Effects of creep feeding, zeranol and breed type on beef production

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Title:
Effects of creep feeding, zeranol and breed type on beef production
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Creep feeding
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x, 92 leaves : ill. ; 28 cm.
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English
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Prichard, David Louis, 1956-
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Beef cattle -- Feeding and feeds   ( lcsh )
Calves -- Feeding and feeds   ( lcsh )
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bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

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Thesis:
Thesis (Ph. D.)--University of Florida, 1983.
Bibliography:
Includes bibliographical references (leaves 79-91).
Statement of Responsibility:
by David Louis Prichard.
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Typescript.
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Vita.

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University of Florida
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Full Text










EFFECTS OF CREEP FEEDING, ZERANOL AND BREED TYPE
ON BEEF PRODUCTION













By

DAVID LOUIS PRICHARD


A DISSERTATION SUBMITTED 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


1983
































DigMe ItM Internet Archive
in 2010 with funding from
University of Florida, George A. Smathers Libraries with support from Lyrasis and the Sloan Foundation


http://www.archive.org/details/effectsofcreepfe00pric















ACKNOWLEDGEMENTS



The author wishes to express his sincere thanks to Dr. D. D.

Hargrove, Major Professor, for his guidance and suggestions during the

course of graduate study and in the preparation of this manuscript.

The author is indebted to Professor Don Wakeman and Dr. Marvin Koger

for their helpful suggestions and constructive criticisms of this

dissertation. Graditude is extended to Drs. John Moore, Gerald Mott,

Bill Ocumpaugh and Tim Olson for serving as committee members.

Appreciation is expressed to the following graduate students

for their help in the collection of data: Sergio Cesar, Anke van Dijk,

Kepler Euclides, Carlos Fontes, Mike Harrison, Alexis Pourrain, Joao

Restle, Barbara Robinson, Morse Solomon and Fred Tucker. Special

thanks are given to Tim Marshall for his friendship while coaching the

Livestock Judging Team together. The author wishes to thank Paul Dixon

and the BRU crew for their help in collecting data used in this

manuscript. The financial support of this project provided by

International Minerals and Chemical Corporation is greatly

appreciated. The author is indeed grateful to the Animal Science

Department for granting him an assistantship for graduate work.

Appreciation is extended to Cheryl Combs for typing this

manuscript. The author wishes, also, to express his sincere

appreciation to his wife, Caren, for her patience and unselfish love

and encouragement throughout this period of study.















TABLE OF CONTENTS


ACKNOWLEDGEMENTS .

LIST OF TABLES .

LIST OF FIGURES .

ABSTRACT . .

INTRODUCTION .

REVIEW OF LITERATURE .

Factors Affecting Cal

Creep Feed .

Zeranol Implants

Breed of Dam .

Breed of Sire

Sex of Calf .

Factors Affecting Cow

Creep Feed .

Breed of Cow .

Breed of Sire of

Sex of Calf .


Factors Affecting Fema

Nutritional Regim

Breed and Age .


PAGE
iii

vii

viii

ix

1

3

3

3

6

8

9

11

12

12

13

15

16


SPerformanc .











Performance .











Calf .



.le Reproductive Tract

ie . .
. . .

Performance .





Calf .



le Reproductive Tract

e . .

. . .


Development











Factors Affecting Adipose Tissue

Nutritional Regime .

Breed . .

Factors Affecting Carcass Charact


C. I





eris


Nutritional Regime .

Zeranol Implants .

Breed of Dam .

Breed of Sire .

STUDY I CALF AND COW PERFORMANCE .

Introduction . .

Experimental Procedure .

Results and Discussion .

Calf Performance .

Weights and Weight Gains

Frame and Condition Scores

Udder and Teat Scores .

Cow Performance .

Summary . .

STUDY II WEANLING HEIFER DEVELOPMENT AND

Introduction . .

Experimental Procedures .

Results and Discussion .

Reproductive Tract Development


ula ILy .





;tics and Compositi






























COMPOSITION .
. .



. .



. .













. .

. .


Udder and Subcutaneous Fat


Carcass Characteristics and Composition .

Summary . . .


i~ > 4**


. 73


PAGE
19

S19

. 22

S23

.23

S25

26

S28

S30

S30

S30

S35

S35

.35

. 44

. 48

S49

S52

S54

S54

S55

S57

57

S60

. 66


. .









PAGE

SUMMARY AND CONCLUSIONS ......... .......... ... 75

LITERATURE CITED . . . 79

VITA . . .. ... .92














LIST OF TABLES


PAGE

1. NUMBER OF CALVES BY BREED OF SIRE, BREED OF DAM AND
SEX OF CALF . . ... .. 32

2. LEAST-SQUARES MEANS FOR CALF TRAITS . .... 36

3. WEIGHT GAINS OF LONG AND SHORT-TERM CREEP-FED CALVES ABOVE
THAT OF THE NONCREEP-FED CONTROLS, CREEP FEED INTAKE AND
CREEP FEED EFFICIENCY . .... ... 39

4. LEAST-SQUARES MEANS FOR AVERAGE DAILY GAIN FROM 146 TO 210
DAYS OF AGE BY CREEP TREATMENT, ZERANOL TREATMENT AND
BREED OF DAM . . 43

5. AVAILABLE DRY MATTER (KG) PER COW-CALF PAIR BY MONTH,
PASTURE AND CREEP TREATMENT WITHIN YEAR AND AVERAGE
MONTHLY RAINFALL . . 45

6. MEAN CRUDE PROTEIN PERCENTAGE BY MONTH, PASTURE AND CREEP
TREATMENT WITHIN YEAR . .... 46

7. MEAN IN VITRO ORGANIC MATTER DIGESTIBILITY PERCENTAGE BY
MONTH, PASTURE AND CREEP TREATMENT WITHIN YEAR 47

8. LEAST-SQUARES MEANS FOR COW TRAITS . .... 50

9. LEAST-SQUARES MEANS FOR REPRODUCTIVE TRACT CHARACTERISTICS 58

10. LEAST-SQUARES MEANS FOR UDDER AND SUBCUTANEOUS FAT
PARAMETERS . . 59

11. LEAST-SQUARES MEANS FOR EMPTY BODY WEIGHT, GASTROINTESTINAL
TRACT FILL, HOT CARCASS WEIGHT AND DRESSING PERCENT .... 61

12. LEAST-SQUARES MEANS FOR CARCASS CHARACTERISTICS ...... 69

13. LEAST-SQUARES MEANS FOR ESTIMATED CARCASS COMPOSITION 70














LIST OF FIGURES


PAGE

1. Average daily creep feed intake . 37

2. Udder and subcutaneous adipocyte size distribution for
noncreep (NC), short-tem (SC) and long-term (LC) creep-
fed weanling heifers . . 62

3. Udder and subcutaneous adipocyte size distribution for
weanling heifers not implanted (NZ) and implanted (Z)
with zeranol . . .

4. Udder and subcutaneous adipocyte size distribution for
Brahman and Romana Red-sired weanling heifers .67

5. Udder and subcutaneous adipocyte size distribution for
weanling heifers from Angus and F1 Angus x Brown Swine 68
dams . . . .


viii













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

EFFECTS OF CREEP FEEDING, ZERANOL AND BREED TYPE ON BEEF
PRODUCTION

By

David L. Prichard

August, 1983

Chairman: D. D. Hargrove
Major Department: Animal Science

Two hundred calves, produced in 1981 and 1982, sired by

Brahman and Romana Red bulls and out of Angus and F1 Angus x Brown

Swiss reciprocal crossbred cows (F ) were stratified by breed type and

sex to the following creep treatments: no creep feed (NC); long-term

(LC), creep-fed from 56 d of age to weaning (210 d); and short-term

(SC), creep-fed from 146 d of age to weaning. Half of the steer and

heifer calves within each breed and creep treatment were implanted with

36 mg of zeranol at 56 and 146 d of age. Twelve heifers were chosen

randomly for slaughter each year from within creep and zeranol

treatments and breed groups.

LC and SC calves were heavier (P<.001) at 210 d of age than NC

calves (264 and 257 vs 231 kg), and LC calves were heavier (P<.001) at

146 d than NC calves. Cows with creep-fed calves gained more weight

during the breeding season than cows with noncreep-fed calves.

Pregnancy rate of dams was not affected (P<.46) by calf creep









treatment. Zeranol increased (P<.001) 146 and 210-d weights of

calves. Brahman-sired calves had heavier (P<.001) 146 and 210-d

weights and higher frame scores than Romana Red sired calves. Calves

out of Angus dams had lower (P<.001) 146 and 210-d weights but higher

(P<.03) 210-d conditions scores than calves produced by F1 dams.

Zeranol implanted LC and SC calves gained .18 and .14 kg/d more (P<

.001), respectively, from 146 to 210-d of age than did non-implanted

calves on the same creep treatments. Implanted NC calves gained only

.06 kg/d more (P>.10) than non-implanted NC calves.

Creep feeding did not increase (P>.19) size of the

reproductive tract in weanling heifers. The LC heifers had larger (P<

.04) udder and subcutaneous adipocytes than NC heifers. Zeranol

implants increased (P<.02) uterine weight and decreased (P<.02) percent

lipid in the udder. Brahman-sired heifers had more (P<.004) total udder

adipocytes than those sired by Romana Red bulls. Heifers out of F1

dams tended (P>.12) to have larger udder adipocytes than heifers

produced by Angus dams. Breed of sire and dam did not affect (P>.25)

carcass composition.














INTRODUCTION



To stay competitive in the purebred cattle industry, the

purebred producer often creep feeds his calves to obtain added weight,

added condition and possibly higher prices. Commercial cattlemen

generally do not creep feed their calves due to the high cost of feed.

However, when pasture conditions do not provide adequate nutrition,

commercial cattlemen may choose creep feeding as an emergency

program to supply added nutrients to the calf. It is essential for

commercial and purebred cattlemen to be able to properly select for

milking ability within their cow herds. However, many cattle producers

have overlooked the possibility that creep feeding may be masking the

cow's milking ability and impairing the future productivity of

replacement heifers. It has been theorized that creep-fed heifers

deposit excess fat in their mammary system, and that this may impair

milk production in later life. Little is known, however, about

differences in body composition and fat distribution patterns between

creep-fed and noncreep fed calves.

