whereas the equation of Moore et al. (1999) was used
to adjust forage digestibility due to associative effects of supplement feeding and thus
forage intake estimates, no additional adjustments to forage digestibility were made for
cows consuming com silage. If feeding com silage resulted in a greater depression of
pasture digestibility, OMI was over-predicted.
Feeding supplemental silage in the bam had no effect on milk production, 4%
FCM production, nor milk fat and protein concentrations or quantities. Bam cows not
receiving silage also tended to gain more than those fed additional roughage in the bam.

178
Because OMI was increased for cows fed silage with no change in milk production,
partitioning of nutrients to BW gain might be expected. This seeming discrepancy could
be a consequence of the postulated difference in gut fill between the two treatments and if
so indicates that condition score measurements were based upon more than changes in fat
depot size. Because neither milk production nor weight gain increased with the increased
OMI, efficiency of nutrient utilization may have decreased with supplemental com silage,
or intake of metabolizable energy may not have been increased.
Cows fed silage in the bam had a different temperature pattern than those not
receiving silage. Body temperatures of cows on both treatments reached the same
temperature within an hour of grazing (1900h), but temperatures of cows fed silage
quickly dropped thereafter, suggesting that they spent less time grazing. Cows not fed
silage but treated with bST had greater drive to graze than cows fed silage, and their
temperatures were sustained until 0130 h, likely due to increased grazing activity.
Estimates of nutrient intake based on NRC recommendations suggest that nutrient
intake did not prevent cows on this trial from producing 20 kg of 4% fat corrected milk/d.
This suggests that either maintenance costs were greater than NRC (1989) estimates, or
nutrient intake or utilization, particularly of energy, was overestimated.
Pasture-based production systems may be viable for dairies in the Southeast, but
they must overcome several obstacles to profitability. Low forage quality, environmental
stresses, greater maintenance costs for grazing cows, and animal adaptation may all limit
the productivity of these systems.
Cows grazing pasture typically have lower peak milk production and are less
persistent (Hoffman et al., 1993). The effects of hot environments likely further

179
compound these problems due to the fact that animals decrease intake during heat stress
to help maintain homeothermy. Further, the strains of heat and humidity place additional
maintenance demands on the cow.
Feeding supplemental silage to housed cows was ineffectual. The lack of positive
response, teamed with the greater forage intakes suggest that feeding silage resulted in
reductions of nutrient utilization efficiency.
Use of management tools such as bST may have merit for periods of the grazing
season when cows are in good condition, but the limited response to bST in this study
suggests that economic returns may be minimal during the summer. Response to bST
typically is greater for cows of lower milk production, and the limited response to
treatment for the mid- to late-lactation cows in this study suggests that bST may be
ineffectual for cows nearer peak production.
Other considerations for pasture-based dairies in the Southeast would include
alternative forage crops which could fit the difficult-to-fill production windows of late
fall and early spring. These seasons are particularly difficult in regions such as North
Central Florida, where transition periods occurring between the growth of warm and cool
season forages limits available forage.
Breed of cattle likely is another area rich for exploration. Holsteins may not be
best suited to pasture dairying in the Southeast, and use of breeds more tolerant of heat
stress may be of advantage for the systems. Currently some graziers are attempting to
improve the productivity of their herds by cross breeding Jersey and Holstein cows to
improve heat tolerance, optimize milk production and reproductive success.

180
Another production model, which has not been explored in modem Florida, is use
of the dual purpose cow. Such systems are commonplace in Latin America where
fluctuations in milk and meat prices allow producers to take advantage of these combined
traits depending upon the market. Some pasture-based producers are breeding cattle that
fit this model, but these cattle and systems are unlikely to gamer wide interest in Florida
due to its status as a milk-deficit state. Indeed, the premium placed on milk production in
the state, and the as-yet more limited production with grazing systems suggests that at
this time, grazing systems may be more effective as a route of entry into dairy production
for producers with limited equity.

APPENDIX 1
SAS PROGRAM OF POND ET AL. (1987) FOR THE ESTIMATION OF FECAL
OUTPUT
=======================SAS PROGRAM= == -
DATA GRAZE 1; INFILE GRAZE;
INPUT ANIMAL TIME CR;
Y = CR;
PROC SORT; BY ANIMAL;
PROC NLIN INTER (sic) = 50 CONVERGENCE = .00001 METHOD
MARQUARDT; BY ANIMAL;
PARMS K0 = 100 LI = .05 TAU = 10;
BOUNDS K0>0, L1>0, TAU>0;
T = TIME TAU;
If T<0 THEN GO TO ALPHA;
El = EXP (-L1 *T);
ONE = T*(L1**2)*E1;
MODEL Y = ((K0* L1 T) (EXP(-L 1 T)))/. 59635;
DER. K0 = ONE;
DER. LI = T*L1*K0*E1*(2-L1*T);
DER. TAU = K0*(L1**2)*E1*(L1*T-1.0);
GO TO BETA;
ALPHA;
MODEL Y = 0;
DER. K0 = 0;
DER. LI =0;
BETA: ;
OUTPUT OUT = POINTSI PREDICTED = YHAT RESIDUAL = RESID;
DATA OK; MERGE POINTSI GRAZE 1;
PROC SORT; BY ANIMAL;
PROC PLOT; BY ANIMAL;
PLOT YHAT TIME = ** Y*TIME = + /OVERLAY;
LABEL TIME = TIME AFTER DOSE, HOURS;
181

APPENDIX 2
SAS PROGRAM TO ADJUST FORAGE INTAKE UNTIL FECAL OUTPUT
OBSERVED AND FECAL OUTPUT PREDICTED DIFFER BY LESS THAN ONE-
HUNDREDTH OF A KILOGRAM PER DAY
Program terms:
FRGDIG
IVOMD
FRGINTAK =
TOTINTAK =
SUPINTAK =
TOTDIG
FRGDIG
SUPDIG
FOP
FOO
DIFF
forage digestibility
in vitro organic matter digestibility
forage intake
total intake (initially predicted from parameters derived from fecal
excretion curves)
supplement intake (assumed constant)
sum of digestible forage and digestible supplement intakes divided by
total intake
forage digestibility (determined from laboratory analysis)
supplement digestibility (assumed constant)
fecal output predicted
fecal output observed
difference of observed and predicted fecal output
OMD is calculated in each iteration call that the "expected" OMD.
Convert "expected" to "adjusted" with the following formula:
Adjusted OMD = 59.71 (0.8948 expected OMD) + (0.01399 (expected OMD)2)/100
DATA ;
SAS PROGRAM
INPUT COW PAR TRT PER PAST YR OMI FOO IVOMD SUPINTAK SUPDIG;
FRGDIG = IVOMD;
DO FRGINTAK =1 TO 40 BY .05 UNTIL (DIFF < .01);
TOTINTAK = FRGINTAK + SUPINTAK;
EXPDIG = (FRGINTAK*FRGDIG + SUPINTAK* SUPDIG)/TOTINTAK* 100;
ADJDIG = (59.71 0.8948*EXPDIG + 0.01399*EXPDIG**2)/100;
FOP = TOTINTAK* (1-ADJDIG);
DIFF = FOO-FOP;
END;
CARDS;
PROC PRINT;
RUN;
182

APPENDIX 3
WEEKLY WEATHER DATA FOR 1995, 1996 AND 1997 GRAZING TRIALS
Date
Rainfall, mm
Minimum
- Temperature, C -
Maximum
Mean
1995
July 10-16
26.3
21.9
34.7
27.5
July 17-23
92.8
20.6
34.7
27.5
July 24-30
38.9
20.0
35.0
26.9
July 31-Aug. 6
52.8
21.1
34.2
27.2
Aug. 7-13
43.4
20.6
34.2
27.3
Aug. 14-20
38.7
20.3
34.2
27.3
Aug. 21-27
71.6
21.1
32.2
26.4
Aug. 28-Sept. 3
8.8
21.7
33.3
27.0
Sept. 4-10
4.3
19.4
31.9
24.9
Sept. 11-17
45.3
20.0
33.3
26.7
Sept. 18-24
9.8
17.5
33.6
26.3
Sept. 25-Oct.l
9.0
18.1
30.8
25.4
Oct. 2-8
81.0
21.4
31.7
26.5
Oct. 9-10
7.5
22.2
30.8
26.3
1996
July 9-15
30.2
22.8
34.2
27.0
July 16-22
20.3
20.6
34.2
27.3
July 23-29
0.0
18.9
36.4
27.7
July 30-Aug. 5
65.5
19.4
35.3
26.8
Aug. 6-12
34.9
19.2
33.9
26.2
Aug. 13-19
31.2
19.4
32.5
25.5
Aug. 20-26
7.0
18.9
33.1
25.5
Aug. 27-Sept. 2
75.7
15.6
31.9
25.1
Sept. 3-9
1.5
18.3
33.3
26.1
Sept. 10-16
15.0
16.4
33.1
25.3
Sept. 17-23
14.2
13.1
31.4
24.5
Sept. 24-30
0.5
13.6
32.2
24.3
Oct. 1-2
23.9
21.4
31.1
26.3
1997
July 28-Aug. 3
103.9
20.3
32.5
26.4
Aug. 4-10
17.0
16.9
33.3
27.0
Aug. 11-17
21.3
21.7
34.4
27.9
Aug. 18-24
1.3
17.8
35.0
27.5
Aug. 25-31
51.3
15.3
34.4
25.4
Sept. 1-7
8.9
15.8
33.3
25.9
Sept. 8-14
0.0
15.0
33.9
25.3
Sept. 15-21
0.0
16.9
34.2
26.5
Sept. 22-28
56.1
20.0
35.0
26.3
Sept. 29 Oct. 5
3.3
15.0
31.7
24.2
Oct. 6 10
5.1
15.6
31.4
24.1
183

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213
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916.

BIOGRAPHICAL SKETCH
John Herschel Fike, son of Herschel Ringgold and Shirley Hayden Fike, was bom
and raised in Franklin County, Virginia. He holds a B.S. in science education from Wake
Forest University, an M.S. in forage agronomy from Virginia Polytechnic Institute and
State University, and with successful defense of this dissertation holds a Ph.D. with
specialization in dairy cattle nutrition from the University of Florida.
After graduating from Wake Forest University, John spent more than a year
traveling and working in Japan, New Zealand, Australia, and several countries in
Southeast Asia. His jobs included painting houses and milking cows in New Zealand,
dagging sheep in Australia, and teaching English to Japanese businessmen.
While completing his Ph.D., John married Wonae (Bong) Fike of South Korea
and started a family. He and Wonae are the proud parents of Jonah Paul Bong Fike.
214

I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
C3l\ (XaS[j/^
Charles R. Staples, Chair
Professor of Animal Science
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
Professor of Agronomy
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
Mary Bdfh Hall
Assistant Professor of Dairy and Poultry
Sciences
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosj
Hanfcenl
Professor of Naftry and Poultry Sciences
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
t. 7/t nM-
phn E. Moore
'rofessor of Animal Science

This dissertation was submitted to the Graduate Faculty of the College of
Agriculture and Life Sciences and to the Graduate School and was accepted as partial
fulfillment of the requirements for the degree of Doctor of Philosophy.
December, 1999
(JaAU
DeaVCollege of Agricultural and Life
Sciences
Dean, Graduate School



136
Glucose in plasma was analyzed following the colorimetric procedure of
Gochman and Schmitz (1972). Plasma was filtered with 16 X 174 mm standard model
serum filters (Fisherbrand, Fisher Scientific, Pittsburgh, PA) and analyzed directly with
an automated analyzer (Bran+Luebbe, Model II, Bran+Luebbe Analyzing Technologies,
Elmsford, NY).
Plasma hormones. Double antibody radioimmunoassay was performed for
determination of insulin and insulin-like growth factor-1 (IGF-1) following the
procedures of Abribat et al. (1990). Second antibodies for use in the assays were
prepared in Florida native sheep maintained at the University of Florida Dairy Research
Unit. Sheep were injected subcutaneously with guinea pig and rabbit gamma globulins
and reinjected 2 wk later. Sheep were bled at 2 and 6 wk after the second injection and
the serum obtained was pooled and frozen. Second antibodies of sheep anti-guinea pig
and sheep anti-rabbit in the pooled plasma were used in the assays. For a complete
description of the antibody collection, preparation, and iodination methods, see Garcia-
Gavidia (1998).
Plasma insulin concentration was determined following procedures described by
Soeldner and Sloane (1965) as modified by Malven et al. (1987). Approximately 100 pg
of highly purified insulin (Sigma Immunochemicals, St. Louis, MO) was dissolved in 30
mM of HC1 (pH = 2.5) in an ultrasonic water bath. This stock insulin was diluted in an
assay buffer of 0.33 M borate, 0.01% merthiolate, and 0.5% BSA to give a final
concentration of 100 ng/ml. Standards of 0, 0.3, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10, 15,20, 25,
and 30 ng insulin/ml were prepared from the solution of insulin in the BSA buffer. First
antibody (guinea pig anti-bovine insulin, Sigma Chemical, Co., St. Louis, MO) was


175
Housing had no effect on IGF-1 at any sampling date. Greater insulin
concentrations were detected for cows kept on pasture continually
Cows kept on pasture during the daylight hours took nearly 30% more
breaths/min than those housed in the bam (89 vs. 69 per min for bam and pasture cows,
respectively). By 0900 h, cows on pasture were hotter than cows kept in the bam.
Temperatures of all cows peaked at approximately 1630 h when cows were washed for
the evening milking. Body temperatures decreased immediately thereafter due to the
cooling effect of the shower wash system. After milking, temperatures increased for both
housing treatments as cows returned to pasture, but the increase post p.m. milking was
greater for bam cows, suggesting greater grazing activity of the cows denied access to
pasture during the day.
Responses to cooling with fans and misters may be greater with more modem
cooling equipment (fans were an older, box-type with slower wind speed), but such
equipment may be more typical of systems put in place by low-input operators.
Regardless, the effect of cooling likely would be greater for cows in earlier stages of
lactation when milk production and heats of metabolism would be greater. Economic
feasibility of constructing such facilities for a pasture-based startup operation seems
unlikely but must consider the life of the system. Use of such pre-existing facilities
might have financial merit.
Research with other types of cooling may warrant exploration. Some producers
have taken advantage of the shallow subsurface waters common to the state by digging
cooling ponds. In these more limited input systems, use of trees as a resource for both
cooling and harvest may have financial benefit.


105
the low supplementation rate (-0.28 points) being much greater than would be expected
given the change in BW (-7 kg/28-d period).
Cows fed the greater SUP lost more BW than those fed the lesser SUP, regardless
of forage, with the exception of cows grazing BG in 1996 which lost the most weight
when offered the least amount of supplement (year by forage by SUP interaction, P <
0.05; Figure 3.8). Increasing the amount of supplement fed frequently results in greater
forage substitution (Davison et al., 1991; Reeves et al., 1996) so that total intake may not
change. This may influence BW changes. This effect of grain feeding on forage intake
will be discussed subsequently.
A year by SR by SUP interaction (P < 0.05) for change of BCS was observed but
will not be discussed due to the complexity of explanation given the changes in SR made
from Year 1 to Year 2 of the experiment.
Respiration, Temperature, and Blood Metabolites
Parity and year effects. Primiparous cows had greater (P < 0.001)
concentrations of PUN than multiparous cows (14.8 vs. 13.3 mg %), and the
concentration of PUN was greater (P < 0.001) in 1996 than 1995 (16.3 vs. 11.8 mg %),
reflecting the increased CP concentration of the supplement in 1996.
Respiration rate and temperature were unaffected by parity or year, indicating
similar levels of heat stress across years. However, primiparous cows had greater RR in
1995 (99 vs. 92 breaths/min) and similar RR in 1996 (92 vs. 94 breaths/min; parity by
year interaction, P < 0.05). Glucose in plasma averaged 58.4 mg% and was unaffected
by parity or year.


32
Average forage substitution rate for animals receiving the starchy supplement was 0.45
kg of herbage/kg concentrate vs. 0.21 kg of herbage/kg of concentrate for animals
receiving the more fibrous supplement. Milk and FCM yields were greater for animals
receiving the fibrous supplement, but feeding the starch-based supplement resulted in
0.17 kg greater ADG vs. fibrous supplement.
Similar responses to type of supplement have been found with cows consuming
com silage as the base forage (Huhtanen, 1993). Supplements were crushed barley alone
or mixed grain (40%) and pelleted fibrous by-products (60%). Cows eating the fibrous
supplement consumed 0.43 kg/d more (P <0.10) silage and more total DM, but lower
ME (212.7 vs. 218.0 MJ/d). Milk production increased 1.5 kg/d when animals consumed
the fibrous supplement. The author suggested that positive associative effects from the
combination of different carbohydrate sources or the greater CP intake (0.20 kg/d) due to
the fibrous supplement may help explain greater milk yields. Though liveweight did not
change due to supplement and insulin concentrations were not reported, greater plasma
insulin concentration for barley supplement have been reported by Miettinen and
Huhtanen (1989). This hormonal change would suggest greater partitioning of nutrients
to body tissues and may explain the results of Meijs (1986).
Gordon et al. (1993) compared the effects of fibrous or starchy supplements on
milk production and energetic efficiency. Fibrous supplements included sugar beet and
citrus pulp as well as cottonseed while starchy concentrates contained barley and wheat.
Cows were fed the supplements with high- or low-digestibility grass silage. The authors
reported greater milk production (23.5 vs. 21.6 kg/d) by cows fed the fibrous supplement.
Milk protein percentage was greater with the starch supplement, potentially indicative of


24
The response of DMI to HA appears to vary depending upon length of the
experiment. Stockdale (1985) reported that average DMI was 2.9 kg/d greater with long
term experiments than short-term experiments, regardless of the HA. The author
suggested that greater intake in long-term experiments was due to adaptation.
Stocking rate may have both short and long-term consequences for both pasture
and animal production, particularly for forage species that exhibit seasonal growth habits.
Intense grazing bouts during initial periods of growth may reduce reproductive tillering
and the deleterious effects of accumulated dead material in the sward later in the grazing
season (Michell and Fulkerson, 1987). Michell and Fulkerson (1987) observed that the
quantities of available green herbage were the same in pastures that had been subjected to
low or high SR (1.9 or 3.4 cows/ha) on ryegrass (Loliumperenne L.)-white clover
(Trifolium repens) pastures. However, quantities of dead herbage were greater in the low
SR pastures over most of the grazing season. Diet digestibilities between treatments were
similar, but production from cows on the low SR appeared compromised due to a
reduction of DMI.
Grazing intensity also affects botanical composition and herbage yield of grasses,
legumes, and weeds (Brougham, 1960; Michell and Fulkerson, 1987). Composition and
yield changes in response to SR are variable depending upon grazing events through the
season and emphasize the importance of management in maintaining high quality
pastures (Brougham, 1960). Because dead plant tissue (Hodgson, 1985) and fecal matter
(Phillips and Leaver, 1985) negatively affect intake and are more prevalent in the fall
than in the spring, Phillips (1989) suggested managing pastures for greater sward height
as the grazing season progresses.


13
maintain adequate intake for high-producing dairy cows. However, the strength of the
negative relationship between fiber and intake (or digestion) for animals consuming
bermudagrass has been questioned (Golding et al., 1976a; Jones et al., 1988; Goetsch et
al., 1991) and bears further investigation.
Some Non-Nutritional Factors Affecting Behavior and Forage Intake Of Grazing
Ruminants
Mechanistic Components of Forage Intake
A mechanistic or mathematical model of forage intake by the grazing ruminant
was first put forth by Allden and Whittaker (1970) following the work of Allden (1962).
The model reduces forage intake (FI; kilograms) to the product of the main components
of grazing behavior; that is time spent grazing (GT; minutes or hours), rate of biting
during grazing (RB; bites per minute), and the intake of forage per bite (IB; grams).
Hence the equation: FI = (IB*RB*GT)/1000.
Research indicates that if herbage mass is maintained above amounts which
restrain intake, animals can maintain fairly constant amounts of intake by adjusting IB,
RB, and GT (Willoughby, 1959; Allden and Whittaker, 1970). Of these three variables,
IB is the most affected by sward conditions (Hodgson, 1985). Intake per bite normally
falls sharply as herbage mass or sward height declines (Hodgson, 1985, p. 340, citing
Allden and Whittaker, 1970 and Hodgson, 1981). Negative correlations between IB and
herbage on offer (r = -0.61) and sward bulk density (r = -0.70) have been shown with
tropical pastures (Stobbs, 1973). Sward height may be positively related to intake of
warm-season species (Flores et al., 1993), though universality is unlikely when one
considers the range in morphologies of tropical forages.


193
Gochman, N., and J. M. Schmitz. 1972. Application of a new peroxide indicatorreaction
to the specific automated determination of glucose with glucose oxidase. Clin. Chem.
18:943-950.
Goetsch, A. L., Z. B. Johnson, D. L. Galloway, Sr., L. A. Forster, Jr., A. C. Brake, W.
Sun, K. M. Landis, M. L. Lagasse, K. L. Hall, and A. L. Jones. 1991. Relationships of
body weight, forage composition, and com supplementation to feed intake and digestion
by Holstein steer calves consuming bermudagrass hay ad libitum. J. Anim. Sci. 69:2634-
2645.
Golding,, E. J., M. F. Carter, and J. E. Moore. 1985. Modification of the neutral
detergent fiber procedure for hay. J. Dairy Sci. 68:2732-2736.
Golding, E. J., J. E. Moore, D. E. Franke, and O. C. Ruelke. 1976a. Formulation of hay-
grain diets for ruminants. I. Evaluation of multiple regression equations for prediction of
bermudagrass hay quality for laboratory analyses. J. Anim. Sci. 42:710-716.
Golding, E. J., J. E. Moore, D. E. Franke, and O. C. Ruelke. 1976b. Formulation of hay-
grain diets for ruminants. II. Depression in voluntary intake of different quality forages
by limited grain in sheep. J. Anim. Sci. 42:717-723.
Gordon, F. J., M. G. Porter, C. S. Mayne, E. F. Unsworth, and D. J. Kilpatrick. 1993.
Effect of forage digestibility and type of concentrate on nutrient utilization by lactating
dairy cattle. J. Dairy Res. 62:15-27.
Greaney, K. B., G. W. Reynolds, M. J. Ulyatt, D. D. S. MacKenzie, and P. M. Harris.
1996. The metabolic cost of hepatic ammonia detoxification. Proc. N.Z. Soc. Anim. Prod.
56:130-132.
Greene, B.B., M. M. Eichom, W. M. Oliver, B. D. Nelson, and W. A. Young. 1990.
Comparison of four hybrid bermudagrass cultivars for Stocker steer production. J. Prod.
Agrie. 3:253-255.
Greenwood, G. B., and M. W. Demment. 1988. The effect of fasting on short-term cattle
grazing behavior. Grass Forage Sci. 43:377-386.
Grovum, W. L., and G. D. Phillips. 1978. Factors affecting the voluntary intake of food
by sheep. 1. The role of distention, flow-rate of digesta, and propulsive motility of the
intestines. Br. J. Nutr. 40:323-336.
Guerrero, J. N., B. E. Conrad, E. C. Holt, and H. Wu. 1984. Prediction of animal
performance on bermudagrass pasture from available forage. Agron. J. 76:577-580.


bermudagrass and Florigraze rhizoma peanut during the summers of 1995 and 1996.
Samples were hand-plucked once each period based on visual appraisal of forage
consumed by grazing cows 118
3.9 Regression groupings and regression coefficients for predicting 1995 and 1996 pre-
and post-graze herbage mass of Tifton 85 bermudagrass and Florigraze rhizoma
peanut pastures 121
3.10 Disk meter estimates of the effect of forage species, stocking rate (SR), and
supplementation rate (SUP) on forage pre- and post-graze herbage mass (HM),
herbage allowance (HA), and dry matter intake (DMI) of grazing, lactating Holstein
cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut during the
summers of 1995 and 1996 122
3.11 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on milk
income minus supplement costs (MIMSC), assuming supplement intake
proportionate to LS means of milk production within a given SUP treatment and
calculated on both per cow and per land area bases 126
4.1 Supplement ingredients 133
4.2 Chemical composition, and nutritive value of supplement, com silage and
bermudagrass pasture 133
4.3 Influence of housing (0800 to 1500 h on pasture or in bams with fans and
sprinklers), bST, and bST with supplemental silage on organic matter intake (OMI)
of Holstein cows grazing Tifton 85 bermudagrass pastures 146
4.4 Influence of housing (0800 to 1500 h on pasture or in bams with fans and
sprinklers), bST, and bST with supplemental silage on milk production and
composition of Holstein cows grazing Tifton 85 bermudagrass pastures 151
4.5 Calculated daily intake of nutrients by cows grazing Tifton 85 bermudagrass (BG)
pastures and not treated (-bST) or treated (+bST) with exogenous growth hormone.
An additional treatment tested the effect of feeding com silage (Silage) to cows
treated with bST 153
4.6 Influence of housing (0800 to 1500 h on pasture or in bams with fans and
sprinklers), bST, and bST with supplemental silage on body weight (BW), body
condition score (BCS), respiration rates (RR), and concentrations of plasma insulin
and insulin-like growth factor-1 (IGF-1) of Holstein cows grazing Tifton 85
bermudagrass pastures 156
vm


61
production systems. Many have looked to forage legumes for suitable alternatives to
grasses because animal performance is often greater when legumes are fed (Rattray and
Joyce, 1974; Thomas et al., 1985; Beever et ah, 1986b; Hoffman et ah, 1998). The
following discussion primarily will consider cool-season perennial legumes, because few
warm-season perennial legumes have proven suitable for intensive grazing systems.
Regarding chemical composition, legumes typically have greater concentrations
of protein than grasses, with a larger percentage of the protein being ruminally
degradable (Beever et ah, 1986a; Glenn, 1994). The soluble portion of legume CP also is
different, having more amino acids and peptides than that of grasses (Glenn et ah, 1989).
Legumes generally have less NDF than grasses, and the composition of NDF in legumes
is markedly different. Legumes have less hemicellulose, typically less cellulose, more
lignin and more pectic substances (Van Soest, 1965) than grasses.
In vitro digestibility studies indicate that legumes typically have a greater rate but
lesser extent of digestion in comparison with grasses (Smith et ah, 1972). Glenn (1994)
noted that, relative to alfalfa, proportionately more grass NDF typically is digested in the
rumen. A review of several comparisons of alfalfa and orchardgrass fed to growing
animals indicated that total tract digestibility of orchardgrass was 94% that of alfalfa
(Glenn, 1994). In comparisons of alfalfa with ryegrass or orchardgrass, researchers
typically have found greater true fiber and DM digestibility for the grasses (Holden et ah,
1994a; Hoffman et ah, 1998), but the greater DM digestibility may in part be related to
the lower intakes of cows on the grass-based diets.
Holden et ah (1994a) fed diets of 55 or 66% forage (orchardgrass and alfalfa hays,
respectively) which were formulated to have equivalent NDF concentrations. Lactating


62
cows consumed 17.5 and 15.1 kg of OM/d for the alfalfa and orchardgrass diets,
respectively, and total tract digestions of NDF, ADF, and DM were greater for cows fed
the grass diets. In the study by Hoffman et al. (1998), lactating cows were fed diets based
on 70% inclusion of alfalfa or perennial ryegrass silage. Intake of DM was greater when
cows ate alfalfa silage (22.5 vs. 20.3 kg of DM/d), though true digestibility of NDF and
DM was greater for the ryegrass silage-based diet. In both studies, milk production was
greater with the alfalfa-based diet.
In a comparison of steers grazing pure stands of ryegrass or white clover, Beever
et al. (1986b) reported a nearly 25% greater DMI of the clover pasture (26.0 vs. 20.9 g/kg
of LW). Although intakes are generally greater with legumes, the better performance
typically associated with their consumption may not be only an intake effect. Glenn
(1994, citing Tyrrell et al. 1992 and Varga et al., 1990) noted that the large differences in
digestible OM composition must have some effect on the composition of absorbed
nutrients.
Differences in digestible OM composition likely contribute to the greater
efficiency of ME use associated with legume consumption (Armstrong, 1982). Greater
energetic efficiency of lactating cows fed alfalfa in comparison with orchardgrass was
reported by Casper et al. (1993). The authors fed ensiled forages (direct-cut and treated
with formaldehyde and formic acid) with two high-starch concentrate sources (barley or
com grain). Intakes of DM and ME and the digestibility of the DM were all greater for
the alfalfa-based diets. Although heat production was greater when cows consumed
alfalfa, heat production per unit of ME intake was greater for the orchardgrass diets. The


4.4. Influence of housing (0800 to 1500 h on pasture or in bams with fans and sprinklers), bST, and bST with supplemental silage on
milk production and composition of Holstein cows grazing Tifton 85 bermudagrass pastures.
Pasture Bam Probability
+silage Housing
Item
-bST
+bST
-bST
+bST
+bST
SEM
Housing
bST
x bST
Silage
Milk yield, kg/d
16.2
17.7
17.0
18.5
17.9
0.6
NS
* *
NS
NS
4% FCM1, kg/d
15.3
17.3
16.3
18.0
17.6
0.6
t
***
NS
NS
Milk fat, %
3.65
3.80
3.76
3.85
3.90
0.04
NS
NS
NS
NS
Milk fat, kg/d
0.59
0.68
0.64
0.70
0.69
0.03
NS
***
NS
NS
Milk protein, %
3.22
3.23
3.23
3.27
3.26
0.03
NS
NS
NS
NS
Milk protein, kg/d
0.52
0.57
0.54
0.60
0.58
0.02
t
***
NS
NS
MUN2, mg%
18.0
18.5
18.1
18.0
15.5
0.3
NS
NS
NS
***
SCC3, x 1000 cells
747
610
443
834
545
236
NS
NS
NS
NS
'P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.
2Fat corrected milk.
3Milk urea nitrogen.
4Somatic cell count.


TABLE 3.5. Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on forage, supplement (suppl.) and total
organic matter intake (OMI) of Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut during the summers of
1995 and 1996.
Tifton 85 bermudagrass Florigraze rhizoma peanut
Stocking Rate1 Stocking Rate2 Probability3 -
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage SR x SR
Item 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 SEM Forage SR SUP x SR x SUP x SUP x SUP
Forage OMI, kg/d
6.7
8.1
7.9
7.7
9.4
11.9
11.4
12.5
0.5
***
*
*
NS
NS
NS
NS
Suppl. OMI, kg/d
7.7
4.1
7.4
4.3
8.4
4.7
7.8
4.5
0.1
***
*
***
NS
NS
t
NS
Total OMI, kg/d
14.4
12.2
15.3
12.0
17.8
16.6
19.2
17.1
0.5
***
NS
***
NS
NS
NS
NS
Forage OMI,%ofBW
1.35
1.61
1.57
1.54
1.93
2.42
2.25
2.46
0.11
***
NS
*
NS
NS
NS
NS
Suppl. OMI, % of BW
1.56
0.82
1.48
0.86
1.70
0.95
1.56
0.91
0.03
**
*
***
NS
NS
t
NS
Total OMI, % of BW
2.91
2.43
3.05
2.40
3.63
3.37
3.81
3.37
0.11
***
NS
***
NS
NS
NS
NS
'High and low stocking rates were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.


77
production responses to two stocking rates within each forage-supplementation rate
combination
Materials and Methods
Cows, Design, and Treatments
Year one. On 10 July 1995, primiparous (n = 22) and multiparous (n = 22, mean
parity = 2.5) Holstein cows (mean DIM = 106 32) at the University of Florida Dairy
Research Unit, (2943 N latitude) were assigned to one of eight management treatments
arranged in a 2 X 2 X 2 factorial in two replicates. The main treatment factors were 1)
forage species grazed: bermudagrass (Cynodon dactylon XC. nlemfuensis cv. Tifton
85) (BG) or rhizoma peanut (Arachis glabrata cv. Florigraze) (RP), 2)
supplementation rate (SUP): 0.33 or 0.5 kg of supplement (as-is)/kg of daily milk
production, and 3) stocking rate (SR): 5 or 7.5 cows/ha for cows grazing BG pastures and
2.5 or 5 cows/ha for cows grazing RP pastures. All cows received 500 mg of
sometribove zinc (Posilac ; Monsanto, St. Louis, IL.) subcutaneously every 2 wk.
Each of the three experimental periods were 28 d in duration, with the first 14 d of
each period used for adjustment to a newly assigned treatment, and the last 14 d for
collection of data. In period 2, storm damage during the adjustment period caused a 10-d
delay. During this time, cows were kept on non-experimental pastures of their respective
forage assignment for period 2, and all cows were fed supplement at the greater rate.
Cows were assigned randomly to treatment for each period with the restriction that no
cow received the same treatment more than once, and the number of changes from a
given treatment to another treatment was balanced.


TABLE 3.11. Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on milk income1 minus supplement costs2
(MIMSC), assuming supplement intake proportionate to LS means of milk production within a given SUP treatment and calculated on
both per cow and per land area bases.
Tifton 85 bermudagrass
Stocking Rate3
Florigraze rhizoma peanut
Stocking Rate4
High Low High Low
Supplementation rate (kg/kg of milk per d)
0.5:1
0.33:1
0.5:1
0.33:1
0.5:1
0.33:1
0.5:1
0.33:1
MIMSC, $/cow per d
3.97
3.85
3.83
3.75
3.98
4.26
4.00
4.29
MIMSC, $/ha per d
34.7
33.7
23.9
23.4
24.9
26.6
15.0
16.1
'Estimated milk income = US $0.33/kg of milk.
Estimated supplement cost = US $0.22/kg of supplement.
3High and low stocking rates were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
4High and low stocking rates were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.


86
grab samples were taken from the next paddock to be grazed in each pasture, dried at
least 48 h at 55 C, and ground through a 1-mm screen with a stainless steel Thomas-
Wiley Laboratory mill. Samples were analyzed by the University of Florida Forage
Evaluation Support Laboratory, Gainesville. For determination of organic matter (OM),
dried samples were ashed for at least 4 h at 500C. The modified aluminum block
procedure of Gallaher et al. (1975) was used to digest samples prior to analysis for N by
the method of Hambleton (1977). Crude protein (CP) was then calculated as N 6.25.
Determination of neutral detergent fiber (NDF) and IVOMD concentrations were made
using the procedures of Golding et al. (1985) and Moore and Mott (1974), respectively.
A single pelleted supplement sample and no whole cottonseed samples were
collected in 1995. In 1996, supplement (including whole cottonseed) samples were
collected three times in each period. Equal amounts of sample within periods were
composited, ground through a 1-mm screen, and submitted to the DHIA Forage Testing
Laboratory (Ithaca, NY) for analysis.
Statistical Analysis
Animals. Two cows from the 1995 trial were used in 1996 but were treated as
different animals for purpose of analysis. Data were analyzed using the GLM procedure
of SAS (1991) with the following model:
Yyicimnop U X¡ + Pj + (xp)y + K(xp)k(¡j) +
a, + pm + (aP)im + Yn + (ay)ln + (pY)mn + (OCpY)lmn +
(pa)j| + (pp)jm + (pap)j,m + (pY)jn + (p (xa)n + (xP)im + (xap)iim + (xY)in + (xaY)iln + (xpY)imn + (xaPY)ilmn +
(xpa)ii + (xpp)im + (xpap)iim + (xpY)in + (xpaY)iln + (xppY)imn +


100
unaffected in 1996 (year by parity by SUP interaction; P < 0.05; Figure 3.5). With
primiparous cows, milk protein production was less affected by supplementation rate in
1995 than in 1996, while multiparous cows had similar improved responses to
supplement in both years (year by parity by SUP interaction, P < 0.05). Primiparous
cows produced 0.52 and 0.55 kg of protein/d at the low and high SUP in 1995 vs. 0.42
and 0.52 kg of protein/d in 1996. Multiparous cows produced 0.46 and 0.53 kg of milk
protein/d in 1995 and 0.43 and 0.51 kg of milk protein/d in 1996 for low and high SUP
treatments, respectively.
Milk Production per Land Area
Because production per land area may be a more appropriate measure of
profitability for dairies using grazing systems this measure also was calculated. Milk
production/cow was multiplied by cow/ha (SR), and the resultant yields per land area
were analyzed without cow effects in the model.
The average SR for BG pastures over the 2 years was 7.5 cows/ha vs. 5 cows/ha
for RP. As a result milk production from BG far exceeded (P < 0.001) production from
cows grazing RP (118 vs. 87 kg of milk/ha per day). This represents a nearly forty
percent difference in favor of BG.
Stocking rate had a greater effect on milk production/ha than did supplementation
rate. Increasing SUP from 0.33 kg of supplement: 1 kg of daily milk to 0.5 kg of
supplements kg of daily milk increased (P < 0.001) milk production 14% on a land area
basis (97 vs. Ill kg of milk/ha per d), but increasing SR resulted in a 51% increase (P <
0.001) in milk production per land area (83 vs. 125 kg of milk/ha per d).


174
injection, and a fifth treatment tested the effect of feeding supplemental silage to cows
treated with bST and housed in bams.
Keeping cows in the bam limited their time spent grazing, but despite the reduced
grazing time, forage intake was not compromised by bam housing. Average forage OMI
of BG, excluding cows on the silage treatment, was 9.2 kg/d, or 1.58% of BW. Because
forage OMI was unaffected by grazing time, housed cows must have grazed with greater
harvesting efficiency (defined as intake over time (Barton et al., 1992; Krysl and Hess,
1993). This might have occurred as a result of an increased bite rate due to temporary
deprivation from pastures as has been reported by Greenwood and Demment (1988).
Supplement and total OMI were unaffected by housing treatment. Average
supplement and total OMI were 7.5 and 16.7 kg/d. Daytime housing with fans and
sprinklers increased (P < 0.11) milk production by 5% for housed cows (17.8 vs. 17.0
kg/cow per d, respectively).
That differences between housing regimes were not greater in this study is
surprising given the presumed greater energy expenditure of cows kept on pasture. The
greater milk production from housed cows despite having similar OMI to those of
pastured cows indicates a greater efficiency of nutrient utilization for housed cows. It is
highly likely that housed cows expended less energy for maintenance because they were
required to walk less and experienced less heat stress.
Housing cows during the day did promote weight gain. Cows kept on pasture lost
approximately 11 kg of BW/24-d period vs. an increase of approximately 6 kg of BW/24-
d period for housed cows. These differences in BW changes further highlight the lower
maintenance costs for housed cows due to reductions in activity and heat stress.