An area of interest, particularly to the commercial cattleman,

is the influence of growth stimulants on weight and condition of the

calf at weaning and on future reproductive performance of heifers

implanted preweaning. Research has shown that growth stimulants, as

well as creep feeding, significantly increase the weight of calves at









weaning. No data exist, however, concerning the interactions of growth

stimulants with creep feeding and their effect on calf performance.

Furthermore, no information is available on the interactions of each

and both of these management practices with differences in milk

production of various breeds of cattle.

The objectives of this study were to

1) evaluate the effects of and interactions among creep

feeding, zeranol implants and breed type on calf and cow

performance and

2) ascertain the effects of creep feeding, preweaning zeranol

implants and breed type on reproductive tract development,

fat deposition in the udder and body composition of

weanling heifers.













REVIEW OF LITERATURE


Factors Affecting Calf Performance


Creep Feed. Creep feeding is the supplemental feeding of calves

while they are nursing their dams. The basic function of creep feeding

is to increase preweaning calf performance, mainly weaning weight and

condition. The basis for this response is an increased intake of

energy during the nursing period.

Creep feeding increases the weaning weight of beef calves

(Furr and Nelson, 1959; Burns and Koger, 1&63; Marlowe et al., 1965;

Stricker et al., 1979). Furr and Nelson (1959) stated that the

response to creep feeding depends on the dam's plane of nutrition. They

observed an increase of 40 kg in weaning weight as a result of creep

feeding when mature Hereford cows were wintered on a low level of

nutrition, compared with a 24 kg increase in weaning weight for

creep-fed calves on dams receiving a high level of nutrition during the

winter. Anthony and Starling (1968) reported that creep feeding gave

greater calf gains when the dams also were supplemented.

Supplementation of only the cow increased her gain but not that of the

calf, while creep feeding the calf without supplementation of the dam

increased both calf and cow weight gain. Temple and Robertson (1961)

observed that calves creep-fed from 150 to 234 days of age gained 16 kg

more than controls in 1959, but less than the controls in 1960. The








authors claimed that conditions and management were identical for both

groups, but this is somewhat difficult to believe since this is one of

a few studies reporting a negative response to creep feeding. Martin

et al. (1981) reported that creep feeding improved (P<.05) weaning

weight in 7 of 10 years, and the overall average response was 15 kg (P<

.01). The range in response varied from a six kg disadvantage to a 41

kg advantage for creep-fed calves. The authors stated that the

negative response for year 6 could be explained by location of the

creep feeder and low feed intake. The feeder was not located near

water or shade, demonstrating the importance of proper placement of the

creep feeder for optimal feed consumption and weight gain. Martin et

al. (1981) also reported that creep feeding increased (P<.01) the

feeder grade of both steer and heifer calves from high Good to low

Choice. Cundiff et al. (1966), in an extensive study involving nearly

14,000 Hereford and Angus calves in Oklahoma, stated that creep feeding

improved 205-day weight by an average of 12.8 kg. They noted that

creep feeding reduced the seasonal effect on weaning weight, in that

seasonal deviations from the overall mean were less than when there was

no creep feeding. The advantage for creep feeding appeared to be

greater for calves born in summer and autumn.

Sticker et al. (1979) conducted a study using Hereford

cow-calf pairs grazing Fescue-Ladino clover pastures. The authors

reported that creep feeding increased (P< .01) average 205-day weight

from 185 to 210 kg, calf feeder grade from average Choice to high

Choice and wither height from 96 to 100 cm.

From the producer's point of view the important issue is not

whether creep feeding improves weaning weight but whether or not it is





5


economical (Preston and Willis, 1974). Hunsley et al. (1967) conducted a

4-year study in which 314 calves were either creep-fed on an ad libitum

or limited (.9 kg/head/day) basis, or not creep-fed from about 3 to 8

months of age. Creep feeding was profitable in all 4 years. Similar

results in favor of creep feeding were obtained by Hammes et al. (1959)

and Wilson et al. (1966).

Burns and Koger (1963) creep-fed, on an ad libitum basis, Angus,

Brangus, Hereford and Santa Gertrudis calves for 57 days prior to weaning

and reported no monetary advantage for creep feeding. The high cost of

creep feeding under pasture conditions is best illustrated by Kuhlman

et al. (1961) in Oklahoma. Creep feeding calves out of mature cows from

60 to 245 days of age increased weaning weight by 32 kg, but the calves

consumed 399 kg of feed. Calves from young cows on the same feeding

regime gained 45 kg but ate 429 kg of feed. Stricker et al. (1979)

reported that calves creep-fed from late April to late October consumed

an average of 316 kg of feed; gained 34 kg more than noncreep-fed calves

and required 9.3 kg of creep per kg of gain above noncreep-fed calves.

Preston and Willis (1974) stated that the uneconomical nature of creep

feeding was apparent when one considered that feed conversions during

final fattening in the feedlot (6 to 8:1) were much less than the range

of values (7-19:1) reported for creep feeding.

Almquist (1968) reported creep feeding to be uneconomical with

heifers (whose growth improvement was only 8%) unless pasture savings

were included, since feed costs were higher than the value of the extra

weight gain. The growth response of steers to creep feeding was 24%

and was economical on the basis of feed conversion alone. Almquist con-

cluded that in areas where pasture land has a relatively high value,

creep feeding can be economic if full account is taken of savings in








pasture rental, since creep-fed calves reach a specified weight much

earlier.

Zeranol Implants. One of the most economical management prac-

tices available to cattlemen in the past 15 years has been the use of growth

promoting implants. One of the growth promoting implants available and

approved for use is zeranol (zearalanol). Zeranol is an anabolic agent

approved by the Food and Drug Administration for use in feedlot steers and

also has been cleared for use in suckling calves, weaned calves, growing

beef cattle and feedlot heifers. Zeranol is a derivative of zearalenone, a

metabolic product isolated, crystallized and produced from a selected strain

of fungi identified as Gibberella zeae (Fusarium graminearum) (Shipchandler,

1975).

Numerous research reports have clearly shown the effect of zeranol

on growth rate of calves implanted at about 90 days of age (Perry et al.,

1970; Thomas et al., 1970; Utley and McCormick, 1976). Ralston (1978) con-

ducted a study using 454 Hereford and Holstein x Hereford calves to evalu-

ate the effectiveness of zeranol on 205-day weights of castrated and intact

male calves. Calves implanted with zeranol at birth and again at 90 days

of age produced gains to weaning at 205 days equal to gains by calves im-

planted with diethylstilbestrol. Zeranol implants did not reduce gains of

intact males. Zeranol was equally effective in crossbred and Hereford calves.

It was noted that Holstein-sired calves from low producing dams received

increased growth stimulus similar to straightbred calves from high producing

dams. Ralston theorized that the propensity to gain from hybrid vigor plus

that of the implant might cause added stress to the calf when the milk

supply was limiting; however, no evidence of stress was observed. The author

also noted that zeranol implants reduced (P<.01) testicular weights and

generally reduced masculinity.






7

Corah (1980) reported that two 36 mg implants of zeranol, one

at birth and one at 4 months of age, improved weaning weight by 8.2 kg

over one implant of zeranol given either at birth or 4 months of age.

In a separate study, the author found that calves implanted one or two

times with zeranol gained 10 and 24.5 kg more than non-implanted

calves during a period of 150 days prior to weaning. The author also

observed that implanted calves at weaning were leaner or had less

condition than non-implanted calves.

Davis (1980), using 286 Hereford and Hereford-cross steer and

heifer calves, reported that calves implanted with 36 mg of zeranol at

2 months of age gained 10 kg more in 200 days than did the

non-implanted calves. Giving a second zeranol implant prior to weaning

was not advantageous and response was not influenced by sex. Davis

stated that calves with more rapid gains and heavier weights at the

time of implanting had the greatest response to zeranol implants.

Zeranol did not compensate for poor performance on pasture if daily

gains were below .59 kg. Davis concluded that such factors as milk

production of the dam, pasture quality, supplements and genetic

potential of the calf for growth might influence the response from

zeranol implants.

Gerken et al. (1978) implanted zeranol in suckling heifer

calves at birth and 100 days of age or only at 100 days of age. They

reported that calves implanted twice gained 20 kg more than

non-implanted calves and calves implanted once gained 12.7 kg more

prior to weaning than the calves that did not receive an implant.

Lowman (1980) reported that calves implanted at 2 months of age and

weighing an average of 90 kg gained 6.5 kg more over a 100 day period.






8

Breed of Dam. Preweaning calf performance is highly

correlated with the milk producing ability of the dam. Many studies

have shown differences due to breed of dam for traits such as calf

weaning weight, condition score and frame score. Peacock et al. (1978)

conducted a crossbreeding program using Angus, Brahman and Charolais

cattle in a diallel design. They reported that average weaning weights

were 236, 181 and 177 kg, respectively, for straightbred Charolais,

Brahman and Angus calves, for an overall average of 198 kg. The mean

weight for all crossbred calves was 211 kg. Heterosis levels for

weaning weight for the F1 crosses were 12.2%, 2.1% and 7.1%,

respectively, for reciprocal Angus x Brahman, Angus x Charolais and

Brahman x Charolais combinations. There was no significant difference

due to breed of dam for condition score. The authors concluded that the

comparative performance of reciprocal F groups of calves indicated

that maternal ability of the three breeds of dams ranked in descending

order of Brahman, Charolais and Angus.

Gaines et al. (1966) reported that calves out of Hereford dams

weighed less at weaning and had lower feeder grades than calves out of

Angus or Shorthorn dams. When they made all possible crosses among the

three breeds, calves out of Hereford dams were 23 kg lighter than

calves from either Angus or Shorthorn dams. This difference probably

was due to the superior milk producing ability of the Angus and

-Shorthorn.

Gregory et al. (1978a) observed a breed of dam effect on

weaning weight. The heaviest calves were those out of Brown Swiss dams

and the lightest were those out of Angus dams. Andrade (1980)

conducted a study in Florida using 2-year-old Angus, Brown Swiss and F1








Angus x Brown Swiss reciprocal crossbred heifers. He reported that

calves from Angus heifers had lower (P<.01) 205-day weights than calves

from the Brown Swiss and crossbred heifers. Smith et al. (1976)

suggested that breeds with greater growth potential responded better to

increased milk production of the dam. This was shown by Olson (1980),

using Angus, Brown Swiss and F1Angus x Brown Swiss reciprocal cross

cows. Calves from crossbred and Brown Swiss dams weighed more at

weaning than those from Angus. This reflects not only the milk

producing ability of the Brown Swiss but also the superior genes for

growth that were being contributed by the Brown Swiss and Fldams.

Euclides et al. (1983), using the same breeds of dam, reported that the

average daily milk production for Angus, Brown Swiss and F1Angus x

Brown Swiss reciprocal cross dams was 5.3, 8.3 and 6.8 kg,

respectively. They reported that calves out of Angus dams had higher

(P<.05) weaning condition scores than calves out of Brown Swiss dams

with the calves from crossbred dams being intermediate. The influence

of breed of dam on calf performance has been clearly documented by many

others (Cobb et al., 1964; Lawson and Peters, 1964; Long and Gregory,

1974; Koger et al., 1975). However, no difference in calf weaning

weight due to breed of dam was observed in straightbreds (Angus,

Brahman and Hereford) by Crockett et al. (1978). Gregory et al. (1966)

stated that little influence of breed of dam exists for preweaning calf

traits when British breeds are compared without F1Zebu crosses.

Breed of Sire. Due to the large numbers of combinations of

beef production resources and variations in market demands, one type of

cattle cannot fit all production systems. The availability of a

variety of cattle types offers the possible opportunity of matching








germ plasm resources with production requirements. Tnis opportunity is

somewhat limited because of the lack of direct comparisons of many

breeds (Mason, 1971).

Peacock et al. (1978) reported significant sire effects for

weaning weight and condition score. Charolais-sired calves were

heavier at weaning (223 kg) than Angus and Brahman-sired calves (199

and 198 kg, respectively). The authors also reported that crossbred

calves were heavier than straightbred calves at weaning. Calves sired

by Angus bulls had the highest condition score (9.9) followed by those

sired by Charolais (9.6) and Brahman (9.4) bulls. A significant breed

of sire by breed of dam interaction for condition score was

observed. Angus x Brahman calves had a condition score of 10.2 compared

to 9.8 for Brahman x Angus calves. Data from Pahnish et al. (1969)

supported this finding.

Smith et al. (1976) reported that calves out of Hereford and

Angus cows and sired by Charolais and Simmental bulls had faster

preweaning average daily gains and were heavier at 200 days of age than

those sired by Hereford, Angus, Jersey, South Devon and Limousin

bulls. Limousin and South Devon-sired calves had similar 200-day

weights to Hereford x Angus calves. Jersey-sired calves were

lightest at 200 days of age.

Crockett et al. (1978) conducted a study comparing

straightbred Angus, Brahman and Hereford and all possible

two-breed-of-sire rotational crosses. They reported that calves from

Brahman bulls were heavier at weaning than those from Angus bulls when

both were crossed with Hereford cows. There was no difference in

weaning weight among the straightbred groups.









Gregory et al. (1978b) observed that calves sired by Gelbvieh,

Maine-Anjou, Chianina and Brown Swiss bulls had superior (P<.01)

average daily gains and 200-day weights when compared to Angus x

Hereford and Red Poll-sired calves. Similar results were obtained by

Cundiff (1970), even though the magnitude of the differences was

smaller. Andrade (1980) and Euclides et al. (1983) reported that breed

of sire did not affect calf 205-day weight or weaning condition score,

in a comparison of Angus, Brown Swiss and F Angus x Brown Swiss bulls.

Olson (1980) reported that Brown Swiss-sired calves were heavier at

weaning than calves sired by Angus or F Angus x Brown Swiss bulls when

all possible matings were made. There was no difference in weaning

weight of calves out of Brown Swiss dams and sired by either Angus or

Brown Swiss bulls. Numerous other workers have shown breed of sire

effects for preweaning performance traits (Baker and Black, 1950;

Brown, 1961; Kincaid, 1962; Chapman et al., 1970; Koger et al., 1975).

Sex of Calf. The effect of sex of calf on preweaning

performance traits is extremely important in today's cattle production

scheme. For the cattleman to accurately assess his cow herd in terms

of production, he must rank his cows on a within sex of calf basis for

weaning parameters or he must use additive or multiplicative factors to

adjust to a constant sex basis. Koger et al. (1962 b) stated that sex

effects can be adjusted more accurately by using a multiplicative

factor rather than adding a constant.

Weaning weights are greater for bulls than heifers (Lasley et

al., 1961; Crockett et al., 1978; Nodot, 1980). Marlowe and Gaines

(1958), Brinks et al. (1961) and Pell and Thayne (1978) reported that

weaning weight differences between male and females were reduced when










males were castrated and that steers were intermediate in weight

between bulls and heifers. Brown (1961) stated that males were heavier

than females, but the magnitude of differences varied among breeds and

herds.

Condition score at weaning reflects the thrift and

adaptability of the calf as well as the maternal ability of the dam.

Peacock et al. (1978) reported that heifer calves were fatter at

weaning than steer calves. Preston and Willis (1974) pointed out that

for sex differences to occur the sex hormone influences must be

manifested; therefore, parameters taken before 150 days of age

may show no significant effect for sex of calf.


Factors Affecting Cow Performance


Creep Feed. Advantages other than weight gains and condition

scores of calves have been reported for creep feeding. Black and

Trowbridge (1930) and Jones and Jones (1932) reported that dams of

creep-fed calves out-gained dams of noncreep-fed calves during the

nursing period. Johnson and Fenn (1943), Foster et al. (1946) and

Nelson et al. (1955), however, found essentially no difference in

weight change of cows nursing creep-fed calves.

Burns et al. (1966) conducted a 4-year study with five breed

groups: Angus, Brahman, Brahman x Angus inter se, Hereford and Santa

Gertrudis. Creep feed was available to the calves about 60 days prior

to weaning. They reported that cows with creep-fed calves gained 24 kg

as compared to 23 kg for cows nursing noncreep-fed calves. The average






13

gain by breed group was 38, 32, 20, 19 and 10 kg, respectively, for the

Hereford, Angus, Santa Gertrudis, Brahman x Angus and Brahman cows.

The authors concluded that the breeds assumed to have the poorest

milking ability responded most to creep feeding in terms of cow and

calf weight gains. All responses appeared to be directly related to

creep intake, which probably was a reflection of the milking ability of

the dams.

Stricker et al. (1979) conducted a 4-year grazing study with

Hereford cows and calves on Tall Fescue-Ladino Clover pastures to

determine if calf production could be economically increased by use of

nitrogen fertilization and(or) creep feeding. Pastures were fertilized

with nitrogen at the rates of 0, 112 and 224 kg/ha and half of the

calves received creep feed. Cows nursing creep-fed calves gained 61 kg

during the nursing period compared with 55 kg for cows with

noncreep-fed calves. Bcth groups of cows gained .65 kg per day during

the breeding season; however, 74% of the cows nursing creep-fed calves

became pregnant compared to only 55% for cows with noncreep-fed

calves. There was a significant creep by level of nitrogen

fertilization interaction for cow gain and pregnancy rate. As nitrogen

fertilization was increased, weight gain and pregnancy rate for cows

with noncreep-fed calves decreased, whereas weight gain and pregnancy

rate for cows with creep-fed calves remained fairly constant across all

three nitrogen treatments. The authors also reported that creep feeding

increased pasture carrying capacity by .9 animal unit months per ha

during the summer (lactation) phase.

Breed of Cow. Breed of cow can have a significant effect on

many traits relating to cow performance and total beef production. Rate








of reproduction in beef cattle is the most important trait influencing

the economy of beef production. Many researchers reported that

crossbred females were superior to straightbred cows for reproductive

rate (Koger et al., 1962a; Turner et al., 1968; Peacock et al., 1971;

Peacock and Koger, 1980). These authors compared Brahman, European and

Flreciprocal Brahman x European cows to evaluate the effect of breed

of cow on reproductive performance.

Crockett et al. (1973), from the Everglades area of south

Florida, reported birth rate for Angus cows to be 88.7% as compared to

73.7% for Brahman cows. Contrary to the above results, data from

Peacock et al. (1971) on straight breeding and reciprocal crossing of

Brahman and Shorthorn cattle on various pasture programs indicated

that the average pregnancy rate for Brahman cows was 71% vs 64% for

Shorthorn cows. Research in south central Florida (Peacock et al.,

1977) from straightbreeding and reciprocal crossing of Angus, Brahman

and Charolais cattle showed no differences in pregnancy rate for breed

of dam. The observed pregnancy rates for straightbred dams were 81.5%

vs 77.1% for the crossbred dams.

Weight and condition score changes due to breed of cow have

been reported by Kropp et al. (1973) and Holloway et al. (1975). These

authors used British, Holstein and British x Holstein crossbred cows

under range and drylot conditions. They concluded that weight and

condition score changes before, during and after lactation were

dependent upon the percentage Holstein breeding.

Wyatt et al. (1977b) compared the performance of

winter-calving 4 and 5-year-old Hereford, Holstein and Hereford x

Holstein cows on tall-grass native range and in drylot confinement.










Two levels (moderate and high) of a 30% protein supplement were fed

during the winter to groups of cows within each breed. A higher level

of supplementation (very high) was fed to an additional group of

Holstein cows. Drylot cows were fed cottonseed hulls and alfalfa hay

as roughage sources to simulate seasonal changes in energy content of

the diet of range cows. All cows, both on range and in drylot, except

the moderate and high Holsteins, regained their winter weight losses

during the subsequent lactation period. This suggests that the lower

supplement levels were inadequate for maintenance and productivity of

the larger, heavier milking Holsteins. A significant breed effect on

condition score was apparent both on range and in drylot, with

Holsteins having the lowest and Herefords the highest condition

scores.