16
In a comparison of grazing of cool- and warm-season grasses, Stobbs (1974b)
reported that RB was much less with Abyssinian barley (Hordeum vulgare) than with S.
anceps, and the decline in RB over time was less with the tropical grass. Cows grazing
barley were observed grasping large mouthfuls of forage with their tongues and chewing
the forage several times before swallowing, whereas cows grazing S. anceps took small
amounts of herbage and their mastication bites accounted for less than 5% of total
grazing bites.
A more apparent behavioral response to decreasing IB is an increase in GT, but
the degree of this compensatory mechanism is also limited, such that daily FI variations
may reflect closely the observed variations in IB (Hodgson, 1985). Stobbs (1974a)
reported that cows rarely take more than 36,000 prehension bites in a day. Based on this
value and the biting rates reported by Chacon and Stobbs (1976), the upper limit to daily
grazing time would be 10 to 12 h, though the latter authors reported 39,600 prehension
bites/d in one study, and GT as great as 800 min/d with cattle grazing tropical legumes
have been reported (Smith, 1959; Stobbs, 1970). In the study by Chacon and Stobbs
(1976), average maximum GT reported was 10.75 h/day, and GT patterns were
curvilinear. Cows grazed approximately 9 h during the first few days on a new pasture.
Grazing time increased to a maximum between days 3 through 6 then subsequently
declined despite a reduction in the quantity of herbage on offer in the later stages of
defoliation (Chacon and Stobbs, 1976, p. 714).
Work by Pulido and Leaver (1997) has shown that level of performance affects
intake. The authors measured intake of cows having initial milk yields of 21 or 35 kg/d.


74
West et al. (1990) indicated that bST is efficacious under hot and humid
conditions, for both Jersey and Holstein cows. Milk production increased 21% with bST
administration, though the increase was greater for cows at one standard deviation below
pretreatment mean milk production. Response to bST for cows one standard deviation
above pretreatment mean milk production was non-significant. Both a.m. and p.m. body
temperatures were increased in cows administered bST. Treatment by breed interactions
were observed for both production and body temperature increases. Compared to
Jerseys, Holsteins had greater milk production increases in response to bST but lower
body temperature increases. The authors hypothesized that the increased body
temperatures partially explain the lower production responses of Jerseys. If this is
correct, then increases in temperature with bST cannot be explained solely by increases in
metabolism due to increased milk production, an idea supported by the work of Cole and
Hansen (1993).
While management strategies such as designed shading and bST improve animal
performance, few have investigated their use with lactating dairy cows grazing pasture
under hot conditions. More generally, grazing systems management for intensive dairy
production in hot climates has received little attention in the United States. While
utilization of grazing represents a potentially viable method of production in the
Southeast, the limited information for producers regarding recently released forages
adapted to the region, as well as responses to various management strategies prompted
the research that follows.


179
compound these problems due to the fact that animals decrease intake during heat stress
to help maintain homeothermy. Further, the strains of heat and humidity place additional
maintenance demands on the cow.
Feeding supplemental silage to housed cows was ineffectual. The lack of positive
response, teamed with the greater forage intakes suggest that feeding silage resulted in
reductions of nutrient utilization efficiency.
Use of management tools such as bST may have merit for periods of the grazing
season when cows are in good condition, but the limited response to bST in this study
suggests that economic returns may be minimal during the summer. Response to bST
typically is greater for cows of lower milk production, and the limited response to
treatment for the mid- to late-lactation cows in this study suggests that bST may be
ineffectual for cows nearer peak production.
Other considerations for pasture-based dairies in the Southeast would include
alternative forage crops which could fit the difficult-to-fill production windows of late
fall and early spring. These seasons are particularly difficult in regions such as North
Central Florida, where transition periods occurring between the growth of warm and cool
season forages limits available forage.
Breed of cattle likely is another area rich for exploration. Holsteins may not be
best suited to pasture dairying in the Southeast, and use of breeds more tolerant of heat
stress may be of advantage for the systems. Currently some graziers are attempting to
improve the productivity of their herds by cross breeding Jersey and Holstein cows to
improve heat tolerance, optimize milk production and reproductive success.


Table 4.3. Influence of housing (0800 to 1500 h on pasture or in bams with fans and sprinklers), bST, and bST with supplemental
silage on organic matter intake (OMI) of Holstein cows grazing Tifton 85 bermudagrass pastures.
Item
Pasture
-bST +bST
-bST
- Bam -
+bST
+silage
+bST
SEM
Housing
Probability
Housing
bST x bST
Silage
Grazing time, h/d
6.5
7.2
5.0
5.6
4.0
0.4
***
*
NS
***
BG2 OMI, kg/d
9.5
9.4
8.9
9.0
7.4
0.6
NS
NS
NS
***
Sup.3 OMI, kg/d
6.7
8.0
7.3
7.9
7.8
0.2
NS
***
*
NS
Silage OMI, kg/d
-
-
-
-
3.0
-
-
-
-
-
Total4 OMI, kg/d
16.2
17.4
16.2
16.9
18.2
0.5
NS
**
NS
**
BG OMI, %BW5
1.65
1.61
1.52
1.54
1.25
0.10
NS
NS
NS
***
Sup. OMI, %BW
1.16
1.37
1.26
1.35
1.32
0.04
NS
***
*
NS
Silage OMI, %BW
-
-
-
-
0.53
-
-
-
-
-
Total OMI, %BW
2.81
2.98
2.78
2.89
3.10
0.09
NS
*
NS
*
'p < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.
2Tifton 85 bermudagrass.
3 Supplement.
4Total OMI (BG OMI + Sup. OMI) = silage OMI of cows receiving the bam + silage + bST treatment.
5Body weight.


26
pastures (Royal and Jeffrey, 1972; Delgado and Randel, 1989; Davison et al., 1991;
Reeves et al., 1996).
To maximize the performance of animals on pasture, supplemental feeds
(primarily energy feeds) are required to balance or increase the nutrient supply (Leaver,
1985a,b; NRC, 1989; Muller et al., 1995). Without supplemental energy, milk
production may be maintained by excessive mobilization of fat stores. This may have
potentially negative consequences in that it may result in metabolic disorders such as
ketosis or fatty liver syndrome.
Although milk yield is the typical performance variable measured, reproduction
has been shown to be compromised in beef cattle when energy intake is limited
(Wiltbank et al., 1964). Muller et al. (1995) noted that reproductive performance of dairy
cows also may be compromised without supplemental energy if pastures are high in CP
due to the negative relationship between high rumen degradable protein and fertility in
the lactating cow (Ferguson and Chalupa, 1989).
Supplement Effects on Production
Though the feeding of supplements is a common practice, production responses to
supplement are inconsistent and may not be profitable. Citing Leaver et al. (1968) and
Joumet and Demarquilly (1979), Meijs and Hoekstra (1984) reported that typical
responses were approximately 0.3 to 0.4 kg of milk per kg of supplement fed to cows
grazing adequate temperate pasture. In a summary of 12 papers, Combellas et al. (1979)
reported similar responses (0.34 kg of milk per kg of supplement) when cows grazed
tropical pastures. Davison et al. (1991) reported similar results but speculated that cows


This dissertation was submitted to the Graduate Faculty of the College of
Agriculture and Life Sciences and to the Graduate School and was accepted as partial
fulfillment of the requirements for the degree of Doctor of Philosophy.
December, 1999
(JaAU
DeaVCollege of Agricultural and Life
Sciences
Dean, Graduate School


31
dietary DMI is affected very little by forage quality when diets contain very large (>
80% of DM) levels of concentrate.
Sarker and Holmes (1974) fed supplement in increments of 2, 4, 6, or 8 kg OM/d
to non-lactating cows grazing ryegrass. Though total OM intake (OMI) increased with
increasing amount of supplement, the average increase in intake was 0.46 kg of OM/kg of
concentrate OM fed.
Combellas et al. (1979) fed 0, 3, or 6 kg of concentrates to lactating heifers
grazing Cenchrus ciliaris pastures. Across rainy and dry seasons, herbage intake
decreased approximately 0.52 kg with each kg of concentrate fed, and the authors noted
that this agreed with the range of 0.41 to 0.60 kg estimated from the equations of Holmes
and Jones (1964) and Holmes (1976) for a forage of 65% digestibility.
Supplements frequently are fed to animals consuming bermudagrass, and
Galloway et al. (1993a, p. 173, citing Galloway et al., 1992) stated that moderate dietary
levels of supplemental grain (e.g., 20 to 30%) can improve nutrient intake and
performance by cattle consuming bermudagrass. At greater amounts, nutrient digestion,
intake, or both, of the forage portion of the diet can be affected negatively.
Type of supplement fed also is an important factor with respect to substitution
effects. Mould and 0rskov (1983) reported that feeding large amounts of rapidly
fermentable starch led to decreased intake. Meijs (1986) fed high-starch supplements
(containing com and cassava) or high fiber supplements (containing beet pulp, palm
kernel expeller, soybean hulls, and com gluten feed) to cows grazing predominantly
perennial ryegrass swards. Supplement intakes were 5.5 and 5.3 kg of OM/d with forage
intakes of 11.5 and 12.6 kg of OM/d for high and low starch treatments, respectively.


210
Tayler, J. C., and J. M. Wilkinson. 1972. The influence of level of concentrate feeding
on the voluntary intake of grass and on liveweight gain by cattle. Anim. Prod. 14:85-96.
Terrill, T. H., S. Gelaye, S. Mahotiere, E. A. Amoah, S. Miller, R. N. Gates, and W. R.
Windham. 1996. Rhizoma peanut and alfalfa productivity and nutrient composition in
Central Georgia. Agron. J. 88:485-488.
Thatcher, W. W., and R. J. Collier. 1986. Effects of climate on bovine reproduction.
Pages 301-309 in Current therapy in theriogenology 2. David Morrow, ed. W. B.
Saunders, Co., Philadelphia, PA.
Thom, W. O., H. B. Rice, M. Collins, and R. M. Morrison. 1990. Effect of applied
fertilizer on Tifton 44 bermudagrass. J. Prod. Agrie. 3:498-501.
Thomas, C., K. Aston, and S. R. Daley. 1985. Milk production from silage. 3. A
comparison of red clover with grass silage. Anim. Prod. 41:23-31.
Thomas, P. C., D. G. Chamberlain, N. C. Kelly, and M. K. Wait. 1980. The nutritive
value of silages. Digestion of nitrogenous constituents in sheep receiving diets of grass
silage and grass silage and barley. Br.. J. Nutr. 43:469-479.
Thomas. C. V., M. A. DeLorenzo, and D. R. Bray. 1994. Capital budgeting for a new
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FL.
Tulloh, N. M., J. W. Hughes, and R. P. Newth. 1965. Physical studies of the alimentary
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Agrie. Res. 8:636-651
Tyrrell, H. F., and P. W. Moe. 1972. Net energy value for lactation of a high and low
concentrate ration containing com silage. J. Dairy Sci. 55:1106-1112.
Tyrrell, H. F., D. J. Thomson, D. R. Waldo, H. K. Goering, and G. L. Haaland. 1992.
Utilization of energy and nitrogen by yearling Holstein cattle fed direct-cut alfalfa or
orchardgrass ensiled with formic acid plus formaldehyde. J. Anim. Sci. 69:3163- 3177.
Udn, P., P. E. Colucci, and P. J. Van Soest. 1980. Investigation of chromium, cerium
and cobalt as markers in digesta. Rate of passage studies. J. Sci. Food Agrie. 31:625-632.
Ushida, K., J. P. Jouany, and P. Thivend. 1986. Role of rumen protozoa in nitrogen
digestion in sheep given to isonitrogenous diets. Br. J. Nut. 56:407-419.


3.8 Interaction of forage, supplementation rate, and year on body weight change (ABW).
Forages were Tifton 85 bermudagrass and Florgraze rhizoma peanut. Low (Lo) and
high (Hi) supplementation rates were 0.33 and 0.5 kg of supplement per 1 kg of
daily milk production. Supplementation rates did not differ by year (1995 or
1996) 106
3.9 Interactions of parity, forage, and stocking rate (SR) on forage and total organic
matter intake (OMI) and forage and total OMI as a percent of body weight
(OMIPBW)- Forages were Tifton 85 bermudagrass (BG) or Florigraze rhizoma
peanut (RP). Average low and high SR for BG pastures were 6.25 and 8.75
cows/ha. Average low and high SR for RP pastures were 3.75 and 6.25 cows/ha.
112
4.1 Vibracorder charts for cows treated with bST and housed in bams from 0800 to
1500 h (A) and for cows housed on pasture (B). Note the greater grazing intensity
for cows housed in the bam during the day 147
4.2 Effect of housing on body temperatures of cows measured over a 24-h period and
averaged over bST treatment regimes 160
4.3 Effect of bST on body temperatures of cows measured over a 24-h period and
averaged over daytime bam and daytime housing regimes 162
4.4 Regression equation estimates of body temperatures of cows measured over a 24-h
period and showing interaction of bST (+ or -) and housing treatments 164
4.5 Effect of bam plus bST (B+) vs. bam plus bST plus silage (B+S) treatment on body
temperatures of cows measured over a 24-h period 165
x


CHAPTER 1
INTRODUCTION
While use of pasture-based production systems is the norm for beef production in
the U.S., pasture use for dairy production was all but abandoned until the mid- to late
1980s when management of pastures using intensive rotational stocking began to be
adopted. During a time of financial duress, pasture systems garnered renewed interest,
primarily due to perceptions that they have reduced production costs, require less initial
investment, have less demanding labor requirements, and are more environmentally
sound than production with confined-housing.
Information regarding their use is limited, however, particularly for producers in
the Southeast. Regardless of the production system, producers in the Southeast must
overcome several challenges to be successful. The lesser quality of perennial forages
adapted to the region and the negative effects of high heat and humidity on animal
performance are the primary limitations to production. Thus, information in this arena is
vital because the challenges to production likely are more formidable for pasture-based
dairies.
Forages adapted to the region typically are of less quality than cool-season species
due to greater concentrations of fiber and lower concentrations of digestible nutrients.
Other potential limitations of pasture-based systems include variability in forage supply
and nutritive value, both of which are highly dependent upon climatological conditions.
1


48
amount of supplement fed. Estimates of forage mass excluded dead material. Average
mass of DM harvested increased 188 kg/ha for each kg increase in concentrate fed,
indicative of reduced forage intake. Herbage on offer ranged from 4000 to 6000 kg of
green DM/ha in summer to 500 to 1500 kg of green DM/ha in winter (below the forage
not limiting intake level). Average length of lactation was greater for supplemented
cows (275 d) compared to those of 0 (222 d) or 2 kg/d (252 d) supplement groups. Cows
assigned to 0 or 2 kg/d treatments had to be removed from treatment early due to
excessive weight loss.
A study of heifers grazing Cenchrus ciliaris pastures showed that grazing time
decreased 11 min/kg of supplement fed (Combellas et al., 1979). Heifers received a high
energy, high protein concentrate at 0, 3, or 6 kg/d. Rate of biting, total bites, and intake
per bite were also decreased. Though not significant, the number of grazing periods was
numerically greater with increased rate of supplementation.
Pulido and Leaver (1997) reported decreased GT of 11 min/kg of concentrate,
though effects were much more dramatic when concentrate fed was greater than 6 kg/d.
For 0, 6, or ad lib kg of daily concentrate intake, GT were 531, 526, and 381 min/d and
rates of forage intake were 31.4, 25.8, and 20.7 g/min. Forage intake decreased 0.69 kg/d
for each kg of concentrate consumed.
A study with beef steers (Adams, 1985) indicated that timing of supplement
feeding affects grazing behavior and forage intake. Steers grazing Russian wild ryegrass
(Elymus junceus) in Montana received forage only (control) or morning or afternoon
feedings of com supplement (0.3 kg of supplement/100 kg of BW). Though
supplemented steers ate less forage than steers on the control treatment, comparison


190
Delaby, L., and J. L. Peyraud. 1997. Influence of concentrate supplementation strategy
on grazing dairy cows performance. Page 29-137-29-138 in XVIII Int. Grassland
Conference. Winnipeg, Manitoba, Saskatoon, Saskatchewan, Canada.
Delgado, I., and P. F. Randel. 1989. Supplementation of cows grazing tropical grass
swards with concentrates varying in protein level and degradability. J. Dairy Sci. 72:995-
1001.
Denbow, C. J., K. S. Perera, R. C. Gwazdauskas, R. M. Akers, R. E. Pearson, M. L.
McGilliard. 1986. Effect of season and stage of lactation on plasma insulin and glucose
following glucose injection in Holstein cattle. J. Dairy Sci. 69:211-216.
DiMarco, O. N., and M. S. Aello. 1996. Gasto energtico extra de vaccunos por efecto
de caminata y pastoreo. Forrajes Journal. 1:7.
Draper, N. R., and H. Smith. 1981. Applied Regression Analysis, p. 252 John Wiley and
Sons, Inc. NY.
Dubl, R. L, J. A. Lancaster, and E. C. Holt. 1971. Forage characteristics limiting animal
performance on warm-season perennial grasses. Agron. J. 63:795-798.
DUrso, G., M. Avondo, S. Bordonaro, D. Marietta, and A. M. Guastella. 1998. Effect
of sustained-release somatotropin on performance and grazing behavior of ewes housed
at different stodking rates. J. Dairy Sci. 81:958-965.
Ealy, A. D., M. Drost, and P. J. Hansen. 1993. Developmental changes in embryonic
resistance to adverse effects of maternal heat stress in cows. J. Dairy Sci. 76:2899-2905.
Elbehri, A., and S. A. Ford. 1995. Economic analysis of major dairy forage systems in
Pennsylvania: The role of intensive grazing. J. Prod. Agrie. 8:501-507.
Ellis, W. C., C. Lascano, R. Teeter, and F. N Owens. 1980. Solute and particulate flow
markers. In Protein Requirements of Cattle: Symposium. F. N. Owens, ed. Oklahoma
Agrie. Exp. Stn. Mise. Publ. 109, Stillwater.
Elvinger, F., R. P. Natzke, and P. J. Hansen. 1992. Interactions of heat stress and
bovine somatotropin affecting physiology and immunology of lactating cows. J. Dairy
Sci. 449-462.
Emery, R. S., and T. H. Herdt. 1991. Lipid nutrition. Veterinary Clinics of North
America: Food Animal Practice. 7:349-352.
Emmick, D. L., and L. F. Toomer. 1991. The economic impact of intensive grazing
management on fifteen dairy farms in New York State. Page 19 in Proc. Amer. Forage
and Grassl. Conf. Amer. Forage and Grassl. Counc., Georgetown, TX.


APPENDIX 3
WEEKLY WEATHER DATA FOR 1995, 1996 AND 1997 GRAZING TRIALS
Date
Rainfall, mm
Minimum
- Temperature, C -
Maximum
Mean
1995
July 10-16
26.3
21.9
34.7
27.5
July 17-23
92.8
20.6
34.7
27.5
July 24-30
38.9
20.0
35.0
26.9
July 31-Aug. 6
52.8
21.1
34.2
27.2
Aug. 7-13
43.4
20.6
34.2
27.3
Aug. 14-20
38.7
20.3
34.2
27.3
Aug. 21-27
71.6
21.1
32.2
26.4
Aug. 28-Sept. 3
8.8
21.7
33.3
27.0
Sept. 4-10
4.3
19.4
31.9
24.9
Sept. 11-17
45.3
20.0
33.3
26.7
Sept. 18-24
9.8
17.5
33.6
26.3
Sept. 25-Oct.l
9.0
18.1
30.8
25.4
Oct. 2-8
81.0
21.4
31.7
26.5
Oct. 9-10
7.5
22.2
30.8
26.3
1996
July 9-15
30.2
22.8
34.2
27.0
July 16-22
20.3
20.6
34.2
27.3
July 23-29
0.0
18.9
36.4
27.7
July 30-Aug. 5
65.5
19.4
35.3
26.8
Aug. 6-12
34.9
19.2
33.9
26.2
Aug. 13-19
31.2
19.4
32.5
25.5
Aug. 20-26
7.0
18.9
33.1
25.5
Aug. 27-Sept. 2
75.7
15.6
31.9
25.1
Sept. 3-9
1.5
18.3
33.3
26.1
Sept. 10-16
15.0
16.4
33.1
25.3
Sept. 17-23
14.2
13.1
31.4
24.5
Sept. 24-30
0.5
13.6
32.2
24.3
Oct. 1-2
23.9
21.4
31.1
26.3
1997
July 28-Aug. 3
103.9
20.3
32.5
26.4
Aug. 4-10
17.0
16.9
33.3
27.0
Aug. 11-17
21.3
21.7
34.4
27.9
Aug. 18-24
1.3
17.8
35.0
27.5
Aug. 25-31
51.3
15.3
34.4
25.4
Sept. 1-7
8.9
15.8
33.3
25.9
Sept. 8-14
0.0
15.0
33.9
25.3
Sept. 15-21
0.0
16.9
34.2
26.5
Sept. 22-28
56.1
20.0
35.0
26.3
Sept. 29 Oct. 5
3.3
15.0
31.7
24.2
Oct. 6 10
5.1
15.6
31.4
24.1
183


203
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Forages: The Science of Grassland Agriculture. M. E. Heath, R. F. Barnes, and D. S.
Metcalfe, ed. Iowa State University Press, Ames, Iowa.
Mould, F. L., and E. R. Orskov. 1983. Manipulation of rumen fluid pH and its influence
on cellulolysis in sacco, dry matter degradation and the rumen microflora of sheep
offered either hay or concentrate. Anim. Feed Sci. and Tech. 10:1-14.
Mould, F. L., E. R. Orskov, and S. O. Mann. 1983. Associative effects of mixed feeds. I.
Effects of type and level of supplementation and the influence of the rumen fluid pH on
cellulolysis in vivo and dry matter digestion of various roughages. Anim. Feed Sci. and
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Muller, L. D., and L. A. Holden. 1994. Intensive rotational grazing. What are the special
nutritional needs? Large Anim. Vet. 49:27-29.
Muller, L. D., E. S. Kolver, and L. A. Holden. 1995. Nutritional needs of high producing
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Rochester, NY, Cornell Univ., Ithaca, NY.
National Research Council. 1989. Nutrient Requirements of Dairy Cattle. 6th rev. ed.
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Newbold, J. R., and S. R. Rust. 1992. Effect of asynchronous nitrogen and energy supply
on growth of ruminal bacteria in batch culture. J. Anim. Sci. 70:538-546.
Niles, W. L., E. C. French, P. E. Hildebrand, G. Kidder, and G. M. Prine. 1990.
Establishment of Florigraze rhizoma peanut (Arachis glabrata Benth.) as affected by
lime, phosphorus, potassium, magnesium, and sulfur. Soil and Crop Sci. Soc. Florida.
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International Symposium on Animal Production Under Grazing. Viqosa, Brazil.


7
high-speed fans with wetting mechanisms (Flamenbaum et al., 1986; Chen et ah, 1993;
Chan et ah, 1997). Such facilities increase shade and evaporative cooling, providing
relief from excessive ambient temperatures.
Ways to cool cows on pasture are limited, however. Fixed and mobile shade
structures, trees, cooling ponds, and strategic movement (e.g. allowing cows access to
cooling bams during times of high ambient temperature) represent the major methods
used to reduce heat stress of pastured animals. In addition, pastured cows face additional
heat stress from the heat of activity caused by grazing and walking to and from the parlor.
Thus, the effect of heat stress is likely of greater concern for graziers.
Recent literature regarding grazing dairy systems in the southeastern United
States is limited, although results with beef steers on pasture may have application. The
majority of data pertaining to dairy cow grazing in North America has been published by
researchers working in the Northeast and Midwest under very different environmental
conditions. Some research from Australia and other tropical areas may be applicable to
the southeastern environment, but the forages grown are typically of different genera and
the amounts of concentrate fed are less than the amounts provided by U.S. producers.
Thus, while pasture-based dairies may be a viable alternative to confined housing
systems in the Southeast, more information on factors affecting their viability is needed.
Energy Considerations for the Grazing Ruminant
Energy requirements for grazing cattle are likely greater than requirements for
cattle housed in confinement (Van Es, 1974; NRC, 1989). For lactating cows housed in
confinement, the NRC (1989) estimates that the maintenance requirement is 80 kcal of
NEi7kg of BW 075 (Moe et al., 1972) which includes an activity requirement of 10%.


171
concentration. Supplement likely increased growth of ruminal microbes and this would
explain the increased milk protein percentage with the greater SUP.
Feeding sizeable quantities of supplemental energy feeds can obscure the effects
of forage quality on animal performance (Waldo, 1986). Further, several researchers
(Blaxter and Wilson, 1963; Golding et al., 1976b; Arriaga-Jordan and Holmes, 1986)
have reported greater substitution with better quality forages. That appeared to be a
particular limitation with RP. With each additional kg of supplement fed above the low
SUP, cows produced an additional 0.87 kg of milk/d if grazing BG vs. an additional 0.43
kg of milk/d if grazing RP.
The response to supplement on a land-area basis was greater when cows grazed
BG than RP (132 and 110 kg of milk/ha per day at high and low SUP for BG vs. 90 and
83 kg of milk/ha per day at high and low SUP for RP). Both the lesser substitution of
forage with supplement by cows on BG and the greater carrying capacity of BG pastures
affected this response.
Surprisingly, SUP had no effect on changes in BW, nor were SUP by treatment
interactions detected. However, BW losses were numerically greater with the greater
SUP, in agreement with the observation that treatments supporting greater milk
production promoted BW loss. Feeding additional supplement caused a 10% increase in
RR (99 vs. 90 breaths/min).
Although total OMI increased approximately 2 kg/d with additional supplement,
forage OMI was reduced approximately lkg/d, and cows grazing RP pastures
experienced a greater decrease in forage consumption when fed more supplement
compared to those grazing BG pastures. The substitution of forage OM by supplement


199
Littell, R. C., G. A. Milliken, W. W. Stroup, and R. D. Wolfinger. 1996. SAS System for
Mixed Models. SAS Institute. Cary, NC.
Lobley, G. E., A. Connell, M. A. Lomax, D. S. Brown, E. Milne, A. G. Calder, and D. A.
H. Famingham. 1995. Hepatic detoxification of ammonia in the ovine liver: possible
consequences for amino acid metabolism. Br. J. Nutr. 73:667-685.
Loeffler, B., H. Murray, D G. Johnson, and E. I Fuller. 1996. Knee deep in grass. A
survey of twenty-nine grazing operations in Minnesota. Minn. Ext. Ser. BU-6693-S.
Lotan, E., H. Sturman, J. I. Weller, and E. Ezra. 1993. Effects of recombinant
somatotropin under conditions of high production and heat stress. J. Dairy Sci. 76:1394-
1402.
Ludri, R. S., R.C. Upadhyay, M. Singh, J. R. M. Guneratne, and R. P. Basson. 1989.
Milk production in lactating buffalo receiving recombinantly produced bovine
somatotropin. J. Dairy Sci. 72:2283-2287.
Mallone, P. G., D. K. Beede, R. J. Collier, and C. J. Wilcox. 1985. Production and
physiological responses of dairy cows to varying dietary potassium during heat stress. J.
Dairy Sci. 68:1479-1487.
Malven, P. V., H. H. Head, R. J. Collier, and F. C. Buonomo. 1987. Periparturient
changes in secretion and mammry uptake of insulin and in concentrations of insulin and
insulin-like growth factors in milk of dairy cows. J. Dairy Sci. 710:2254-2265.
Manalu, W, H. D. Johnson, R. Li, B. A. Becker, and R. J. Collier. 1991. Assessment of
thermal status of somatotropin-injected lactating Holstein cows maintained under
controlled-laboratory thermoneutral, hot and cold environments. J. Nutr. 121:2006-2019.
Mandevbu, P., J. W. West, R. N. Gates, and G. M. Hill. 1998. In vitro digestion kinetics
of neutral detergent fiber extracted from Tifton 85 and Coastal bermudagrasses. Anim.
Feed Sci. Tech. 73:263-269.
Marai, I. F. M., and J. M. Forbes. 1989. New techniques in environmental control for
cattle. Pages 121-129 in New Techniques in Cattle Production. C. J. C. Phillips, ed.
Butterworths. Boston.
Maraschin, G. E., S. C. Mella, G. S. Irelegui, and J. Riboldi. 1983. Performance of a
subtropical legume-grass pasture under different grazing management systems. Pages
457-461 in Proc. XIV Int. Grassland Congr. Lexington, KY. Westview Press, Boulder,
CO.
Marsh, W. H., B. Fingerhut, and H. Miller. 1965. Automated and manual direct methods
for the determination of blood urea. Clin. Chem. 11:624-627.


177
The increase in body temperature is in agreement with several other studies and
contradicts popular press and technical reports of Monsanto which suggest that cows are
capable of dissipating additional heat via greater RR and sweating.
Cows not injected with bST increased body temperature at a slower rate from
approximately 1100 h until 1630 h. Treatment with bST also affected body temperature
patterns once cows returned to pasture, with treated cows maintaining increased body
temperatures far longer than untreated cows. Though this temperature pattern for bST-
treated cows appears to reflect a greater drive to graze. Also cows receiving bST may
have been more aggressive grazers (greater bite rate) upon initial return to pastures.
Feeding silage curtailed grazing time by more than 25% (5.6 vs. 4.0 h of
grazing/d). The decreased grazing time resulted in decreased BG OMI of about
18% (from 9.0 to 7.4 kg/d, respectively), but total forage OMI was increased
approximately 17% with supplemental silage (from 9.0 to 10.5 kg of forage OMI/d).
As feeding silage did not affect milk production, supplement OMI was not
different between the plus or minus silage treatments. Cows fed silage consumed more
total OMI per day by nearly 8%. Whereas the equation of Moore et al. (1999) was used
to adjust forage digestibility due to associative effects of supplement feeding and thus
forage intake estimates, no additional adjustments to forage digestibility were made for
cows consuming com silage. If feeding com silage resulted in a greater depression of
pasture digestibility, OMI was over-predicted.
Feeding supplemental silage in the bam had no effect on milk production, 4%
FCM production, nor milk fat and protein concentrations or quantities. Bam cows not
receiving silage also tended to gain more than those fed additional roughage in the bam.


2.26 vs. 1.52% of BW) and total (17.7 vs. 13.5 kg/d; 3.54 vs. 2.70% of BW) organic
matter intakes (OMI). Increased supplement provision increased daily OMI, but
decreased forage intake. Substitution of forage with supplement (kg/kg) was 0.51 for RP
and 0.18 for BG.
A third experiment tested the effects of housing pasture-based cows in bams or on
pasture from 0800 to 1530 h. Within housing treatments, cows did or did not receive
bST. A fifth treatment tested the effect of feeding silage to barn-housed cows injected
with bST.
Intake of pasture and milk production were similar for both housing managements
although cows housed in bams spent less time grazing. Treatment with bST increased
milk production (18.1 vs. 16.6 kg/d). Production was unaffected by silage intake.
Housed cows and bST-treated cows maintained or gained BW. Respiration rates
and body temperatures were greater for pastured cows, and body temperatures were
greater in cows given bST.
Improved grasses in combination with large amounts of supplemental feeds are
likely most suited for pasture-based dairy production systems in Florida. Providing fans
and sprinklers to relieve heat stress and injecting with bST was only moderately effective
to stimulate milk production of midlactation cows in a pasture-based system.
xiii


209
Stobbs, T. H. 1970. Automatic measurement of grazing time by dairy cows on tropical
grass and legume pastures. Tropical Grasslands. 4:237-244.
Stobbs, T. H. 1973. The effect of plant structure on the intake of tropical pastures. II.
Differences in sward structure, nutritive value, and bite size of animals grazing Setaria
anceps and Chloris gayana at various stages of growth. Aust. J. Agrie. Res. 24:821-829.
Stobbs, T. H. 1974a. Components of grazing behaviour of dairy cows on some tropical
and temperate pastures. Proc. Aust. Soc. Anim. Prod. 10:299-302.
Stobbs, T. H. 1974b. Rate of biting by Jersey cows as influenced by the yield and
maturity of pasture swards. Tropical Grassl. 8:81-86.
Stobbs, T. H. 1976. Milk production per cow and per hectare from tropical pastures.
Pages 129-146 in Produccin de Forrajes. Memoria. Seminario Internacional de Ganderia
Tropical, Acapulo, Mexico.
Stobbs, T. H. 1977. Short-term effects of herbage allowance on milk production, milk
composition and grazing time of cows grazing nitrogen-fertilized tropical grass. Aust. J.
Exp. Agrie. Anim. Husb. 17:892-898.
Stobbs, T. H., D. J. Minson, and M. N. McLeod. 1977. The response of dairy cows
grazing a nitrogen fertilised grass pasture to a supplement of protected casein. J. Agrie.
Sci. (Camb.) 89:137-141.
Stockdale, C. R. 1985. Influence of some sward characteristics on the consumption of
irrigated pastures grazed by lactating dairy cattle. Grass and Forage Sci. 40:31-39.
Stockdale, C. R., A. Callaghan, and T. E. Trigg. 1987. Feeding high energy supplements
to pasture-fed dairy cows. Effects of stage of lactation and level of supplement. Aust. J.
Agrie. Res. 38:927-940.
Stuth, J. W., D. R. Kirby, and R. E. Chmielewski. 1981. Effect of herbage allowance on
the efficiency of defoliation by the grazing animal. Grass Forage Sci. 36:9-15.
Sullivan, J.L. Huber, J.T. DeNise, S.K. Hoffman, R.G. Kung, L. Jr. Franson, S.E.
Madsen, K.S. 1992. Factors affecting response of cows to biweekly injections of
sometribove. J. Dairy Sci. 75:756-763.
Sutton, J. D., I. C. Hart, W. H. Broster, R. J. Elliot, and E. Schuller. 1986. Feeding
frequency for lactating cows: effects on rumen fermentation and blood metabolites and
hormones. Br. J. Nutr. 56:181-192.
Takahashi, H., H. Murata, and H. Matsumoto. 1986. Secretory responses of plasma
insulin, glucagon, cortisol, and glucose to heat exposure in calves. Jpn. J. Vet. Sci.
48:1287-1289.


38
bacterial N as a percentage of N flowing to the small intestine was greatest for cows
grazing pasture, N flow to the small intestine relative to N intake was least for cows
grazing pasture, indicative of the greater N losses. Flows of certain essential amino acids
also tended to be less with pasture-fed cows. Holden et al. (1994b) also suggested that
diet selection over time may affect fermentation patterns because intake of CP and
ruminally degradable protein likely decline with time spent grazing (Chacon and Stobbs,
1976).
Loss of N from the rumen is costly due to significant energetic expenditure
associated with urea synthesis and excretion. Urea synthesis and excretion cost
approximately 5 kcal/g of N excreted (NRC, 1989). Greaney et al. (1996) estimated that
25% or more of liver oxygen consumption was for the detoxification of ammonia to urea
when diets were pelleted alfalfa (2.7% N) or fresh white clover (4.4% N). The authors
noted that these energetic costs of N loss were likely underestimated because increased
ammonia loading would likely result in increased amino acid catabolism, sodium pump
activity and oxidative phosphorylation. In addition to the greater energetic expenditure,
additional N costs are incurred with hepatic removal of NH3 due to amino acid
catabolism (Lobley et al., 1995; Greaney et al., 1996). This may further limit animal
performance if supplies of essential amino acids are limited.
Though microbial protein is the primary protein source for lactating dairy cows
(Glenn, 1994), Leng and Nolan (1984) noted that it alone cannot provide an adequate
supply of amino acids to the small intestine for maximum growth and production by the
host, as reported by Holden et al. (1994b). This might in part account for reduced
persistency observed with grazing dairy cows (Hoffman et al., 1993). To offset these


72
bST in Hot Environments
Because of the increase in body temperatures associated with the use of bST,
concerns have been raised about its use on heat-stressed cattle (Kronfeld, 1988). In a
study by Mollett et al. (1985) milk production was not increased with bST administration,
and the authors suggested that a period of high heat and humidity affected the response to
treatment.
In a study of bST and shade effects, Zoa-Mboe et al. (1989) reported no increases
in milk production due to bST though milk production was increased with shade.
However, on a 3.5% fat-corrected basis, both shade and bST treatments increased milk
production to approximately 24 kg/d vs. 22 kg/d for control cows. Several positive
responses to bST when used in hot climates have been reported across Bos taurus breeds,
Bos species, and ruminant genera (Amiel et al. unpublished data; Ludri et al., 1989;
Phipps et al., 1991; West et al., 1990). Generally, provided sufficient quantities of a
balanced diet are available, bST is effective in hot conditions.
Amiel et al. (unpublished data) tested the effects of bST in several herds in
Jamaica. Milk production responses were similar across a variety of management
conditions, increasing approximately 17% with bST (9.9 vs. 11.6 kg of milk/d).
Performance responses from eight herds of Jamaican Hope cattle ranged from 16 to 30%
whereas 6 and 14% increases were observed for Holstein and Holstein cross cattle
injected with bST, respectively. Conditions were hot and humid, pasture forages were
generally inadequate due to a period of drought, and extra concentrate typically was not
fed to compensate for lack of sufficient pasture.


119
NDF in BG decreased from 1995 to 1996 (81.9 vs. 80.4%) while that in RP increased
(43.5 vs. 45.5%; year by forage interaction, P < 0.05).
Stocking rate effects. Increased SR had no effect on IVOMD or concentration of
NDF but did tend (P < 0.10) to increase CP concentrations (15.3 vs. 15.8% for low and
high SR, respectively) as evidenced by the tendency (P <0.10) of greater MUN
concentrations of cows kept at the greater SR. Year by SR interactions would indicate
forage rather than SR effects, and their absence in these data represents the confounding
effect of averaging the results over both forages. Although year by forage by SR
interactions were not observed for any nutritive value measure, the numeric patterns were
consistent with such interactions but masked by large standard error.
Supplementation rate effects. Supplementation rate had no effect on any
nutritive value measures. Increasing SUP had little effect on IVOMD of RP pastures
(71.0 vs. 71.5% for low and high SUP treatments, respectively) while IVOMD of BG
pastures increased with increasing SUP (57.5 vs. 60.1%; forage by SUP interaction, P <
0.05). Similarly, greater SUP resulted in no change in CP concentration (17.8%) of RP,
whereas CP concentration of BG tended to increase at the greater SUP (12.8 vs. 13.8;
forage by SUP interaction, P < 0.10).
These results do not imply that increasing SUP improved forage nutritive value,
but rather those cows fed more supplement consumed forage of greater nutritive value as
well. Forage OMI data (Table 3.6) support this idea, since greater supplement intake
decreased forage intake, which would have allowed for greater selection.


127
supplement on BG but was $0.29/cow per day lower for cows eating more supplement on
RP. These responses reflect the effects of substitution. One aspect of substitution not
accounted for in this analysis is the potential for greater SR when feeding more
supplement to cows grazing RP pastures.
The greater dollar return on a per cow basis for RP pastures is dwarfed by the
greater income per unit land area capable with BG pastures. By these calculations, use of
BG resulted in a 40% greater dollar retum/ha. Average income/ha for BG was $28.95 vs.
$20.65 for cows grazing RP.
Conclusions
Successful utilization of pasture-based forage systems in Florida is likely to
depend upon a variety of factors. Along with forage type, SR, supplement type and
feeding regime, pasture and animal management factors such as fertilization, forage
components for other seasons, types of supplement provided, exogenous growth hormone
(bST), cooling systems for cows (trees, shades, ponds, bams with misters and fans), breed
differences, and reproductive management must be considered. Further, despite its
potential for reduced costs, the rather low production per cow in this study suggests that
use of pasture for lactating dairy cows in Florida may limit its consideration by most
producers.
For producers using grazing, RP is likely to be of limited use in Florida dairy
grazing systems until N fertilizers become prohibitively expensive. The greater milk
production/cow associated with RP cannot compensate for the forages limited ability to
support large numbers of lactating cows/ha. Tifton 85 bermudagrass, however, appears


34
54.7%) in true ruminal digestion of cool-season forage DM was reported when lactating
dairy cows were fed supplemental corn at 6.4 kg/d. Total tract digestibility of DM was
less affected (71.9 vs. 69.9%), however (Berzaghi et al., 1996).
Research with steers (Vadiveloo and Holmes, 1979; Galloway et al., 1993a,b) and
sheep (Chenost et al., 1981, cited by Arriaga-Jordan and Holmes, 1986) has shown that
when forages are of low to moderate digestibility, supplement often improves overall
total diet digestibility, likely due to the greater digestibility of the supplement (Galloway
et al., 1993a). Diet digestibility is often unimproved when supplements are fed with high
quality forages, however. Arriaga-Jordan and Holmes (1986) studied the effects of
concentrate supplementation on herbage digestibility in dairy cattle. Feeding a grain-
based supplement to cows eating high quality pasture increased total intake, but reduced
herbage intake and depressed digestibility of the herbage consumed, thus reducing the
potential nutritional benefit of the concentrates.
Supplements also affect diet digestibility by affecting rates of passage of digesta
through the digestive tract. Waldo et al. (1972) were the first to model the relationship
between rates of digestion and passage on total digestion: k]/(ki +k2), where ki and k2 are
rates of digestion and passage, respectively. In theory, if passage is 0 then digestion will
equal 100% of potential extent of digestion (ki/ki = 1). Conversely, if passage is rapid, it
will have a large, depressive effect on diet digestion. For example, Tyrrell and Moe
(1972) fed increasing amounts of com grain as a supplement to cows fed com silage
diets. Although intakes increased with supplementation, the decreased digestibility of the
diet due to increased passage resulted in decreased concentration of dietary ME.


47
Hongerholt and Muller (1998) also found no response of grazing, lactating cows
to increased dietary ruminally undegradable protein, but Stobbs et al. (1977) reported that
escape protein from protected casein stimulated intake. When Davison et al. (1991)
provided meat and bone meal to lactating cows, they were not able to measure forage
intake changes. However, by calculations of energy requirements for observed milk
production and weight changes, the authors determined that forage intake was likely
increased. Consumption of meat and bone meal did not result in greater milk yield, but
did result in less (P = 0.068) BW loss over the first 100 d of the trial and greater (P =
0.054) gain over the entire lactation. The authors concluded that responses to protein
supplements ... vary with the type of pasture, the level of grain or energy supplement fed
and the level of pasture on offer (Davison et al., 1991, p. 162).
Effect of Supplements on Grazing Behavior
Several researchers have reported reduced grazing time with supplementation.
Sarker and Holmes (1974) fed 2, 4, 6, or 8 kg of concentrate supplement/d. They
reported large decreases in GT (an average of 28 min/kg of supplement) with
supplementation. Although total OM intake increased 2 kg from the low to the high
supplementation rate (11.5 vs. 13.6 kg of OM/d), herbage OM intake decreased from 9.9
to 7.4 kg of OM/d.
Cowan et al. (1977) fed a 4:1 cormsoybean meal concentrate at 0, 2, 4, or 6 kg/d
to cows grazing green panic (Panicum maximum var. trichoglume) and glycine (Glycine
wightii cv. Tinaroo) pastures. They reported decreased grazing time with increased
supplement (23 min/d per kg of supplement fed) during autumn and winter months (time
of reduced HA), but not during summer. Available pasture increased with increasing


14
Leaf distribution in the canopy has the greatest influence on IB, (Stobbs, 1973;
Hodgson, 1985) because IB is the product of bite volume (depth x area) and the bulk
density (weight per unit volume) of herbage within the sward horizons encompassed in a
bite (Hodgson, 1985, p. 342-343). Other factors that influence IB include sward height,
presence of stem and pseudostem horizons, and the height of these horizons relative to
total sward height, all of which affect ease of prehension and depth of biting into the
canopy (Flores et al., 1993).
Sward maturity has strong effects on efficiency of the grazing activity due to its
effect on leaf distribution in the canopy (Stobbs, 1973; 1974a). Stobbs (1973) studied IB
in dairy cows grazing tropical swards at 2, 4, 6, or 8 wk of regrowth. The IB was limited
by the low yield and density of herbage at 2 wk of age even though pastures contained
82% leaf. Intake per bite increased at 4 wk with increasing available herbage, but
decreased with increasing maturity (6 and 8 wk) primarily due to decreasing leaflstem
ratio. Mean IB at 2, 4, 6, and 8 wk were approximately 0.23, 0.27, 0.17, and 0.15 g
OM/bite. This research also compared responses between species (Setaria anceps and
Chloris gayana) that showed that sward maturity affected IB differently between species
(Stobbs, 1973). Mayne et al. (1997) reported intakes of 0.4 to 1.1 g of DM/bite for cows
grazing ryegrass pastures. These values are quite high, but their estimates were made
indirectly. Pulido and Leaver (1997) did not report IB but reported rates of intake of
perennial ryegrass of 20 to 30 g of OM/min. Assuming a bite rate of 55 bites/min, IB
ranged from 0.36to0.55gof OM/bite.
Research into the effect of progressive defoliation on intake of tropical pastures
showed that cows selected more than 80% leaf from the upper layers of the sward in the


APPENDIX 2
SAS PROGRAM TO ADJUST FORAGE INTAKE UNTIL FECAL OUTPUT
OBSERVED AND FECAL OUTPUT PREDICTED DIFFER BY LESS THAN ONE-
HUNDREDTH OF A KILOGRAM PER DAY
Program terms:
FRGDIG
IVOMD
FRGINTAK =
TOTINTAK =
SUPINTAK =
TOTDIG
FRGDIG
SUPDIG
FOP
FOO
DIFF
forage digestibility
in vitro organic matter digestibility
forage intake
total intake (initially predicted from parameters derived from fecal
excretion curves)
supplement intake (assumed constant)
sum of digestible forage and digestible supplement intakes divided by
total intake
forage digestibility (determined from laboratory analysis)
supplement digestibility (assumed constant)
fecal output predicted
fecal output observed
difference of observed and predicted fecal output
OMD is calculated in each iteration call that the "expected" OMD.
Convert "expected" to "adjusted" with the following formula:
Adjusted OMD = 59.71 (0.8948 expected OMD) + (0.01399 (expected OMD)2)/100
DATA ;
SAS PROGRAM
INPUT COW PAR TRT PER PAST YR OMI FOO IVOMD SUPINTAK SUPDIG;
FRGDIG = IVOMD;
DO FRGINTAK =1 TO 40 BY .05 UNTIL (DIFF < .01);
TOTINTAK = FRGINTAK + SUPINTAK;
EXPDIG = (FRGINTAK*FRGDIG + SUPINTAK* SUPDIG)/TOTINTAK* 100;
ADJDIG = (59.71 0.8948*EXPDIG + 0.01399*EXPDIG**2)/100;
FOP = TOTINTAK* (1-ADJDIG);
DIFF = FOO-FOP;
END;
CARDS;
PROC PRINT;
RUN;
182


37
negative effects due to slug feeding of supplements such as periodic reductions in intake
and ruminal acidosis.
Synchronizing Nitrogen And Carbohydrate Supplements To Increase Microbial
Protein Synthesis in the Rumen
Loss of Feed Nitrogen in Ruminants
Proteins in pasture forages can be degraded rapidly and extensively by ruminal
microbes (Beever et al., 1986a, b; Van Vuuren et al., 1991) and considerable N losses
have been reported for animals grazing pasture. For example, steers grazing ryegrass or
white clover pastures consumed approximately 0.61 and 1.18 g of N/kg of live weight,
and non-NH3-N (NAN) flow to the small intestine was greater with clover diets (0.60 vs.
0.76 g of NAN/kg of live weight for ryegrass and clover, respectively; Beever et al.,
1986b). However, the differential between intake N and NAN flow represented a 35%
loss of N prior to the duodenum for cows grazing clover pastures and little loss of N for
cows grazing ryegrass. Ruminal NH3 concentrations typically ranged between 20 and
100 mg of NH3-N/L of ruminal fluid for grass diets, but ranged from 250 to 300 mg of
NH3-N/L of rumen fluid for clover diets.
Similar ruminal N losses (37%) were reported for non-lactating cows consuming
unfertilized fresh cool-season pasture grasses (Holden et al., 1994b). Cows were fed
fresh pasture, silage, or hay and consumed similar quantities (13.0 to 13.7 kg of DM/d) of
the mixed-grass forage. The CP concentration of the forage was approximately 17% in
each forage form with the OM:CP ratio ranging from 4.5 to 5.1. Ruminal NH3
concentrations were greater for cows consuming pasture. The authors, citing work by
Ushida et al. (1986), suggested that the greater ruminal NH3 concentrations might have
been related to greater protozoal counts they observed in the pasture-fed cows. Though


201
Meijs, J. A. C, and J. A. Hoekstra 1984. Concentrate supplementation of grazing diary
cows. 1. Effect of concentrate intake and herbage allowance on herbage intake. Grass and
Forage Sci. 39:59-66.
Meijs, J. A. C., R. J. K. Walters, and A. Keen. 1982. Sward methods. Pages 11-36 in
Herbage Intake Handbook. J. D. Leaver (ed.). Brit. Grassl. Soc. Hurley. U.K.
Mertens, D. R., and J. R. Loften. 1980. The effect of starch on forage fiber digestion
kinetics in vitro. J. Dairy Sci. 63:1437-1446.
Michel, A., S. N. McCutcheon, D. D. S. Mackenzie, R. M. Tait, and B. W. Wickham.
1990. Effects of exogenous bovine somatotropin on milk yield and pasture intake in dairy
cows of low or high genetic merit. Anim. Prod. 51:229-234.
Michell, P., and W. J. Fulkerson. 1987. Effect of grazing intensity in spring on pasture
growth, composition and digestibility, and on production by dairy cows. Aust. J. Exp.
Agrie. 27:35-40.
Miettinen, H., and P. Huhtanen. 1989. The concentrations of blood metabolites and the
relations between blood parameters, fatty acid composition of milk and estimated ME-
balance in dairy cows given grass silage ad libitum with five different carbohydrate
supplements. Acta Agrie. Scandinavia. 39:319-330.
Milne, J. A.,T. J. Maxwell, and W. Souter. 1981. Effects of supplementary feeding and
herbage mass on the intake and performance of grazing ewes in early lactation. Anim.
Prod. 32:185-195.
Minson, D. J. 1990. Forage in Ruminant Nutrition. Academic Press, San Diego, CA.
Minson, D. J., and M. N. McLeod. 1970. The digestibility of temperate and tropical
grasses. Pages 719-722 in Proc. XI Int. Grassl. Congr. Surfers Paradise. Queensland,
Australia.
Minson, D. J., and J. R. Wilson. 1994. Prediction of intake as an element of forage
quality. Pages 533-563 in Forage Quality, Evaluation, and Utilization. G. C. Fahey, Jr.,
M. Collins, D. R. Mertens, and L. E. Moser, ed. Amer. Soc. Agron., Madison, WI.
Moe, P. W., W. P. Flatt, and H. R. Tyrrell. 1972. Net energy value of feeds for lactation.
J. Dairy Sci. 55:945-958.
Mohammed, M. E., and H. D. Johnson. 1985. Effect of growth hormone on milk yields
and related physiological functions of Holstein cows exposed to heat stress. J. Dairy Sci.
68:1123-1133.


TABLE 3.3. Effect of forage, stocking rate (SR), and supplementation rate (SUP) on milk production and composition of Holstein
cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut during the summers of 1995 and 1996.
Tifton 85 bermudagrass Florigraze rhizoma peanut
Stocking Rate1 Stocking Rate2 Probability3
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage SR x SR
Item 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 SEM Forage SR SUP x SR x SUP x SUP x SUP
Milk, kg/d
17.9
14.9
17.4
14.6
18.1
16.6
18.2
16.7
0.3
***
NS
***
NS
*
NS
NS
FCM, kg/d
16.3
13.9
16.0
13.7
16.1
15.1
16.2
15.3
0.3
**
NS
***
NS
**
NS
NS
Fat, %
3.44
3.6
3.48
3.6
3.38
3.4
3.3
3.50
0.0
**
NS
***
NS
NS
NS
NS
Fat, kg/d
0.61
0.5
0.60
0.5
0.59
0.5
0.6
0.58
0.0
*
NS
***
NS
***
NS
NS
Protein, %
2.99
2.9
3.01
2.9
3.01
2.9
3.0
2.98
0.0
NS
t
**
NS
NS
NS
NS
Protein, kg/d
0.53
0.4
0.52
0.4
0.54
0.4
0.5
0.49
0.0
***
NS
***
NS
t
NS
NS
see4
375
530
447
490
374
413
478
423
41
NS
NS
NS
NS
NS
NS
NS
MUN5, mg %
17.2
18.2
16.0
17.0
17.0
18.8
17.0
18.2
0.4
t
*
**
NS
NS
NS
NS
'High and low stocking rates for Tifton 85 bermudagrass were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates for Florigraze rhizoma peanut were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and +, respectively.
4Somatic cell count, xlOOO.
5Milk urea nitrogen.


104
Parity
Figure 3.6. Interaction of parity, forage, and stocking rate on body weight change (ABW).
Average low (Lo) and high (Hi) stocking rates were 6.25 and 8.75 cows/ha for Tifton 85
bermudagrass (BG) and 3.75 and 6.25 cows/ha for Florigraze rhizoma peanut (RP) pastures.
Stocking rates were the same across parities.
T3
00
c/5
U
03
<
"O
oo
(N
'So
r\
£
CQ
<
0.00
Lo Hi
Lo
Hi
-5 -
10 -
-15
-12
1995
-0.28
Lo
Hi
Lo
Hi
-4
-7
1996
Year
SE = 0.07
P < 0.05
SE = 2
P < 0.05
Figure 3.7. Interaction of supplementation rate and year on changes of body condition
score (ABCS 5 point scale) and body weight (ABW). Low (Lo) and high (Hi) supple
mentation rates were 0.33 and 0.5 kg of supplement per kg of daily milk production.


109
Intake of OM and Nutrients
Parity and year effects. Expressed in terms of daily amount, intake of forage
OM, supplement OM, and total OM were not different between parities. It was assumed
that cows of all parities ate equal amounts of supplement within a treatment. Therefore
supplement OMI as a percentage of BW (OMIPBW) was necessarily greater (P < 0.001)
for the lighter, primiparous cows. Because forage OMI was not different by parity, total
OMIPBW also was greater (P <0.01) for primiparous cows as a consequence of our
assumptions. Forage, supplement, and total OMI was 1.96, 1.30, and 3.26% of BW/d for
primiparous cows compared to 1.79, 1.14, and 2.94% of BW/d for multiparous cows.
Forage effects. Cows grazing RP pastures consumed 49% more (P < 0.001)
forage OM than cows grazing BG pastures (11.3 vs. 7.6 kg of OM/d; Table 3.5). Cows
grazing RP pastures were fed more (P < 0.01) supplement because they produced more
milk, thus supplement intakes were 6.4 and 5.9 kg of OM/d for RP and BG pastures,
respectively (P < 0.01). Total OMI were 31% greater (P < 0.001) for cows grazing RP in
comparison with cows grazing BG pastures (17.7 vs. 13.5 kg/d. The measures of
OMIPBW followed the same patterns as OMI. Cows grazing RP pastures consumed
more (P < 0.001) forage (2.26 vs. 1.51% of BW), more (P < 0.01) supplement (1.28 vs.
1.18% of BW) and more (P < 0.001) total OM (3.54 vs. 2.70% of BW) than cows grazing
BG pastures.
Stocking rate effects. Greater SR reduced (P < 0.05) both forage OMI and
forage OMIPBW. Cows consumed 9.0 and 9.9 kg of forage OM/d (1.82 and 1.95% of
BW), when assigned to the high and low SR, respectively. However, cows stocked at the
higher rate consumed slightly more (P < 0.05) supplement (6.2 vs. 6.0 kg of OM/d; 1.26


81
Cows were milked at approximately 0600 and 1800 h. An unpelleted supplement
(Table 3.1) was fed after each milking in troughs located in each paddock. The amount
of supplement fed was recalculated twice weekly. Feed troughs were moved with the
shade and water tubs each day.
Experimental Procedures
Animal measures. Milk weights were recorded at each milking. Milk samples
were collected at six consecutive milkings during each of the last 2 wk of each period.
Samples were analyzed by Southeast Dairy Labs (McDonough, GA) for fat and protein
concentrations and somatic cell count (SCC). Samples were analyzed for milk urea
nitrogen (MUN) in 1996.
Cows were weighed on three consecutive days at the initiation of the trial and at
the end of each period. Body weights were recorded after the a.m. milking and prior to
feeding of supplement. Body condition scores (BCS) were recorded on one of the weigh
days within each period (Wildman et al., 1982).
Respiration rates were recorded on 1 d of each period. Movement of the flank or
bobbing of the head was monitored over 1 -min intervals. Measures took place while cows
were on pasture during the time of greatest potential ambient temperature (approximately
1400 to 1600 h). In 1996, rectal temperatures were measured with small, digital
thermometers (Medline, Medline Industries, Inc., Mundelein, IL) after the p.m.
milking.
Blood was obtained from the coccygeal vessels on d 27 of periods 1 and 2 and d
19 in period 3 in 1995. Samples were collected on d 22 or 23 of each period in 1996.
Samples were collected into 9 ml Na-heparinized syringes (Luer Monovette, LH,


121
TABLE 3.9. Regression1 groupings and regression coefficients for predicting 1995 and
1996 pre- and post-graze herbage mass of Tifton 85 bermudagrass and Florigraze
rhizoma peanut pastures.
1995
Period
- Year
1996
Period -
Item 1
2
3
1
2
3
Bermudagrass
regression grouping
Pregraze estimates
Measurements, n
16
13
16
13
13
14
Intercept
21.81
51.73
75.70
23.17
124.59
96.24
Slope
6.797
9.902
10.245
8.989
4.972
5.444
r2
0.896
0.528
0.421
0.784
0.562
0.344
Postgraze estimates
Measurements, n
14
15
15
14
13
16
Intercept
40.24
77.13
109.37
27.87
83.74
55.28
Slope
5.597
8.053
8.503
7.227
7.449
7.230
r2
0.937
0.719
0.579
0.646
0.619
0.872
Rhizoma peanut
regression grouping
Pregraze estimates
Measurements, n
15
16
15
16
16
16
Intercept
32.68
61.80
46.98
1.186
-0.303
8.836
Slope
7.798
7.927
12.506
10.21
12.14
9.75
r2
0.700
0.495
0.595
0.730
0.722
0.580
Postgraze estimates
Measurements, n
13
12
14
16
16
16
Intercept
40.08
73.28
72.67
-18.624
-10.517
-8.791
Slope
7.674
7.046
10.547
14.39
15.24
12.31
r2
Itt i r
0.735
0.675
0.540
0.693
0.776
0.889
'Herbage mass = Intercept + Slope Disk meter height, cm.


5
[National Research Council (NRC), 1989], Even at similar NDF and lignin
concentrations, warm-season grasses are less digestible than cool-season grasses (Barton
et al., 1976; Mertens and Lofton, 1980). Minson and McLeod (1970) reported that the
mean DM digestibility coefficient for tropical grasses was 13 percentage units less than
that of temperate grasses. When grown at warmer temperatures, forages have greater
concentrations of fiber and are less digestible than those grown under more temperate
conditions (Deinum and Dirven, 1976; Fales, 1986). Greater humidity also creates
potential for additional plant stresses via increased phytopathogen load.
For southeastern producers using confined-housing systems, growing high quality
forages may be of limited concern. Despite the climatological challenges, acceptable
quality maize (Zea mays L.) silage can be grown locally and high quality alfalfa
(Medicago sativa L.) hay is available for purchase from growers in western states.
Moreover, producers in the region using confined-housing frequently use by-product
feeds such as brewers and distillers grains, whole cottonseed, and cottonseed hulls.
These feeds may supply substantial portions of the diets roughage, potentially reducing
the need for homegrown forages.
The ability to grow superior quality forages is of particular concern for graziers
(producers using grazing systems). Perennial, warm-season forages typically are of
lower quality than cool-season forages as measured by comparisons of animal
performance (Galloway et al., 1993b). Stobbs (1976, cited by Ruiz, 1983) showed that
Jersey cows grazing immature tropical pastures produced approximately 60% as much
milk as those grazing temperate pastures. Cool season species generally are considered
to be of greater quality due to greater digestibility because of differences in the relative


187
Brody, S. 1945. ed. Bioenergetics and Growth. Reinhold, New York, NY.
Brougham, R. W. 1960. The effects of frequent hard grazings at different times of the
year on the productivity and species yields of a grass-clover pasture. N.Z. J. Agrie. Res.
3:125-136.
Brumby, P. 1956. Milk production in first-calf heifers following growth-hormone
therapy. N.Z. J. Sci. Tech. A37:152-157.
Brumby, P. J., and J. Hancock. 1955. The galactopoietic role of growth hormone in
dairy cattle. N.Z. J. Sci. Tech. A36:417-436.
Burton, G. W., R. N. Gates, and G. M. Hill. 1993. Registration ofTifton 85
bermudagrass. Crop Sci. 33:644.
Burton, G. W., and W. W. Hanna. 1995. Bermudagrass. Pages 421-429 in Forages Vol.
I, An Introduction to Grassland Agriculture. R. F. Barnes, D. A. Miller, and C. J. Nelson,
ed. Iowa State University Press, Ames, Iowa.
Buxton, D. R., D. R. Mertens, and K. J. Moore. 1995. Forage quality for ruminants:
Plant and animal considerations. Prof. Anim. Sci. 11:121-131.
Caird, L. and W. Holmes. 1986. The prediction of voluntary intake of grazing dairy
cows. J. Agrie Sci. 107:43-54.
Campling, R. C., and J. C. Murdoch. 1966. The effect of concentrates on the voluntary
intake of roughages by cows. J. Dairy Res. 33:1-11.
Carruthers, V. R., P. G Neil, and D. E. Dailey. 1996. Microbial protein synthesis and
milk production in cows offered pasture diets differing in non-structural carbohydrate
contents. Proc. N.Z. Soc. Anim. Prod. 56:255-259
Carver, L. A., K. M. Barth, J. B. McLaren, H. A. Fribourg, J. T. Connell, and J. M.
Bryan. 1978. Total digestible nutrient content of consumed forage and total digestible
nutrient consumption by yearling beef steers grazing nitrogen-fertilized bermudagrass
and orchardgrass-ladino clover pastures. J. Anim. Sci. 47: 699-707.
Casper, D. P., B. P. Glenn, and C. K. Reynolds. 1993. Energy metabolism of lactating
dairy cows fed two formaldehyde- and formic-acid treated forages with two nonstructural
carbohydrate sources. J. Dairy Sci. 76(Suppl.):209(Abstr).
Castle, M. E., A. D. Drysdale, and J. N. Watson. 1968. The effect of stocking rate and
supplementary concentrate feeding on milk production. J. Br. Grassl. Soc. 23:137-143.
Chacon, E., and T. H. Stobbs. 1976. Influence of progressive defoliation of a grass sward
on the eating behaviour of cattle. Aust. J Agrie. Res. 27:709-727.


204
Ocumpaugh, W. R. 1990. Production and nutritive value of Florigraze rhizoma peanut in
a semiarid climate. Agron. J. 82:179-182.
Oldham, J. D. 1984. Symposium: Protein nutrition of the lactating dairy cow. Protein-
energy interrelationships in dairy cows. J. Dairy Sci. 67:1090-1114.
Orskov, E. R. 1999. Supplement strategies for ruminants and management of feeding to
maximize utilization of roughages. Preventive Vet. Med. 38:179-185.
Ortega-S., J. A., L. E. Sollenberger, K. H. Quesenberry, J. A. Cornell, and C. S. Jones, Jr.
1992. Productivity and persistence of Rhizoma peanut pastures under different grazing
managements. Agron. J. 84:799-804.
Osuji, P. O. 1974. The physiology of eating and the expenditure of the ruminant at
pasture J. Range Manage. 27:437-443.
Owens, F. N., and C. F. Hanson. 1992. Symposium: External and Internal Markers.
External and internal markers for appraising site and extent of digestion in ruminants. J.
Dairy Sci. 75:2506-2617.
Parker, W. J., L. D. Muller, and D. R. Buckmaster. 1992. Management and economic
implications of intensive grazing on dairy farms in the Northeastern States. J. Dairy Sci.
75:2587-2597.
Parker, W. J., L. D. Muller, S. L. Fales, and W. T. McSweeny. 1993. A survey of dairy
farms in Pennsylvania using minimal or intensive pasture grazing systems. Prof. Anim.
Sci. 9:77-85.
Parsch, L. D., M. P. Popp, and O. J. Loewer. 1997. Stocking rate risk for pasture-fed
steers under weather uncertainty. J. Range Manage. 50:541-548.
Pearson, C. J., and R. L. Ison. 1997. Agronomy of Grassland Systems. 2nd ed.
Cambridge University Press. New York, NY.
Peel, C. J., L. D. Sandies, K. J. Quelch, and A. C. Herington. 1985. The effects of long
term administration of bovine growth hormone on the lactational performance of
identical-twin dairy cows. Anim. Prod. 41:135-142.
Petit, H. V., and G. F. Tremblay. 1995a. Milk production and intake of lactating cows
fed grass silage with protein and energy supplements. J. Dairy Sci. 78:353-361.
Petit, H. V., and G. F. Tremblay. 1995b. Ruminal fermentation and digestion in lactating
cows fed grass silage with protein and energy supplements. J. Dairy Sci. 78:342-352.
Phillips, C. J. C. 1988. The use of conserved forage as a supplement for grazing dairy
cows. Grass Forage Sci. 43:215-230.


124
Greater SR resulted in decreased (P< 0.001) HA by nearly 40% (1.3 vs. 2.1 kg of
pasture DM/kg BW). In 1995, HA at the high and low SR were 1.7 and 2.8 kg of DM/kg
of BW vs. HA of 1.0 and 1.5 kg of DM/kg of BW in 1996 (year by SR interaction, P <
0.001).
Estimates of DMI were less (P < 0.05) for cows assigned to the greater SR
treatment (14.1 vs. 17.8 kg DMI/d for high and low SR treatments, respectively). Forage
DMI for cows grazing RP pastures differed slightly between SR treatments (15.8 and
17.0 kg of DM/cow per d) while forage DMI was markedly less at the high SR when
cows grazed BG (12.5 vs. 18.7 kg of DM/cow per; forage by SR interaction, P < 0.10).
Supplementation rate effects. No carry-over effects of SUP treatment were
observed in pre-graze HM, but post-graze HM was greater (P < 0.05) when cows were
fed greater amounts of supplement (5060 vs. 4840 kg of DM/ha). The effect of SUP
treatment on HA was not significant. Estimated forage DMI decreased (P < 0.05) with
the greater SUP treatment (14.4 vs. 17.6 kg of DM/cow per d).
Minson and Wilson (1994) suggested that the lower limit of HA which would not
limit individual animal performance is 60 g of OM/kg of BW. The smallest HA observed
during the study was 0.75 kg of DM/kg of BW, occurring in 1996 in RP pastures stocked
at the greater rate with the low SUP. Based on these estimates, HA was not limiting for
any treatment. However, taking samples from ground level inflated the HA values,
particularly for BG, due to the inclusion of large amounts of dead herbage. The estimate
also has limits due to inclusion of standing dead and stemmy herbage which cows
avoided grazing. Thus, a more suitable estimate would have been HA adjusted for the
proportion of green material in the sward (Piaggio and Prates, 1997).


125
Intake may be limited when HM in tropical grass-legume pastures is less than
2000 kg/ha (Cowan and OGrady, 1976). All pre-graze estimates of HM were greater
than 2000 kg/ha, but as with HA, the inclusion of large amounts of dead material may
limit the value of the estimate, particularly for BG. Also, the post-graze HM of RP
pastures combined with high SR and low SUP treatments in 1996 was 1770 kg of DM/ha,
suggesting that forage may have been limiting with that treatment.
All intake estimates via disk meter were quite large relative to the estimates of
intake using the marker technique. The effect of supplement on the substitution of forage
reported earlier was not observed. The use of a disk meter to estimate DMI is thought
best limited to situations where pasture swards are uniform.
Simple Economic Assessment of Supplementation
Using only the milk production data, a simple assessment of income per cow or
income per land area was performed (Table 3.11). Milk income was calculated as
$0.33/kg of milk, and supplement costs were calculated as $0.22/kg of supplement.
Supplement intake was estimated as one third or one half of milk production, depending
upon the supplement treatment. Supplement cost was subtracted from milk production to
provide a simple economic assessment of supplementation.
Cows grazing RP returned equal or greater income on a per cow per day basis
than cows grazing BG ($4.13 vs. $3.85/cow per day) illustrating the higher digestibility
and intake potential of RP. This advantage of RP over BG pastures was greatest when
the amount of supplement fed was lowest ($4.27 vs. $3.80/cow per day, compared to
$3.99 vs. $3.90/cow per day for the low and high SUP respectively). Feeding additional
supplement was more profitable only when BG was grazed. Milk income minus
supplement costs (MIMSC) was $0.10/cow per day greater for cows eating more


138
100 pi of 0.855 M Trizma base were added. A final 1:14 dilution was made by adding
350 pi of assay buffer.
The IGF-1 (highly purified Human IGF-1 from Upstate Biotechnology, Inc.,
Richmond, CA) for iodination was dissolved (0.5 pg/pl) in 0.1-M acetic acid (pH = 2.5).
Highly purified bovine IGF-1 supplied by Monsanto Company (St. Louis, MO) was
dissolved in 0.1-M acetic acid (10 pg/100 pi) to prepare Stock 0. Stock solutions 1 and 2
were made by adding 10 pi of Stock 0 to 490 and 990 pi of assay buffer, respectively.
Using Stock 2, standards containing 0, 50, 100, 200, 300, 400, 500, 600, 800, 1000, 1200,
1500, and 1500 pg of IGF-l/ml were prepared.
First antibody, rabbit anti-bovine IGF-1 was provided by Drs. Louis Underwood
and Judson J. Van Wyk, Division of Pediatric Endocrinology, University of North
Carolina, Chapel Hill, NC. The first antibody was dissolved in assay buffer [200 mg of
protamine/1, 4.4 g/L of sodium monobasic phosphate, 10 ml of 2% sodium azide, 3.72
g/L of EDTA (0.013 M), and 2.5 g/L of BSA] at a 1:4000 ratio. Second antibody (sheep
anti-rabbit) was diluted in EDTA-PBS for use.
Ten microliters of plasma extract were combined with 190 pi of assay buffer in
duplicate. One hundred pi of diluted primary antiserum and iodinated IGF-1 were both
added to all tubes immediately thereafter. Tubes were vortexed on a plate vortexer and
allowed to incubate for 20 to 30 h at 4C. Diluted sheep anti-rabbit antibody (100 pi) and
50 pi normal rabbit serum (1:50) were added to all but total count tubes and allowed to
stand for 30 min. Assay buffer with 6% polyethylene glycol (1 ml) then was added to all
but total count tubes. Tubes were vortexed, allowed to stand for 15 min, centrifuged for
30 min (2000 x g) at 4C (RC-3B, refrigerated centrifuge, Sorvall Instruments), and then


44
Though McLachlan et al. (1994) did not report changes in body condition, their
results of increased FCM and reduced forage substitution with increased feeding
frequency support the observations of Robinson (1989).
Hongerholt et al. (1997) fed a supplement 2 or 4 times per day and reported that
BW change and non-esterified fatty acids (NEFA) concentrations were unaffected when
grain intakes were similar across treatments. In contrast, feeding 6 rather than 2 times
per day resulted in greater milk fat concentrations and decreased concentrations of
plasma NEFA (Sutton et al., 1986), indicative of enhanced cellulolytic activity and
energy availability from the diet.
Effects of Timing of Supplement Provision Relative to Forage Intake
Timing of forage and concentrate provision relative to each other may affect
intake and performance. Morita et al. (1991; cited by Morita et al., 1996) reported that
steers ate more roughage when concentrate was fed after roughage provision. Work from
Germany (Voigt et al., 1978, cited by Robinson, 1989, p. 1205) indicated that providing
grain supplements before feeding roughage (chopped ryegrass) had different effects upon
ruminal pH and digestion of cellulose depending upon the fermentability of the grain.
Barley, a rapidly fermented grain, caused a greater depression in ruminal pH than com, a
more slowly grain. Feeding the ryegrass before the grains caused a greater increase in
forestomach whole-diet cellulose digestion if barley was the grain supplement (63.6 vs.
75.0%) rather than com (72.1 vs. 78.3%). Differences in ruminal cellulose digestion
were unaffected by feeding sequence if the ryegrass was pelleted and total diet digestion
was reduced. Morita et al. (1996) also noted that roughage consumption and fiber


176
Treatment with bST encouraged increased grazing activity (6.3 vs. 5.6 h of
grazing/d), but forage OMI was unaffected by bST treatment. Given the conditions
imposed, cows treated with bST would not be expected to increase intake of forage OM
since supplement provided was increased with increasing milk production. If bST-
treated cows consumed only pasture, forage intakes likely would have increased given
adequate amounts of available herbage.
Cows injected with bST increased milk production approximately 9% (18.1 vs.
16.6 kg/d) and thus were fed an average of 8.0 kg of supplement OMI/d vs. 7.0 kg/d for
untreated cows. Although within the range of reported production increases in response
to bST, greater responses to bST might have been expected given the relatively low
amount of pretreatment milk production.
On average, and despite increased milk production, cows treated with bST gained
small amounts of BW (2.5 kg/24-d period), but cows not given bST lost about 7 kg of
BW/24 d period. The BW gain response was likely a result of the increased supplement
provided to bST-treated cows because they produced more milk.
Use of bST increased concentrations of plasma IGF-1 over controls nearly 70%
(143.vs. 84.5 pg/ml of plasma). The bST treatment likely affected IGF-1 both directly
and indirectly via increased concentrate provision. Averaged over all sampling dates,
insulin concentrations tended to increase due to bST treatment. As with IGF-1, bST
likely affected insulin concentrations directly and indirectly via increased
supplementation.
Increased RR with bST treatment has been reported but did not occur in this
study. However, cows treated with bST had greater temperatures throughout the day.