Breed of Sire of Calf. Cartwright and Carpenter (1961)

suggested that milk production may be affected not only by the genotype

of the dam but also by the genotype of the calf. These researchers

conducted a study using Hereford and F1 Brahman x Hereford bull and

heifer calves. Nursing habits of calves were monitored for four

consecutive weeks. They observed that crossbred calves nursed more

frequently and for longer periods of time than Hereford calves. In

another phase of the study, weight gains during lactation of the

Hereford dams nursing either Hereford or crossbred calves were

correlated with 180-day weights of their calves. The absolute magnitude

of the correlation coefficient was greater for crossbreds (-.62) than

for Herefords (-.20). These data suggest that breed of sire of calf

may indirectly affect pregnancy rate through changes in cow weight

(Warnick et al., 1967).








Kaiser (1975) mated Guernsey cows to Angus, Friesian and

Brahman bulls and reported no significant change in cow weight at 12

and 26 weeks of lactation due to breed of sire of calf. He also

reported no influence of breed of sire of calf on the interval to first

postpartum estrus. Campos (1982) and J. Restle (unpublished data)

reported no breed of sire of calf effect on cow condition score or

pregnancy rate when comparing Angus, Brown Swiss and F Angus x Brown

Swiss reciprocal crossbred bulls.

Sex of Calf. Conflicting reports have been published as to

the effect of sex of calf on cow performance (milk production and

pregnancy rate). Cartwright and Carpenter (1961) correlated lactation

gains of Hereford cows with 180-day weights of their calves. They

reported that the correlation coefficient was greater for bull calves

(-.35) than for females (-.19). They concluded that bull calves

apparently nursed more vigorously, and that cow weight change possibly

could be influenced by sex of calf. Wettemann et al. (1978) stated that

suckling intensity increased the postpartum anestrous interval in range

Hereford x Holstein cows but did not influence body weight loss during

lactation.

Melton et al. (1967) and Christian et al. (1965) found no

significant difference in dam's milk yield attributable to sex of

calf. However, Melton et al. reported that cows nursing bull calves

gave 53 kg more milk over a 175-day lactation than cows nursing heifer

calves. Pope et al. (1968) reported a significant advantage in milk

yield for cews nursing bulls alves. Rutledge et al. (1971), on the

other hand, observed that Hereford dams nursing heifer calves produced

significantly more milk than those nursing bull calves.








Nodot (1980) reported that Brahman cows nursing male calves

had a longer average calving interval than those nursing heifer calves.

Warnick et al. (1967) found that pregnancy rate was not influenced by

sex of calf in Angus, Brahman, Brangus, Hereford and Santa Gertrudis

cows.


Factors Affecting Female Reproductive Tract Development


Nutritional Regime. A positive relationship exists between

weight and age at which puberty is reached in the bovine female. If

the heifer is to reach puberty at an early age, the reproductive tract

must be fully developed. A major factor affecting the weight of a

heifer at a given age is nutritional level.

Hill et al. (1970), using 18 to 20-month old Angus and

Hereford heifers, studied the effects of undernutrition on ovarian

function and fertility in beef heifers. Undernutrition reduced the

follicle population and caused some unusual ovarian development by days

15 to 17 of the estrous cycle. No major differences in follicle

populations between control and undernourished heifers were detected

after mating or at the time of slaughter, although three undernourished

heifers had negligible numbers of medium size follicles (3-5 mm). The

authors concluded that a decline in follicle number and size after 10

to 12 days feed restriction was followed by a recovery in most heifers

at or soon after the next estrus.

Spitzer et al. (1978) fed two groups of yearling beef heifers

either a ration meeting N.R.C. recommendations for all nutrients or a

restricted diet with only one-third the recommended energy. Heifers on








the low energy diet had smaller ovaries than those on the

non-restricted diet (9,088 vs 14,296 mm3). No significant differences

among heifers on different diets were noted in either number of

follicles or follicular volume.

Cornwell (1981) fed Angus and Brahman heifers either at

maintenance level or above or below maintenance. She reported that

uterine horn diameter and ovarian size and weight were not affected by

level of nutrition. She did report, however, a significant breed by

level of nutrition interaction. The number of follicles for Brahmans

increased with level of nutrition. Angus heifers showed an increase in

number of follicles from the low level to maintenance level of

nutrition, but there was a decrease in follicle number from the

maintenance to the high level of nutrition. The author concluded that

the variation in number and size of follicles and in size and weight of

the ovaries indicated that nutritional level may influence the

production and(or) release of gonadotrophic hormones.

Breed and Age. Foley et al. (1964) examined the effects of

age, breed and live weight on ovarian and luteal tissue weights. They

reported mean ovarian weights of 2.25, 4.78 and 5.61 g, respectively,

for Holstein heifer calves that were 47, 103 and 165 days old. These

authors conducted a separate study using 83 pregnant Ayrshire,

Guernsey, Holstein and Jersey cows and heifers. They observed highly

significant correlations between total ovarian weight and age and live

weight (.70 and .65, respectively). Mean ovarian weights (all ages)

differed only slightly among the four breeds. The authors concluded

that physiological age was more important than chronological age and

weight in determining size and weight of ovaries in prepubertal








heifers. Furthermore, it appeared that age and weight had more affect

than breed on ovarian weights of normal pregnant cattle.

Cornwell (1981) reported that Angus heifers had more follicles

than Brahman heifers at similar ages. Angus heifers tended to have

larger follicles than Brahman heifers; however, Brahman heifers had

larger and heavier (P<.01) varies. The author reported no significant

difference in uterine horn diameter between the two breeds.

Sixty-five Holstein heifers were slaughtered at monthly

intervals in groups of five from birth through 12 months of age to

determine morphological and biochemical changes in their reproductive

organs (Desjardins and Hafs, 1969). Ovarian weight increased 2.7 times

faster than live weight. While no ovarian follicles were visible at

birth, their numbers increased to a maximum at 4 months (16), decreased

to 8 months of age (6) and remained relatively constant thereafter.

Similar data were reported by Erickson (1966). Desjardins and Hafs

(1969) also observed that uterine weight increased proportionately more

than did body weight from 1 to 12 months of age. The authors stated

that rapid increases in the size of ovaries and the number of follicles

suggested that a concurrent increase in ovarian secretary activity

might be expected. They further concluded that the increased rate of

uterine growth relative to body weight prior to puberty may be the

result of ovarian estrogen secretion. This theory was supported by

Parker (1974).


Factors Affecting Adipose Tissue Cellularity


Nutritional Regime. Adipose tissue metabolism, cellularity

and deposition in ruminants have been studied for their intrinsic





20

values and economic implications in animal production. For example,

the grading of carcasses in the U.S.A. is influenced by the amount of

intramuscular adipose tissue (marbling). Within certain limits, the

more marbling the higher the grade. In addition, the adipose tissue

serves a vital role as an energy source in cattle during lactation, yet

it has been implicated in the depression of milk yield in animals fed

high-concentrate diets (Vernon, 1980).

The relative contributions of adipocyte (fat cell) number and

size to the deposition of the excessive mass of adipose tissue

characteristic of obesity have been the subject of research for several

years in man, rats and mice (Hood and Allen, 1973). The problem of

hyperplasia versus hypertrophy of adipose tissue in relation to

subcutaneous, intermuscular and intramuscular fat deposition in beef

cattle is of great practical importance. However, limited and less

extensive information is available for beef cattle where adipose

cellularity has economic as well as scientific interest. Garbutt et

al. (1979) stated that the study of adipose cellularity in young beef

animals has been hampered by the limitations of identifying small

adipocytes as well as difficulty in finding homogeneous fat depots at

an early age. Researchers have questioned the time in an animal's

development when its adipocyte numbers become fixed, and whether

nutritional or environmental conditions near this fixation time can

alter fat cell production. In all species, adipose tissue develops by

hyperplasic growth until one or more specific periods in the animal's

development is reached, after which further increases in fatness result

primarily from cellular hypertrophy.





21

Hood and Allen (1973) showed that during growth of the bovine

animal, an increase in adipose tissue mass was accompanied by cellular

hypertrophy and hyperplasia. Hyperplasia of subcutaneous and perirenal

depots was nearly complete by 8 months of age or shortly thereafter.

However, hyperplasia was still an active process in intramuscular

adipose tissue at 14 months of age. Allen (1976) reported that, in

over-fattened cattle, a second population of small subcutaneous

adipocytes was observed, suggesting that hyperplasia may recommence

after a given period of time on a high energy diet.

Fat accumulation and adipose tissue cellularity changes in the

udder of over-conditioned bovine females have not been studied in

detail. Fat infiltration in the udders of beef and dairy heifers has

long been cited as the culprit of turning potentially good milkers

intc poor milkers by overfeeding during periods of early growth (Herman

and Ragsdale, 1946; Herman et al., 1948; Burt, 1956; Hansson, 1956).

Swanson (1960) conducted a study using twin dairy heifers

under one year of age. One of each pair was fed a normal growing

ration while its twin was fed heavily on concentrates until first

calving to produce rapid growth and fattening. The fattened heifers

weighed 32% more than the control heifers at 2 years of age; however,

the average fat-corrected-milk production by the fattened heifers in

the first lactation was only 84.8% of that of the controls. The

average production difference between the fattened and normal twins

remained through the second lactation. In addition, Swansor noted that

alveolar-secreting tissue had not filled the spaces in the framework of

the mammary gland of the fattened heifers. This may have been due to

excess fat within the mammary gland prior to the first lactation. Most









if not all of the excess fat was probably eliminated by the time the

second lactation had been completed, thereby leaving large open spaces

in the mammary gland void of secretary tissue.

Creep feeding beef heifer calves may result in over

conditioning. This practice has economic implications that may be

beneficial when selling feeder calves; however, many producers have

failed to consider the possible detrimental results of creep feeding

replacement heifers.