161
average time at which cows arrived at the parlor for milking. The temperature increases
were greater for pasture cows, however, as indicated by the greater slope, and at 1630 h,
temperatures were approximately 0.5 C greater for cows coming from pasture (39.5 vs.
39.0 C). Temperatures decreased immediately thereafter due to the cooling effect of the
shower wash system. After milking, temperatures increased for both treatments as cows
returned to pasture. This increase post p.m. milking was greater for bam cows,
suggesting greater grazing activity than cows given access to pasture continually.
Effect of bST. Increased RR with bST treatment have been reported (Zoa-Mboe
et al., 1989) but did not occur in this study, in agreement with Manalu et al. (1991). Cole
and Hansen (1993) also reported no effect of bST on RR, but RR were much greater in
their study and the authors suggested that the lack of difference due to treatment might
have been due to second-phase panting which is associated with respiratory alkalosis
(Bianca and Findlay, 1962).
Cows treated with bST had greater temperatures (p< 0.05) throughout the day,
although temperatures were similar in the early morning (0730 to 0800) after a period of
night cooling (Fig. 4.3). Cows not injected with bST increased body temperature at a
slower rate from approximately 1100 h until 1630 h (Fig. 4.3). Treated cows had a nearly
linear rate of temperature increase from the morning to evening milking. These results
agree with the findings of others (Zoa-Mboe et al., 1989; West et al., 1990, 1991;
Elvinger et al., 1992; Sullivan et al., 1992; Cole and Hansen, 1993) and contradicts early
reports (Mohammed and Johnson, 1985; Manalu et al., 1991) that bST had no effect on
rectal temperatures. Although the greater body temperatures associated with bST have
been associated with increased milk production (West et al., 1990) work of Cole and


133
Table 4.1. Supplement ingredients.
Item
(%, DM basis)
Hominy
35.8
Soybean hulls
23.9
Soybean meal
9.5
Whole cottonseed
20.1
Mineral mix'
2.7
Limestone
1.3
Trace mineral salt2
1.3
Molasses
4.0
Sodium bicarbonate
1.3
'Composition: > 55% Dyna-Mate, > 0.7% 1% Se, > 0.4% C0SO4, > 1.9% Q1SO4,
> 2.6% ZnS04, 0.7% MnS04, 36.9% MgO, > 0.001% Cal, 1200 IU/g of vitamin A, > 700
IU/g of vitamin D3, > 300 IU/g of vitamin E.
Composition (g/100 g): NaCl, 92 to 97; Mn, > 0.25; Fe, > 0.2; Cu, > 0.033; I, > 0.007;
Zn, > 0.005; Co, > 0.0025.
Table 4.2. Chemical composition, and nutritive value of supplement, com silage and
bermudagrass pasture.
Item
Maize Silage'
- Feedstuff
Supplement Bermudagrass2"5
Dry matter, %
26.2
92.5

IVOMD, %
65.6

60.3
TDN, %
62.0
76.0
57.4
NEL, Mcal/kg
1.38
1.83
1.29
NDF, %
57.2
38.0
77.6
ADF, %
33.4
23.0
35.1
CP, %
7.97
17.35
14.7
Ash, %
3.4
9.1
5.1
Ca, %
0.25
1.16
0.41
P,%
0.27
0.52
0.31
Mg, %
0.18
0.33
0.26
K, %
1.11
1.35
1.70
Na, %
0.013
1.27
0.038
S,%
0.11
0.20
0.29
Cl, %
0.3
1.24
0.53
Fe, ppm
51
503
55
Zn, ppm
26
194
38
Cu, ppm
4
48
5
Mn, ppm
22
93
42
Mo, ppm
<1
<1.4
1.3
'Estimate of TDN and NEL from NRC (1989) for com silage, few ears.
2Estimate of TDN calculated with the following equation: % TDN = [(%IVOMD*0.59)
+ 32.2] OM concentration (J. E. Moore, personal communication).
3NEL calculated from the estimate of TDN described in Footnote 2, using NRC (1989)
equations: NEL = [0.0245*TDN(% of DM) 0.12],


178
Because OMI was increased for cows fed silage with no change in milk production,
partitioning of nutrients to BW gain might be expected. This seeming discrepancy could
be a consequence of the postulated difference in gut fill between the two treatments and if
so indicates that condition score measurements were based upon more than changes in fat
depot size. Because neither milk production nor weight gain increased with the increased
OMI, efficiency of nutrient utilization may have decreased with supplemental com silage,
or intake of metabolizable energy may not have been increased.
Cows fed silage in the bam had a different temperature pattern than those not
receiving silage. Body temperatures of cows on both treatments reached the same
temperature within an hour of grazing (1900h), but temperatures of cows fed silage
quickly dropped thereafter, suggesting that they spent less time grazing. Cows not fed
silage but treated with bST had greater drive to graze than cows fed silage, and their
temperatures were sustained until 0130 h, likely due to increased grazing activity.
Estimates of nutrient intake based on NRC recommendations suggest that nutrient
intake did not prevent cows on this trial from producing 20 kg of 4% fat corrected milk/d.
This suggests that either maintenance costs were greater than NRC (1989) estimates, or
nutrient intake or utilization, particularly of energy, was overestimated.
Pasture-based production systems may be viable for dairies in the Southeast, but
they must overcome several obstacles to profitability. Low forage quality, environmental
stresses, greater maintenance costs for grazing cows, and animal adaptation may all limit
the productivity of these systems.
Cows grazing pasture typically have lower peak milk production and are less
persistent (Hoffman et al., 1993). The effects of hot environments likely further


155
The equation used to predict NEl of BG and silage indicates the BG to be of
much lesser energy concentration, but this likely underestimates the quality of the BG.
West et al. (1997) reported that Tifton 85 can make up a substantial portion of dairy cow
rations with limited effect on intake and production. The authors reported that the NDF
of BG underwent greater and more rapid in vitro digestion than NDF of com silage and
rates of passage were not different between the cows fed a com silage-based control diet
and diets having 30% BG hay, despite the fact that the BG diet was nearly 40% greater in
NDF concentrations.
Body Weight and Condition
Effect of housing. Housing cows during the day promoted weight gain. Cows
kept on pasture lost (P < 0.001) approximately 11 kg of BW/24-d period, but cows kept
in the bam gained approximately 6 kg of BW/24-d period (about 1% of BW/month)
(Table 4.6). These differences in BW changes further highlight the lower maintenance
costs for housed cows due to reductions in activity and heat stress.
Effect of bST. On average, cows treated with bST gained small amounts of BW
(2.5 kg/24-d period), but cows not given bST lost about 7 kg of BW/24 d period (Table
4.6). The BW gain response was likely a result of the increased supplement provided to
bST-treated cows.
Effect of supplemental silage. Cows receiving silage tended (P <0.10) to not
gain as much as those not fed additional roughage in the bam. Because OMI was
increased for cows fed silage with no change in milk production, partitioning of nutrients
to BW gain might be expected. However, changes in BW do not necessarily reflect
changes in body reserves, particularly in trials with a change-over design and involving
feeds with different physical characteristics (Combellas et al., 1979, p. 308). Cows not


APPENDIX 1
SAS PROGRAM OF POND ET AL. (1987) FOR THE ESTIMATION OF FECAL
OUTPUT
=======================SAS PROGRAM= == -
DATA GRAZE 1; INFILE GRAZE;
INPUT ANIMAL TIME CR;
Y = CR;
PROC SORT; BY ANIMAL;
PROC NLIN INTER (sic) = 50 CONVERGENCE = .00001 METHOD
MARQUARDT; BY ANIMAL;
PARMS K0 = 100 LI = .05 TAU = 10;
BOUNDS K0>0, L1>0, TAU>0;
T = TIME TAU;
If T<0 THEN GO TO ALPHA;
El = EXP (-L1 *T);
ONE = T*(L1**2)*E1;
MODEL Y = ((K0* L1 T) (EXP(-L 1 T)))/. 59635;
DER. K0 = ONE;
DER. LI = T*L1*K0*E1*(2-L1*T);
DER. TAU = K0*(L1**2)*E1*(L1*T-1.0);
GO TO BETA;
ALPHA;
MODEL Y = 0;
DER. K0 = 0;
DER. LI =0;
BETA: ;
OUTPUT OUT = POINTSI PREDICTED = YHAT RESIDUAL = RESID;
DATA OK; MERGE POINTSI GRAZE 1;
PROC SORT; BY ANIMAL;
PROC PLOT; BY ANIMAL;
PLOT YHAT TIME = ** Y*TIME = + /OVERLAY;
LABEL TIME = TIME AFTER DOSE, HOURS;
181


50
To investigate the interactions of herbage availability and level of concentrate
supplementation on OMI, Meijs and Hoekstra (1984) stocked lactating Friesians on
perennial ryegrass pastures at 16.3 or 24.8 kg of pasture OM/cow per d. Values for HA
are 2-yr averages within treatments. Three rates of concentrate (1, 3, or 5 kg/cow per d in
1981 and 1, 4, or 7 kg/cow per d in 1982) were fed. Greater herbage intake was reported
at the greater HA (13.6 vs. 11.3 kg of OM/cow per d for the greater and lesser HA,
respectively). Increasing concentrate intake negatively affected forage OMI. This was
primarily due to the decrease in forage intake by cows on the greater HA treatment
(forage by concentrate interaction). Forage OMI of 14.9, 13.6, and 12.3 kg/cow per d
were reported for cows fed the low, medium and high concentrate rates, respectively, for
cows on the greater HA treatment, whereas forage OMI decreased only from 11.4 to 11.0
kg/cow per d with increasing concentrate for cows on the lesser HA treatment.
Relatively few experiments have been conducted on tropical pastures to
determine objectively the relationship between herbage availability and the performance
of dairy cattle. There is therefore little evidence on which to determine the pasture
conditions under which supplementary feeding might be most efficiently employed
(Jennings and Holmes, 1984b, p. 270). Little research has been published on this topic in
the last 15 years.
Cowan and Davison (1978) investigated effects of supplementing maize (0 or 3
kg/d) to cows grazing tropical pastures of mixed forage species at 1800 or 3300 kg of
DM/ha. Milk production was increased from 6.5 to 9.3 kg/cow per day with supplement
offered to cows assigned to the lower level of HM but was unaffected by supplement
(13.0 kg/d) offered at the greater level of HM.


TABLE 3.7. Effect of forage, stocking rate (SR), and supplementation rate (SUP) on bodyweight (BW) change, 4% fat corrected milk
(FCM) production, and measures of energy (E) status of Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut
during the summers of 1995 and 1996
Tifton 85 bermudagrass Florigraze rhizoma peanut
Stocking Rate1 Stocking Rate2 Probability3
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage SR x SR
Item 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 SEM Forage SR SUP x SR x SUP x SUP x SUP
Average BW, kg
507
504
508
507
497
500
504
513
3.0
NS
*
NS
NS
NS
NS
NS
FCM, kg/d
16.5
14.2
16.6
13.8
15.8
15.7
16.5
15.5
0.4
t
NS
***
NS
**
NS
NS
Maintenance E, Mcal/d4
10.1
10.1
10.1
10.1
10.0
10.0
10.1
10.2
0.3
NS
NS
NS
NS
NS
NS
NS
FCM E, MCal/d5
12.2
10.5
12.3
10.2
11.7
11.6
12.2
11.5
0.3
t
NS
***
NS
**
NS
NS
Total E output, Mcal/d6
22.4
20.6
22.4
20.3
21.7
21.6
22.3
21.7
0.4
NS
NS
**
NS
*
NS
NS
BW change, kg/d
-0.2
-0.3
-0.1
-0.1
-0.5
-0.3
-0.2
-0.1
0.1
NS
*
NS
NS
NS
NS
NS
Tissue E, Mcal/d7
0.9
1.3
0.5
0.6
2.3
1.5
1.1
0.4
0.5
NS
*
NS
NS
NS
NS
NS
Forage E intake, Mcal/d8
9.3
10.9
10.9
9.4
14.3
18.2
17.7
19.2
0.8
***
t
*
f
t
*
NS
Suppl. E intake, Mcal/d9
14.3
7.7
13.8
8.0
15.7
8.9
14.5
8.4
0.3
* *
t
***
t
*
t
NS
Dietary intake E, Mcal/d
23.5
18.6
24.7
17.5
29.9
27.1
32.2
27.7
0.7
***
NS
***
NS
*
t
NS
Total E input, Mcal/d
24.5
19.9
25.2
18.1
32.2
28.6
33.3
28.1
0.8
***
NS
***
NS
NS
NS
NS
E status, Mcal/d10
2.1
-0.7
2.7
-2.2
10.6
7.0
11.0
6.4
0.9
***
NS
***
NS
NS
NS
NS
'High and low stocking rates for Tifton 85 bermudagrass were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates for Florigraze rhizoma peanut were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.
4Calculated using NRC equations for maintenance and activity, maintenance E = 0.073*BW75. Requirement was also increased 25% for energy of activity and
increased an additional 10% above maintenance for primiparous cows.
Calculated using NRC equations, milk energy = 0.74Mcal/kg*FCM, kg/d.
6Total E output = Maintenance E + FCM E, Mcal/d.
Calculated using NRC (1989) equations. Tissue E = +4.92 Mcal/kg BW loss and -5.12 Mcal/kg BW gain.
Calculated using the NRC (1989) conversion of TDN to NEL, where NEL = [0.0245*TDN(% of DM)-0.12]. Calculation of TDN was based on the equation for
estimation of TDN in warm-season grasses used by the University of Florida Forage Evaluation Support Laboratory (J. E. Moore, personal communication), where %
TDN = [(IVOMD, % 0.49) + 32.2] OM concentration.
Calculated using estimated supplement digestibility of 86%. TDN was calculated using tabular values, and NEL was calculated from estimated TDN using NRC
(1989) equations.
'"Energy status = Energy input energy output.


173
Stocking rate did not influence milk production, but cows grazing at lower SR
tended to produce milk with greater concentrations of protein which may reflect
opportunity to select plant parts of greater nutritive value. Likewise, in 1996 MUN was
lower when cows were stocked at the lower rate suggesting more efficient use of dietary
CP for milk protein.
On a land area basis, the effect of SR on milk production was greater than the
effect of feeding additional supplement. Increasing SUP from 0.33 kg of supplements
kg of daily milk to 0.5 kg of supplement: 1 kg of daily milk increased (P < 0.001) milk
production 14% on a land area basis (97 vs. Ill kg of milk/ha per d), but increasing SR
resulted in a 51% increase (P < 0.001) in milk production per land area (83 vs. 125 kg of
milk/ha per d).
Cows assigned to the greater SR lost 7 to 8 kg more per 28-d period than cows
assigned to the lower SR across years and forages with one exception. In 1996, cows
grazing BG lost 7 kg less BW when grazing at the greater vs. lesser SR
Increasing SR resulted in reduced forage OMI, but cows stocked at the greater
rate were fed slightly more supplement because of greater milk production. Thus, total
OMI and OMIPBW were not different due to SR (15.3 and 15.9 kg of OM/d and 3.08 and
3.16% of BW/d).
In a third study, the effect of additional management strategies on milk production
was investigated. Cows were housed in bams (with fans and sprinklers) or on pastures
(with shade cloth only) between AM and PM milkings. After PM milking all cows
returned to BG pastures. Within housing treatments, cows did or did not receive bST


TABLE 3.10. Disk meter estimates of the effect of forage species, stocking rate (SR), and supplementation rate (SUP) on forage pre-
and post-graze herbage mass (HM), herbage allowance (HA), and dry matter intake (DMI) of grazing, lactating Holstein cows grazing
Tifton 85 bermudagrass and Florigraze rhizoma peanut during the summers of 1995 and 1996.
Tifton 85 bermudagrass Florigraze rhizoma peanut
- Stocking Rate1 Stocking Rate2 Probability3
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage x SR x SR
Item
0.5:1
0.33:1
0.5:1
0.33:1
0.5:1
0.33:1
0.5:1
0.33:1 SEM Forage
SR
SUP
x SR
x SUP x SUP x SUP
Pre-graze HM,
7220
6980
7320
7540
4460
4460
4890
4780 110
***
**
NS
NS
NS
NS
NS
kg/ha
Post-graze HM,
6290
5960
6460
6310
3380
3120
4140
3960 100
***
***
*
**
NS
NS
NS
kg/ha
Average HM, kg/ha
6760
6470
6890
6920
3920
3790
4510
4370 100
***
***
t
t
NS
NS
NS
HA, kg of forage/kg
1.6
1.5
2.3
2.3
1.1
1.1
2.0
1.9 0.0
***
***
NS
NS
NS
NS
NS
of BW
Forage DMI4, kg/d
12.0
13.0
15.0
22.3
14.3
17.3
16.3
17.7 1.8
NS
*
*
t
NS
NS
NS
'High and low stocking rates were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.
4DMI calculated as [(pre-graze post-graze HM, kg/ha) paddock size, ha/paddock]/(cows/paddock).


30
decreased, without or with supplement. Feeding supplement reduced DE intake from hay
at all maturities but had the greatest depressing effect on DE intake of wethers fed the
highest quality (4-wk maturity) hay. When fed supplement, wethers fed the 4-wk
maturity hay decreased hay DE intake by 80 kcal/BW0 7:1 per day, while those fed the 10-
wk maturity hay had decreased hay DE intake by 1 kcal/BW0 75 per day. The increase in
DE intake due to supplement for the 4-wk maturity hay was approximately half that of
the 10-wk maturity hay (26 vs. 51 kcal/BW per day for 4- and 10-wk maturities,
respectively). Intermediate decreases in hay DE intake with concomitant increases in
total DE intake occurred when supplements were fed in combination with hays of
intermediate maturity.
Concentrates had limited effects on forage intake in a study by Galloway et al.
(1993a). The researchers compared five supplement combinations fed to Holstein steers
eating bermudagrass hay in confinement. The hay was of moderate quality, averaging
11.4% CP, 75% NDF, and 52% digestibility. Supplements, fed at 0.75% of BW, were
ground com, dried whey, dried molasses product, or a combination of com and whey or
com and molasses. Although intake of bermudagrass as a percent of BW was
numerically less for all of the three corn-based supplements, only the com plus molasses
treatment significantly decreased bermudagrass intake.
Several researchers have reported forage intake depressions that varied with the
amount of supplement fed (Campling and Murdoch, 1966; Tayler and Wilkinson, 1972;
Sarker and Holmes, 1974; Cowan et al., 1977; Combellas et al., 1979). Though forage
quality may affect the response of intake to supplement, Waldo (1986) noted that total


132
Pastures (Cynodon dactylon XC. nlemfuensis cv. Tifton 85) were fertilized with
NH4NO3 at a rate of 67 kg of N/ha on 18 July and 4 September. Pastures were divided
into 16 paddocks, allowing a 15-d rotation. The integrity of bermudagrass (BG)
paddocks was maintained with energized poly wire fencing. Fencing prevented cows
from grazing the next days forage allotment as well as BG in its regrowth phase. Cows
were provided shade structures (80% sun-block shade cloths stretched over metal pipe
frames) and water tubs that were moved to a fresh paddock each morning. Shade
structures were designed to provide 4.6 m2 of shade/cow. Stocking rates were 13.3 and
10 cows/ha for cows fed or not fed silage, respectively.
Cows were milked at 0530 and 1630 h. After the morning milking, cows assigned
to Treatments 1 and 2 were returned to pastures. Cows assigned to Treatments 3, 4, and 5
were taken to a freestall bam where they were housed within their respective treatment
groups. After the p.m. milking all cows were moved to pasture where they remained
until the a.m. milking.
Supplement was fed at a rate of 0.50 kg (as-fed)/kg of milk produced per day. Averages
of 3- or 4-d milk weights were reviewed twice weekly and the amount of supplement
provided was adjusted accordingly. Fifty percent of this daily amount was fed after each
milking in the pastures or in the bam, according to treatment assignment. When housed,
cows were fed in the bam by treatment group. When cows were on pasture, supplement
was fed to each replicate within treatment. Supplement ingredients are listed in Table
4.1. Average nutritive value characteristics of the supplement and forages are reported in
Table 4.2.


172
OM (kg/kg) was 0.51 for RP and 0.18 for BG. Cows grazing BG pastures and provided
greater amounts of supplement increased total OMI by 22 % vs. a 10 % increase in total
OMI with additional supplement for cows grazing RP.
The limited improvement in production with RP over that with BG suggests that
use of adapted leguminous forages has little merit in these systems (Rouquette et al.,
1993). This likely will remain true as long as inexpensive by-product energy feeds are
available. However, production limits due to forage substitution may be offset by the
ability to increase SR, and to a greater degree with RP than BG.
The calculated nutritional deficiency for cows grazing BG and fed the low SUP
indicates that large amounts of supplement must be fed or the supplement nutrient
concentrations must be adjusted to ensure adequate nutrient intake when BG is managed
as in these experiments. Oppositely, supplement intakes caused RP-based diets to
contain excessive CP, likely increasing maintenance costs due to the need for increased N
excretion. With RP, only S intake appeared marginal regardless of SUP.
Nutrient intake estimates with both forages highlights the need for feeding suitable
amounts of supplement with appropriate nutrient concentrations.
One limitation of the study presented was the use of the same supplement for
animals grazing both forage types. Though this prevented the confounding of forage
effects with supplement effects, the response to supplement likely would be improved by
more appropriately balancing the supply of nutrients available to the cow. Although this
may not affect production, a more economical supplement could be offered (Hoffman et
al., 1993).


19
Characteristics of an ideal marker were outlined by Owens and Hanson (1992)
and include the following traits: 1) it should be unabsorbable, 2) it should not affect or be
affected by animal or microbial digestive processes, 3) its flow should closely mimic that
of the material it marks, and 4) it must be analyzable with a specific and sensitive
methodology. No single marker currently meets all these criteria.
Both internal (a dietary fraction such as lignin or plant alkanes) and external (e.g.,
colored plastic chips or rare earth metals) markers have been employed. Use of either
type of marker relies upon an accurate estimate of its intake. This is controlled by the
researcher using external markers, but calculation of internal marker intake depends upon
accurate estimates of what the animal consumes. This may be a particular problem in
grazing situations where herbage consumed may not be the same as selected by the
researcher.
The external marker, CT2O3, has been used extensively but its suitability has been
questioned (Ellis et al., 1980). The CT2O3 does not associate with a particular liquid or
feed fraction and thus may settle out of the rumen contents and flow with large
variability, particularly when animals consume forage diets. Holden et al. (1995, p. 158)
worked with CT2O3 and noted that significant daily variation in DMI indicates that
analysis of composited samples of forages and feces for intake determination may not be
adequate for estimation of intake under grazing conditions. Another disadvantage of
using Cr23 is the multiple doses required over several days in order for Cr to reach
equilibrium concentrations in the digestive tract. Additional handling of animals is
undesirable, particularly when it has potential to disturb established patterns of grazing
behavior


82
Sarstedt, Inc., Newton, NC) after the p.m. milking and placed on ice. Blood was
centrifuged (2000 x g for 30 min) and plasma was collected and frozen at -20 C on the
same day. Plasma from 1995 was analyzed for urea N (PUN) and glucose at the
USDA/ARS Subtropical Agriculture Research Station (Brooksville, FL) following the
procedures of Marsh et al. (1965) and Gochman and Schmitz (1972), respectively. In
1996, PUN was determined by kit (Kit 535-A, Sigma, St. Louis, MO) and read on a
plate reader at 540 nm.
Chromium-mordanted fiber was used as an inert marker to determine organic
matter intake (OMI). Each period, forage was collected across all pastures and
composited for each species. Efforts were made to gather forage of quality similar to that
consumed. Forages were dried at 55 C and ground with a stainless steel Thomas-Wiley
Laboratory Mill (Thomas Scientific, Philadelphia, PA) using a 2-mm screen. Fiber
from the forage was chromium mordanted according to the method of Udn et al. (1980).
The dried, ground forages (approximately 100 g/L FLO) were boiled approximately 2 h in
a mixture of water and liquid laundry detergent (approximately 50 mL). After boiling,
the fibers were washed repeatedly with tap water to remove all soap, rinsed with acetone,
dried at 105 C, and weighed. The dried forage (500 to 700 g) was placed in a metal
container, and sodium dichromate (100 to 140 g) dissolved in four volumes
(approximately 4 L) of water was added to the forage. Addition of Cr (as sodium
dichromate) equaled 7% of the fiber DM. This slurry was sealed with aluminum foil and
heated in a forced-air drying oven at 105 C for 24 h. The liquid was then poured off and
the fiber was gently rinsed with tap water to remove excess and unbound Cr. Ascorbic
acid (Aldrich, Milwaukee, WI) at half the dry fiber weight was mixed with water, added


67
hemicellulose tended to be greater (P < 0.07) when goats ate the diet containing RP.
Though not stated, this may have been due to slower rate of passage.
Staples et al. (1997) showed that RP silage is suitable for lactating dairy cows.
The researchers fed 50:50 forage:concentrate diets, substituting RP for com silage at 0,
40, 70, and 100% of the forage source (0, 20, 35, and 50% of dietary DM). Milk yield
was greatest when cows ate diets with 20% RP silage, following the same pattern as
DMI. Linear decreases (P < 0.10) of both total VFA concentrations and body weight
gain (P < 0.05) were observed with increasing RP silage. This likely reflects lesser
concentrations of energy in RP silage as compared with com silage.
Use of RP in grazing systems for lactating dairy cows has not been reported
previously. Questions needing research include effects of SR and supplementation rate
for animals grazing RP. Economic costs must particularly be considered because slow
establishment, vegetative propagation, and the need for chemical weed control... [make]
rhizoma peanut...a high-input, management-intensive forage crop ... [requiring]
appropriate attention to all production needs and inputs (Mooso et al., 1995). Such
requirement costs may be prohibitive despite its excellent pest resistance and nutritive
value characteristics.
Some Management Strategies for the Improvement of Milk Production in
Subtropical Environments
Bovine Somatotropin (bST)
Some of the original investigations of the efficacy of exogenous bST were
conducted with animals on pasture (Brumby and Hancock, 1955; Brumby, 1956), but the
majority of the related literature investigates its effects on the performance of cows in
confinement. Further, investigations of the use of bST with pastured cows primarily have


194
Gustafsson, A. H., L. Andersson, and U. Emanuelson. 1993. Effect of hyperketonaemia,
feeding frequency and intake of concentrates and energy on milk yield in dairy cows.
Anim. Prod. 56:51-60.
Hallberg, M. C., and E. J. Partenhiemer. 1991. The structural character and recent trends
of Pennsylvania agriculture economy. Bull. 869. College Agrie., Penn.O State Univ.,
University Park. PA.
Hambleton, L. G. 1977. Semiautomated method for simultaneous determination of
phospohrus, calcium and crude protein in animal feeds. J.A.O.A.C. 60:845-852.
Hamilton, B. A., K. J. Hutchinson, P. C. Annis, and J. B. Donnelly. 1973. Relationships
between the diet selected by grazing sheep and the herbage on offer. Aust. J. Agrie. Res.
245:271-277.
Hart, R. H. 1972. Forage yield, stocking rate, and beef gains on pasture. Herbage Abstr.
42:345-353.
Hartnell, G. F., S. E. Franson, D. E. Bauman, H. H. Head, J. T. Huber, R. C. Lamb, D. S.
Madsen, W. J. Cole, and R. L. Hintz. 1991. Evaluation of Sometribove in a prolonged-
release system in lactatingdairy cowsproduction responses. J. Dairy Sci. 74:2645-
2663.
Henderson, M. S., and D. L. Robinson. 1982. Environmental influences on yield and in
vitro true digestibility of warm-season perennial grasses and the relationship to fiber
components. Agron. J. 74:943-946.
Hespell, R. B., and M. P. Bryant. 1979. Efficiency of rumen microbial growth: influence
of some theoretical and experimental factors on Yatp. j. Anim. Sci. 49:1640-1659.
Hill, G. M., R. N. Gates, and G. W. Burton. 1993. Forage quality and grazing steer
performance from Tifton 85 and Tifton 78 bermudagrass pastures. J. Anim. Sci.
71:3219-3225.
Hodgson, J. 1975. The influence of grazing pressure and stocking rate on herbage intake
and animal performance. Pages 93-103 in Pasture Utilization by the Grazing Animal. J.
Hodgson and D. K. Jackson, ed. Occasional Symposium No. 8, Br. Grassland Society,
Hurley.
Hodgson, J. 1981. Variations in the surface characteristics of the sward and the short
term rate of herbage intake by calves and lambs. Grass Forage Sci. 36:49-57.
Hodgson, J. 1985. The control of herbage intake in the grazing ruminant. Proc. Nutr.
Soc. 44:339-346.


68
been limited to temperate climates (Brumby, 1956; Peel et al., 1985; Hoogendoom et al.,
1990; Chilliard et al., 1991).
Generally, bST injections increase milk production of cows on pasture. Results
from Chilliard et al. (1991) indicated no effect of bST on milk production, but the results
were confounded by a greater amount of concentrate feeding to control cows. Treated
cows tended to lose more weight, which was attributed to medium quality available
pasture and low amounts of concentrate supplementation.
Peel et al. (1985) tested the effects of growth hormone with five pairs of
monozygotic twins. One twin from each pair received a daily injection of 50 mg of
growth hormone for 22 wk. The animals grazed ryegrass-white clover pastures, and the
SR was intentionally kept low so as not to limit the animals genetic potential. Milk
production increased nearly 18% with bST injection (19.8 vs. 23.3 kg of milk/d) but milk
composition was unchanged. Pasture intake, measured twice, was numerically greater
(8%) at the eighth week of the trial and significantly greater (14%) by the 22nd wk. Feed
conversion efficiency and BW were not changed, but the treatment group appeared to
have greater body condition loss during the first 4 wk of the trial.
A 10% increase in milk production due to bST was reported by Hoogendoom et
al. (1990). Cows grazed ryegrass-white clover pastures and were injected bi-weekly with
a controlled release formulation that delivered 25-mg of bST/d. Milk yields totaled 2360
and 2600 kg/cow for the control and bST-treated cows over the 26-wk trial, with similar
increases in milk fat and protein production. Milk yield was greater when pasture was
not limiting. A period of warm, dry weather resulted in a decline in herbage production
and a concomitant convergence of group milk yields. Differences due to treatment


20
More recently, use of pulse-dosed markers has gained acceptance. Animals are
dosed once with labeled feed fractions, and numerous fecal samples are collected over a
period of time long enough for the label source to have cleared the animal (typically 96 or
more hours). A nonlinear equation relating time after dosing to fecal [Cr] is used to
generate parameters for the estimation of fecal output (Pond et al., 1987). This method
has advantages in that the animals observed need only be handled once for dosing.
Fiber mordants, especially Cr-mordanted fiber, have been used as markers due to
the tenacity with which heavy metals bind the fiber particles. Disadvantages to this
method include the amount of effort involved in preparing mordanted fiber and the
potential negative effects of mordanting upon passage characteristics of the fiber particles
(Ellis et ah, 1980).
Estimation of intake using external markers also requires an accurate estimate of
diet digestibility. Pasture samples may be obtained with surgically altered animals
(esophogeally- or ruminally-fistulated) or by hand plucking. Estimates of diet
digestibility are then obtained with in vitro techniques. Either method can be inaccurate
because potential exists for the sampling animal or for the researcher to select plant
material that is different from the plant material chosen by the animals being studied. If
supplements are fed, they may further alter diet digestibility, thwarting accuracy of
estimation.
With each of these methods, care must be taken during the laboratory analysis,
since feces must go through several preparation steps prior to the Cr analysis. An
additional difficulty with marker methodologies is the large number of samples which
must be collected and processed to make reasonable estimates of intake.


189
Conrad, H. R., A. D. Pratt, and J. W. Hibbs. 1964. Regulation of feed intake in dairy
cows. I. Change in importance of physical and physiological factors with increasing
digestibility. J. Dairy Sci. 47:54-62.
Coulon, J. B., and B. Remond. 1991. Variations in milk output and milk protein content
in response to the level of energy supply to the dairy cow: a review. Livestock Prod. Sci.
29:31-47.
Cowan, R. T. 1985. Pasture and supplements in the subtropics and tropics. Pages 109-
117 m The Challenge: Efficient Dairy Production. T. I. Phillips, ed. Proc. Aust. N.Z.
Societies Anim. Prod. Albury, Wodonga.
Cowan, R. T., I. J. R. Byford, and T. H. Stobbs. 1975. Effects of stocking rate and
energy supplementation on milk production from tropical grass-legume pasture. Aust. J.
Exp. Agrie. Anim. Husb. 15:740-746.
Cowan, R. T., and T. M. Davison. 1978. Feeding maize to maintain milk yields during a
short period of low pasture availability. Aust. J. Exp. Agrie Anim. Husb. 18:325-328.
Cowan, R. T., T. M. Davison, and P. OGrady. 1977. Influence of level of concentrate
feeding on milk production and pasture utilization by Friesian cows grazing tropical
grass-legume pasture. Aust. J. Exp. Agrie. Anim. Husb. 17:373-379.
Cowan, R. T., and P. O. OGrady. 1976. Effect of presentation yield of a tropical grass-
legume pasture on grazing time and milk yield of Friesian cows. Tropical Grassl. 10:213-
218.
Crampton, E. W., E. Donefer, and L. E. Lloyd. 1960. A nutritive value index for forages.
J. Anim. Sci. 19:538-544.
Dado, R. G., and M. S. Allen. 1995. Intake limitations, feeding behavior, and rumen
function of cows challenged with rumen fill from dietary fiber or inert bulk. J. Dairy Sci.
78:118-133.
Davison, T. M., D. Williams, W. N. Orr, and A. T. Lisle. 1991. Responses in milk yield
from feeding grain and meat-and-bone meal to cows grazing tropical pastures. Aust. J.
Exp. Agrie. 31:159-163.
Decker, A. M., R. W. Hemken, J. R. Miller, N. A. Clark, and A. V. Okorie. 1971.
Nitrogen fertilization, harvest management, and utilization of Midland bermudagrass
(Cynodon dactylon (L.) Pers.). MD Agrie. Exp. Stn. Bull. 447.
Deinum, B., and J. G. P. Dirven. 1976. Climate, nitrogen and grass. 7. Comparisons of
production and chemical composition of Brachiaria ruziziensis and Setaria shpacelata
grown at different temperatures. Neth. J. Agrie. Sci. 24:67-78.


10
intake and digestibility may be strongly correlated (Anderson et al., 1973), intake of
digestible nutrients is affected more by differences in intake than by differences in
digestibility (Waldo, 1986, p. 618).
Much effort has been made to determine whether voluntary intake was limited
primarily through physical or physiological control mechanisms. Conrad et al. (1964)
examined results from 114 trials with lactating cows and reported the relative importance
of physical and physiological factors regulating feed intake changes as diet digestibility
increases. Intake of diets having between 50 and approximately 67% digestibility was
thought to be limited by physical factors such as digestibility of a feed and its rate of
passage through the digestive tract. Intake of diets having a digestibility greater than
67% was limited primarily by physiological control mechanisms. This breakpoint
[67%] is likely a convenient mathematical simplification (Allen, 1996, p. 3064) because
voluntary intake is likely regulated by numerous, integrated signals from the intestinal
tract and digestive organs (Forbes, 1996). Regardless of the breakpoint or precise
mechanisms of intake control, research supports the theory that intake often is restricted
by rumen distention, i.e. physical constraint (Balch and Campling, 1962; Grovum and
Phillips, 1978; Friggens et al., 1998).
Constraints on feed intake by physical mechanisms are, in part, a function of
digestive tract capacity and are related to energy balance (Allen, 1996). Voluntary DMI
of cows in negative or slightly positive energy balance decreased in response to inert fill
added to the reticulorumen but was unaffected in cows having greater positive energy
balance (Johnson and Combs, 1991, 1992; Dado and Allen, 1995). This is of particular
relevance for the grazing dairy cow which has increased maintenance energy


97
Greater 4% FCM (P < 0.05) and milk fat production (P <0.01) and greater milk
protein concentration (P <0.10) in response to additional supplement were observed in
1996 compared with 1995 (year by SUP interaction; Figure 3.4). Production responses to
supplement are greater when forage is limiting (Phillips, 1988) and this would seem a
plausible explanation for the increased 4% FCM response to supplement in 1996.
However, based on estimates of intake to be presented subsequently, forage intake was
not limited by increasing SR in 1996. Opposite the effects of supplement and year on
milk protein concentration, the depression in milk fat concentration in response to
additional supplement was greater in 1995 than in 1996 (year by SUP interaction, P <
0.05; Figure 3.4). That the greatest changes in protein and fat concentrations did not
occur in the same year is surprising: milk fat concentrations often decrease with greater
supplement feeding with a concomitant increase in milk protein concentrations due to
increased microbial growth. Milk protein concentrations essentially did not change due
to SUP in 1995 (2.96 and 2.98%) but increased from 2.97 to 3.05% with increasing SUP
in 1996. This suggests improved N capture by rumen microbes when cows were fed the
greater amount of supplement in 1996.
In 1996, increased supplementation resulted in milk, 4% FCM, and fat production
increases between 14 and 20% across parities. In 1995, a similar response was observed
for multiparous cows but not for primiparous cows (year by parity by SUP interaction, P
< 0.05; Figure 3.5). Likewise, milk fat percent was not similarly affected by SUP across
parity and years. Reduction in milk fat concentration was similar in 1995 and 1996 for
primiparous cows fed the greater SUP. However, milk fat concentration of multiparous
cows was more dramatically decreased by greater supplementation in 1995 but was


57
specifically test genotype by location, their research indicated that Tifton 78 was
unsuitable for central Florida conditions even though it had been released and was
finding some use in Georgia.
Numerous investigators have studied the suitability of use of bermudagrass as an
animal feed. Typically, the grass is used more in extensive feeding systems such as
pasture for beef cattle or dry dairy stock.
Stocking rates on bermudagrass may have a large influence on animal
performance once some critical level is reached. Working with a biophysical model,
Parsch et al. (1997) simulated forage production responses to a range of beef cattle SR.
According to the model, with improved bermudagrass pastures weight gain per head is
essentially unaffected by grazing intensity until a critical SR (6 head/ha) is reached.
Bransby et al. (1988, p. 278) also reported that grazing systems on bermudagrass appear
to be well buffered against changes in grazing intensity across a wide range of stocking
rates and available herbage.
The interaction of forage and SR with continuously stocked bermudagrass
pastures was investigated by Guerrero et al. (1984). Forages were Callie, Coastal, and
three experimental hybrids. Stocking rates varied by cultivar but the range averaged from
4.6 to 11.0 steers/ha. Forage digestibility was increased with increasing SR, and greater
digestibility occurred primarily at medium and heavy SR. However, ADG decreased as
available herbage declined, and cultivar differences in digestibility and yield were
observed.
Roth et al. (1984, 1990) studied bermudagrass growth, morphology, and
compositional responses at four different HA under continuous stocking management.


89
averaged 4.5 percentage units more CP (17.8 vs. 13.3 %) and contained less NDF (44.5
vs. 81.2%) and ADF (32.6 vs. 41.0%) on a DM basis. Rhizoma peanut had greater
average IVOMD (71.2 vs. 58.8%) also. These estimates of nutritive value are similar to
values reported by others (Beltranena et al., 1981; Gelaye et al., 1990; Hill et al., 1993;
Mandebvu et al., 1998).
Milk Production and Composition Per Cow
Parity and year effects. No main effects of parity were observed, and year
effects occurred only for SCC. In 1995, milk contained fewer (P < 0.001) somatic cells
(286 vs. 596 thousands of cells).
Forage effects. Cows grazing RP pastures produced more (P < 0.001) milk than
cows grazing BG (17.3 vs. 16.2 kg/d), but milk was of lower fat concentration (P <0.01;
3.42 vs. 3.54 %; Table 3.3). Milk fat production is stimulated by more fibrous diets, and
the differences in fiber concentration between the two forages likely explains the
difference in milk fat concentration. Greater milk production by cows grazing RP
pastures offset the reduced milk fat concentration, as shown by the greater (P <0.01)
production of 4% FCM (15.7 vs. 15.0 kg/d) and greater (P < 0.05) amount of milk fat
produced (0.58 vs. 0.56 kg/d) by cows eating RP. Forage type had no effect on milk
protein percent, but greater (P < 0.001) quantities of milk protein were produced by cows
grazing RP (0.52 vs. 0.48 kg/d). Measured only in 1996, MUN concentrations tended (P
< 0.052) to be greater when cows grazed RP (17.7 vs. 17.1 mg%). Compared with
multiparous cows, primiparous cows had greater SCC when grazing RP (500 vs. 350
thousands of somatic cells) but lower SCC when grazing BG (420 vs. 480 thousands of
somatic cells; parity by forage interaction, P < 0.01).


123
A year by forage interaction (P <0.01) for HM was observed, and as with the
nutritive value estimates, the interaction more likely indicates the effect of increased SR
from 1995 to 1996 rather than changes in the forages or their growing conditions.
Increasing SR from 1995 to 1996 had less effect on BG, decreasing BG HM by 17%
(7390 vs. 6130 kg of DM/ha), but the increased SR decreased RP HM by 38% (5120 vs.
3180 kg of DM/ha).
As with HM, HA was greater (P < 0.001) for BG than for RP pastures (1.9 vs. 1.5
kg of pasture DM/kg of animal BW) despite the lower SR used with RP. Because the
change in HM due to SR was similar across years, increasing the SR from 1995 to 1996
had less effect on HA in 1996 (year by forage interaction, P < 0.001). Thus, the ratios of
the HA values were a mathematical consequence of, and very nearly reflect the ratios of
the low and high SR within years. Effect of forage was not significant with respect to
forage DMI. Average estimated DMI across forages was 16.0 kg of DM/cow per d.
Stocking rate effects. Greater SR reduced (P <0.01) pre-graze HM (5780 vs.
6130 kg of DM/ha (Table 3.10). This was likely due to carry-over effects from previous
grazing events within each grazing season as reflected in differences in post-graze HM.
The difference (P < 0.001) between SR treatments for post-graze HM (4690 vs. 5210 kg
of DM/ha for greater and lesser SR, respectively) was approximately 65% larger than the
difference between SR treatments for pre-graze HM. Post-graze HM for RP pastures
decreased by 800 kg of DM/ha as SR increased (4050 vs. 3250 kg of DM/ha) compared
with a 260 kg/ha decline in BG pastures (6380 vs. 6120 kg of DM/ha; forage by SR
interaction, P < 0.01).


BIOGRAPHICAL SKETCH
John Herschel Fike, son of Herschel Ringgold and Shirley Hayden Fike, was bom
and raised in Franklin County, Virginia. He holds a B.S. in science education from Wake
Forest University, an M.S. in forage agronomy from Virginia Polytechnic Institute and
State University, and with successful defense of this dissertation holds a Ph.D. with
specialization in dairy cattle nutrition from the University of Florida.
After graduating from Wake Forest University, John spent more than a year
traveling and working in Japan, New Zealand, Australia, and several countries in
Southeast Asia. His jobs included painting houses and milking cows in New Zealand,
dagging sheep in Australia, and teaching English to Japanese businessmen.
While completing his Ph.D., John married Wonae (Bong) Fike of South Korea
and started a family. He and Wonae are the proud parents of Jonah Paul Bong Fike.
214


GRAZING SYSTEMS AND MANAGEMENT STRATEGIES FOR LACTATING
HOLSTEIN COWS IN FLORIDA
By
JOHN HERSCHEL FIKE
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1999


4
supporting large herds (Parker et al., 1992, p. 2587, citing Hallberg and Partenhiemer,
1991, and citing Kaffka, 1987), thus it is understandable that most interest in grazing
systems has been shown by dairy producers with herds of fewer than 100 cows (Parker
et al., 1992, p. 2587).
Milk production per cow or farm may decrease in grazing herds as producers
change from management of confined housing to management of grazing systems, but
graziers assume that the decrease in production costs is greater than the cost of lost milk
production, thus gamering greater net profit. Some studies (Emmick and Toomer, 1991;
Parker et al., 1992) have indicated returns per cow can increase from $85 to $165 with
the use of pasture (Muller and Holden, 1994). Other reasons cited for choosing pasture-
based production systems include reduced labor, best land use, improved cow health, and
reduced manure handling, as well as improved quality of lifestyle for the owner/manager
(Loeffler et al., 1996). One survey indicated that total hours of labor were not decreased
in grazing-based systems, but that time devoted to various tasks changed as that activitys
importance in the system changed (Loeffler et al., 1996).
Climatic Challenges to southeastern Dairies
Regardless of the production system, the climate of the Southeast presents unique
challenges for producers in the region. Of particular concern is the effect of heat and
humidity on both plants and livestock. The effect of the climate may be more adverse for
animals on pasture.
Climatic Effects on Forages
The perennial, warm-season forages adapted to the Southeast are typically of
lower nutritive value than either cool-season perennials or warm-season annuals


84
(Atomic Absorption Spectrophotometer 5000, Perkin Elmer, Norwalk, Conn.) following
the methods of Williams et al. (1962). For calculating DM intake, results from the fecal
sample analysis were evaluated with PROC NLIN following the method described by
Pond et al. (1987; Appendix 1). The parameters generated by this program then were
used to estimate fecal output for each cow.
To calculate the intake of pasture, the following assumptions were made:
1) intake of supplement was the same for all cows within a pasture replicate,
2) digestibility of supplement OM was equivalent to calculated TDN from NRC
(1989), and
3) digestibility of forage was affected by the level of supplement intake, as
determined by the equation of Moore et al. (1999; Appendix 2).
The measure of forage in vitro organic matter digestibility (IVOMD) for each
paddock was used to calculate forage intake by cows grazing that paddock (Pond et al.,
1987). Fecal output (kg/d) should equal total intake (kg/d) multiplied by the indigestible
fraction of a feed. Thus, estimates of fecal output are dependent upon accurate
determination of diet digestibility.
The fecal output observed based on the mordanted-fiber methodology did not
equal the fecal output predicted based on estimated forage and supplement digestibilities.
For this reason, an iterative SAS (1991) program (developed by J. E. Moore) was
employed to adjust the forage intake until the difference between fecal output observed
and fecal output predicted differed by less than 0.01 kg/d (Appendix 2).
Expected diet digestibility (% of OM) = [(forage intake, kg of OM forage
digestibility, %) + (supplement intake, kg of OM* supplement digestibility, %)]/total


CHAPTER 5
FINAL SUMMARY AND CONCLUSIONS
In the USA, interest in the use of pasture-based forage systems for dairy
production has increased in the past decade. Renewed interest in grazing for dairy cattle
has been driven primarily by tightened economic conditions in which production costs
increased while milk prices dropped. Southern producers wanting to know more about
grazing have had little information upon which to make management decisions. Most
information about dairy grazing in the USA comes from research conducted in temperate
climates and is of limited relevance for producers in the South whose primary forage base
is warm-season pasture. Thus, a series of experiments was conducted to quantify the
responses of lactating Holstein cows to different grazing systems and management
strategies.
The first two experiments tested the effects of grazing systems. Forages were
bermudagrass (BG; Cynodon spp. cv. Tifton 85) and rhizoma peanut (RP; Arachis
glabrata cv. Florigraze), two relatively new forages available to producers. The forages
were tested in combination with two stocking rates (SR) and two supplementation rates
(SUP). The SR differed between forages to account for the different growth rates of the
two species. The BG pastures were stocked at 5.0 or 7.5 cows/ha in 1995 and 7.5 and
10.0 cows/ha in 1996. The RP pastures were stocked at 2.5 and 5.0 cows/ha in 1995 and
5.0 and 7.5 cows/ha in 1996. Supplementation rates were 0.33 and 0.5 kg of supplement
(as-fed basis)/kg of daily milk production.
167


101
The response to supplement on a land-area basis was greater when cows grazed
BG than RP (132 and 110 kg of milk/ha per day at high and low SUP for BG vs. 90 and
83 kg of milk/ha per day at high and low SUP for RP; forage by supplement interaction,
P < 0.001). In this case, both the lesser substitution of forage by supplement for cows on
BG and the potential to carry more cows on BG pastures overwhelmed RPs greater
production per cow.
Production per land area response to increased supplement feeding was greater at
the high SR (SUP by SR interaction, P < 0.01). Milk production of cows fed the high and
low SUP treatments was 135 and 115 kg/ha per day at the greater SR vs. 88 and 78 kg of
milk/ha per day with the high and low SUP treatments at the lesser SR. Others (Blaser et
al., 1960; Phillips, 1988) have reported a greater response to supplement when forage is
limiting, but forage was likely only limiting for RP at the high SR.
Body Weight and Condition
Parity and year effects. Over the two years, multiparous cows weighed an
average of 65 kg more (P < 0. 001) than their primiparous counterparts (537 vs. 472 kg)
but had less (P < 0.01) body condition (2.49 vs. 2.78). Multiparous cows lost more (P <
0.05) weight than did primiparous cows (-9 vs. -6 kg/28-d period), but this difference
was not reflected in BCS change. Cow BCS was greater (P <0.01) in 1995 than 1996
(2.78 vs. 2.48), but changes in BCS were less (P < 0.05) in 1995 than in 1996 (-0.07 vs.
-0.16).
Forage effects. Cows grazing RP lost approximately 5 kg more (P < 0.05) BW
per 28-d period (-10 vs. -5 kg) than cows grazing BG (Table 3.4). Though the RP was
of greater nutritive value and would be expected to support greater weight gain, weight


69
returned with provision of supplemental greenchop com and increased pasture herbage.
Although the authors were unable to discern measurable differences in DMI, the changes
in production with changes in feed supply indicated that cows treated with bST likely had
greater intakes.
Intake differences were shown by Michel et al. (1990), who fed cut pasture
(ryegrass-white clover) to lactating dairy cows and found significant increases in DMI
within 4 wk of treatment with bST. Means of milk response were not reported, but cows
of low genetic merit had greater response to bST than did cows of high genetic merit.
Little difference in BW was observed over the course of the 50-d trial, but body condition
score was generally less for bST treated cows than for controls. This indicates the
necessity of providing adequate feed to meet the energy requirements of cows treated
with bST.
Valentine et al. (1990) reported that bST injections increased milk production
from cows grazing ryegrass-subterranean clover pastures and supplemented with a
barley-faba bean (Vicia faba) concentrate. Injections of 320 mg of a sustained release
formulation every 28, 21, or 14 d resulted in average dosages of 11.4, 15.2, or 22.8 mg/d.
Milk production was 17.6, 18.1, and 18.8 kg/d vs. 15.9 kg/d for control cows,
corresponding to 10.7, 13.8, and 18.2% increase in milk production with increased dose.
Live weights were also increased, and the authors attributed this to greater gut fill due to
greater pasture intake, although intake was not measured
Hartnell et al. (1991) explored dose responses within parities with much greater
levels of bST administered (biweekly doses of 250, 500, or 750 mg of bST) to cows in
confinement in four different geographic regions within the U.S.A. Averaged over


Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
GRAZING SYSTEMS AND MANAGEMENT STRATEGIES FOR
LACTATING HOLSTEIN COWS IN FLORIDA
By
John Herschel Fike
December, 1999
Chairman: Charles R. Staples
Major Department: Dairy and Poultry Sciences
Two experiments tested effects of two pasture forage species, the legume rhizoma
peanut (RP; Arachis glabrata) or bermudagrass (BG; Cynodon spp. cv. Tifton 85), two
supplementation rates (SUP; 0.33 or 0.5 kg/kg of milk), and two stocking rates (SR) on
performance of mid-lactation Holstein cows.
The RP supported more milk per cow (17.3 vs. 16.3 kg/d), but less milk per
hectare than BG pastures. With each additional kg of supplement fed above the low SUP,
cows produced an additional 0.87 kg of milk/d if grazing BG vs. an additional 0.43 kg of
milk/d if grazing RP.
Respiration rates and body weight (BW) losses generally were greater when
treatments stimulated milk production. Optimum SR for BG and RP pastures were
approximately 10 and 5 cows/ha. Cows grazing RP had greater forage (11.3 vs. 7.6 kg/d;
Xll


154
fat from cows treated with bST. The numerical increases in milk fat concentration are
consistent with reports of increased milk fat concentration due to bST treatment in short
term trials and especially when cows are in negative energy balance (Chalupa and
Galligan, 1989; Hoogendoom et al., 1990). This suggests that the increased feed
provided to cows treated with bST (due to increased milk production) did not completely
compensate for the increased energy associated with increased milk production.
However, calculation of energy balance using NRC (1989) equations and feed intake
estimates did not confirm differences in energy balance due to bST treatment (data not
shown).
Increased (P < 0.001) daily production of milk fat and milk protein occurred
primarily because of the increase in milk production due to bST (Table 4.4).
Effect of supplemental silage. Feeding supplemental silage in the bam had no
effect on milk production, 4% FCM production, nor milk fat and protein concentrations
or quantities. Similar results have been reported by Australian researchers utilizing
mixed warm- and cool-season pastures (Moran and Stockdale, 1992) and by researchers
studying use of com silage with temperate pastures (Holden et al., 1995).
When pasture was limited or when supplemental forage was of greater quality
than the grazed forage, milk yield typically increased with silage inclusion (Huber et al.,
1964; Phillips, 1988). No difference in herbage disappearance due to any treatment was
observed (data not shown). The lack of influence of silage supplementation indicates that
forage availability did not limit production of cows fed silage and also implies that the
increased stocking rate used for that treatment was appropriate.


80
Cows were divided into their respective SUP treatment groups (n = 2) post
milking and fed on a concrete feedbunk line. Amount of supplement offered was based
on the average milk production for each group, with feed amounts adjusted twice weekly.
This method of feeding potentially confounded the effects of SUP with effects of SR and
forage treatments but was considered a typical management practice of commercial
farms.
Year two. Holstein cows (n = 62) were evenly divided between one and > 1
parity. Mean parity for multiparous cows was 3.1 lactations and mean DIM for all cows
was 126 38.
Experimental design and choice of treatments were as in Year 1. However, based
on results from 1995, some modifications to protocol were implemented. Cows were not
/R\
treated with Posilac In 1995 pastures were deemed underutilized, so stocking rate
treatments were increased to 7.5 and 10 cows/ha for BG and 5 and 7.5 cows/ha for RP
pastures. During Year 2, NH4NO3 fertilizer was applied more frequently to BG pastures,
but the total quantity applied was slightly less than in 1995. Bermudagrass pastures
received 45 kg of N/ha as NH4NO3 on 21 May, 8 June, and 7 August. A fourth
application of 56 kg of N/ha occurred on 11 September. Potassium was applied at 40 kg
of K^O/ha on 7 June. Pastures were irrigated from 15 May to 12 June at a rate of 25
mm/wk for a total of 100 mm of water. Due to the loss of BG stand, one replicate pasture
assigned the low SR and low SUP treatments was removed from the study. Pastures were
staged with animals as previously described from 10 June to 6 July. The trial was from 9
July through 2 October 1996.


46
Total intake was an average of 2.5 kg/d greater for supplemented cows. Production of
milk, 4% FCM, and milk protein were not different between concentrate treatments but
were greater than for the unsupplemented treatment. Cows fed fatty acids produced
greater quantities of milk fat. Volatile fatty acids in ruminal fluid were essentially
unchanged between concentrate treatments, indicating that the fatty acids used did not
affect microbial function. However the low amount of added dietary fat and the small
percentage of which was unsaturated fatty acid would not be expected to significantly
hinder microbial function (Jenkins, 1993).
Escape proteins
In a review, Oldham (1984) noted that supplemental proteins might directly affect
control of food intake in ways not directly related to improvements in digestibility. This
has been shown by Froetschel et al. (1997) who reported that ruminal undegradable
proteins contain peptide sequences that may increase gut motility.
Because of the rapid and extensive degradation of proteins in lush pastures
(Beever et al., 1986a,b), some researchers have explored the utility of supplementing
cows with less ruminally degradable sources of protein. Jones-Endsley et al. (1997)
compared amounts (6.4 vs. 9.6 kg/d) and concentrations (12 and 16% CP) of protein
supplements for lactating dairy cows. The 16% supplement appeared designed to provide
additional ruminally undegradable protein, but this was not made clear by the presented
feed analysis. Amount of supplement did not affect forage intake, but animals
consuming the 16% CP concentrate tended to consume more forage (1.6 kg/d) than did
those fed the 12% CP supplement.


12
diets, respectively. Milk production was greatest from cows initially fed the non
constraining diet, but when switched to a constraining diet, intake declined rapidly even
though, immediately prior to the changeover, cows on [the non-constraining] diet had a
much greater milk yield and thus a much greater presumed energy requirement, (p.
2236). The authors concluded that milk yield had no effect on the capacity of the cow to
consume a constraining diet... [and] intake capacity is independent of cow
performance (p. 2237). The authors noted that intake capacity might be expected to
change during very early and very late phases of lactation as others have shown (Hunter
and Siebert, 1986; Stanley et al., 1993).
The results of Friggens et al. (1998) underscore the importance of dietary factors
that affect gut fill. Of a forages intrinsic characteristics, fiber is thought to be the main
component limiting voluntary intake due to its filling properties (Jung and Allen,
1995). In 1965, Van Soest reported large negative correlation between percent of plant
cell wall constituents (NDF) and voluntary intake. Neutral detergent fiber represents the
total cell wall fraction of a feedstuff, and is considered a mechanism controlling forage
intake by ruminants (Waldo, 1986; Jung and Allen, 1995).
Intake of perennial, warm-season grasses in the Southeast typically is considered
limited by physical (fill) effects due to their high fiber concentrations and low
digestibilities. The National Research Council recommends dietary NDF concentrations
of 25 to 28% in rations for lactating cows (NRC, 1989), but the majority of summer,
perennial grasses common to the region generally have concentrations of NDF in excess
of 70% (DM basis). If warm-season perennial grasses are the sole forage source in the
diet, their large NDF concentrations might represent a steep hurdle for producers trying to


45
digestibility in the rumen were greater when cows ate roughage before concentrate rather
than in the reverse order.
Timing might also be important relative to ruminal heat production. Russell
(1986) reported that adding pulses of glucose to glucose-limited cultures immediately
doubled heat production with little increase in cell protein. In addition to reduced
efficiency of microbial protein production, consumption of primarily soluble
carbohydrate-based supplements in asynchrony with dietary protein might increase
ruminal heat. Heat in the rumen negatively affects intake of DM and water and alters
ruminal fermentation patterns (Gengler et al., 1970). A 3 C increase in rumen
temperature (from 38.0 to 41.3 C) resulted in a 14% decrease in feed intake (13.2 vs.
11.4 kg/d for control and treatment cows, respectively) in the study by Gengler et al.
(1970).
Additional Energy and Protein Supplements for Animals on Pasture
Fats
Fat feeding may improve milk production but has potential for negative side
effects with respect to microbial fermentation, growth, and feed digestion (Emery and
Herdt, 1991). Fat feeding to lactating cows typically has been limited to mixed rations,
and information on feeding fats to cows on pasture is limited.
King et al. (1990) compared production from cows grazing ryegrass pastures and
receiving no supplement, 3.5 kg of a grain-based pelleted concentrate, or 3.8 kg of pellets
containing 0.5 kg of added fatty acids (primarily palmitic, stearic, and linoleic acids).
Diets were not isocaloric. Forage intakes were similar and were estimated at 17.0, 16.3,
and 15.6 kg of DM/d for control, concentrate, and concentrate plus fatty acid treatments.


141
(Atomic Absorption Spectrophotometer, Model 5000, Perkin Elmer, Norwalk, Conn.)
following the methods of Williams et al. (1962).
Results from the intake study were evaluated with PROC NLIN using the method
of Pond et al. (1987; Appendix 1). Parameters generated by this program were used to
estimate fecal output for each cow. Estimates were based on the following assumptions:
1) supplement intake was the same for all cows within a pasture replicate,
2) supplement digestibility was constant regardless of forage intake,
3) digestibility of forage was affected by the level of supplement intake, as
determined by the equation of Moore et al. (1999; Appendix 2).
Theoretically, fecal output should equal total intake multiplied by the indigestible
fraction of a feed. Because fecal output observed, based on the mordanted-fiber
methodology, was not equal to the fecal output predicted based on forage and supplement
digestibilities, an iterative SAS (1991) program (developed by Dr. J. E. Moore) was
employed to adjust the estimate of bermudagrass intake until the difference between fecal
output observed and predicted differed by less than 0.01 kg/d (Appendix 2).
Expected diet digestibility (%) = [(bermudagrass intake, kg bermudagrass
digestibility, %) + (silage intake, kg silage digestibility, %) + (supplement intake, kg *
supplement digestibility, %)]/total intake, kg. Because feeding concentrate supplements
often alters forage digestibility (Arriaga-Jordan and Holmes, 1986; Berzaghi et al., 1996),
the iterative program also employed the equation of Moore et al. (1999; Appendix 2 to
adjust total diet digestibility.
Feed sampling. Forage was collected once each period to characterize forage
nutritive value (Table 4.2). Forage was collected in a manner similar to that used for


144
1, all data were shifted so that peak temperature for all cows occurred at 1624 h, just
before milking. For Segment 2, the time from peak pre- to peak post-shower
temperatures was adjusted to equal 2 h 42 min. This adjustment allowed the minimum
temperature for all cows in section 2 to occur at 1745 h, during the time of showering,
milking, and drinking. Segment 3 data were shifted so that all cows had near-peak or
peak temperature at 1906 h, when cows returned to pasture.
After adjustments, data were modeled by segment using PROC MIXED
procedure of SAS (Littell et al., 1996). Because our interest was in plotting the effect of
treatment over time without individual cow effects, cow was not included in the model.
Regression coefficients generated from the analysis were used to plot the data.
The resultant curves were evaluated visually for congruity of temperature between
segments. Since the generated curves were not always congruent from one section to the
next, algebraic operands using dummy variables were applied to the original data set to
force the joining of sections within each curve (Draper and Smith, 1981). Both PROC
MIXED and PROC GLM were used to evaluate the adjusted curves. The curves were
modeled using PROC GLM since the PROC MIXED method partitioned out only very
little variability due to cow within treatment and period. (After partitioning, overall
residual error was greater than residual error due to Cow(treatment by period) by a factor
greater than 106.)
Several different points in time (hour) were substituted into the model equation
and the ESTIMATE procedure of GLM was then used to calculate differences in
temperature between treatments. After taking the derivative of the model equation with


197
Joanning, S. W., D. E. Johnson, and B. P. Barry. 1981. Nutrient digestibility depressions
in com silage-com grain mixtures fed to steers. J. Anim. Sci. 53:1095-1103.
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Page 35 in Bioclimatology and the Adaptation of Livestock. H. D. Johnson, ed. Elsevier,
Amsterdam, The Netherlands.
Johnson, T. R., and D. K. Combs. 1991. Effects of prepartum diet, inert rumen bulk, and
dietary polyethylene glycol on dry matter intake of lactating dairy cows. J. Dairy Sci.
74:933-944.
Johnson, T. R., and D. K. Combs. 1992. Effects of inert rumen bulk on dry matter intake
in early and midlactation cows fed diets differing in forage content J. Dairy Sci. 75:508-
519.
Johnson, H. D., R. Li, W. Manalu, K. J. Spencer-Johnson, B. A. Becker, R. J. Collier,
and C. A. Baile. 1991. Effects of somatotropin on milk yield and physiological responses
during summer farm and hot laboratory conditions. J. Dairy Sci. 74:1250-1262.
Jolliff, G. D., A. Garza, and J. M. Hertel. 1979. Seasonal forage nutritive value variation
of Coastal and Coastcross-1 bermudagrass. Agron. J. 71:91-94.
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Evaluation: Concepts and Techniques. J. L. Wheeler and R. D. Mochrie, eds. Griffen
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Sci. 66:194-203.
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Jones-Endsley, J. M., M. J. Cecava, and T. R. Johnson. 1997. Effects of dietary
supplementation on nutrient digestion and the milk yield of intensively grazed lactating
dairy cows. J. Dairy Sci. 80:3283-3292.
Joumet, M., and C. Demarquilly. 1979. Grazing. Pages 295-321 in Feeding Strategies for
the High Yielding Dairy Cow. W. H. Broster and H. Swan, ed. Granada, London.
Jung, H. G., and M. S. Allen. 1995. Characteristics of plant cell walls affecting intake
and digestibility of forages by ruminants. J. Anim. Sci. 73:2774-2790.
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US. Page 7 in Proc. Conf. Sustaining the Smaller Dairy Farm in the Northeastern U.S. S.
R. Kaffka, ed. Sunny Valley Foundation, Inc., New Milford, CT.


LIST OF FIGURES
Figure page
3.1 Interaction of forage [Tifton 85 bermudagrass (BG) or Florigraze rhizoma peanut
(RP)] and year (1995 or 1996) on production of milk, 4% fat corrected milk (FCM),
and milk fat and milk fat percent 92
3.2 Interaction of forage, stocking rate (SR), and year on milk and 4% fat corrected milk
(FCM) yields and body weight change (DBW). Forages were Tifton 85
bermudagrass and Florigraze rhizoma peanut. Low and high SR for BG were 5.0
and 7.5 cows/ha in 1995 and 7.5 and 10.0 cows/ha in 1996. Low and high SR for
RP were 2.5 and 5.0 cows/ha in 1995 and 5.0 and 7.5 cows/ha in 1996 93
3.3 Interaction of supplementation rate and forage species on production of milk, 4% fat
corrected milk (FCM), milk fat, and protein. Supplementation rates were 0.33 (Lo)
and 0.5 (Hi) kg of supplement per kg of daily milk production. Forage species were
Tifton 85 bermudagrass and Florigraze rhizoma peanut 95
3.4 Interaction of supplementation rate and year on production of 4% fat corrected milk
and milk fat, and percentages of milk fat and protein. Low (Lo) and high (Hi)
supplementation rates were 0.33 and 0.5 kg of supplement per 1 kg of daily milk
production, respectively 98
3.5 Interaction of parity, year, and supplementation rate on production of milk, 4% fat
corrected milk (FCM), and milk fat and milk fat percent. Low (Lo) and high (Hi)
supplementation rates were 0.33 kg and 0.5 kg of supplement per kg of daily milk
production. Supplementation rates did not differ by year (1995 or 1996) 99
3.6 Interaction of parity, forage, and stocking rate on body weight change (ABW).
Average low (Lo) and high (Hi) stocking rates were 6.25 and 8.75 cows/ha for
Tifton 85 bermudagrass (BG) and 3.75 and 6.25 cows/ha for Florigraze rhizoma
peanut (RP) pastures. Stocking rates were the same across parities 104
3.7 Interaction of supplementation rate and year on changes of body condition score
(ABCS 5 point scale) and body weight (ABW). Low (Lo) and high (Hi)
supplementation rates were 0.33 and 0.5 kg of supplement per kg of daily milk
production 104
IX


202
Mollett, T. A., M. J. DeGeeter, R. L. Belyea, R. A. Youngguist, and G. M. Lanza. 1985.
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for Pasture Management, University of Missouri, Columbia.
Moore, J.E, W.E. Kunkle, M.H. Brant, and D.I. Hopkins. 1999. Effects of
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J. Anim. Sci. 77(Suppl. 2):122-135.
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digestion of forages. J. Dairy Sci. 57:1258-1259.
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Effect of level of silage feeding, and responses to cottonseed meal while grazing
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Moran, J. B., and T. E. Trigg. 1989. Feed intake and utilization of maize silage-based
complete diets by Australian Friesian cows and heifers at various stages of lactation.
Livestock Prod. Sci. 23:275-293.
Morita, S., S. Devir, C. C. Ketelaar-De Lauwere, A. C. Smits, H. Hogeveen, and J. H. M
Metz. 1996. Effects of concentrate intake on subsequent roughage intake and eating
behavior of cows in an automatic milking system. J. Dairy Sci. 79:1572-1580.
Morita, S., M. Hirano, and S. Nishino. 1991. Effect of arrangement of feeding order of
diets on probability of eating bout continuing and frequency of eating bout in steers. Jpn.
J. Livest. Manage. 26:75.
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of forage quality. Agron. J. 51:221-226.


205
Phillips, C. J. C. 1989. New techniques in the nutrition of grazing cattle. Pages 106-120
in New Techniques in Cattle Production. C. J. C. Phillips, ed. Butterworths. Boston, MA.
Phillips, C.J.C., and S. P. J. Denne. 1988. Variation in the grazing behaviour of dairy
cows, measure by a Vibrarecorder and bite count monitor. Appl. Anim. Ethology.
21:329-335.
Phillips, C. J. C., and J. D. Leaver. 1985. Supplementary feeding of forage to grazing
dairy cows. 1. Offering hay to dairy cows at high and low stocking rates. Grass and
Forage Sci. 40:183-192.
Phipps, R. H., C. Madakadze, T. Mutsvangwa, D. L. Hard, and G. DeKerchove. 1991.
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Pitman, W. D., and E. C. Holt. 1982. Environmental relationships with forage quality of
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methodology in grazing studies. Pages 49-53 in Proc. Grazing Livestock Nutr. Conf.,
Jackson, WY.
Poole, D. A. 1987. Flat v. step feeding of medium or high levels of concentrates for dairy
cows. Anim. Prod. 30:341-354.
Poppi, D. P., and S. R. McLennan. 1995. Protein and energy utilization by ruminants at
pasture. J. Anim. Sci. 73:278-290.
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Gainesville.


145
respect to hour (dy/dhour), the ESTIMATE procedure was used to determine differences
among the slopes of the treatments.
Results and Discussion
Grazing Time and Intake of Organic Matter
Effect of housing. Per design, keeping cows in the bam limited their opportunity
to graze (Table 4.3). Cows on pasture spent more time (P < 0.001) in grazing activities as
measured by vibracorder than did cows kept in the bam from 0800 to 1500 h (6.9 vs. 5.3
h of grazing time/cow per d). The estimates of grazing time for cows grazing pastures
through the day in this study are less than those reported by Stobbs (1970), who tested a
variety of forage species and fed little supplement. Results are similar to those of
Combellas et al. (1979) who reported 6.6 hours of grazing/d for heifers receiving 6 kg/d
of supplement. However, direct comparison of grazing times is difficult due to
differences in milk production, BW, environment, forage species, and pasture
management.
Though grazing time was greater for cows on pasture, grazing intensity appeared
greater for cows housed in bams (Figure 4.1), and the estimates of forage OMI indicate
that grazing time did not affect forage intake (Table 4.3). Average forage OMI of BG,
excluding cows on the silage treatment, was 9.2 kg/d, or 1.58% of BW. Because forage
OMI was unaffected by grazing time, housed cows must have grazed with greater
harvesting efficiency [defined as intake over time (Barton et al., 1992; Krysl and Hess,
1993)]. This might have occurred as a result of an increased bite rate due to temporary
deprivation from pastures as has been reported by Greenwood and Demment (1988).


159
Insulin concentrations tended (P <0.10) to increase due to bST at the second
sampling date and as an average of all sampling dates. In a study involving increasing
plane of nutrition and bST administration, plasma insulin concentrations increased with
bST treatment for cows fed diets greater in energy density and crude protein
concentration (diet by bST interaction) (McGuire et al., 1992).
Effect of supplemental silage. Feeding silage increased (P < 0.05) plasma IGF-1
concentrations at the second blood sampling date only. Concentrations of plasma IGF-1
might be expected to increase based on the results of McGuire et al. (1992) if total energy
intake was increased in this group of cows.
Respiration Rates and Body Temperatures
Effect of housing. Cows kept on pasture during the daylight hours took nearly
30% more (P < 0.001) breaths/min than those housed in the bam (89 vs. 69 per min for
bam and pasture cows, respectively). The RR of housed cows were somewhat greater
than those reported for cows maintained in a thermoneutral environment, indicating some
level of heat stress, but RR were somewhatlower than those typical of cows subjected to
heat stress (Manalu et al., 1991; Zoa-Mboe et al., 1989). The RR of cows under shade on
pasture were only 10% less than the RR of shaded cows in dirt lots reported by Zoa-
Mboe et al. (1989), but the cows in this study had much lower levels of milk production.
Further, a report of RR of 120 breaths/min for unshaded lactating cows (Zoa-Mboe et al.,
1989) illustrates the degree of cow discomfort under Southeastern conditions without
some method of reducing heat load.
By 0900 h, cows on pasture were hotter than cows kept in the bam (Figure 4.2).
Temperatures of all cows continued to increase, peaking at approximately 1630 h, the


71
likely less suitable because of the potential for continued camping and concomitant
fouling in those areas of prolonged congregation. Increases in pests (flies and other
parasites) and infection (primarily mastitis) are possible. Generally, any mechanical
methods of cooling such as fans and misters are likely to be difficult to apply to large-
scale grazing systems and would be of limited suitability due to increased costs and the
potential for fouling the pastures. Some use of shades and misters with mobile irrigation
units have been attempted in Florida (J. Trout, personal communication), but no research
as to their efficacy has been reported.
Work by Missouri researchers indicates that the pattern of cooling is more
beneficial to improving production than provision of cooling in a general sense (Spain
and Spiers, 1999; Spiers et al., 1999). Cows had better performance responses when kept
at cooler environmental temperatures during the night. Cooling fans were more effective
at improving performance when used at night rather than in the daytime. Thus, cows
grazing in environments where differences between day and night temperatures are great
may not suffer the effects of heat stress as severely as cows in environments with little
change between day- and nighttime temperatures.
This cooling opportunity can be diminished, however, if the nighttime relative
humidity is high because moist air reduces the efficiency of evaporative cooling (West,
1994). Thus, a more appropriate measure of heat stress would be some combination of
temperature and humidity, such as a temperature humidity index (THI), as the one
referred to by West (1994). The THI is calculated as the dry bulb temperature (0.55 -
0.55 relative humidity) (dry bulb temperature 58), and mean THI greater than 72
reduce milk production (Johnson, 1987, cited by West, 1994).


198
King, K. R., C. R. Stockdale, and T. E. Trigg. 1990. Influence of high energy
supplements containing fatty acids on the productivity of pasture-fed dairy cows. Aust. J.
Exp. Agrie. 30:11-16.
Klopfenstein, T. J., and F. Owen. 1987. Soybean hulls. An energy supplement for
ruminants. Anim. Health Nutr 43(4):28-32.
Kolver, E. S., and L. D. Muller. 1998. Performance and nutrient intake of high producing
Holstein cows consuming pasture or a total mixed ration. J. Dairy Sci. 81:1403-1411.
Kolver E. S., L. D. Muller, and G. A. Varga. 1995. Synchronizing ruminal degradation
of supplemental carbohydrate with pasture N in lactating dairy cows. J. Anim. Sci.
73(Suppl.):261(Abstr).
Kronfeld, D. S. 1988. Biologic and economic risks associated with use of bovine
somato tropins. J. Am. Vet. Med. Assoc. 192:1693-1696.
Krysl, L. J., and B. W. Hess. 1993. Influence of supplementation on behavior of grazing
cattle. J. Anim. Sci. 71:2546-2555.
Lanyon, L. E. 1995. Does nitrogen cycle?: Changes in the spatial dynamics of nitrogen
with industrial nitrogen fixation. J. Prod. Agrie. 8:70-78.
Leaver, J. D., 1973. Rearing of dairy cattle. 4. Effect of concentrate supplementation on
the live-weight gain and feed intake of calves offered roughages ad libitum. Anim. Prod.
17:43-52.
Leaver, J. D. 1985a. Milk production from grazed temperate grassland. J. Dairy Res.
52:313-344.
Leaver, J. D. 1985b. Effects of supplements on herbage intake and performance. Pages
79-88 in Grazing. J. Frame, ed. Proc. Conf. held at Malvern, Worcestershire. Occasional
Symp. No. 19, Br. Grassl. Soc.
Leaver, J. D., Campling, R. C., and W. Holmes. 1968. Use of supplementary feeds for
grazing dairy cows. Dairy Sci. Abstr. 30:355-361.
Le Du, Y. L. P., J. Combellas, J. Hodgson, and R. D. Baker. 1979. Herbage intake and
milk production by grazing dairy cows. 2. The effects of level of winter feeding and daily
herbage allowance. Grass Forage Sci. 34:249-260.
Leng, R. A., and J. V. Nolan. 1984. Symposium: Protein nutrition of the lactating dairy
cow. Nitrogen metabolism in the rumen. J. Dairy Sci. 67:1072-1089.