Holloway and Totusek (1973a,b) conducted an intensive study in

Oklahoma involving 206 Angus and Hereford heifer calves. Creep-fed

heifers consumed an average of 195 kg of creep feed per head, had no

permanent advantage in size, tended to produce less milk and lighter

calves at weaning, and had no apparent advantage in total productivity

over normal weaned noncreep-fed heifers. Similar results were reported

by Martin et al. (1970), Mangus and Brinks (1971), Kress and Burfening

(1972) and Hixon et al. (1982).

Martin et al. (1981) stated that what appears to be a simple

management practice to increase the weaning weight of calves turns out

to be a very complex problem when the future productivity of the heifer

calf is considered. They concluded that creep feeding can produce a

permanent detrimental effect on cow productivity, since fat deposition

in the udder during the preweaning period may hinder secretary tissue

development.

Breed. Although breed has been used to provide an explanation

for differences in adipocyte size and number found in different

studies, there have been few if any studies specifically designed to

investigate variation due to breed. Yet such variations clearly must









occur, as shown by differences between beef and dairy cattle. Beef

cattle tend to mature and fatten at an earlier age than dairy cattle,

which tend to have more internal fat and less subcutaneous fat than

beef cattle (Callow, 1961).

Hood and Allen (1973) compared Holstein, Hereford x Angus and

Hereford steers in a study on the cellularity of bovine adipose tissue.

Perirenal and subcutaneous adipose tissues in Hereford x Angus steers

contained larger (P<.05) cells than the same tissues from Holstein

steers. Hereford steers had significantly smaller adipocytes than

either Holstein or Hereford x Angus steers; however, they were fed a

totally different diet (low energy roughage diet vs a high energy corn

diet). The number of adipocytes in subcutaneous fat of Holstein steers

was less (P<.05) than that in Hereford x Angus steers. Hood and Allen

(1975) reported similar findings from an updated study of the same

breed types.


Factors Affecting Carcass Characteristics and Composition


Nutritional Regime. The effect of plane of nutrition on

carcass traits has been well documented (Wanderstock and Miller, 1948;

Brown, 1954; Klosterman et al., 1965; Moody, 1976). In general,

increasing the length of feeding and(or) the nutritional plane appears

to enhance carcass quality traits but lowers carcass cutability.

Grain-fed (high concentrate) beef generally has physical and sensory

quality traits superior to those of forage-fed beef (Meyer et al.,

1960; Chapman et al., 1961; Kropf et al., 1975; Bowling et al., 1977;
Harrison et al., 1978; Schroeder et al., 1980).









Rouquette et al. (1983) investigated the effects of creep

feed, stocking rate and electrical stimulation on carcass traits of

weanling Simmental-sired calves out of F Brahman x Hereford dams.

They reported that creep feeding did not produce any significant

improvement in physical or sensory traits of the carcass. However,

there was evidence that electrical stimulation of carcasses from

creep-fed calves had a greater effect on carcass characteristics than

on those carcasses from noncreep-fed calves. Rib steaks from

electrically-stimulated carcasses of creep-fed calves had higher (P<

.05) tenderness values than steaks from nonelectrically stimulated

carcasses.

Corah and Bishop (1975) examined the effects of creep feeding

oats on the carcass characteristics of weanling heifers and of steers

slaughtered after a period in the feedlot. Carcasses from creep-fed

heifers had significantly heavier hot carcass weights, higher dressing

percentages, larger ribeye areas and more fat cover than carcasses

from noncreep-fed heifers. The differences in carcass traits at

weaning between creep-fed and noncreep-fed heifers were not apparent in

the carcasses of steers that had been fattened in the feedlot. Similar

results were observed by Greathouse and Henderson (1968), Scarth et al.

(1968) and Martin et al. (1980).

The influence of plane of nutrition on relative tissue growth

is best illustrated from the results of Guenther et al. (1965) and from

Waldman et al. (1971). Both groups of researchers fed high

and moderate levels of nutrition. Guenther et al. (1965) fed half-sib

Hereford steers and estimated body composition at the start and as the

experiment progressed. Waldman et al. (1971) fed Holstein steers and








estimated composition using rib-cut dissection at slaughter. Both

groups of researchers concluded that steers on the high plane of

nutrition fattened more rapidly relative to muscle and bone growth than

those on the moderate plane. In addition, they concluded that body

composition in terms of fat, lean and bone tissue could be altered by

the plane of nutrition.

Corah and Bishop (1975) reported that carcasses from weanling

heifers fed creep feed approximately 160 days prior to slaughter had

less (P<.01) water and more (P<.01) fat than carcasses from

noncreep-fed heifers. There was no difference in percent protein.

Carcasses from noncreep-fed heifers had a higher percentage of bone

than those from creep-fed heifers. Creep feeding did not significantly

affect percent water, fat and protein in the carcasses of steer

comtemporaries slaughtered after a period in the feedlot. The apparent

difference in percent bone remained through the feedlot phase.

Zeranol Implants. Gregory and Ford (1983) evaluated the

effect of zeranol on the carcass traits of late maturing, intact bovine

males. They concluded that zeranol treatment effects on carcass traits

were of little consequence other than through zeranol treatment effects

on weight. Similar data have been reported for ram, ewe and wether

lambs (Wiggins et al., 1976) and steers (Borger et al., 1973).

Sharp and Dyer (1971) conducted a study to determine the

effects of zeranol on the carcass composition of growing ruminants.

Using heifers, steers and wether lambs in separate studies, they

observed no significant effect of zeranol on carcass quality traits.

However, in one study the percentages of protein and water in the








carcasses of steers were significantly increased with zeranol implants,

while the percentage of fat was reduced.

Breed of Dam. Characterization of breeds of cattle for

carcass characteristics and composition is of utmost importance with

today's widespread use of crossbreeding. Knowing the carcass

attributes of the breed of dam and breed of sire may help the producer

use available genetic material wisely to increase production

efficiency.

Peacock et al. (1979) compared the Angus, Brahman and

Charolais breeds in a 3 x 3 diallel mating scheme to evaluate breed and

heterosis effects on carcass characteristics of steers. They reported

that maternal effects for Angus dams were positive for quality grade

but negative for estimated retail yield and slightly negative for

carcass weight. Effects for Brahman dams were positive for estimated

retail yield but negative for carcass weight and quality grade. The

effects for Charolais dams were positive for carcass weight,

intermediate for quality grade and negative for estimated retail

yield. Peacock et al. (1982) observed that additive maternal effects

for Angus dams were nonsignificant for all measured carcass traits.

Effects for Brahman dams were significantly positive for ribeye

area/100 kg carcass weight and negative for fat over the ribeye. The

additive maternal effects for Charolais dams were significantly

positive for fat over the ribeye and negative for ribeye area/100 kg

carcass weight. Significant maternal heterosis effects were observed

only for chilled weight and fat over the ribeye for first cross Angus x

Brahman dams and for chilled carcass weight in Angus x Charolais dams.








Hargrove et al. (1983) conducted a study to evaluate the

carcass characteristics of Angus, Brown Swiss, F, F2 and backcross

steers. They reported that steers out of Brown Swiss dams had heavier

hot carcass weights and larger ribeye areas than steers out of Angus

dams. Steers produced by F1 dams were intermediate for hot carcass

weight and ribeye area. There was a tendency for carcasses from steers

out of Brown Swiss dams to have lower quality grades than those out of

either Angus or F dams. The superiority of the Angus breed for

carcass quality grade over other breeds has been observed by other

researchers (Hedrick et al., 1975; Luckett et al., 1975; Young et al.,

1978; Koch et al., 1982).

Several studies (Cole et al., 1964; Solomon et al., 1981;

Adams et al., 1982) have confirmed that distinct differences in carcass

compositional components exist between breeds of cattle. The preceding

authors reported that carcasses from Angus cattle were fatter and had

less lean and bone on a percentage basis than those from Brahman

cattle. Cole et al. (1964) also compared dairy type cattle to British

and Zebu cattle and reported that carcasses from Holstein steers were

very similar in composition to those from Brahman steers. However,

data used in these particular studies were collected from steers and

heifers which were slaughtered at a constant end point of live weight,

days on feed or age. LeVan et al. (1979) reported that breed had no

marked effect on relative distribution of carcass retail lean, fat or

bone when straightbred Angus and Charolais steers were compared at

similar percentages of the corresponding breed average mature weight.

Solomon (1983) compared carcass components of Angus and Brahman bulls

slaughtered at similar percentages of mature cow weight. Solomon








reported no major breed differences in predicted carcass lean, fat and

bone based on the 9-10-11 rib cut. He concluded, based on overall

carcass composition that the bulls were slaughtered at similar points

in their respective growth curves and were compared on an equivalent

basis.

Breed of Sire. Peacock et al. (1979), using Angus, Brahman,

Charolais and crossbred steers, reported that the direct effects of

Angus breeding from either the sire or dam were positive for quality

grade, intermediate for retail yield and negative for carcass weight.

Breed effects for the Brahman were slightly positive for carcass

weight, with negative effects for retail yield and carcass quality.

The direct effects of Charolais breeding were positive for carcass

weight and retail yield, but negative for quality grade.

Crockett et al. (1979) found that carcasses from steers with

Brahman, Beefmaster or Brangus sires had higher marbling scores, more

fat over the ribeye and smaller ribeye areas than those with Limousin,

Maine-Anjou and Simmental sires. Other studies indicated that Brahman-

sired cattle ranked low in breed group comparisons for marbling score

and quality grade (Damon et al., 1960; Luckett et al., 1975; Young et

al., 1978).

Koch et al., (1982) mated Angus and Hereford cows to Angus,

Hereford, Tarentaise, Pinzgauer, Brahman and Sahiwal bulls. They

reported that Brahman-sired steers had the heaviest carcass weights and

Sahiwal-sired steers the lowest carcass weights at a constant age.

Dressing percentages at a common carcass weight were lower for

Pinzgauer crosses (62.0%) and higher for Brahman and Sahiwal crosses

(63.8 and 64.0%) than for Hereford x Angus (63.2%) or Tarentaise








crosses (63.2%). Several reports have attributed advantages in dressing

percentage for Brahman cattle to lower gastrointestinal tract weights

and contents than other cattle breeds (Carpenter et al., 1961; Ramsey

et al., 1965; Tucker, 1981). Koch et al. (1982) reported that

differences in carcass composition were greatest at a common weight

because that contrast emphasized differences in rates of maturity.