TABLE 3.4. Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on body weight (BW) and body condition
score change (ABCS), respiration rate (RR), body temperature (TEMP), and plasma urea nitrogen (PUN) and plasma glucose of
Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut during the summers of 1995 and 1996.
Tifton 85 bermudagrass Florigraze rhizoma peanut
Stocking Rate1 Stocking Rate2 Probability3
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage SR x SR
Item 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 SEM Forage SR SUP x SR X SUP x SUP x SUP
Average BW, kg
507
506
508
507
498
500
504
508
2
*
*
NS
t
NS
NS
NS
ABW, kg/28-d period
-6
-4
-4
-5
-16
-11
-9
-4
3
*
t
NS
NS
NS
NS
NS
BCS
2.67
2.68
2.63
2.63
2.60
2.65
2.59
2.61
0.04
NS
NS
NS
NS
NS
NS
NS
ABCS/28-d period
0.01
-0.11
-0.20
-0.12
-0.04
-0.10
-0.12
-0.24
0.08
NS
f
NS
NS
NS
NS
NS
RR, breaths/min
93
85
100
89
100
90
102
95
2
*
*
***
NS
NS
NS
NS
TEMP, C
39.2
39.1
39.2
38.9
39.4
39.3
39.4
39.5
0.1
*
NS
NS
NS
NS
NS
NS
PUN, mg %
13.0
13.4
12.9
12.0
14.9
16.2
14.6
15.3
0.5
***
t
NS
NS
t
NS
NS
Plasma glucose, mg %
59.6
57.4
59.9
57.4
59.9
56.4
59.0
57.6
0.6
NS
NS
***
NS
NS
NS
NS
'High and low stocking rates were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.


Thanks for the generous financial assistance given by the Dean for Academic
Programs for the first year and the Department of Dairy and Poultry Sciences for the
remaining years. Thanks also go to American Farm Bureau, CBAG, and Monsanto for
their financial assistance of the research.
in


6
amount and arrangement of tissues (Akin, 1986a,b, p. 194). However, warm-season
species do have the agronomic advantage of being adapted to the region. Thus, despite
their lower quality, forages such as bahiagrass (Paspalum notation) and bermudagrass
(Cynodon dactylon (L.) Pers.) are the foundation of forage production systems for
grazing animals in the Southeast.
Other forage quality concerns for graziers may include pasture variability in
supply and nutritive value over the course of the growing season (Holt and Conrad,
1983). Changes may correspond with changes in climatic conditions, such as
temperature, soil moisture, leaf/stem ratio and the proportions of dead leaves in the sward
(Beaty et al., 1982; Henderson and Robinson, 1982). Grazing dairies, reliant upon locally
grown perennial forages, thus are likely more susceptible to changing forage quality than
many dairy farms using confined housing.
Climatic Effects on Animals
Higher environmental heat and humidity affect dairy cows negatively by limiting
their ability to dissipate body heat. In such circumstances, cows are likely to decrease
DMI, and in more severe conditions may also suffer from heat-related disorders such as
respiratory alkalosis/metabolic acidosis, ketosis related to excessive decrease of DMI,
and laminitis associated with feeding diets of large concentrations of grain (Sanchez et
al., 1994; Nocek, 1997; 0rskov, 1999). Heat stress also impairs the cows reproductive
performance and embryo survival (Thatcher and Collier, 1986; Wolfenson et al., 1988;
Ealy et al., 1993).
Heat stress can be mitigated with cooling technologies. The technological
advances in confined-housing systems include well-ventilated bams with high roofs and


Total OMI, kg/d Forage OMI, kg/d
Parity Parity
Figure 3.9. Interactions of parity, forage, and stocking rate (SR) on forage and total organic matter intake (OMI) and forage and total
OMI as a percent of body weight (OMIPBW). Forages were Tifton 85 bermudagrass (BG) or Florigraze rhizoma peanut (RP). Average
low and high SR for BG pastures were 6.25 and 8.75 cows/ha. Average low and high SR for RP pastures were 3.75 and 6.25 cows/ha.


116
Predicted energy inputs were greater than outputs by an average of 4.8 Mcal/d (23% of
estimated energy requirement) and quite variable. The standard deviation of all energy
difference estimates was 7.0 Mcal/d, 32.4% above estimated requirements. The results
indicate that either energy intake was overestimated or maintenance energy requirements
were underestimated, although maintenance energy requirement was increased from 10%
to 25%. Estimates of energy status (energy intake minus energy output) for cows grazing
RP pastures were particularly poor, especially for cows fed the greater SUP. Energy
states were over-estimated (P < 0.001) by 8.8 Mcal/d for cows grazing RP, compared
with -0.5 Mcal/d for cows grazing BG. The over-estimate (P < 0.001) of energy status
was 2.5-fold greater with additional supplementation (2.6 vs. 6.6 Mcal/d for low and high
SUP rates, respectively). Some of the variability may be attributed to the method of
feeding in 1995. When cows were fed at the feedbunk (1995), intakes would likely vary
to a greater degree than when cows were fed from troughs in their individual pastures
(1996). However, comparison of energy status predictions between years indicated no
improvement, and energy status difference was less in 1995 than in 1996.
These data are subject to several sources of error. Overestimates of intake,
underestimates of maintenance requirements, and overestimates of diet digestibility (due
to predictions of associative effects) all may have limited the accuracy of prediction.
Regardless, the differences between energy inputs and outputs suggest that nutrients of
RP were poorly utilized, and that different feeding strategies with respect to supplements
are likely necessary to optimally utilize RPs better nutritive characteristics.


207
Rooke, J. A., N. H. Lee, and D. G. Armstrong 1987. The effects of intraruminal infusions
of urea, casein, glucose syrup and a mixture of casein and glucose syrup on nitrogen
digestion in the rumen of cattle receiving grass-silage diets. Br. J. Nutr. 57:89-98
Roth, L. D., F. M. Rouquette, and W. C. Ellis. 1984. Sward attributes and nutritive value
of Coastal bermudagrass as influenced by grazing pressure. Progress Report, Tex. Agrie.
Exp. Sta. P.R.-4215. Pp. 11-13.
Roth, L. D., F. M. Rouquette, Jr., and W. C. Ellis. 1990. Effects of herbage allowance on
herbage and dietary attributes of Coastal bermudagrass. J. Anim. Sci. 68:193-205.
Rouquette, M., D. Bransby, and B. Kunkle. 1993. It is not advantageous (economically
and biologically) for producers to include legumes in cow-calf production systems in the
SPFCIC region. Pages 5-9 in Proc. 49th Southern Pasture and Forage Crop Improvement
Conf. Sarasota, FL.
Royal, A. J. E., and Jeffrey, H. 1972. Energy and protein supplements for dairy cows
grazing tropical pasture. Proc. Aust. Soc. Anim. Prod. 9: 292-295.
Ruiz, M. E. 1983. Supplementing dairy cows in the tropics. Pages 337-348 in Dairy
Science Handbook, F. H. Baker, ed. Vol. 15. Westview Press, Inc. Boulder, CO.
Russell, J. B. 1986. Heat production by ruminal bacteria in continuous culture and its
relationship to maintenance energy. J. Bacteriol. 168:694-707.
Russell, J. B., and D. B. Dombrowski. 1980. Effect of pH on the efficiency of growth by
pure cultures of rumen bacteria in continuous culture. Appl. Environ. Microbiol. 39:604-
610
Saldivar, A. J., W. R. Ocumpaugh, R. R. Gildersleeve, and J. E. Moore. 1990. Growth
analysis of Florigraze rhizoma peanut: Forage nutritive value. Agron. J. 82:473-477.
Sanchez, W. K., M. A. McGuire, D. K. Beede. 1994. Macromineral nutrition by heat-
stress interactions in dairy-cattle. Review and original research. J. Dairy Sci. 77:2051-
2079.
Sarker, A. B., and W. Holmes. 1974. The influence of supplementary feeding on the
herbage intake and grazing behaviour of dry cows. J. Br. Grassl. Soc. 29:141-143.
SAS Institute Inc. 1991. SAS*' System for Linear Models. Third Edition. 329 pp. Cary,
NC, USA.
Seath, D. M., and G. D. Miller. 1947. Effect of hay feeding in summer on milk
production and grazing performance of dairy cows. J. Dairy Sci. 30:921-926


39
limitations, some have fed rumen escape proteins, but performance responses to
ruminally undegradable intake proteins have been inconsistent, both for cows in
confinement and on pasture (Davison et al., 1991; Aldrich et al., 1993; Petit and
Tremblay, 1995a,b; Jones-Endsley et al., 1997). Such responses highlight the need for
first optimizing ruminal fermentation to maximize microbial protein synthesis (Aldrich et
al., 1993; Glenn, 1994).
To maximize microbial cell yields per unit of nutrient input (e.g., feed materials)
the rate of ATP production from fermentation reactions must equal the usage rate by
biosynthetic reactions at all times (Hespell and Bryant, 1979). With adequate ATP
(derived primarily from carbohydrate fermentation), rumen microbes can incorporate
amino acids into microbial protein (Nocek and Russell, 1988). Thus, providing
supplemental energy (typically grains high in carbohydrates) may be an effective way to
increase microbial yield and reduce excess N excretion.
Responses to Supplemental Carbohydrate
Responses to providing carbohydrate energy sources are mixed, however. With
continuous culture studies, Hoover and Stokes (1991) reported a high correlation (r =
0.99) between percent carbohydrate digestion and nonstructural carbohydrate (NSC) as a
percentage of dietary carbohydrate. However, the correlation of microbial efficiency to
NSC as a percentage of dietary carbohydrate was much lower (r = 0.33). These results
have been confirmed using cows on pasture by Carruthers et al. (1996) who found that
increasing the proportion of NSC in pasture without increasing energy intake did not
increase ruminal microbial protein synthesis or increase milk solids production in early
lactation.


49
between morning and afternoon feedings indicated greater forage intake with afternoon
feeding (2.6 and 2.9 percent of BW for morning and afternoon feedings, respectively).
Total intakes were not different among the three treatment groups, but forage intake and
total intake were greater for afternoon-supplemented steers in comparison with morning
supplemented animals. Feeding supplement to steers in the morning resulted in a 24%
decrease in forage intake/h of grazing time in comparison with control and afternoon
feeding treatments (Adams, 1985).
Reid (1951) noted that DMI and grazing time are not necessarily correlated.
Similarly, Krysl and Hess (1993) noted that a decrease in grazing time does not
necessarily mean a decrease in forage intake because harvest efficiency (defined as g of
forage OMI/kg of BW per min spent grazing) may change. Work of Barton et al. (1992)
confirmed these ideas. The authors observed grazing behavior of dairy steers fed
supplemental cottonseed meal at 0 or 2.5% of BW in the AM or PM. The steers reduced
grazing time on intermediate wheatgrass (Thinopyrum intermedium Host) pastures by
approximately 1.5 h when provided cottonseed meal supplement, but forage intakes were
not different across treatments. Steers receiving cottonseed meal had numerically greater
forage intake.
Interactions of Supplement and Herbage Allowance on Performance of Lactating
Cows in Pasture-Based Dairy Systems
The two main factors considered to cause the variable responses to supplement
are forage availability and forage nutritive value. Work by Blaser et al. (1960)
demonstrated that concentrate supplements were used more efficiently when herbage was
limited.


9
Grazing is energetically expensive for the cow, and any improvement in
performance will hinge upon increasing energy intake or increasing the efficiency with
which ingested energy is utilized (McCollum and Horn, 1990, p. 1). Even with
relatively high quality cool-season pastures, animal performance is often less than might
be expected given the chemical composition and nutritive value of the forage. This may
be due to the lower efficiency of utilization of fresh forage (Osuji, 1974) or to differences
in energy intake (Kolver and Muller, 1998). Kolver and Muller (1998) examined the
reason behind performance differences of cows consuming high quality pasture and those
eating a totally mixed ration (TMR) primarily composed of com and legume silages,
high moisture shelled com, whole cottonseed, soybean meal, legume hay and wheat
middlings. The concentration of NEl of the diets was similar (1.63 and 1.65 Mcal/kg of
DM for pasture and TMR), but NEl intake was less (32.4 vs. 40.2 Mcal/d) for cows
grazing pasture. The apparent DM digestibility of the diets was approximately equal (77
and 76% for pasture and TMR, respectively), but dietary NDF and ADF concentrations
were 40 and 20% greater for the pasture diets. The authors reported that differences in
intake rather than differences in energy between pasture and TMR limited energy intake
by pastured cows.
Some Animal and Nutritional Factors Influencing Feed Intake
Understanding the mechanisms regulating feed intake historically has been a key
research objective, because the amount of forage consumed is the major determinant of
production by animals fed forage-based diets (Buxton et al., 1995, p. 10). As much as
60 to 90% of the variation in digestible energy intake may be due to animal variability,
with 10 to 40% due to diet digestibility (Crampton et ah, 1960; Reid, 1961). Though


180
Another production model, which has not been explored in modem Florida, is use
of the dual purpose cow. Such systems are commonplace in Latin America where
fluctuations in milk and meat prices allow producers to take advantage of these combined
traits depending upon the market. Some pasture-based producers are breeding cattle that
fit this model, but these cattle and systems are unlikely to gamer wide interest in Florida
due to its status as a milk-deficit state. Indeed, the premium placed on milk production in
the state, and the as-yet more limited production with grazing systems suggests that at
this time, grazing systems may be more effective as a route of entry into dairy production
for producers with limited equity.


117
Treatment Effects on Forage Nutritive Value Estimates
Analysis values in Table 3.8 represent the least squares means of hand-plucked
samples from individual pastures, rather than an average across all pastures within a
given forage.
Year effects. Of the nutritive value measures, only NDF was unaffected by year.
Decreased (P < 0.001) CP (16.3 vs. 14.8% for 1995 and 1996, respectively) would
suggest that samples containing lesser concentrations of CP likely included more plant
stems, dead leaf, or both. This is contradicted, however, by increased (P < 0.001)
IVOMD (63.3 vs. 66.7%) and the lack of change in forage NDF concentration (62.7 vs.
62.9%) between years.
Forage effects. The IVOMD and CP concentration of RP exceeded (P < 0.001)
those of BG pastures by 21 and 33%, respectively, while NDF concentrations of RP were
approximately 55% less (P < 0.001) than those of BG. Concentrations of in vitro
digestible OM, CP, and NDF were 71.2, 17.8, and 44.5% for RP and 58.8, 13.3, and
81.8% for BG, agreeing with the findings of others (Beltranena et al., 1981; Hill et al.,
1993).
The IVOMD of sampled BG increased from 1995 to 1996 (55.5 vs. 62.1%) which
may indicate that the greater SR increased the quality of BG, while the digestibility of
sampled RP pastures was unchanged by year (71.2%; year by forage interaction, P <
0.001). Concentrations of CP in BG remained essentially unchanged across years (13.5
vs. 13.1% for 1995 and 1996, respectively), while CP in RP sampled decreased from
1995 to 1996 (19.0 vs. 16.6%; year by forage interaction, P < 0.01). Concentration of


195
Hoffman, P. C., D. K. Combs, and M. D. Casler. 1998. Performance of lactating dairy
cows fed alfalfa silage or perennial ryegrass silage. J. Dairy Sci. 81:162-168.
Hoffman, K., L. D. Muller, S. L. Fales, and L. A. Holden. 1993. Quality evaluation and
concentrate supplementation of rotational pasture grazed by lactating cows. J. Dairy Sci.
76:2651-2663.
Holden, L. A., B. P. Glenn, R. A. Erdman, and W. E. Potts. 1994a. Effects of alfalfa and
orchardgrass on digestion by dairy cows J. Dairy Sci. 77:2580-2594.
Holden, L. A., L. D. Muller, T. Lykos, and T. W. Cassidy. 1995. Effect of com silage
supplementation on intake and milk production in cows grazing grass pasture. J. Dairy
Sci. 78:154-160.
Holden, L. A., L. D. Muller, G. A Varga, and P. J. Hillard. 1994b. Ruminal digestion
and duodenal nutrient flows in dairy cows consuming grass as pasture, hay or silage. J.
Dairy Sci. 77:3034-3042.
Holmes, W. 1976. Aspects of the use of energy and of concentrate feeds in grazing
management. Pages 141-145 in Pasture Utilization by the Grazing Animal. J. Hodgson,
R. D. Baker, A. Davies, A. S. Laidlaw, and J. D. Leaver, eds. Br. Grassl. Soc. Hurley,
England
Holmes, W., and J. G. W. Jones. 1964. The efficiency of utilisation of fresh grass. J. Br.
Grassl. Soc. 19:119-129.
Holt, E. C., and B. E. Conrad. 1983. Season, age and cultivar effects on bermudagrass
forage production and quality. Tex. Agrie. Exp. Sta. P.R. 4141. Pp. 50-57.
Holt, E. C., and B. E. Conrad. 1986. Influence of harvest frequency and season on
bermudagrass cultivar yield and forage quality. Agron. J. 78:433-436.
Hongerholt, D. D. Muller, L.D. 1998.: Supplementation of rumen-undegradable protein
to the diets of early lactation Holstein cows on grass pasture. J. Dairy Sci. 81:2204-2214.
Hongerholt, D. D., L. D. Muller, and D. R. Buckmaster. 1997. Evaluation of a mobile
computerized grain feeder for lactating cows grazing grass pasture. J. Dairy Sci.
80:3271-3282.
Hoogendoom, C. J., S. N. McCutcheon, G. A. Lynch, B. W. Wickham, and A. K. H.
MacGibbon. 1990. Production responses of New Zealand Friesian cows at pasture to
exogenous recombinantly derived bovine somatotropin. Anim. Prod. 51:431-439.
Hoover, W. H. 1986. Chemical factors involved in ruminal fiber digestion. J. Dairy Sci.
69:2755-2766.


KEY TO ABBREVIATIONS
ADF acid detergent fiber
ADG average daily gain
BCS body condition score
BG Tifton 85 bermudagrass
bST bovine somatotropin
BW body weight
CP crude protein
DE digestible energy
DM dry matter
DMI dry matter intake
FCM fat corrected milk
FI forage intake
GT grazing time
HA herbage allowance
HM herbage mass
IB intake per bite
IGF-1 insulin-like growth factor 1
IVDMD in vitro dry matter digestibility
IVOMD in vitro organic matter digestibility
ME metabolizable energy
MUN milk urea nitrogen
MY milk yield
N nitrogen
NAN non-ammonia nitrogen
NDF neutral detergent fiber
NEl net energy of lactation
NEFA non-esterified fatty acid
NRC National Research Council
NSC non-structural carbohydrate
OM organic matter
OMI organic matter intake
PUN plasma urea nitrogen
RB rate of biting
RP Florigraze rhizoma peanut
SCC somatic cell count
SR stocking rate
SUP supplementation rate
THI temperature-humidity index
TMR totally mixed ration
TT temperature transponder
xi


73
Johnson et al. (1991) tested the effects of bST in a 30-d farm trial in Florida, and
in a 10-d trial with cows in an environmental chamber in Missouri. Injections of bST
increased milk production by 21% (28.8 vs. 34.9 kg of 3.5% FCM/d) and 35% (21.0 vs.
28.3 kg of 3.5% FCM/d) for the farm and chamber studies, respectively. While the THI
in the farm trial generally remained above 72, and was maintained above 75 in the
chamber study, cows appeared capable of dissipating additional heat due to increased
production, likely by increased respiration rates. Elvinger et al. (1992) found that cows
treated with bST increased milk yield in both cool and hot environments. However, in
both environments, the bST treated cows had greater rectal temperatures, contrary to the
findings of Johnson et al. (1991).
Though administration of bST may or may not increase rectal temperatures
(Mohammed and Johnson, 1985; Zoa-Mboe et al., 1989; Elvinger et al. 1992) it often
causes increased respiration rates for cows in hot environments (Mohammed and
Johnson, 1985; Staples et al., 1988; Zoa-Mboe et al., et al., 1989). Mohammed and
Johnson (1985) and Staples et al. (1988) reported increased respiration rates with no
increases in rectal temperature, but increased temperatures were reported by Zoa-Mboe et
al. (1989) and West et al. (1990).
During a 10-d injection period in the study by Staples et al. (1988), respiration
rates tended (P = 0.084) to increase (78.2 vs. 84.1 breaths/min) with bST administration,
but body temperatures were not different (39.6 vs. 39.7 C). Zoa-Mboe et al. (1989)
reported increases in respiration rates (107 vs. 113 breaths/min) and rectal temperatures
(39.8 vs. 40.0 C) with bST treatments.


134
Five days prior to the experiments start, all cows were moved into the freestall
bam for adaptation. At this time, cows were fed a diet consisting of a mixture of the
farms high-herd TMR, com silage, and the experimental supplement. The high-herd
TMR portion of the diet was phased out over 5 d with an increasing percentage of
supplement and com silage being fed.
Experimental Measurements
Milk production, body weight, and body condition score. Milk weights were
recorded at each milking. Milk samples were collected at six consecutive milkings
within the last 12 d of each period. Samples were analyzed by Southeast Dairy Labs
(McDonough, GA) for milk fat and protein percentages, somatic cell count (SCC), and
milk urea nitrogen (MUN).
Cows were weighed after the a.m. milking on three consecutive days at the
initiation of the trial and at the end of each period. Body condition scores were recorded
on one of the weigh days within each period (Wildman et al., 1982).
Respiration rates and body temperatures. Respiration rates were measured by
monitoring the movement of the flank or bobbing of the head over a 1-min interval.
Measures took place during the afternoon before the p.m. milking during a time of
greatest potential ambient temperature.
Body temperatures were not measured in Period 1 because the units for measuring
body temperatures were unavailable. In Periods 2 and 3, fifteen cows (three per
treatment) were used to determine the effect of treatment on body temperature. Intra-
vaginal telemetric temperature transponders (Telonics, Mesa, AZ) were used to record
body temperatures. Since only five temperature transponders (TT) were available, one


66
Sollenberger et al. (1987) compared performance of Stockers grazing either RP or
bahiagrass (Paspalum notation Fliigge) pastures in a rotational stocking system without
supplement. Animals grazing RP had greater ADG than animals grazing bahiagrass (0.98
vs. 0.37 kg/d, respectively). Although bahiagrass pastures supported more animals (4.3
vs. 3.0 head/d) for a greater number of days (157 vs. 119 d), total gain/ha over the
growing season was greater for animals grazing RP (316 vs. 232 kg/ha).
Trials with growing goats also indicate that RP is a high quality forage. When fed
RP or alfalfa hays, growing goats eating RP always had numerically greater voluntary
intake, and significantly greater (P < 0.07) intakes for 9 wk of the 20-wk study (Gelaye et
al., 1990). Concentrations of NDF (45.3 vs. 45.8%), ADF (34.4 vs. 33.3%), and ADL
(8.9 vs. 8.0%) were similar for alfalfa and RP, respectively. Organic matter (OM)
concentration was 2 percentage units greater for RP. Apparent digestibility of OM and
fiber fractions was greater for RP. Goats consuming RP had both greater gain in BW and
feed conversion efficiency but less (P < 0.08) retained nitrogen and less ruminal
propionate concentration. Numerically less N retention, less (P < 0.09) ruminal
propionate concentration, and greater acetate:propionate ratio were also observed by
Gelaye and Amoah (1991).
Gelaye and Amoah (1991) fed growing goats complete diets containing either
10.5% (as-fed basis) ground RP or ground alfalfa hay. Diets containing RP had about
10% more NDF than those containing alfalfa, mostly due to a greater hemicellulose
concentration. Feed intake and ADG were numerically less but not significantly different
for animals consuming the RP diet. Apparent digestion coefficients for CP, NDF, and


192
Froetschel, M. A., J. K. Courchaine, S. W. Nichols, H. E. Amos, and A. C. Murry, Jr.
1997. Opioid-mediated responses of dietary protein on reticular motility and plasma
insulin. J. Dairy Sci. 80:511-518.
Gallaher, R. N., C. O. Weldon, and J. G. Futral. 1975. An aluminum block digester for
plant and soil analysis. Soil Sci. Soc. Amer. Proc. 396:803-806.
Galloway, D. L., Sr., A. L. Goetsch, W. Sun, L. A Forster, Jr., G. E. Murphy, E. W.
Grant, and Z. B. Johnson. 1992. Digestion, feed intake, and live weight gain by cattle
consuming bermudagrass supplemented with whey. J. Anim. Sci. 70:2533-2541.
Galloway, D. L., Sr., A. L. Goetsch, L. A Forster, Jr., A. R. Patil, and Z. B. Johnson.
1993 a. Voluntary intake, digestion, and average daily gain by steers consuming
bermudagrass supplemented with whey, molasses, and(or) com. Prof. Anim. Sci. 9:173-
177.
Galloway, D. L., Sr., A. L. Goetsch, L. A Forster, Jr., A. R. Patil, W. Sun, and Z. B.
Johnson. 1993b. Feed intake and digestibility by cattle consuming bermudagrass or
orchardgrass supplemented with soybean hulls and(or) com. J. Anim. Sci. 71:3087-3095.
Galyean, M. L., and A. L. Goetsch. 1993. Utilization of forage fiber by ruminants. Page
33 in Cell Wall Structure and Digestibility. H. G. Jung, D. R. Buxton, R. D. Hatfield, and
J. Ralph, ed. ASA-CSSA-ASSA, Madison, WI.
Garcia-Gavidia, A. 1998. Use of bovine somatotropin (BST) in management of growing
heifers and transition cows to improve growth rates and milk production. Ph.D.
Dissertation, University of Florida, Gainesville.
Gelaye, S., and Amoah, E. A. 1991. Nutritive value of florigraze rhizoma peanut as an
alternative leguminous forage for goats. Small Ruminant Res. 6:131-139.
Gelaye, S., E. A. Amoah, and P. Guthrie. 1990. Performance of yearling goats fed alfalfa
and florigraze rhizoma peanut hay. Small Rum. Res. 3:353-361.
Gengler, W. R., F. A. Martz, H. D. Johnson, G. R. Krause, and L. Hahn. 1970. Effect of
temperature on food and water intake and rumen fermentation. J. Dairy Sci. 70:434-437.
Glenn, B. P. 1994. Grass and Legumes for growth and lactation. Pages 1-18 in Proc. 56th
Cornell Nutr. Conf. Feed Manufi, Rochester, NY. Cornell Univ., Ithaca, NY.
Glenn, B. P., G. A. Varga, G. B. Huntington, and D. R. Waldo. 1989. Duodenal nutrient
flow and digestibility in Holstein steers fed formaldehyde and formic acid treated alfalfa
or orchardgrass silage at two intakes. J. Anim. Sci. 67:513-528.


ABW, kg/28d 4% FCM, kg/d Milk yield, kg/d
93
Forage
Figure 3.2. Interaction of forage, stocking rate (SR), and year on milk and 4% fat cor
rected milk (FCM) yields and body weight change (ABW). Forages were Tifton 85
bermudagrass and Florigraze rhizoma peanut. Low and high SR for BG were 5.0 and
7.5 cows/ha in 1995 and 7.5 and 10.0 cows/ha in 1996. Low and high SR for RP were
2.5 and 5.0 cows/ha in 1995 and 5.0 and 7.5 cows/ha in 1996.


65
and ADF and lower CP concentrations for leaves of RP grown in summer vs. fall.
Response to regrowth intervals between leaf and stem fractions was variable, but
investigation of combined leaf and stem fractions showed increasing fiber and decreasing
CP concentrations with increasing maturity.
The concentration of CP in RP was less than that in alfalfa, while concentrations
of neutral and acid detergent fiber were greater (Romero et al., 1987; Terrill et ah, 1996).
In situ experiments showed RP to have slower rates of DM disappearance than alfalfa
(Romero et ah, 1987) but similar concentrations of highly soluble DM (24 vs. 27%) and
less potentially digestible (43 vs. 45%) DM (Romero et ah, 1987). Although alfalfa had
greater disappearance of CP after 24 h (85 vs. 72%), the authors noted that even with less
CP, RP may potentially contribute more protein post-ruminally than alfalfa due to its
less ruminally soluble and potentially degradable protein.
In the study by Beltranena et ah (1981), yields of DM were 6.6 and 10.0 t/ha at
the 4- and 6-wk clipping intervals, respectively. Clipping intervals greater than 6 wk did
not increase DM yield. Forage had greater concentrations of CP and IVOMD at 4 wk
(20.1 and 72.9%) than at 6 wk (17.9 and 70.4%), and the authors suggested a 4 wk
defoliation interval might be a suitable compromise between quantity and nutritive value
for intensive grazing systems.
Ortega-S. et ah (1992) studied the effects of different grazing frequencies and
intensities by beef heifers on performance of RP pastures. With a 42-d grazing cycle, a
stand of 80% RP could be maintained if residual DM was 1700 kg/ha or greater. With a
21-d grazing cycle, the residual DM needed to maintain an 80% stand was 2300 kg/ha.
The study underscores the importance of proper grazing management of RP pastures.


LIST OF TABLES
Table page
3.1 Ingredient and chemical composition of supplements fed to lactating Holstein cows
on pasture 79
3.2 Nutritive value characteristics, chemical composition, and calculated net energy of
lactation (NEl) and total digestible nutrients (TDN) of Tifton 85 bermudagrass and
Florigraze rhizoma peanut pastures. Samples were hand-plucked once each period,
based on visual appraisal of forage consumed by grazing cows.
88
3.3 Effect of forage, stocking rate (SR), and supplementation rate (SUP) on milk
production and composition of Holstein cows grazing Tifton 85 bermudagrass and
Florigraze rhizoma peanut during the summers of 1995 and 1996 90
3.4 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on
body weight (BW) and body condition score change (ABCS), respiration rate (RR),
body temperature (TEMP), and plasma urea nitrogen (PUN) and plasma glucose of
Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut
during the summers of 1995 and 1996 102
3.5 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on
forage, supplement and total organic matter intake (OMI), and on forage,
supplement, and total organic matter intake as a percent of bodyweight (OMIPBW)
of Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma peanut
during the summers of 1995 and 1996 110
3.6 Calculated daily intake of nutrients by cows grazing Tifton 85 bermudagrass (BG)
or Florigraze rhizoma peanut (RP) pastures. Cows received supplement (SUP) at
either 0.33 kg (Low) or 0.5 kg (High) (as-fed) per kg of daily milk production 114
3.7 Effect of forage, stocking rate (SR), and supplementation rate (SUP) on bodyweight
(BW) change, 4% fat corrected milk (FCM) production, and measures of energy (E)
status of Holstein cows grazing Tifton 85 bermudagrass and Florigraze rhizoma
peanut during the summers of 1995 and 1996 115
3.8 Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on
forage, supplement and crude protein (CP), in vitro organic matter digestibility
(IVOMD), and neutral detergent fiber (NDF) concentrations in Tifton 85
Vll


103
losses on RP pastures may be attributable to greater energy expenditure associated with
greater milk production, or due to less gut fill due to greater intake and faster passage of
forage OM, or both.
Stocking rate effects. Cows stocked at the greater SR were slightly lighter, on
average, (approximately 4 kg; P < 0.05) than cows at the lesser SR. Likewise, BW loss
tended (P < 0.070) to be greater for cows stocked at the greater rate (-9 vs. -5 kg/28-d
period).
Cows assigned to the greater SR lost 7 to 8 kg/28-d period more than cows
assigned to the lower SR across years and forages with one exception (Figure 3.2). In
1996, cows grazing BG lost 7 kg less when grazing at the greater vs. lesser SR (year by
forage by SR interaction P < 0.10).
Primiparous cows lost 6 to 8 kg of BW/28-d period across forage species and SR
except when assigned to BG pastures at the low SR on which BW loss was zero (Figure
3.6). Conversely, the BW loss of multiparous cows was similar (4 to 9 kg of BW/28-d
period) except when grazing RP at the high SR, in which multiparous cows lost 19 kg of
BW/28-d period (parity by forage by SR interaction, P < 0.05).
Supplementation rate effects. Strikingly, SUP had no effect on changes in BCS
or BW, nor were SUP by treatment interactions detected. In 1995, the greater SUP
resulted in a loss of BW and body condition, likely due to greater milk production, but in
1996, providing additional supplement had little effect on BW and helped maintain body
condition (year by SUP interaction, P < 0.05; Figure 3.7). The year by SUP interaction
patterns for change of BW and BCS are dissimilar in 1996, with the decrease in BCS at


98
3.75 -
N
ox
.0$
3.55 -
s
3.35 -
3.15 -
vO
3.10 -
o'
e\
C
S
3.00 -
o
a,
2.90 -
1
2.80 -
2.96
2.98
3.05
1995 1996
Year
SE 0.03
P < 0.05
3.51
Lo
3.54
Lo
3.29
Hi
Hi
SE = 0.01
P<0.10
Figure 3.4. Interaction of supplementation rate and year on production of 4% fat corrected
milk and milk fat, and percentages of milk fat and protein. Low (Lo) and high (Hi) sup
plementation rates were 0.33 and 0.5 kg of supplment per 1 kg of daily milk production,
respectively.


Temperature,
39.8 -
39.6 -
39.4 -
39.2 -
39.0
38.8
38.6
38.4
38.2
B +
a B + S
Hour
Figure 4.5. Effect of bam plus bST (B +) vs. bam plus bST plus silage (B + S) treatment on body temperatures of
cows measured over a 24-h period.
4:30 AM


60
Mandebvu et al. (1998) compared DM and NDF digestibilities of first and second
cuttings (3.5 wk of growth) of Tifton 85 hay with that of Coastal bermudagrass hay of 4
wk growth. The IVDMD was reported as 63.6, 59.9, and 52.0% for the first and second
cuttings of Tifton 85 and the Coastal bermudagrass hay, respectively. The NDF
digestibilities were 61.4, 58.5, and 47.5%. First-cut Tifton 85 had a greater potentially
digestible NDF fraction in whole forage (77.9 vs. 67.1%) and in extracted NDF (81.5 vs.
70.7) than did Coastal bermudagrass.
Much literature details performance of beef animals grazing bermudagrass
pastures, with some information released comparing Tifton 85 with Tifton 78 (Hill et al.,
1993), but information regarding use of bermudagrass for grazing dairy animals is
limited. A study by Martinez et al. (1980, cited by Jennings and Holmes, 1984b) may
have overpredicted the potential use of bermudagrass as a pasture forage for dairy cows.
The authors reported that cows grazing Coast-cross I bermudagrass produced 4125 kg of
milk/cow per yr without supplementation.
West et al. (1997) indicated that Tifton 85 may be suitable for confinement
dairies, but no information is presently available regarding use of Tifton 85 by lactating
cows in grazing systems without or with supplemental feeds. In the study by West et al.
(1997), 3.5% FCM yields were not different for cows fed diets of either 15 or 30%
bermudagrass or alfalfa hays. Results suggested that the NDF digestion of Tifton 85 was
more rapid and more extensive than that of alfalfa or com silage components of the diets.
Comparisons of Grasses and Legumes
The high concentrations of NDF and low concentrations of digestible nutrients
associated with warm-season perennial grasses limit their desirability for use in animal


200
Martin, S. K., and C. A. Hibberd. 1990. Intake and digestibility of low quality native
grass hay by beef cows supplemented with graded levels of soybean hulls. J. Anim. Sci.
68:4319-4325.
Martinez, R. O., R. Ruiz, and R. Herrera. 1980. Milk production of cows grazing Coast
Cross No. 1. Bermudagrass (Cynodon dactylon). 1. Different concentrate
supplementation levels. Cuban J. Agrie. Sci. 14:225-232.
Matches, A. G. and G. O. Mott. 1975. Estimating the parameters associated with grazing
systems. Pages 203-208 in Proc. Ill World Conf. Anim. Prod. R. L. Reid, ed. Sydney
Univ. Press, Adelaide.
Mathews, B. W., L. E. Sollenberger, and C. R. Staples. 1994a. In vitro digestibility and
nutrient concentration of bermudagrass under rotational stocking, continuous stocking,
and clipping. Commun. Soil Sci. Plant Anal. 25:301-317.
Mathews, B. W., L. E. Sollenberger, and C. R. Staples. 1994b. Sulfur fertilization of
bermudagrass and effect on digestion of nitrogen, sulfur, and fiber by nonlactating cows.
J. Haw. Pac. Agrie. 5:21-30.
Mayne, C. S., D. McGilloway, A. Cushnahan, and A. S. Laidlaw.1997. The effect of
sward height and bulk density on herbage intake and grazing behaviour of dairy cows.
Pages 2-15-2-16 in Proc. XVIII Int. Grassl. Cong. Winnipeg, Manitoba and Saskatoon,
Saskatchewan.
McCollum, F. T. Ill, and G. W. Horn. 1990. Protein supplementation of grazing
livestock: A review. Prof. Anim. Scientist 6:1-16.
McGuire, M. A., D. E. Bauman, D. A. Dwyer, and W. S. Cohick. 1995. Nutritional
modulation of the somatotropin/insulin-like growth factor system: response to feed
deprivation in lactating cows. J. Nutr. 125:493-502.
McGuire, M. A., D. E. Bauman, M. A. Miller, and G. R. Hartnell. 1992 Response of
somatomedins (IGF-I and IGF-II) in lactating cows to variations in dietary energy and
protein and treatment with recombinant n-methionyl bovine somatotropin. J. Nutr. 128-
136.
McLachlan, B. P., W. K. Ehrlich, R. T. Cowan, T. M. Davison, B. A. Silver, and W. N.
Orr. 1994. Effect of level of concentrate fed once or twice daily on the milk production
of cows grazing tropical pastures. Aust. J. Exp. Agrie. 34:301-306.
Meijs, J. A. C. 1986. Concentrate supplementation of grazing dairy cows. 2. Effect of
concentrate composition on herbage intake and milk production. Grass Forage Sci.
41:229-235.


ACKNOWLEDGMENTS
This work could not have been completed without the assistance of several
people. Thanks first go to my wife, Wonae, without whose patience, assistance and
understanding this work could not have been completed. The support and encouragement
of the authors parents and family also were instrumental in making this dissertation
possible.
The author wishes to express his gratitude for the teaching, direction and patience
received from his advisors Dr. Charles R. Staples and Dr. Lynn E. Sollenberger. The
Churchillian words of encouragement from Dr. Staples that came during some dark hours
will not be forgotten.
Thanks also go to Dr. John E. Moore for encouragement, mentoring, and excellent
teaching. Drs. Mary Beth Hall and Peter J. Hansen also were instrumental to this work
by providing excellent teaching and assistance whether in or out of the classroom.
To my plastic-sleeved compatriots, Bisoondat Maccoon and Renato Fontanelli,
the wish is extended that though you have adequate sample, your fecal-sample cups will
never runneth over.
Others to be recognized for their help include D. Hissem, J. Lindsay, and M.
Russell for farm support, Drs. R. E. Littell and C. R. Wilcox for statistical assistance, and
Dr. H. H. Head for assistance with immunoassays. Thanks to O. A. Carrijo, Jr., J. Hayen,
E. M. Hirchert, and J. P. Jennings for assistance in the laboratory, at the farm, or both.
li


85
intake, kg of OM. Because feeding concentrate supplements often alters forage
digestibility (Arriaga-Jordan and Holmes, 1986; Berzaghi et al., 1996), the iterative
program also employed the equation of Moore et al. (1999; Appendix 2) to adjust total
diet digestibility.
Pasture measures. A double sampling technique was used to quantify pre- and
post-graze forage mass (Meijs et al., 1982). Every 2 wk of each period, 25 measures of
forage height were taken using a 0.25-m aluminum disk meter. Pre-graze measures
were recorded in paddocks to be grazed the following d, and post-graze measures were
made 1 or 2 d after the cows had grazed the paddock. At one sampling event in each
period, two or three samples were collected pre- and post-graze from one paddock per
pasture to establish a relationship between herbage mass (HM) and the recorded disk
heights. After dropping the plate of the disk meter on the forage, a metal ring was used to
mark the outline of the disk meter, and the forage within the ring was clipped at ground
level. The forage was dried at 55 C for a minimum of 48 h to a constant weight.
Equations to predict pre- and post-graze forage mass were calculated by
regressing mass on disk height measured at double sampling sites. Regression equations
were assessed for the following data: all samples within a forage species, all pre- or all
post-graze samples within a forage, and pre- or post-graze samples within a period and
within a forage. After review of the data, HM equations for both years were derived from
pre- and post-graze measurements within periods within a forage.
Feed sampling. Once per period, forage was collected for characterization of
chemical composition and digestibility. Attempts were made to collect forage of quality
similar to that consumed after first inspecting an adjacent, grazed paddock. Twenty to 30


135
cow per treatment was fitted with a TT and temperatures measured for 48 h. This was
repeated for a second and third group of five cows each. The TT were taped to
progesterone-free Eazi Breed, controlled intravaginal drug releasing devices (InterAg,
Hamilton, NZ) and inserted into the vagina.
Each TT broadcast a signal at its own frequency, and the frequencies were preset
into a radio scanner. The scanner moved sequentially through the preset TT frequencies,
recording three signals per given TT in approximately 1 min. Thus, a set of three
readings for all treatments was obtained approximately every 5 min.
Factoring out 2 h for set-up, installation and TT adaptation, the theoretical
maximum number of readings per treatment was approximately 10,000 (36 readings/h per
cow times 46 h times 3 cows per treatment-period times 2 periods). Differences in TT
signal strength, distance from TT to the scanner (0.75 km maximum), computer shut
down, and environmental and atmospheric conditions often resulted in loss of signals, or
signals which did not represent physiological temperatures. Across the two periods, an
average of 4400 readings were taken for cows on pasture and 5400 readings for cows in
the bam.
Plasma metabolites. Blood samples were collected from the coccygeal vessels
thrice at 2- to 4-d intervals within the last week of each period. Vacutainors (Becton
Dickinson, Franklin Lakes, NJ) containing EDTA were used for the first sample taken.
At the remaining 8 dates, blood was collected into 9-ml Na-heparinized (Luer
Monovette LH, Sarstedt, Inc., Newton, NC,) syringes. Blood was sampled after the
p.m. milking and placed on ice. Blood was then centrifuged for 0.5 hr (2000 x g), plasma
collected, and plasma frozen at -20C for future analyses.


208
Smith, A. J., and R. W. Mathewman. 1986. Aspects of the physiology and metabolism
of dairy cows kept at high ambient temperatures: dissertation review 1. Tropic. Anim.
Health Prod. 18:248-253.
Smith, C. A. 1959. Studies on Northern Rhodesia Hyperrhenia veld. I. The grazing
behaviour of the indigenous cattle grazed at light and heavy stocking rates. J. Agrie. Sci.
(Camb.) 52:369-375.
Smith, L. W., H. K. Goering, and C. H. Gordon. 1972. Relationships of forage
composition with rates of cell wall digestion and indigestion of cell wall. J. Dairy Sci.
55:1140-1147.
Soeldner, J. S., and d. Slane. 1965. Critical variable in the radioimmunoassay of serum
insulin using the double antibody technique. Diabetes 124:771-779.
Sollenberger, L. E., G. M. Prine, and C. S. Jones, Jr. 1987. Animal performance on
perennial peanut pasture. Pages 145-146 in Agron. Abstr. ASA, Madison, WI.
Spain, J. N., and D. Spiers. 1999. Production responses of dairy cattle to night cooling
when exposed to different ambient temperatures. J. Dairy Sci. 82(Suppl.):79(Abstr.)
Spiers, D., J. N. Spain, and J. M. Zulovich. 1999. Development of the thermal benefit of
night cooling in dairy cows exposed to different ambient temperatures. J. Dairy Sci.
82(Suppl.):79( Abstr.)
Stallcup, O. T., K. F. Harrison, P. Bayley, and R. Thornton. 1986. Responses in nutritive
characteristics of Hardie bermudagrass to varying levels of nitrogen fertilization. Pages
220-224 in Proc. Forage and Grassl. Cong., Athens, GA. Amer. Forage Grassl. Counc.,
Georgetown, TX.
Stanley, T. A., R. C. Cochran, E. S. Vanzant, D. L. Harmon, and L. R. Corah. 1993.
Periparturient changes in intake, ruminal capacity, and digestive characteristics in beef
cows consuming alfalfa hay. J. Anim. Sci. 71:788-795.
Staples, C. R., S. M. Emanuele, and G. M. Prine. 1997. Intake and nutritive value of
Florigraze rhizoma peanut silage for lactating dairy cows. J. Dairy Sci. 80:541-549.
Staples, C. R., H. H. Head., and D. E. Darden. 1988. Short-term administration of bovine
somatotropin to lactating dairy cows in a subtropical environment. J. Dairy Sci. 71:3274-
3282.
Staples, C. R. and W. W. Thatcher. 1999. Dietary fat and protein effects on fertility of
lactating dairy cows. Pages 133-155 in Proc. Intermountain Nutr. Conf. Salt Lake City,
Utah.


17
On average, cows grazed an additional 2.45 min for each additional kg of daily milk
produced.
Grazing time also may be dependent upon the system of grazing management
utilized. Le Du et al. (1979) reported that with rotational stocking, cows did not
compensate for decreased herbage availability with increased GT. Rapid defoliation with
strip-grazed pastures would be expected to make large alterations in canopy structure,
requiring animals to increase manipulative jaw movements (Hodgson, 1981) in order to
consume a large proportion of leaf material.
Daylight and Temperature
In general, cows graze primarily during daylight hours, exhibiting strong
periodicity in grazing behavior (Hughes and Reid, 1951; Stobbs, 1970). Adams (1985)
noted that most grazing behavior studies show that cows typically have a major grazing
period occurring early in the morning and one later in the afternoon. Additional
intermittent grazing bouts occur throughout other periods of the day and night.
Phillips (1989) reported marked reluctance of cattle to eat at night (Phillips and
Denne, 1988) even in hot climates (Alhassan and Kabuga, 1988), but this may be true
more for steers than for lactating animals which likely are under greater heat strain.
Stobbs (1970, p. 242) reported that during the night cows grazing tropical pastures
behave more as individuals and that high yielding cows can spend a considerable
length of time grazing during this period. While Stobbs (1970) indicated that night
grazing might be limited to 30% of grazing time, work by Seath and Miller (1947)
indicated that in hot, humid environments (Louisiana), cows would graze more during
night time. Part of the differences in these studies may be in the designation of night,


TABLE 3.8. Effect of forage species, stocking rate (SR), and supplementation rate (SUP) on forage, supplement and crude protein
(CP), in vitro organic matter digestibility (IVOMD), and neutral detergent fiber (NDF) concentrations in Tifton 85 bermudagrass and
Florigraze rhizoma peanut during the summers of 1995 and 1996. Samples were hand-plucked once each period based on visual
appraisal of forage consumed by grazing cows.
Tifton 85 bermudagrass Florigraze rhizoma peanut
Stocking Rate1 Stocking Rate2 Probability3
High Low High Low Forage
Supplementation rate (kg, as-fed/kg of milk per d) Forage Forage SR x SR
Item 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 0.5:1 0.33:1 SEM Forage SR SUP x SR X SUP x SUP x SUP
CP, %
14.3
13.1
13.2
12.4
17.7
18.2
17.9
14.5
0.4 ***
t
NS
NS
t
NS
NS
IVOMD, %
60.2
58.3
60.0
56.8
70.8
71.4
71.2
71.5
0.9 ***
NS
NS
NS
*
NS
NS
NDF, %
80.7
81.6
81.3
81.0
45.8
44.4
44.5
43.4
0.8 ***
NS
NS
NS
NS
NS
NS
'High and low stocking rates were 7.5 and 5.0 cows/ ha in 1995 and 10.0 and 7.5 cows/ha in 1996.
2High and low stocking rates were 5.0 and 2.5 cows/ ha in 1995 and 7.5 and 5.0 cows/ha in 1996.
3P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.


59
produces an abundance of stems and leaves in spring, followed by more vegetative
growth later in the season (Hill et al., 1993, p. 3222). The authors reported greater NDF
concentrations in the forage earlier in the grazing season and suggested that this might be
due to the cultivars growth habit.
Tifton 85 has [rjapid growth rate and high IVDMD values relative to other
bermudagrass hybrids (Hill et ah, 1993 p. 3219). Hill et ah (1993) tested Tifton 85
grown in small plots and found that it produced greater quantities of DM with greater
digestibility than all other cultivars in the comparison. In comparison with Coastal
bermudagrass, [at one time the predominant cultivar in the Southeast (Holt and Conrad,
1983)], Tifton 85 produced more than 25% more DM (16.7 vs. 13.3 t of DM/ha) the and
forage was more than 12% more digestible (58.8 vs. 52.3% IVDMD).
Hill et ah (1993) also compared Tifton 85 with Tifton 78 in a grazing study.
Tifton 78 is a cultivar widely used because of its relatively high digestibility and yield.
The researchers maintained HM of both forages at approximately 2500 kg of DM/ha over
2 yr and sampled esophageally fistulated steers to estimate forage nutritive value
characteristics. Tester steers and variable SR also were used to determine ADG and to
calculate grazing d/ha. Steers grazed 169 d each year, and though the ADG with the two
forages were similar (0.67 vs. 0.65 kg/ for Tifton 85 and 78, respectively) Tifton 85
supported in excess of 500 more grazing days over the 3 yr of the study. The BW gain/ha
was 46% greater for steers grazing Tifton 85 as a consequence (1160 vs. 790 kg/ha). Hill
et ah (1993, p. 3224) noted a strong tendency for Tifton 85 to remain more productive
later in the grazing season than Tifton 78 did. This translated into slightly greater rates
of BW gain in August and September.


40
Nocek and Russell (1988) noted that even seemingly appropriate amounts of
dietary CP and carbohydrate may not provide an ideal balance of protein and
carbohydrate to the rumen microorganisms. The authors compared four theoretical diets
that were isonitrogenous and isocaloric but which had variable concentration of ruminally
available CP and carbohydrate. Theoretical bacterial synthesis and amino acid supply to
the small intestine were markedly different among the diets and demonstrated the
potential difficulty inherent in formulating diets for maximum microbial production.
This challenge may be even greater when forage and concentrates are consumed as
individual components such as occurs in grazing systems.
A batch culture study more similar to pasture feeding conditions was conducted to
test the effects of asynchronous nitrogen and energy supplies on microbial growth
(Newbold and Rust, 1992). Cultures were supplied glucose and urea or com and soybean
meal processed for slow or rapid microbial digestion, respectively. Regardless of
substrate, only transient effects of nutrient imbalance on cell yield were reported.
Though the mean bacterial population was greater from 5 to 8 h of incubation,
populations were similar at 12 h. However, the authors could not rule out end-product
inhibition as a reason for similar bacterial mass at the end of the experiments.
Rooke et al. (1987) studied the effects of constant-rate infusions of urea, casein,
glucose syrup, or casein and glucose syrup into the rumens of cows consuming ryegrass
silage. Infusions did not affect ruminal pH or VFA concentrations, but glucose and the
casein-glucose mixture reduced the rumen NH3-N concentration. Glucose and the casein-
glucose mixture also increased the quantities of OM, ADF, NAN, amino acid N, and
microbial N entering the small intestine, indicating that microbial yield was increased but


78
Soils were primarily of the Tavares (hyperthermic, uncoated Typic
Quartzipsamments) and Chipley (thermic, coated Aquic Quartzipsaments) series with
average P, K, and Mg concentrations of 99, 26, and 50 mg/kg, respectively.
Bermudagrass pastures were fertilized with 67 kg of N/ha on 22 May, 30 June,
and 1 September. Nitrogen was applied as NH4NO3 at the latter dates and as a
combination of NH4NO3 and (NP^StTt on 22 May. All pastures received a total of 33
kg of S/ha on 22 May, with sulfur applied to RP pastures in the form of CaSC>4. In
addition, all pastures were fertilized with 67 kg of K20/ha in May.
In order to stage the forage growth, Holstein heifers (approximately 400 kg of
body weight (BW)) grazed both forages from 7 June to 1 July 1995. Stocking rates were
10 and 5 heifers/ha for BG and RP pastures, respectively, and animals were fed no
supplement. Experimental cows went onto pastures on 6 July, 4 d before the official start
of the trial.
Bermudagrass and RP pastures were divided into 22 and 29 paddocks
respectively, allowing for 21 and 28-d rest periods between grazing events. Cows were
kept in the bounds of individual paddocks with poly wire fencing and paddocks were
back-fenced. Cows were provided shade structures and water tubs that were moved with
the cows to a fresh paddock each morning. Shade structures were 3-m tall, constructed of
galvanized metal pipe, stretched with 80 % shade cloth, and designed to provide a
minimum of 4.65 m2 of shade/cow.
Cows walked 0.4 to 1.2 km from pasture to the parlor for milking and back to
pastures twice daily. Cows were milked at approximately 0700 and 1800 h. Supplement
was a 4:1 mixture (as-fed) of high energy pellets:whole cottonseed (Table 3.1)


63
greater heat production/ME likely indicated an increased energy cost associated with
digestion of orchardgrass.
Although the greater DMI and efficiency of utilization reported with legumes is
desirable, legume use in pasture systems in warm climates often has been limited. Few
perennial legumes have been satisfactorily productive or persistent in forage systems in
subtropical regions of the humid Southeast, and some researchers have argued that
legumes have little place in production systems in the region (Rouquette et al., 1993). To
date, insects, nematodes, phytopathogens and poor persistence under grazing conditions
have relegated tropical legumes to limited roles in forage production systems in the
tropics (Maraschin et al., 1983).
Rhizoma Peanut
One legume with promise for the region, however, is rhizoma peanut (Arachis
glabrata Benth.). The legume is fine-stemmed and leafy, with potential for use in
grazing or stored-forage production systems (Prine et al., 1981). Introduced to Florida
from Brazil in 1936 and first distributed to commercial growers in 1978 (Prine et al.,
1986), most acreage expansion has occurred since 1980 (French, 1988). In 1990, an
estimated 1200 ha of rhizoma peanut (RP) had been planted in Florida (Niles et al.,
1990), with plantings increasing to 8100 ha by 1999 (E. C. French, personal
communication). The plant is being tried in other Deep South states as well (Prine et al.,
1986; Ocumpaugh, 1990; Mooso et al., 1995). Factors slowing its use by producers
include farmer unfamiliarity with the crop and high establishment costs (Prine et al.,
1986).


51
Two Perennial Forages for Lactating Cows in Pasture-Based Dairy Systems
in the Southeast
Bermudagrass
Bermudagrass is one of the most extensively grown improved, perennial, warm-
season forages for the Southeast. According to G. W. Burton, bermudagrasses occupy
more than half the pasture acreage in the southern United States (cited in Adams, 1992,
p. 19). First introduced to the U.S. in 1751 (Burton and Hanna, 1995, citing the diary of
Thomas Spalding), bermudagrass has been the subject of much research. Numerous
improved cultivars of the grass have been released since the 1940s (Burton and Hanna,
1995), and a review of the literature reveals improvements in both yield and digestibility
(Monson and Burton, 1982). Today, more than 5 million hectares in the Southeast have
been sprigged with improved bermudagrasses, with many more supporting common
bermudagrass (Burton and Hanna, 1995).
Though well adapted to much of the region, bermudagrasses typically have high
concentrations of NDF and low concentrations of NEl and digestible nutrients (West et
al., 1997). A compilation of 18 experiments in which bermudagrass hay harvested at
vegetative to mature growth stages, obtained from local producers and grown with a
variety of management practices was reported by Goetsch et al. (1991, p. 2635). Mean
NDF concentration was 74.5% with a range of 65.6 to 86.7% (DM basis). Though mean
OM digestion was 54.9 %, the range of OM digestion was quite wide, from 27.5 to
75.4%.
Bermudagrass yield responses and nutritive value characteristics are affected by
numerous factors, including frequency of defoliation (grazing or clipping), fertility,
temperature, season, and location, and responses vary by cultivar (Wilkinson et al., 1970;


152
evaporative cooling similar to the increases found in this study, while Chen et al. (1993)
noted a 9% increase in milk production with evaporative cooling over shade alone.
Milk fat percentage was unaffected by treatment, but housed cows tended to have
numerically greater (P <0.12) milk fat production. Cows kept in the bam during the day
tended (P <0.10) to produce greater quantities of milk protein (0.57 vs. 0.55 kg/d) than
cows on pasture, largely due to milk production.
Effect of bST. Injections of bST increased (P <0.01) milk production
approximately 9% (18.1 vs. 16.6 kg/d) (Table 4.4). Use of bST increased (P < 0.001)
production of 4% FCM approximately 12% (17.7 vs. 15.8 kg/d).
In a review, West (1994) reported that responses to bST treatment by cows in hot
environments ranged from 3.4 to 48.6%, and response to bST typically decreased with
increasing amount of pre-treatment milk production (Lotan et al., 1993; West et al.,
1990). Thus, given the relatively low amount of pretreatment milk production, greater
responses to bST might have been expected. However, the percentage increase in
production in response to bST was similar to that found by Staples et al. (1988) whose
cows produced similar quantities of milk in a 30-d trial.
Estimates of nutrient intake based on NRC recommendations suggest that nutrient
intake did not prevent cows on this trial from producing 20 kg of 4% fat corrected milk/d
(Table 4.5). This suggests that either maintenance costs were greater than NRC (1989)
estimates, or nutrient intake, particularly energy, was overestimated.
Although bST treatment did not affect milk fat concentration, the greater
percentage increase in 4% FCM production compared to the percentage increase in milk
production (12 vs. 9%) partially resulted from numerically greater concentrations of milk


96
Increasing supplement had similar depressing effects on milk fat percentage
across forages. Thus, FCM responses to forage and SUP treatments were similar to that
of milk production (forage by SUP interaction, P < 0.01; Figure 3.3). For cows grazing
BG, the increase in FCM produced with additional supplement (2.3 kg/d) was double the
response (0.9 kg/d) of cows grazing RP. Response of daily fat production to SUP
followed the same trend (forage by SUP interaction, P < 0.01; Figure 3.3). Total protein
produced tended to be greater in response to additional supplement when cows grazed
BG (forage by SUP interaction, P < 0.10; Figure 3.3).
Multiparous cows produced more milk, 4% FCM, and milk fat in response to
increased SUP than primiparous cows (parity by SUP interaction, P < 0.05). When fed
the greater SUP treatment, primiparous cows produced an additional 1.7 kg of milk (18.1
vs. 16.4 kg of milk/d), compared with 2.7 additional kg of milk for multiparous cows
(17.7 vs. 15.0 kg/d). Increases of 1.2 and 2.0 kg of 4% FCM due to additional
supplement were observed for primiparous and multiparous cows, respectively. Milk fat
production within high and low SUP treatments were 0.61 and 0.57 kg/d for primiparous
cows compared to 0.59 and 0.52 kg/d for multiparous cows, following the milk
production responses to supplement. Milk fat concentrations in response to SUP were
not different between parities.
Primiparous cows had lesser SCC when provided additional supplement,
compared with greater SCC at the greater SUP rate for multiparous cows (parity by
supplement interaction, P < 0.01). With the low and high SUP treatments, SCC (in
thousands of cells) were 483 and 422 for primiparous cows vs. 360 and 499 for
multiparous cows.


21
Herbage intake for individual animals also can be estimated with measurements
of grazing behavior, where FI = GT*RB*IB. This method may be beneficial in
overcoming any effects that supplemental feeds may have on estimates of diet
digestibility. However, all three measures for the estimate are quite variable over time,
especially with changes in sward conditions (Stobbs, 1973; Chacon and Stobbs, 1976;
Hodgson, 1985). Further, it is unlikely that a researcher would have access to more than
a few esophogeally-fistulated animals, limiting the number of estimates of IB, and the
fistulated animals may not be representative of the population of interest.
Another common method of estimating intake is by disappearance of herbage
mass (HM). On rotationally stocked pastures with short (1 to 3 d) grazing periods, HM is
estimated both pre- and post-graze with devices such as sward sticks, rising plate meters
or capacitance meters that allow rapid collection of numerous measurements. The
difference between pre- and post-graze HM (disappearance) is the herbage assumed eaten
by the grazing animal(s). Such estimates are more suitable when measuring group
intakes and are advantageous with respect to eliminating effects of supplement on forage
digestibility (Milne et al., 1981). However, their usefulness is limited to conditions
where pastures are uniform.
Herbage Allowance or Stocking Rate Effects on Forage Intake and Performance of
Ruminants
Due to the complexity of plant-animal interactions and the difficulty of obtaining
such information, most research regarding these relationships considers only the gross
effects of herbage allowance (HA; kg of forage DM/kg of animal live weight), grazing
pressure, or stocking rate (SR) on animal performance. Several models have been
proposed to describe these effects (Mott, 1960; Jones and Sandland, 1974; Mott and


149
means because supplement OMI matched the raw means for milk production of each
treatment.
Increased supplement OMI in response to bST treatment was greater for cows
kept on pasture than for cows kept in bams during the day (housing by bST treatment
interaction, P < 0.05), matching raw means of milk production.
Across all treatments, total OMI averaged 17.0 kg/d (2.87% of BW) and were
greater than those reported for TMR-fed cows in a similar stage of a lactation and milk
production under heat stress conditions (Staples et al., 1988). Housing had no effect on
total OMI/d, contradictory to the results of Zoa-Mboe et al. (1989).
Effect of supplemental silage. Feeding silage curtailed grazing time by more (P
< 0.001) than 25% (5.6 vs. 4.0 h of grazing/d). Phillips and Leaver (1986) noted that the
effect of supplemental forage provision on grazing time depended on whether the
supplemental forage was a substitute for or a supplement to the grazed forage. With
decreased grazing time came a concomitant decrease (P < 0.001) in BG OMI of about
18% (from 9.0 to 7.4 kg/d, respectively). However, total forage OMI was increased
approximately 17% with supplemental silage (from 9.0 to 10.5 kg of forage OMI/d).
Moran and Stockdale (1992) also compared intake and milk production of cows fed
pasture alone or pasture with supplemental com silage. They reported no effect of silage
on pasture DMI, but pasture intake was numerically less than that for unsupplemented
cows.
As feeding silage did not affect milk production, supplement OMI was not
different between the two silage treatments. Cows fed silage consumed more (P <0.01)
total OMI per day by nearly 8%. Whereas the equation of Moore et al. (1999) was used


191
England, P., and M. Gill. 1985. The effect of fishmeal and sucrose supplementation on
the voluntary intake of grass silage and live-weight gain of young cattle. Anim. Prod.
40:259-265.
Enright, W. J., L. T. chapin, W. M. Moseley, S. A. Zinn M. B. Kamdar, L. F. Krabill,
and H. A. Tucker. 1989. Effects of infusions of various doses of bovine growth
hormone-releasing factor on blood hormones and metabolites in lactating Holstein cows.
J. Endocrionl. 122:671-679.
Ethridge, J., E. R. Beaty, and R. M. Lawrence. 1973. Effects of clipping height, clipping
frequency and rates of nitrogen on yield and energy content of Coastal bermudagrass.
Agron. J. 65:717-719.
Fales, S. L. 1986. Effects of temperature on fiber concentration, composition, and in
vitro digestion kinetics of tall fescue. Agron. J. 78:963-966.
Fales, S. L., L. D. Muller, S. A. Ford, M. OSullivan, R. J. Hoover, L. A. Holden, L. E.
Lanyon, and D. R. Buckmaster. 1995. Stocking rate affects production and profitability
in a rotationally grazed pasture system. J. Prod. Agrie. 8:88-96.
Ferguson, J. D., and W. Chalupa. 1989. Symposium: Interactions of nutrition and
reproduction. Impact of protein nutrition on reproduction in dairy cows. J. Dairy Sci.
72:746-766.
Flamenbaum, I., D. Wolfenson, M. Mamen, and A. Berman. 1986. Cooling dairy-cattle
by a combination of sprinkling and forced ventilation and its implementation in the
shelter system. J. Dairy Sci. 69:3140-3147.
Flores, E. R., E. A. Laca, T. C. Griggs, and M W. Demment. 1993. Sward height and
vertical morphological differentiation determine cattle bite dimensions. Agron. J.
85:527-532.
Forbes. J. M. 1996. Integration of regulatory signals controlling forage intake in
ruminants. J. Anim. Sci. 74:3029-3035.
French, E. C. 1988. Perennial peanut: A promising forage for dairy herd management in
the trrpics. Pages C-20-C-25 in Proc. Int. Conf. on Livestock in the Tropics. Gainesville,
FL.
French, E. C., G. M. Prine, and L. J. Krouse. 1987. Perennial peanut; developments in
animal research. Pages A-6-A13 in Proc. Int. Conf. on Livestock and Poultry in the
Tropics. Gainesville, FL.
Friggens, M. C., G. C. Emmans, I Kyriazakis, J. D. Oldham, and M. Lewis. 1998. Feed
intake relative to stage of lactation for dairy cows consuming total mixed diets with a
high or low ratio of concentrate to forage. J. Dairy Sci. 81:2228-2239.


157
fed supplemental silage could have had greater gut fill because they consumed more BG
which contained greater concentrations of fiber and indigestible OM. Because neither
milk production nor weight gain increased with the increased OMI, efficiency of nutrient
utilization may have decreased with supplemental com silage, or intake of metabolizable
energy may not have been increased. All cows lost body condition and the losses were
typical for cows on pasture in the summer. Feeding silage tended (P < 0.11) to lower
body condition score, but numerical changes indicated greater tissue losses for cows
receiving the additional forage (Table 4.6). Others (Moran and Stockdale, 1992; Holden
et al., 1995) reported numeric increases in BW gain or condition score with similar levels
of supplemental silage, but the trials were 8 to 10 wk in duration. Our results may be a
consequence of the postulated difference in gut fill between the two treatments and if so
indicates that condition score measurements were based upon more than changes in fat
depot size.
Plasma IGF-1 and Insulin
Effect of housing. Housing had no effect on IGF-1 at any sampling date.
McGuire et al. (1995) reported 50% reductions in circulating IGF-1 concentrations 48 h
after the initiation of feed deprivation, but differences due to short-term deprivation were
undetectable.
Greater (P < 0.05) insulin concentrations were detected for cows kept on pasture
continually. Average concentrations were 59.5 and 54.5 ng of insulin/mL for pasture and
bam cows, respectively. Others have reported decreased plasma insulin concentrations
during the summer (Denbow et al., 1986), but results from work with cows in
environmental chamber studies are mixed. Johnson et al. (1991) reported no effect of


147
Figure 4.1 Vibracorder charts for cows treated with bST and
housed in bams from 0800 to 1500 h (A) and for cows housed
on pasture (B). Note the greater grazing intensity for cows
housed in the bam during the day.


88
TABLE 3.2. Nutritive value characteristics, chemical composition, and calculated net
energy of lactation (NEl) and total digestible nutrients (TDN) of Tifton 85 bermudagrass
and Florigraze rhizoma peanut pastures. Samples were hand-plucked once each period,
based on visual appraisal of forage consumed by grazing cows.
Item
Bermudagrass Rhizoma peanut
Year
1995 1996 1995 1996
CP, % of DM1
13.5
13.1
19.0
16.6
ADF, % of DM
45.5
36.5
32.7
32.5
NDF, % of DM 1
81.9
80.4
43.5
45.5
IVOMD12, % of OM
55.5
62.1
71.2
71.2
TDN3, %
55.2
58.2
62.1
62.1
NEl4, Mcal/kg of DM
1.23
1.31
1.41
1.41
Ash, % of DM
5.64
5.13
8.67
8.48
Ca, % of DM
0.41
0.42
1.64
1.70
P, % of DM
0.33
0.27
0.27
0.26
Mg, % of DM
0.24
0.25
0.39
0.45
K, % of DM
1.97
1.77
1.71
1.58
Na, % of DM
0.018
0.045
0.004
0.008
S, % of DM
0.30
0.24
0.16
0.15
Cl, % of DM
0.57
0.43
0.46
0.41
Fe, ppm of DM
51
65
32
42
Zn, ppm of DM
44.5
43
42
37
Cu ppm of DM
5
4
3.5
2
Mn, ppm of DM
49
101
47
25
Mo, ppm of DM
1.2
1.4
1.2
1.3
Least squares mean from two samples within each treatment combination collected over
three periods within each experimental year.
2In vitro organic matter digestibility
Calculated using the equation % TDN = [(%IVOMD*0.49) + 32.2]*OM concentration
(J. E. Moore, personal communication).
Calculated using NRC (1989) equations: NEL = [0.0245 TDN(% of DM) 0.12].


CHAPTER 4
PASTURE BASED DAIRY PRODUCTION SYSTEMS: INFLUENCE OF HOUSING,
bST, AND FEEDING STRATEGIES ON ANIMAL PERFORMANCE
Introduction
For dairy farmers in the Southeast considering pasture-based production systems
for lactating dairy cows, environmental stress is a particular concern. Cool, comfortable
cows produce more milk, and in areas where the climate is typically hot and humid, milk
production is likely to be compromised due to the inverse relationship between milk
production and heat stress tolerance. This situation is exacerbated for pasture dairies by
at least three factors. First, as temperature increases, DMI typically decreases to a greater
degree with increasing concentration of roughage in the diet. Secondly, more direct
exposure to solar radiation results in greater heat load for cows on pasture with limited
shelter. Thirdly, grazing cows have larger heats of maintenance due to greater activity
(walking and grazing).
Typical cooling methods for pasture systems include cooling ponds, fixed or
mobile shade structures, and trees. Technologies for heat stress abatement in confined-
housing production systems have seen great advances in the past decade but remain
limited for animals on pasture. However, such structures may be available for producers
switching to grazing systems, and their efficacy for pasture-based dairy systems have not
been tested.
Another possible way to improve production of cows in grazing systems is with
the use of bST. Few studies using bST have been conducted with cows grazing pastures
130


55
fertilization were 50% of those when both N and K were applied. Pratt and Darst (1986)
also indicated that response to K fertilization was not always immediate. In their work, K
deficiency was seen (vis-a-vis large decline in yield) in the third year of study, and they
emphasized the need for long-term observation.
Effects of other fertilizers on animal responses have been investigated. Mathews
et al. (1994b) fed non-lactating cows chopped Tifton 78-common bermudagrass hays
which had or had not been fertilized with S (gypsum). The authors reported a 30.4
percentage unit increase in the apparent digestibility of S (vs. unfertilized control) and a
10.6 percentage unit increase in the apparent digestibility of lignin. Apparent N
digestibility slightly increased with S fertilization. Digestibility of ADF and NDF tended
(P = 0.18) to be increased by 1.5 percentage units, and DMI also tended (P = 0.14) to be
increased with S supplementation.
Henderson and Robinson (1982) grew bermudagrass in chambers to study the
effects of differing light intensity, moisture, and temperature on bermudagrass harvested
at 14 or 21 d. Yield increased with increased temperature and with increased photon flux
density, and in vitro digestibility decreased with increased temperature. When soil
moisture was low, light level did not affect forage digestibility across the array of
temperatures. Similarly, increased age reduced digestibility to a lesser degree under
moisture-limited conditions.
Seasonal effects on digestibility have been observed. Forage digestibility
typically is greatest in spring, declines in summer and increases in late summer or early
fall (Carver et al., 1978; Holt and Conrad, 1986), though this pattern is not always
observed (Guerrero et al., 1984). Holt and Conrad (1986, p. 435-436) noted that


70
parities, production ranged from 25.2 to 31.5 kg of milk/cow per d, and increases above
control were 12.3, 15.9, and 25.3% for the three treatments, respectively.
Effects of Heat on Milk Production, and Cooling Strategies for Pastured Cows
Cool, comfortable cows produce more milk. Milk production and tolerance to
heat stress are likely inversely related (Smith and Mathewman, 1986) due to the high rate
of metabolism associated with milk synthesis (Marai and Forbes, 1989). Generally, feed
intake begins to decline when mean daily environmental temperatures reach 25 to 27C,
though this is modulated by climatic and nutritional factors (Beede et al., 1985; Beede
and Collier, 1986). Reductions in DMI occur due to decreased grazing activity, increased
water consumption and increased respiration, benefiting the heat-stressed ruminant by
reducing heat load via lessened heat of fermentation and gut metabolism (Roman Ponce
et al., 1978; Mallone et al., 1985). Ruminal contraction rates and ingesta passage rates
also decrease with elevated temperatures (Attebery and Johnson, 1969; Warren et al.,
1974).
Typically, the greater concentration of dietary roughage, the greater the reduction
in DMI with elevated ambient temperature (Beede and Collier, 1986). Thus, the negative
effects of high ambient temperature on animal production are generally greater for
grazing animals because reduction in feed intake is due mainly to reduced forage
consumption (Beede and Collier, 1986).
Technologies for heat stress abatement in confined-housing production systems
have made great advances in the past decade but are limited for animals on pasture.
Typical cooling methods for pasture systems include cooling ponds, fixed or mobile
shade structures, trees, and permanent structures such as barns. Immobile structures are


168
Cows grazing RP pastures produced more milk than cows grazing BG (17.3 vs.
16.2 kg/d), but milk was of lower fat concentration. Because production per land area
may be a more appropriate measure of profitability for dairies using grazing systems this
measure also was calculated. Despite lower milk production per cow with BG, milk
production per ha with BG pastures exceeded production per ha with RP pastures (118
vs. 87 kg of milk/ha per day) by nearly forty percent though this took more cows.
Across all treatments, cows lost an average of 6 kg/28-d period, with the majority
of the loss occurring during the first period. Cows grazing RP were more heat stressed,
having greater respiration rates, and they lost more BW (-10 vs. -5 kg/28-d period) than
cows grazing BG. These measures are indicative of greater energy expenditure
associated with greater milk production.
Tifton 85 and RP have both proven of acceptable quality for use in the diets of
high-producing dairy cows kept in confinement housing (Staples et al., 1997; West et al.,
1997), but dietary NDF and ADF concentration in these studies were much greater than
recommended by NRC (1989) and may have limited intake, particularly for BG-based
diets. Cows grazing RP pastures consumed 49% more forage OM than cows grazing BG
pastures (11.3 vs. 7.6 kg of OM/d) and supplement intakes were greater when cows
grazed RP because of their greater milk production.
In comparison with the NRC (1989) recommendation for feeding a reference cow
of 500 kg and producing 20 kg of 4% FCM/d, DMI of the BG-based diets were limiting,
and daily intakes of energy, CP, Ca and P were limiting when cows were fed the low
SUP.


213
some physiological functions of Holstein cows during heat stress. J. Dairy Sci. 72:907
916.