They observed that Brahman crosses had a significantly higher retail

product percentage (71.0%) than other breed groups, except for

Tarentaise crosses (70.2%). Hereford x Angus crosses had the lowest

retail product percentage (66.9%). They found, in addition, that at a

common fat thickness Brahman and Sahiwal crosses had less fat trim than

Tarentaise and Pinzgauer crosses because of significantly lower kidney

and pelvic fat percentages. Other studies reporting breed of sire

effects of carcass traits and tissue components of cattle slaughtered

at some common end point include Koch et al. (1976) and Winks et al.

(1979).













STUDY I
CALF AND COW PERFORMANCE

Introduction

Gross income in the cow-calf phase of the beef industry is

highly dependent on the production of heavy weight calves at weaning.

Creep feeding and implanting with growth stimulants are two means of

increasing preweaning gains (Cundiff et al., 1966; Scarth et al., 1968;

Utley and McCormick, 1976; Stricker et al., 1979; Corah, 1980; Lowman,

1980; Ochoa et al., 1981). Little is known about the combined effects

of growth stimulants with creep feeding and variations in the milk

producing abilities of the dam on calf performance.

Advantages other than weight gain of calves have been reported

for creep feeding. These included increased weight, condition and

pregnancy rate of the dam (Jones and Jones, 1932; Stricker et al.,

1979). Creep feeding, however, has been implicated in the possible

altering of the maternal rank (weaning weight of calf) of cows within a

herd (Burns et al., 1966; Ochoa et al., 1981). Furthermore, it has

been suggested that creep feed is utilized best by calves suckling dams

with limited milk production (Christian et al., 1965).

The objective of this study was to evaluate the effects of and

interacticns among creep feeding, zeranol implants and breed type on

calf and cow performance.

Experimental Procedure

This project was conducted at the Beef Research Unit,

Gainesville, from April 1 through September 1, 1981, and 1982. The








research unit is located in north central Florida (latitude 29" 40'N)

and the climate is considered semitropical. Average maximum and

minimum temperatures for the 1981 and 1982 experimental periods

respectively were 32.8 and 19.3C and 31.3 and 19.1C. Monthly rainfall

averages during the experimental periods (April-September) in 1981 and

1982 were 80.9 and 170.3 mm, respectively. Soils in the research unit

vary from moderately well drained to very poorly drained. The major

soil type is Leon fine sand.

Two hundred calves, sired by Brahman and Romana Red bulls and

out of Angus and F1 Angus x Brown Swiss reciprocal crossbred dams

(table 1), were stratified by breed type and sex to the following creep

treatments: (1) no creep feed (NC); (2) long-term creep (LC),

creep-fed from an average age of 56 d to weaning (210 d ); and (3)

short-term creep (SC), creep-fed from an average age of 146 d to

weaning.

A commercial creep feed with 14% crude protein, not more than

8% crude fiber, not less than 2.5% crude fat and 9000 U.S.P. units of

vitamin A per .45 kg was fed. Creep feeders were located near shade

and water. Alternate calves within sex, breed type and creep treatment

subgroups were implanted with 36 mg of zeranol at about 56 d of age

and reimplanted 90d later.

A 60-d breeding season from about April 1 to June 1 was used.

Calves were identified and weighed and bull calves castrated within 24

of birth. Calves were weaned on September 1, when their average age

was 210-d, and weaning weights of all calves were adjusted to this age.

Cows were palpated for pregnancy at weaning time.































TABLE 1. NUMBER OF CALVES BY BREED OF
SIRE, BREED OF DAM AND SEX OF CALF

Breed of dam

Breed Angus F1 Angus x Brown Swiss
of
sire Steer Heifer Steer Heifer

Brahman 18 30 26 37
Romana Red 8 21 30 30









Cows and calves were maintained in pastures consisting

primarily of Pensacola bahiagrass (Paspalum notatum Flugge) and white

clover (Trifolium repens L.). Brood cows were wintered on corn silage

(IFN 3-20-506) plus molasses (IFN 4-04-696) and protein supplement to

meet NRC requirements from early December until about March 15, when an

adequate quantity of clover was available in the pastures.

PastLres were monitored for both quantity and quality of

available forage. Quantity of available forage was estimated using a

simple-disk meter (.5m2 ) as described by Santillan et al. (1979).

Hand-plucked samples of grass and clover were obtained from each

pasture once a month from April through August. The ratio of grass to

clover was estimated visually each month. Grass and clover samples

were analyzed (AOAC, 1980) for crude protein using a Technicon

Autoanalyzer II and in vitro organic matter digestibility (IVOMD) was

determined using the procedure described by Moore and Mott (1974). The

estimated ratio of grass to clover was combined with the crude protein

and IVOMD determinations from the samples to obtain mean pasture crude

protein and IVOMD percentages.

Cow-calf pairs within the LC and SC creep treatments were

randomized to one of two replicates (pastures). Cow-calf pairs in the

NC groups were considered one replicate and placed in a single pasture.

The same four pastures were used both years for the LC and SC creep

groups; however, the two pastures used for the LC creep treatment in

1981 were used for the SC creep treatment in 1982. A different pasture

was used for the NC group each year. Stocking rates across both years

varied from 1.17 to 1.69 cow-calf pairs per ha.

Data were analyzed by least squares, fixed model procedures
analyses of calf traits included the fixed main effects of creep,








analyses of calf traits included the fixed main effects of creep,

zeranol, breed of sire, breed of dam, sex, year and pasture. Fixed

main effects used in the model for cow traits included creep, zeranol,

breed of cow, breed of sire of calf, sex of calf, year and pasture.

Age of calf at the beginning of the trial was used as a covariate

(linear, quadratic) in final calf and cow models, except for 146 and

210 d weight which were age adjusted variables. Dam age (linear,

quadratic) was included in preliminary analyses; however, it was

removed from the calf model due to lack of significance. All cows in

this study were 4 yr of age and older, with the exception of six

which were 3 yr of age. All two and three-factor interactions were

included in the preliminary analyses. Only significant interactions

remained in the final models. Linear contrasts of the least-squares

means for creep treatment were computed for calf and cow traits

affected (P<.10) by creep treatment. Dry matter (kg) available per

cow-calf pair, mean pasture crude protein percentage and mean pasture

IVOMD percentage were used as covariates in independent analyses in an

attempt to account for pasture differences. However, pasture nested

within creep treatment and year was used in the final models.

Cow response traits for the calf model were 146 and 210-d

weights and conditions scores, preweaning average daily gain, frame

score and heifer udder and teat scores. Cow response traits included

cow weight change -from the beginning (which was also the start of

long-term creep feeding) to the end of the breeding season, from the

end of the breeding season to July 1, and from July 1 (start of

short-term creep feeding) to weaning. Other dependent variables

included condition scores at the beginning and end of the breeding









season and at weaning and pregnancy rate. A range of 1 to 17 was used

for condition scores of both cows and calves (Andrade, 1980). Frame

scores were from 1 to 5 (Wakeman, 1978). Udder and teat size were

subjectively scored, where 1 = below average, 2 = average, and 3 =

above average.

Results and Discussion


Calf Performance


Weights and Weight Gains. Least-squares means for calf

preweaning performance traits are shown in table 2. Mean 210-d weight

was 252 kg. Long-term (LC) and short-term (SC) creep-fed calves were,

respectively, 33 and 26 kg heavier (P<.001) at 210 d than noncreep-fed

calves (NC). The LC calves were 7 kg heavier (P<.08) than SC calves

at 210 d. The LC calves were heavier (P<.001) at 146 d and had a

higher (P<.001) average daily gain from 56 to 146 d than SC and NC

calves. Both SC and NC calves were considered to be noncreep-fed at

this time, since the SC calves did not receive creep feed until they

averaged 146 d of age. The SC and NC calves had comparable 146-d

weights (177 and 174 kg) and average daily gains from 56 to 146 d of

age (1.02 and 1.00 kg). The higher (P<.001) average daily gain of the

LC calves from 118 to 146 d of age accounted for their heavier 146 and

210-d weights and greater average daily gain from 56 to 146 d. The LC

calves were consuming an average of about .7 kg of creep feed/d at

118 d of age and about 1.15 kg/d by .46 d of age (figure 1). There was

no difference (P>.10) among creep treatments for average daily gain

from 56 to 118 d of age. This is of interest since most purebred




















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DAYS OF AGE


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cattle producers who creep feed begin when their calves are about 2 mo

of age. Prior to the time calves are about 4 mo of age, however,

the producers may be obtaining very little benefit in terms of calf

weight gain. The LC and SC calves had higher (P<. 01) average daily

gains from 146 to 210 d of age (1.20 and 1.25 kg, respectively) and

from 56 to 210 d of age (1.14 and 1.11 kg) t an did NC calves (.90 and

.96 kg). The SC calves gained faster (P<.08) from 146 to 210 d of age

than did the LC calves. This may have been a compensatory response,

since the LC calves had higher average daily gains from 118 to 146 d of

age. Similar advantages for creep feeding calves from about 60 d of age

to weaning were reported by Kuhlman et al. (1961), Stricker et al.

(1979) and Martin et al. (1981). Burns et al. (1966) reported a 14.kg

advantage due to creep feeding calves for 60 d prior to weaning at 215

d of age. The 14 kg advantage observed by Burns et al. is about half

as much as was obtained in this study for an equivalent time period.

Average weight gains of LC and SC calves above the gains of

the NC calves, creep feed intakes and creep feed efficiencies are

presented in table 3. The LC calves gained 28 kg more weight from 56

to 210 d of age than did the NC calves. They consumed an average of

about 187 kg of creep feed during this time and required 6.7 kg of

creep feed/kg live weight gain above the NC calves. The SC calves

gained 22 kg more than the NC calves and had a creep efficiency of 5.3.

Efficiency of creep utilization for gain did not differ (P<.10) between

LC and SC calves.

Calves implanted with zeranol were 9 kg heavier (P<.001) at
146 d of age and 16 kg heavier (P<.001) at 210 d than non-implanted

calves (table 2). Zeranol implanted calves gained .08 kg/d more (P<






























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.001) from the first implant date to the date of the second implant (56

to 146 d of age) than did the non-implanted calves and .12 kg/d more (P<

.001) from the second implant to weaning. These findings are in

agreement with Corah (1980), who reported an increase in weight gain of

about 10 and 24 kg, respectively, for one and two implants preweaning.

Zeranol implanted LC and SC calves gained .18 and .14 kg/d

more (P<.001), respectively, from 146 to 210 d of age than did the

non-implanted calves on the same creep treatments, whereas implanted

NC calves only gained .06 kg more (P<.10) than non-implanted calves.

The additional growth response obtained from zeranol was expressed

to a greater degree when nutrition was increased, a finding similar to

that reported by Davis (1980).

Calves produced by F1 Angus x BroWn Swiss reciprocal crossbred

dams (F1) were heavier (P<.001) at 146 and 210 d of age and had higher

average daily gains (P<.01) during all periods except from 146 to 210 d

of age than calves from Angus cows (table 2). Similar advantages in

weaning weight of calves produced by Angus x Brown Swiss crossbred and

straightbred Angus cows were reported by Andrade (1980) and Olson

(1980). There was no significant creep treatment by breed of dam

interaction for any calf trait, which would suggest that there was an

additive effect of creep feed and milk consumption on preweaning weight

gain. LC calves nursing F1 dams gained an average of .18 kg/d more

from 56 to 210 d of age than NC calves nursing F1 dams, compared to a

.17 kg/d higher average daily gain for LC than for NC calves nursing

Angus dams. Comparable differences in average daily gains between SC

and NC calves from 146 to 210 d of age, the period in which the SC

calves received creep feed, were .32 kg/d for SC calves nursing F1 dams.









The F1 dams produced about 1.5 kg/d more milk than did the

Angus dams (Euclides et al., 1983). Ereed of dam was confounded in

this study with breed composition of calf. All calves nursing F, dams

were 1/4 Brown Swiss 1/4 Angus and 1/2 either Brahman or Romana Red

breeding. Calves nursing Angus dams were 1/2 Angus and 1/2 either

Brahman or Romana Red. Calves nursing the F1 dams had more growth

potential than those nursing Angus dams (Gregory et al., 1978b;

Andrade, 1980; Euclides et al., 1983). The additive response for

growth rate obtained from creep feed and milk consumption was partially

confounded in this study by the fact that calves with greater growth

potential were nursing the dams with higher milk production. These

data do not concur with the findings of Christian et al. (1965); Burns

et al. (1966) and Ochoa et al. (1981), who suggested that creep feeding

tends to mask the milk production differences among ccws, anc that

calves nursing poorer milking dams may compensate by eating more creep

feed than those nursing high producing dams. Wyatt et al. (1977a) also

stated that as milk intake of the calf increases the non-milk inputs,

forage and creep feed, are reduced.

Zeranol implants increased (P<.03) the rate of gain from 146
to 210 d of age more in calves nursing Angus dams than in those nursing

F1 dams (table 4). Non-implanted calves nursing F1 dams gained an

average of 1.10 kg/d from 146 to 210 d of age as compared to an average
daily gain of 1.02 kg/d for non-implanted calves nursing

Angus cows. Zeranol implanted calves nursing Angus dams,

however, gained slightly faster than implanted calves nursing F1 dams

(1.19 and 1.17 kg/d, respectively). The interaction of creep, zeranol

and breed of dam affected (P<.03) average daily gain from 146 to 210 d






42

of age. The greatest response to zeranol for average daily gain from

146 to 210 d of age was shown by SC calves nursing Angus dams and by LC

calves nursing Angus and F1 dams (table 4).

Brahman-sired calves were heavier (P<.001) at 146 and 210 d of

age and had higher (P<.02) average daily gains from 56 to 210 d of age

than calves sired by Romana Red bulls.

Steer calves were heavier (P<.001) at 146 and 210 d of age and

gained faster in all periods (P<.001) than heifer calves (table 2).

The zeranol effect on 210-d weight was greater (P<.09) in steers than

heifers. Implanted steers were 22 kg heavier than non-implanted

steers, whereas the 210-d weight of implanted heifers was 11 kg

heavier than that of those not implanted with zeranol. Davis (1980),

on the other hand, reported that there was no significant zeranol

treatment by sex of calf interaction effect on calf weaning weight. The

breed of dam by sex of calf interaction affected 146-d (F<.05) and

210-d (P<.06) weights. Steer calves nursing F dams were 25 and 33 kg

heavier at 146 and 210 d of age, respectively, than heifers nursing F1

dams. Comparative advantages for steers nursing Angus dams over

heifers nursing dams of the same breed were 14 and 20 kg.

Pasture, nested within creep treatment and year, affected (P<

.003) average daily gain from 56 to 118, 118 to 146, and 146 to 210 d

of age. Pastures were monitored each month for quality and quantity of

available forage. Available dry matter (kg) per cow-calf pair, mean

pasture crude protein percentage and mean pasture IVOMD percentage were

used in independent analyses in an attempt to account for variability

due to effect of pasture. However, due to reduced R2 values and lack

of agreement between actual means and least-squares means, these




























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44
covariables were dropped from the final analyses in favor of the total

effect of pasture. Values for available dry matter per cow-calf pair,

mean pasture crude protein percentage and mean pasture IVOMD percentage

are presented in tables 5, 6 and 7 respectively. Large variations in

available dry matter per cow-calf pair, mean pasture crude protein and

mean pasture IVOMD existed across months and years in this study. The

data presented in table 5 would indicate that quantity of available

forage was not limited in any pasture during this study. The low crude

protein and IVOMD values in July and August of 1982 (tables 6 and 7)

would suggest that quality of forage might have been limited for

optimal calf performance during this period.

Frame and Condition Scores. Least-squares means for frame and

condition scores are presented in table 2. Creep feeding did not

affect (P<.20) frame score at weaning. Stricker et al. (1979), on the

other hand, reported that creep feeding resulted in an increased frame

size. The LC calves were fatter (P<.001) at 146 d or age than calves

not receiving creep feed, and LC and SC calves were fatter (P<.001)

than NC calves at 210 d. There was no difference (P<.16) in condition

at 210 d between LC and SC calves.

Zeranol implants did not affect (P>.20) frame score at weaning

or condition score at either 146 or 210 d of age. These results are in

agreement with those of Davis (1980) and Gerken et al. (1978). Corah

(1980), however, reported that calves implanted at birth with 36 mg of

zeranol and again at 4 mo of age had less condition at weaning than

non-implanted calves.

Calves produced by F1 dams were larger framed (P<.001) than

those out of Angus dams, but had lower condition scores at 210 d (P<



























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.03). The F, dams produced more milk as cited earlier, but were

nursing calves with one-fourth Brown Swiss breeding. These calves were

larger framed and later maturing, thus, did not fatten as early as the

one-half Angus calves nursing Angus dams. Brahman-sired calves had

larger frames (P<.001) than those sired by Romana Red bulls.

Steer calves had higher frame scores (P<.001) and lower

condition scores at 146 (P<.08) and 210 d (P<.001) than heifer calves.

Breed of dam by sex of calf interaction affected (P<.06) frame score.

Steers and heifers nursing F1 dams had larger frames ( 3.5 and 3.0,

respectively) than those nursing Angus dams (2.8 and 2.6). There was a

greater difference between the two steer groups than between the two

groups of heifers.

Udder and Teat Scores. Udder score at weaning, which was a
subjective measure of udder size, was affected by creep treatment (P<

.02) and breed of sire (P< .002) The LC heifers had a higher average

udder score (2.0) than the SC and NC heifers (1.7 and 1.8,

respectively). The higher udder score of the LC heifers might reflect

increased fat deposition in the udder. Hansson (1956), Swanson (1960)

and Martin et al. (1981) have suggested that fat infiltration in the

udder, as a result of overfeeding heifers during periods of early

growth, may negatively affect future maternal performance.

Brahman-sired heifers had a higher (P<.002) average udder
score than those sired by Romana Red bulls. This may be due in part to

more fat being deposited in the udder of the Brahman-sired heifers and

(or) excessive amounts of skin which is characteristic of the Brahman

breed, but not of the Romana Red.









Teat size was affected (P<.001) only by zeranol treatment.

Average teat size was greater in implanted than non-implanted heifers,

a finding similar to that of Lowman (1980).

Cow Performance

Least-squares means for cow weight change, condition score and

pregnancy rate are presented in table 8. Cow condition score at the

beginning of the breeding season did not differ (P>.57) among the three

assigned calf creep-treatment groups. However, cows with LC calves

gained more (P<.09) weight during the 60-d breeding season and had a

higher (P<.02) average condition score at the end of the breeding

season than those nursing NC calves. Other authors have suggested that

increasing cow weight gain and condition during the breeding season, by

creep feeding the calves, may result in a subsequent increase in

pregnancy rate (Jones and Jones, 1932; Stricker et al., 1979). In this

study, however, pregnancy rate was not affected (P>.46) by creep

treatment of calf (89.5% for the non-creep group vs 92.7% for the

creep-fed group) even though a difference did exist in cow weight

change and condition sccre.

Creep treatment of the calf did not affect (P>.11) cow weight

gain from the end of the breeding season to July 1, the start of

short-term creep treatment, but cows nursing SC and LC calves gained

more (P<.001) weight from July 1 till the calves were weaned on

September 1. There was no difference (P> .28) in cow condition score

at weaning due to creep treatment of calf.

Cow weight gain, condition score and pregnancy rate were not
affected by zeranol implants in their calves. In this study, zeranol

implanted calves gained more rapidly throughout the nursing period than

























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did non-implanted calves. Since zeranol implants in calves had no

affect on cow weight gain, condition score or pregnancy rate, the

increased weight gain of the calf apparently did not place an added

stress on the cow.