Effect of Supplements on Grazing Behavior 47
Interactions of Supplement and Herbage Allowance on Performance of Lactating
Cows in Pasture-Based Dairy Systems 49
Two Perennial Forages for Lactating Cows in Pasture-Based Dairy Systems in the
Southeast 51
Bermudagrass 51
Comparisons of Grasses and Legumes 60
Rhizoma Peanut 63
Some Management Strategies for the Improvement of Milk Production in
Subtropical Environments Systems 67
Bovine Somatotropin (bST) 67
Effects of Heat on Milk Production and Cooling Strategies for Pastured Cows 70
bST in Hot Environments 72
CHAPTER 3. PASTURE-BASED DAIRY PRODUCTION SYSTEMS:
INFLUENCE OF FORAGE, STOCKING RATE, AND
SUPPLEMENTATION RATE ON ANIMAL PERFORMANCE 75
Introduction 75
Materials and Methods 77
Cows, Design, and Treatments 77
Experimental Procedures 81
Statisitical Analyses 86
Results and Discussion 87
Forage Composition 87
Milk Production and Composition per Cow 89
Milk Production per Land Area 100
Body Weight and Condition 101
Respiration, Temperature, and Blood Metabolites 105
Intake of Organic Matter and Nutrients 109
Treatment Effects on Forage Nutritive Value Estimates 117
Treatment Effects on Herbage Mass, Availability, and Intake Estimates as
Determined by Pasture Sampling 120
Simple Economic Assessment of Supplementation 125
Conclusions 127
CHAPTER 4. PASTURE-BASED DAIRY PRODUCTION SYSTEMS:
INFLUENCE OF HOUSING, bST, AND FEEDING STRATEGY ON
ANIMAL PERFORMANCE 130
Introduction 130
Materials and Methods 131
Cows, Design, and Treatments 131
Experimental Measurements 134
Statistical Analysis 142
Results and Discussion 145
Grazing Time and Intake of Organic Matter 145
Milk Production and Composition 150
v


79
TABLE 3.1. Ingredient and chemical composition of supplements fed to lactating
Holstein cows on pasture.
Item
1995
- Year -
1996
Ingredients (% of DM)
Com meal
40.2

Hominy

35.3
Soybean hulls
24.0
23.9
Soybean meal (48%)
7.2
9.6
Whole cottonseed
20.0
19.8
Dried cane molasses
4.0
5.0
Mineral mix'
1.0

Mineral mix2

2.5
Calcium carbonate
1.0
1.3
Mono-Dical phosphate
0.4

Salt
0.4

Trace mineralized salt3

1.3
Diabond
0.8

Sodium bicarbonate
1.0
1.3
Chemical composition
Dry matter, %
90.4
91.4
Ash, %
9.5
7.5
NEL, Mcal/kg of DM4
1.90
1.89
NDF, % of DM
32.6
42.5
ADF, % of DM
23.3
27.7
CP, % of DM
15.6
18.0
Ca, % of DM
1.16
0.91
P, % of DM
0.43
0.61
Mg, % of DM
0.34
0.34
K, % of DM
1.13
1.33
Na, % of DM
0.64
0.93
S, % of DM
0.19
0.20
Cl, % of DM
0.26
0.82
Fe, ppm, of DM
537
355
Zn, ppm, of DM
121
159
Cu, ppm, of DM
29.8
33
Mn, ppm, of DM
1^ ^ .
65.4
66
'Composition: > 55% Dyna-Mate, > 0.7% 1% Se, > 0.4% C0SO4, > 1.9% CuS04,
> 2.6% ZnS04, 0.7% MnS04, 36.9% MgO, > 0.001% Cal, 1200 IU/g of vitamin A, > 700
IU/g of vitamin D3, > 300 IU/g of vitamin E.
"Composition: 3.8% N, 10.5% Ca, 3% P, 4.5% K, 2% Mg, 7.4% Na, 1.1% S, 5.4% Cl,
1525 ppm Mn, 1750 ppm Fe, 425 ppm Cu, 1500 ppm Zn, 12.8 ppm I, 49 ppm Co, 24.2
IU of vitamin A/g, 35.2 IU of vitamin D/g, and 0.88 IU of vitamin E/g.
"Composition (g/100 g): NaCl, 92 to 97; Mn, > 0.25; Fe, > 0.2; Cu, > 0.033; I, > 0.007;
Zn, > 0.005; Co, > 0.0025.
Calculated using 1989 NRC values for whole cottonseed.


76
U.S. producers. Thus, our first objective was to investigate animal and pasture
productivity when two recently released forages were used as a grazing base for lactating
dairy cows.
Supplemental concentrate feeds typically are fed to lactating dairy cattle in the
U.S. The availability of inexpensive concentrates makes this possible and desirable,
especially since wholly forage-based diets cannot meet the energy requirements of high-
producing, lactating dairy cows. However, supplement can have a large effect on DMI
and rumen function, and thus production responses to supplement are inconsistent.
Providing supplement may not be profitable, and factors such as pasture and animal
management should be included when considering the efficacy of supplementation.
Thus, our second objective was to test animal and pasture production responses to two
rates of supplementation within each forage base.
The response to forage and supplement may depend upon stocking rate. Most
models describing the effect of stocking rate on production indicate that while production
per animal decreases with increasing stocking rate, production per land area increases.
Optimum pasture utilization typically requires stocking rates at which forage
consumption is limited, but excessively high stocking rates may limit production per land
area if pasture productivity is compromised. With high stocking rates, however, the
response to forage type or supplement may be greater than in situations in which forage is
not limiting. Because information about the effect of stocking rate and its interactions
with forage type and supplement level on the productivity of grazing, lactating dairy
cattle was not available, our third objective was to determine animal and pasture


2
Pasture-based production systems are energetically demanding of the animal.
Cows face greater energy requirements for walking and foraging in addition to energy
demands for dissipation of heat load during periods of high ambient temperature and high
humidity. Such requirements may limit severely the nutrients available for production.
Production potential of pasture-based dairies may also be affected by numerous
management practices. Issues of particular concern include suitability of available forage
species, types and amounts of supplement to feed, appropriate stocking rates, effects of
management strategies upon animal production and physiology, and the interactions of
these factors.
The studies described herein were conducted to test the effects of forage species,
supplementation rate, stocking rate, and some potential management practices on animal
intake and performance. Some simple estimates of income are also reported along with
concluding statements regarding the viability of such systems.


142
chromium mordanting as previously described. Samples taken from a fresh paddock in
each pasture were dried at least 48 h at 55C, and ground through a 1-mm screen
(Thomas-Wiley Laboratory mill, Philadelphia, PA). Samples within pasture within
period were analyzed by the University of Florida Forage Evaluation Support Laboratory,
Gainesville. For determination of organic matter (OM), dried samples were ashed for at
least 4 h at 500C. The modified aluminum block procedure of Gallaher et al. (1975)
was used to digest samples prior to analysis for N by the method of Hambleton (1977).
Crude protein (CP) was then calculated as N 6.25. Determination of neutral detergent
fiber (NDF) and IVOMD concentrations were made using the procedures of Golding et
al. (1985) and Moore and Mott (1974), respectively.
Silage and supplement samples were collected three times in each period
(approximately every 8 d) and frozen till future analysis. Silage samples were dried at
55C for 48 h for determination of % DM. Dried silage was ground, and an equal weight
of sample within period was composited and submitted to the DHI Forage Testing
Laboratory, Ithaca, NY, for analysis. Equal weights (as-fed basis) of supplement were
composited by period and submitted to the above lab for analysis.
Statistical Analysis
Animal measures. One cow was removed from the trial during Period 2 due to a
health problem unrelated to treatment. A replacement cow was used in Period 3 to
maintain the stocking rate, but her data were not used in the analyses.
Most data were analyzed using the GLM procedure of SAS (1991) with the
following model:


Ill
vs. 1.20% of BW). Thus, total OMI and OMIPBW were not different due to SR (15.3
and 15.9 kg of OM/d and 3.08 and 3.16% of BW/d).
At the high SR, primiparous cows ate less BG whereas multiparous cows ate more
BG (parity by forage by SR interaction, P < 0.05; Figure 3.9). Conversely, SR had little
effect on forage consumption when primiparous cows grazed RP but multiparous cows
decreased RP OMI more than 2.5 kg/d with increasing SR (13.0 vs. 10.4 kg of OMI/d for
low and high SR, respectively). Similar interactions were observed for total OMI as well
as forage and total OMIPBW (Figure 3.9).
Supplementation rate effects. Providing additional supplement led to reduced
(P < 0.05) forage OMI (10.1 vs. 8.8 kg/d for high and low SUP treatments, respectively).
Total OMI was 2.2 kg/d greater (P <0.001) for cows on the high SUP treatment (16.7 vs.
14.5 kg/d). Results for OMIPBW followed the same pattern.
Cows grazing RP pastures experienced a greater decrease in forage consumption
when fed more supplement compared to those grazing BG pastures. The substitution of
forage OM by supplement OM (kg/kg) was 0.51 for RP and 0.18 for BG. Though the
forage by SUP interaction was not significant for forage OMI, cows grazing BG pastures
and provided greater amounts of supplement increased total OMI by 22 % vs. a 10 %
increase in total OMI with additional supplement for cows grazing RP. Greater
substitution rates of supplement for forage have been reported for greater quality forages
(Golding et al., 1976b). The forage by supplement interaction for milk production
(Figure 3.3) further supports the conclusion of greater substitution rates of grain for
forage for cows grazing RP because cows were better able to maintain milk production at
the low SUP when grazing RP compared with cows grazing BG. Assuming that SR


212
Welch, C. D., C. Gray, and J. N. Pratt. 1981. Phosphorus and potassium fertilization for
Coastal bermudagrass hay production in East Texas. Tex. Agrie. Ext. Ser. Leaf. 1961.
Tex. A&M Univ. Sys.
Welch, J. G., and R. H. Palmer. 1997. Supplementing lactating dairy cows on pasture
with concentrate or TMR. J. Dairy Sci. 80(Suppl):222(Abstr).
West, J. W. 1994. Interactions of energy an d bovine somatotropin with heat stress. J.
Dairy Sci. 2091-2102.
West, J.W., G. M. Hill, R. N. Gates, and B. G. Mullinix. 1997. Effects of dietary forage
source and amount of forage addition on intake, milk yield, and digestion for lactating
dairy cows. J. Dairy Sci. 80:1656-1665.
West, J. W., B. G. Mullinix, J. C. Johnson, Jr., K. A. Ash, and V.N. Taylor. 1990.
Effects of bovine somatotropin on dry matter intake, milk yield and body temperature in
Holstein and Jersey cows during heat stress. J. Dairy Sci. 73:2896-2906.
Weston, R. H., and J. A. Cantle, 1982. Voluntary roughage consumption in growing and
lactating sheep. Proc. Nutr. Soc. Aust. 7:147.
Wildman, E. E., G. M. Jones, P. E. Wagner, R. L Boman, H. F. Troutt, Jr., and T. N.
Lesch. 1982. A dairy cow body condition scoring system and its relationship to selected
production characteristics. J. Dairy Sci. 65:485-501.
Wilkinson, S. R., W. E. Adams, and W. A. Jackson. 1970. Chemical composition and in
vitro digestibility of vertical layers of Coastal bermudagrass (Cynodon dactylon L.)
Agron. J. 62:39-43.
Williams, C. H., D. J. David, and O. Hsmaa. 1962. The determination of chromic oxide
in faeces samples by atomic absorption spectrophotometry. J. Agrie Sci. (Camb.)
59:381-385.
Willoughby, W. M. 1959. Limitations to animal production imposed by seasonal
fluctuations in pasture and by management procedures. Aust. J. Agrie. Res. 10:248-258.
Wiltbank, J. N., W. W. Rowden, J. E. Ingalls, and D. R. Zimmerman. 1964. Influence of
post-partum energy level on reproductive performance of Hereford cows restricted in
energy intake prior to calving. J. Anim. Sci. 23:1049-1053.
Wolfenson, D., I. Flamenbaum, and A. Berman. 1988. Hyperthermia and body energy
stress effects on estrous behavior, conception rate, and corpus luteum function in dairy
cows. J. Dairy Sci. 71:3497-3504.
Zoa-Mboe, A., H. H. Head, K. C. Bachman, F. Baccari, Jr., and C. J. Wilcox. 1989.
Effects of bovine somatotropin on milk yield and composition, dry matter intake, and


22
Moore, 1985). In all the models, as SR increases, animal gain decreases but gain per land
area increases. A variant model by Jones (1981) suggested that at very low SR,
gain/animal also might be compromised, and Stuth et al. (1981) reported that at high
amounts of daily HA of bermudagrass pastures, defoliation efficiency is reduced.
Much of the debate among researchers appears to center on the nature of the
animal responses at the extremes of HA. Hart (1972) stated that animal gain decreases
linearly in response to increasing SR (animals/land area), and thus gain to land area is
necessarily curvilinear. Matches and Mott (1975, p. 205) noted that the exact form of
trends reported in the literature have differences depending on the researcher and
circumstances of experimentation. The rapid declines in output (per animal or land
area) proposed by Mott (1960) are likely most applicable to limited-input, extensive
grazing systems (Pearson and Ison, 1997) unsuited for intensive milk production.
Contention also has arisen over the nature of DMI in response to HA. Hodgson
(1975, cited by Stockdale, 1985) reported that intake followed HA in a linear fashion.
Others have reported asymptotic intake responses to HA (Allden and Whittaker, 1970;
Stuth et al., 1981). Stockdale (1985) reviewed eight experiments under Australian
conditions and noted that though DMI of grazing dairy cows was reduced with
decreasing HA, the relationship was not always curvilinear. He noted that combining the
data from all the experiments resulted in a significant quadratic term. The intake
response to increasing HA reported by Le Du et al. (1979) was positive and asymptotic
and similar responses were reported in a review by Phillips (1989). However, the nature
of the response likely is linear over the range of SR typically used (Jones and Sandland,
1974).


36
consumption were not as evident as when starch-based supplements were fed (Martin and
Hibberd, 1990). Klopfenstein and Owen (1987) reported that supplementation with
soybean hulls had less effect on ruminal pH compared with supplementation with cereal
grains. The lack of starch in soybean hulls may prevent the decreases in fibrolytic
activity caused by preferential starch utilization by fiber-digesting microbes (Hoover,
1986).
Other supplement sources such as beet pulp and by-product feeds have also been
considered with varying results. Thus, Galloway et al. (1993b) noted that the optimum
supplement composition might vary with the forage source with which it is fed.
Though the characteristics of a forage affect both ruminal conditions and
absorption of nutrients (Minson, 1990), it should be noted again that the effects of
[forage] quality differences may decrease and even disappear if enough grain is fed. In
such a case there would be no effect of forage quality on animal performance (Golding
et al., 1976b). However, extent of production may confound the effect and interpretation
of responses to supplement. From work with steers, Joanning et al. (1981) reported that
at intake below twice maintenance, associative effects between forage and concentrate
might not occur, though this suggestion was based on extrapolations. Ultimately, with
high-performance dairy cows, optimizing use of feed supplements will require a balance
between improvements in intake and concomitant decreases in digestion.
Besides the changes in digestibility, additional concerns with feeding large
amounts of high-starch concentrate may include reduced milk fat concentrations (Huber
et al., 1964; Jennings and Holmes, 1984a; Polan et al., 1986; Sutton et al., 1986) and


211
Vadiveloo, J., and W. Holmes. 1979. The effects of forage digestibility and concentrate
supplementation on the nutritive value of the diet and performance of finishing cattle.
Anim. Prod. 29:121-129.
Valentim, J. F., O. C. Ruelke, and G. M. Prine. 1987. Interplanting of alfalfa and
rhizoma peanut. Proc. Soil Crop Sci. Soc. Fla. 46:52-55.
Valentine S. C., G. J. Ball, B. D. Bartsch, and L. B. Lowe. 1990. Effect of bovine
somatotropin injected as a sustained-release formulation at three infection intervals on the
production and composition of milk from dairy cattle grazing pasture and supplemented
with a grain concentrate. Aust. J. Exp. Agrie. 30:457-461.
Van Es. A. J. H. 1974. Energy intake and requirement of cows during the whole year.
Livestock Prod. Sci. 1:21-32.
Van Soest, P. J. 1965. Symposium on factors influencing the voluntary intake of
herbage by ruminants: Voluntary intake in relation to chemical composition and
digestibility. J. Anim. Sci. 24:834-843.
Van Vuuren, A. M., S. Tamminga, and R. S. Ketelaar. 1991. In sacco degradation of
organic matter and crude protein of fresh grass (Lolium perenne) in the rumen of grazing
dairy cows. J. Agrie. Sci. (Camb.)l 16:429-436.
Varga, G. A., H. F. Tyrrell, G. B. Huntington, D. R. Waldo, and B. P. Glenn. 1990.
Utilization of nitrogen and energy by Holstein steers fed formaldehyde- and formic acid-
treated alfalfa or orchardgrass silage at two intakes. J. Anim. Sci. 68:3780-3791.
Vercoe, J. E. 1973. The energy cost of standing and lying in adult cattle. Br. J. Nutr.
30:207-210.
Voigt, J., B. Pitatkowski, and R. Krqwielitzki. 1978. The effect of order of roughage and
concentrates in feeding on carbohydrate digestion and bacterial protein synthesis in the
rumen of the dairy cow. (In German with English abstract.) Arch. Tierenaehr. 28:67.
Waldo, D. R. 1986. Effect of forage quality on intake and forage-concentrate
interactions. J. Dairy Sci. 69:617-631.
Waldo, D. R., L. W. Smith, and E. L. Cox. 1972. Model of cellulose disappearance from
the rumen. J. Dairy Sci. 55:125 129.
Warren, W. P., F. A. Martz, K. H. Asay, E. S. Hilderbrand, C. G. Payne, and J. R. Vogt.
1974. Digestibility and rate of passage by steers fed tall fescue, alfalfa and orchardgrass
hay in 18 and 32 C ambient temperatures. J. Anim. Sci. 39:93-96.


143
Y¡jk= u + a¡ + Pj + Y k(j) + Al + e¡jki,
where
]i = overall mean
cq = effect of cow
Pj = effect of treatment
yk(j) = effect of pasture(trt)
A| = effect of period
¡jki = effect of residual error.
Single degree of freedom contrasts for treatment were housing (1+2) vs. (3 + 4),
bST (1 + 3) vs. (2 + 4), interaction (1 + 4) vs. (2 + 3), and silage supplement (4 vs. 5).
Treatment effects were considered significant at P levels < 0.05 and trends at P < 0.10.
Temperature measures. Plots of the temperature data were evaluated visually
and readings exhibiting spontaneous spiking and readings outside of 38 to 40C were
deleted. Greater signal variability for cows on pasture resulted in an average of 13.7% of
readings being deleted vs. an average of 8.5% of readings deleted for cows in the bam.
Visual evaluation showed three general trends in the data. First, an increase in
body temperature was observed through the daylight hours until the p.m. milking.
Secondly, a parabolic decrease and subsequent increase in temperature was observed as
cows went onto showers for cleaning, were milked, and returned to pasture. Thirdly, a
decrease in temperature was observed through the night until after the a.m. milking.
To evaluate the curves, the data were divided into these respective segments on
the horizontal (time) axis. Because bam and pasture cows did not arrive at the shower at
the same time and because time on the showers and time back to pasture varied slightly
for each group, further adjustments on the horizontal axis were necessary. For Segment


33
greater microbial synthesis, but milk protein production did not differ due to milk
production differences. Partial efficiency of milk production was unaffected by
supplement type.
Galloway et al. (1993b) compared provision of soy hulls, com, or a combination
of the two at equal digestible energies (differing amounts in kg/d) to steers consuming
bermudagrass hay. Providing hulls resulted in a greater decrease in bermudagrass intake
relative to com or com plus soy hull supplementation, but total DMI were similar for
steers fed the supplemented diets and greater than for steers fed bermudagrass alone.
Supplement increased particulate rate of passage from the rumen (avg. 4.71 vs. 4.18%/h),
which could have negative effects on digestibility of bermudagrass. However, the overall
supplement effect was an increased diet digestibility.
A comparison of a TMR or grain concentrate as a supplement for pasture-fed
dairy cattle indicated that a TMR supplement may not be an improvement over
concentrate feeds. Welch and Palmer (1997) fed 1) no supplement, 2) 7.3 kg of
concentrate/d, or 3) an equal quantity of TMR balanced for 38.5 kg of daily milk to cows
grazing unspecified cool-season pastures. Milk production was greatest for concentrate
fed cows and least for unsupplemented cows, but milk fat concentration followed an
opposite pattern. The researchers speculated that pasture intake fiber in the TMR
probably reduced pasture DM intake (p. 222).
Supplement Effects on Forage Digestibility
Energy supplements often affect forage digestibility and DMI in a similar manner.
Milne et al. (1981) fed sheep increasing amounts of grain concentrate and found a linear
decrease in digestibility of ingested herbage. A 9.6 percentage unit decrease (64.3 vs.


LIST OF REFERENCES
Abribat, T. H., H. Lapierre, P. Dubreuil, G. Pelletier, P. Gaudreau, P. Brazeau, and D.
Petitclerc. 1990. Insulin-like growth factor-1 concentration in Holstein female cattle:
variation with age, stage of lactation and growth hormone-releasing factor administration.
Domest. Anim. Endocrinol. 7:93-102.
Achmadi, J., T. Yanagisawa, H. Sano, and Y. Terashima. 1993. Pancreatic insulin
secretory response and insulin action in heat-exposed sheep given a concentrate or
roughage diet. Com. Anim. Endo. 10:279-287.
Adams, D. C. 1985. Effect of time of supplementation on performance, forage intake and
grazing behavior of yearling beef steers grazing Russian wild ryegrass in the fall. J.
Anim. Sci. 61:1037-1042.
Adams, S. 1992. Cattle gain faster on Tifton 85. Agricultural Research. 40:19.
Adjei, M. B., P. Mislevy, R. S. Kalmbacher, and P. Busey. 1989. Production, quality,
and persistence of tropical grasses as influenced by grazing frequency. Proc. Soil Crop
Sci. Soc. Fla. 48:1-6.
Adjei, M. B., P. Mislevy, and C. Y. Ward. 1980. Response of tropical grasses to stocking
rates. Agron. J. 72:863-868
Akin, D. E. 1986a. Chemical and biological structure in plants as related to microbial
degradation of forage cell walls. Pages 139-157 in Digestive Physiology and Metabolism
in the Ruminant. L. P Milligan, W. L. Grovum, and A. Dobson, ed. Reston Publishing
Co., Reston, VA.
Akin, D. E. 1986b. Interaction of ruminal bacteria and fungi with southern forages. J.
Anim. Sci. 63:962-977.
Ala-Seppal, H., P. Huhtanen, and M. Nasi. 1988. Silage intake and milk production in
cows given barley or barley fibre with or without distillers solubles. J. Agrie. Sci.
Finland. 60:723-733.
Aldrich, J. M., L. D. Muller, G. A. Varga, and L. C. Griel, Jr. 1993. Nonstructural
carbohydrate and protein effects on rumen fermentation, nutrient flow, and performance
of dairy cows. J. Dairy Sci. 76:1091-1105.
184


35
Forage intake and digestibility in response to supplement feeding also is related to
supplement effects on ruminal microbes. Growth of ruminal microbes is reduced in vitro
with decreased ruminal pH (Russell and Dombrowski, 1980). Low rates of starch
supplementation may increase numbers of cellulolytic microbes, but feeding diets with
large concentrations of rapidly fermentable starch may lead to a cascade of events
including decreased ruminal pH, reduced cellulolytic microbes, and ultimately, decreased
intake (Mould and 0rskov, 1983).
Cellulolysis is decreased not only by reduced pH but also by preferential starch
digestion by the microbes (Mould et al., 1983; Hoover, 1986). Mould et al. (1983) fed
increasing amounts of barley to sheep, with or without additional bicarbonate salt to
buffer ruminal pH. Diets were fed at a fixed rate, just below maximum voluntary intake,
so passage should not have confounded the findings. Even when pH was maintained at
approximately 6.7, DM digestibility decreased with increasing concentration of barley in
the diet, and the depression in apparent DM digestion was greater in sheep fed the more
processed barley, suggesting that fiber-digesting microbes preferentially selected starch.
Moreover, reduction in cellulolysis in response to starch supplementation was greater
when roughages were of lower DM degradability (Mould et al., 1983), which has
implications for cows grazing warm-season pastures.
Caird and Holmes (1986, p. 53, citing Jennings and Holmes, 1984a) stated that
the response in intake to concentrates depends on the influence of the concentrate on
herbage digestibility. Others have reported that extensively fermented, fiber-based
supplements have less negative effects on forage intake and digestion. For example,
when soybean hulls were used as a supplement for beef cattle, reductions in forage


128
to be an excellent forage for dairy grazing given its relatively high nutritive value
characteristics and great yields.
Ability to optimize SR for both animal and forage production will be critical for
producer success with grazing. Results from this study indicated that increasing SR on
productive forages such as BG might improve forage quality. Stocking rates of 10
cows/ha may not be great enough in conditions of rapid growth of Tifton 85, but this
depends upon factors such as rainfall and fertilization practices. At SR of 7.5 cows/ha on
RP pastures, HA may limit animal production. Although estimates of OMI suggest that
the high SR, low SUP treatment within RP pastures did not limit forage OMI, such high
SR may have negative consequences in terms of maintenance and productivity of stand,
and would only be advisable under excellent growing conditions.
Providing supplement is a cost-effective way to improve performance of cows on
pasture, particularly forages of moderate quality and of more limited availability. The
positive milk production and MIMSC responses to additional supplement when cows
grazed BG pastures indicate the value of providing supplement to cows grazing this
moderate quality forage. However, the limited production response and negative
MIMSC response to supplement when cows grazed RP indicates the potential for
substitution with high quality forage. Further, the over-prediction of energy input with
RP pastures indicates that the supplementation treatments in this study were not effective
in combination with RP.
Although several studies have indicated greater response to supplement when
forage availability was limited, forage availability likely was not limited in these studies,
and no such responses were observed.


CHAPTER 2
LITERATURE REVIEW
Since the 1980s, the economics of dairying in the United States has put farmers in
a severe cost-price squeeze (Muller et al., 1995). Reducing feed costs has become critical
because these costs are estimated to account for 50 to 60% of operating costs (Elbehri
and Ford, 1995). To cope with this economic reality, many dairies using confined
housing have increased herd size. Technological advances have helped drive this change
(Lanyon, 1995), and typically are most profitable when employed on a large scale
(Thomas et al., 1994). Increasing herd size can help farmers reduce feed costs per cow
by increasing purchasing power with larger commodity purchases (Lanyon, 1995).
Further, fixed costs can be reduced by increased use of farm equipment and greater
throughput of cows through the milking parlor. These management changes rely upon
increased efficiencies and greater milk production to increase profit but both increased
herd size and increased technological sophistication have resulted in dairy production
becoming an even more capital-intensive agribusiness (Thomas et al., 1994, p. 1).
Facing the same economic and environmental pressures as other dairies but
without the ability or desire to expand the size of their herd and facilities, some producers
have opted for another way to improve profitability. Their strategy relies on reduced
levels of inputs and lower cost structures (Parker et al., 1993). This is attempted by use
of alternative forage feeding systems, particularly, intensive grazing (Elbehri and Ford,
1995). Smaller farms have been subjected to greater financial stress than properties
3


83
to the fiber, and allowed to stand for 1 to 1.5 h. The fiber was rinsed thoroughly with tap
water and dried at 105 C. Three 0.02 g (air dry) of mordanted fiber were weighed into
28-g gelatin capsules (Jorgenson Laboratories, Loveland, CO). Across the three periods,
average Cr concentration was 42,000 and 46,000 ppm (OM basis) for BG fiber, and
51,000 and 53,000 ppm for RP fiber for 1995 and 1996, respectively.
In all periods of both years, 32 cows were orally-dosed with nine gelatin capsules
containing Cr-mordanted fiber (27 g, as-fed) from their respective forage assignments.
Capsules were administered with a multiple dose balling gun (NASCO, Ft. Atkinson,
WI). In 1995, average dosing time was 1130 h on d 23 of each period. Fecal samples
were collected at approximately 0, 7.5, 19.5, 23, 27, 31, 44.5, 55.5, 68.5, 79.5, 92.5, and
103.5 h post-dosing. Samples at 23, 27, and 31 h post-dosing were collected on pasture at
the cows leisure, while the remainder were grab samples taken in holding pens at the
milking parlor.
In 1996, cows were dosed after the evening milking on d 25, and fecal samples
were collected at approximately 0, 12, 15, 18, 21, 24, 27, 36, 42, 48, 60, 72, and 84 h
post-dosing. Collections were made on pasture at h 15, 18, 21,27, and 42.
Fecal samples were refrigerated or frozen immediately after collection. In 1995,
samples from period 1 were dried at 55 C and samples from periods 2 and 3 were freeze-
dried. In 1996, all samples were dried at 55 C for at least 48 h. All fecal samples were
ground through a 1-mm screen with a Wiley mill. Samples (2 g, as-is) were dried at 105
C and ashed at 550 C for determination of DM and OM according to AO AC (1990)
procedures. Ash was digested in a solution of H2PO4 (with added MnS04) and KBr03
using heat on a hot plate and analyzed for Cr by atomic absorption spectrophotometry


58
Decreased HA affected leaf chemical characteristics and the proportion of leaf in the HM.
Leaf NDF decreased from 75.2 to 71.3% from high to low HA, and the average
proportion of leaf in the HM decreased by 51.6 and 39.7% for low and high HA
treatments, respectively.
Leaf proportion in the diet was unaffected across grazing pressures (82.7% for
low and 78.5% for high pressures), however, demonstrating diet selectivity of the grazing
animal. Animals also showed selectivity for leaves of greater quality as the concentration
of NDF in leaves selected was less than that in leaves in the standing herbage. With the
lower HA treatments, the proportion of dead material increased as leaf declined during
the hotter months. The dead material consisted primarily of uprooted stolons and dead
stems, and their disappearance later in the grazing season was due to consumption.
Although dead herbage is not high quality, the concentration of NDF in the dead
herbage of the low HA treatment was approximately 9.0 percentage units less than that of
the other treatments. As HA decreased, NDF concentration of the herbage was reduced
in the two pastures with the lowest HA compared with the two pastures with the greatest
HA. Moreover, reductions in NDF concentrations with decreased HA were observed in
all herbage components, and particularly in the senesced herbage.
Other studies (Arnold, 1960; Hamilton et al., 1973; Adjei et al., 1980) have not
shown the positive relationship between HA and NDF concentration of the herbage or the
diet found by Roth et al. (1990). The latter noted that the previous studies were
conducted using greater HA, however.
In 1993, a new cultivar, Tifton 85, was released (Burton et al., 1993). The grass is
actually an interspecific hybrid between bermudagrass and stargrass (Tifton 68), and it


95
"O
'Sb
2
a>
i4
>
T3
'Sb
u
tu
n
ox
^1-
20.0
10.0
-
16.1
15.2
16.1
SE = 0.2
P<0.01
13.8
-
Lo
Hi
Lo
Hi
Figure 3.3. Interaction of supplementation rate and forage species on production of milk,
4% fat corrected milk (FCM), milk fat, and protein. Supplementation rates were 0.33
(Lo) and 0.5 (Hi) kg of supplement per kg of daily milk production. Forage species were
Tifton 85 bermudagrass and Florigraze rhizoma peanut.


TABLE OF CONTENTS
page
ACKNOWLEDGMENTS ii
LIST OF TABLES vii
LIST OF FIGURES ix
KEY TO ABBREVIATIONS xi
ABSTRACT xii
CHAPTER 1. INTRODUCTION 1
CHAPTER 2. LITERATURE REVIEW 3
Climatic Challenges to Southeastern Dairies 4
Climatic Animals 6
Energy Considerations for the Grazing Ruminant 7
Some Animal and Nutritional Factors Influencing Feed Intake 9
Some Non-Nutritional Factors Affecting Behavior and Forage Intake of Grazing
Ruminants 13
Mechanistic Components of Forage Intake 13
Daylight and Temperature 17
Measurement of Forage Intake in Grazing Ruminants 18
Herbage Allowance and Stocking Rate Effects on Forage Intake and Performance
of Ruminants 21
Supplement Effects on Animal Performance with Particular Emphasis on
Lactating Cows in Pasture-Based Dairy Systems 25
Supplement Effects on Production 26
Supplement Effects on Intake 29
Supplement Effects on Forage Digestibility 33
Synchronizing Nitrogen and Carbohydrate Supplements to Increase Microbial
Protein Synthesis in the Rumen 37
Loss of Feed Nitrogen in Ruminants 37
Responses to Supplemental Carbohydrate 39
Effects of Supplement Feeding Frequency 42
Effects of Timing of Supplement Provision Relative to Forage Intake 44
Additional Energy and Protein Supplements for Animals on Pasture 45
Fats 45
Escape Proteins 46
IV


87
(TpaPY)jimn +
V0 +
5p(ttPy)lmn
Gjklmnopi
where
p = overall mean
Tj = effect of year
Pj = effect of parity
K(xp)k(ij) = effect of cow within year and within parity
oci = effect of forage
pm = effect of SUP
yn = effect of SR
v0 = effect of period
6P = effect of pasture replicate within forage, SUP and SR treatments
cykimnop = effect of residual error.
Single degree of freedom orthogonal contrasts were made to test for treatment
effects. Treatments were considered different at P levels < 0.05 and trends are reported
for P < 0.10. Cow, parity, and their interactions were removed from the model for the
analysis of herbage data.
Results and Discussion
Forage Composition
Averaged across all pastures within forage treatments, estimates of digestibility
and nutritive value of RP were greater than for BG (Table 3.2). The RP pastures


15
early stages of defoliation (Chacon and Stobbs, 1976). Work by Roth et al. (1990)
showed that cattle continued to select large proportions of leaf even as leaf percentage of
the canopy decreased. As the quantity of leaf decreases, animals increased GT, RB, and
total number of eating bites, but these activities were not sustained as pastures became
severely defoliated (Chacon and Stobbs, 1976). Chacon and Stobbs (1976) suggested
that leaf yield would give a better expression of forage on offer than the more commonly
used grazing pressure.
Biting rates between 51 and 63 bites/min were reported by Chacon and Stobbs
(1976) when cows grazed warm-season forages. Rates as great as 90 bites/min on
temperate pasture were reported by Hodgson (1985) but this likely represents total jaw
movements. Rates of biting declined linearly with increasing length of grazing period
when forage was not limiting (Stobbs, 1974b). Greenwood and Demment (1988)
compared intake behavior of unfasted steers or those fasted for 36 h. They reported that
ingestive bites increased approximately 30% (38.9 vs. 29.7 bites/min) due to fasting, but
this response was seen during the morning only.
Under forage-limiting conditions with temperate pastures, RB increases as IB
decreases, but RB rarely increases enough to maintain herbage intake (Allden and
Whittaker, 1970; Hodgson, 1981). Moreover, the changes in RB likely are due to the
manipulative jaw movements required to harvest the forage (Stobbs, 1974b; Chambers et
al., 1981). With temperate pastures, RB may increase when forage is limited due to a
reduction in manipulative jaw movements (Hodgson, 1985), but low availability of
herbage would likely decrease ingestive RB with most tropical pastures, as animals
would spend more time selecting leaf material.


Table 4.6. Influence of housing (0800 to 1500 h on pasture or in bams with fans and sprinklers), bST, and bST with supplemental
silage on body weight (BW), body condition score (BCS), respiration rates (RR), and concentrations of plasma insulin and insulin-like
growth factor-1 (IGF-1) of Holstein cows grazing Tifton 85 bermudagrass pastures.
Item
Pasture
-bST +bST
-bST
- Bam -
+bST
+silage
+bST
SEM
Housing
Probability
Housing
bST x bST
Silage
ABW", kg/24-d
-12.9
-8.8
-1.3
13.8
5.4
5
***
**
NS
t
ABCS3/24-d
-0.17
-0.29
-0.24
-0.04
-0.29
0.14
NS
NS
NS
NS
RR, breaths/min
89
88
69
70
68
2
***
NS
NS
NS
IGF-1, ng/ml
88
141
91
144
146
7
NS
***
NS
NS
Insulin, ng/ml
0.58
0.61
0.52
0.57
0.61
0.01
*
t
NS
NS
'P < 0.001, 0.01, 0.05, and 0.10 represented by ***, **, and t, respectively.
Change in body weight.
3Change in body condition score.


Hour
Figure 4.4. Regression equation estimates of body temperatures of cows measured over a 24-h period and showing
interaction of bST (+ or -) and housing treatments.


91
Interactions of forage and year with respect to milk production, 4% FCM
production, milk fat percentage, and milk fat production (Figure 3.1) reveal greater
reductions in performance in 1996 for animals grazing BG. For cows grazing RP
pastures, the 0.26 percentage-unit increase in milk fat concentration from 1995 to 1996
offset the 1-kg decrease in daily milk production. This resulted in the same amount of
4% FCM production over the two years. A smaller increase in milk fat percentage did
not offset the decreased milk production in 1996 for cows grazing BG, however.
Stocking rate effects. Stocking rate did not influence milk production, but cows
grazing at lower SR tended (P < 0.053) to produce milk with greater concentrations of
protein (3.00 vs. 2.97%). These responses may be indicative of greater concentrations of
degradable protein and digestible OM in the diet and may reflect opportunity to select
plant parts of greater nutritive value. Likewise, MUN was lower (P < 0.05) when cows
were stocked at the lower rate (17.1 vs. 17.8 mg %) suggesting more efficient use of
dietary CP for milk protein.
In 1995, greater SR resulted in greater milk and 4% FCM production for cows
grazing RP but reduced milk and 4% FCM production for cows grazing BG. Results for
1996 were opposite, with the greater SR causing decreased milk and 4% FCM production
for cows grazing RP but increased production for cows grazing BG (year by forage by
SR interaction, P < 0.05; Figure 3.2). Based on the visual appraisal of the BG pastures at
the high SR in 1996 (10 cows/ha), herbage allowance and forage nutritive value were
near optimum. Intake of digestible OM may have been greater and thus stimulated milk
production. However the RP pastures at the high SR in 1996 (7.5 cows/ha) appeared to
lack sufficient high quality forage which likely resulted in a reduction in milk production.


129
Concerns about pasture-based production systems include the losses of BW and
body condition, and the poor reproductive performance associated with their use. Cows
in these studies were moved directly from bams to pastures in the heat of the summer.
No time was given for adaptation to either the heat or the new system of forage
consumption, and BW losses were greatest in the first treatment period. In year-round
pasture-based systems, however, losses of BW might be reduced due to better adaptation.
Further, strategies such as winter calving might limit the losses associated with the heat
of summer and allow for greater reproductive success. However, changing the season of
production may strain the graziers ability to utilize rapidly growing summer