Angus cows gained less (P<.02) weight from the beginning of

the breeding season to July 1 but had higher (P<.001) condition scores

than did F1 cows. The F1 cows had a higher (P<.07) pregnancy rate than

Angus cows (96.6 vs 86.8%). Previous studies with the same two breed

groups have reported no difference in the pregnancy rates (Olson, 1980;

Euclides et al., 1983).

Cows with Brahman-sired calves gained more (P<.09) weight

during the breeding season than those with Romana Red-sired calves.

There was no difference, however, in weight gain during the breeding

season of calves sired by the two breeds of bulls (table 2). Breed of

sire of calf did not affect (P>.19) cow condition score or pregnancy

rate. Sex of calf did not affect (P>.55) cow weight gain or condition

score; however, cows with heifer calves had a higher (P<.10) pregnancy

rate than those with bull calves.

It can be concluded that calves receive very little benefit

from creep feed prior to 120 d of age. Creep feeding calves from about

5 mo of age until weaning at 7 mo results in more efficient utilization

of creep feed and almost as much increase in weight gain as creep

feeding from 2 mo of age. The effect of creep feed intake on

preweaning weight gain may be additive with milk intake in calves with

above average growth potential. Increased levels of nutrition, from

creep feed and milk, may result in increased growth response to

zeranol. Pregnancy rate in the cow herd is not increased by creep





52
feeding the calves, when cows have adequate nutrition during the

breeding season.

Summary
A 2-yr study was conducted to evaluate the effects of creep

feeding, preweaning zeranol implants and breed type on calf and cow

performance. Two hundred calves sired by Brahman and Romana Red bulls

and out of Angus and F1 Angus x Brown Swiss reciprocal crossbred (F1 )

dams were stratified by breed type and sex to three creep treatments:

(1) no creep feed (NC); (2) long-term creep (LC), creep-fed from 56 d

of age to weaning (210 d); and (3) short-term creep (SC), creep-fed

from 146 d of age to weaning. Alternate calves within sex, breed type

and creep treatment were implanted with 36 mg of zeranol at about 56 d

of age and reimplanted 90 d later. The LC and SC calves had higher (P<

.001) 210 d weights than NC calves (264 and 257 vs 231 kg

respectively). The LC calves had higher (P<.001) 146 d weights than NC

calves. Frame score was not affected (P>.20) by creep treatment. The

LC calves had higher (P<.001) average daily gains from 118 to 210 d of

age and superior 146 and 210-d condition scores than did NC calves.

Cows with creep-fed calves gained more weight during the breeding

season than cows with noncreep-fed calves. Pregnancy rate was not

affected (P>.46) by creep treatment. Zeranol implants increased (P<

.01) both 146 and 210-d weights (184 vs 175 kg and 259 vs 243 kg) and

average daily gains during all periods to weaning. Cow weight gain,

condition score and pregnancy rate were not affected (P>.14) by zeranol

treatment of calves. Brahman-sired calves had higher (P<.005) 146 and

210-d weights and frame scores than Romana Red-sired calves. Calves

out of Angus dams had lower (P<.001) 146 and 210-d weights, frame





53

scores and average daily gains from 56 to 146 and 210 days of age, but

higher ( P<.03) 210-d condition scores than calves out of F1 dams. The
F1 cows gained more weight (P<.007) during the breeding season, had a
lower (P<.001) condition score and a higher pregnancy rate (96.5 vs
86.8%) than the Angus cows. Cows with heifer calves had a higher (P<

.10) pregnancy rate than those with steer calves.













STUDY II
WEANLING HEIFER DEVELOPMENT AND COMPOSITION.

Introduction

The effects of creep feeding and preweaning growth stimulants

on future reproductive performance and maternal ability of replacement

heifers are of concern to many cattlemen. Most commercial cattlemen

sell some of their weaned heifers as feeder-stocker calves. By using

creep feed and growth stimulants, cattlemen can sell these heifers at

heavier weignts and for more total dollars.

Excessive conditioning or fattening of suckling heifers may

influence subsequent development of desired maternal traits (Holloway

and Totusek, 1973b). A detrimental effect of above average maternal

environment during the early life of heifer calves on their subsequent

producing ability has been shown by Mangus and Brinks (1971), Kress and

Burfening (1972) and Beltran (1978). Swanson (1960) and Holtz et al.

(1961) suggested that over-conditioned dairy heifers deposited excess

fat in their mammary system, which impaired future milk production

potential.

The effects of growth stimulants on the future reproductive

performance of heifers are controversial. An important issue from the

producer's point of view is not whether creep feeding and growth

stimulants improve weaning weight, but how these practices affect

future productive potential of replacement heifers.








The purpose of this study was to evaluate the effects of creep

feeding, preweaning zeranol implants and breed type on reproductive

tract development, fat deposition in the udder, and body composition of

weanling heifers.

Experimental Procedure

The preweaning creep feeding and zeranol treatments and breed

types compared in this study were described in study I. Calf and Cow

Performance. Twenty-four weanling heifers were used in this study.

These heifers were selected so that one heifer was chosen from each

creep treatment, zeranol treatment, breed of sire, and breed of dam

subgroup.

Heifers were slaughtered one day following weaning. The

gastrointestinal tract from each heifer was cleaned of digesta for

determination of empty body weight. Carcasses were quality and yield

graded after e 24-h chill at 1 to 2"C. The 9-10-11 rib section from

the right side of each carcass was removed and physically separated

into fat, lean and bone tc estimate separable carcass components, as

outlined by the procedure of Hankins and Howe (1946). The soft tissue

components (lean plus fat) of the 9-10-11 rib section were thoroughly

mixed, ground and analyzed for chemical composition by AOAC (1980)

procedures. Chemical determinations of the soft tissue components were

used to estimate edible fat, protein and moisture, according to the

prediction equations developed by Hankins and Howe (1946).

Reproductive tracts were removed from each heifer at time of

slaughter. Ovaries were weighed, measured and follicles greater than 3

mm were counted. Uterine weight (horns and body of uterus) was

recorded and the outside diameter of the right uterine horn was









measured at the bifurcation. The udder was removed and weighed. Half

of each udder was ground and sampled for percent lipid. Percent lipid

was determined using the Soxhlet Ether Extraction procedure according

to AOAC (1980).

Adipose tissue samples were taken from the udder and

tail-head region of each heifer. The subcutaneous sample from the

tail-head region was taken 5 cm to the right of the tail-head. Three

thin slices (approximately 200 mg) were obtained from each tissue

sample using a Stadie-Riggs microtome. Slices were fixed with 5ml of

3% osmium tetroxide and 3 ml of 50 mM collidine-HCL buffer solution

(pH 7.4), as described by Hirsch and Gallian (1968). The connective

tissue matrix surrounding the adipocytes was solubilized with 8 M urea

as described by Etherton et al. (1977). Adipocytes were rinsed through

a 250-pm nylon mesh screen, with distilled water containing .01%

triton x-100 (pH 10) into 200 ml volumetric flasks. A NaCI solution

(.154 M) was added to increase volume to 200 ml. DLplicate 10 ml

aliquots were removed from each flask, added to 190 ml of a 45% sucrose

solution, counted and sized using a Coulter Counter Model TA II. A

560-vm aperture was used. A 77.8-vm standard of corn pollen was used

to determine the volume of each of the instrument's 16 channels.

Standard particles and fixed adipocytes were assumed to be spherical.

Data were analyzed by least-squares, fixed model procedures

using the Statistical Analysis System (SAS, 1979). The model used to

analyze all response variables included the fixed main effects of year,

creep treatment, zeranol treatment, breed of sire and breed of dam.

Age at the time of slaughter was used as a covariate. All

interactions were pooled and remained in the error term. Linear






57


contrasts of the least-squares means for creep treatments were computed

for all response variables affected (P<.10) by creep treatment.

Results and Discussion

Reproductive Tract Development. Least-squares means and P

values for reproductive tract characteristics are shown in table 9.

Creep treatment did not affect (P>.19) the ovarian weight, ovarian

size, uterine horn diameter or follicle number of weanling heifers.

Long-term (LC) and short-term (SC) creep-fed heifers tended (P>.11) to

have heavier uterine weights than noncreep-fed (NC) heifers. No

comparable data were found in the literature. Cornwell (1981) fed

long-yearling heifers on three levels of nutrition and reported no

significant effect of nutritional level on ovarian size or weight or on

uterine horn diameter. Research by Hill et al. (1970) and Spitzer et

al. (1978), using long-yearling and yearling heifers, respectively,

indicated that ovarian size was reduced when heifers were on a

restricted plane of nutrition.

Heifers implanted with 36 mg of zeranol at 56 and 146 d of age

had a greater (P<.03) uterine horn diameter and heavier (P<.02) uterine

weight than non-implanted heifers. There was no effect (P>.20) of

zeranol implants on ovarian weight or size or on number of follicles.

Breed of dam did not have an effect (P> .17) on the

development of the reproductive tract of the weanling heifers.

Brahman-sired heifers had a greater ovarian weight (P<.04) and size (P<

.02) than Roman Red-sired heifers. Uterine horn diameter, uterine

weight and follicle number were not affected (P>.14) by breed of sire.

The differences in ovarian weight and size due to breed of sire may

have been due to differences in size of the heifers. Brahman-sired



















































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(233 vs 211 kg). Foley et al. (1964), using dairy cattle of all ages,

reported a highly significant correlation (.65) between weight of both

ovaries and live weight. They stated that age and live weight appeared

to have more effect on ovarian weight than did breed. However, the LC

heifers in this study were heavier (P<.02) at slaughter than NC

heifers, yet there were no differences in ovarian size and weight due

to creep treatment. Therefore, the differences found in ovarian size

and weight between the Brahman and Romana Red-sired heifers might have

been due to genetic differences, independent of body size.

Udder and Subcutaneous Fat. Creep feeding did not increase (P>

.25) udder weight, percent lipid or total lipid in the udder (table

11). Though not significant, the least-squares means would indicate a

tendency for heifers to deposit more fat in the udder as length of

creep feeding increases. Furthermore, the subjective udder scores,

presented in study I were higher for LC than for NC heifers. The NC

heifers had a greater (P<.02) number of adipocytes/g of udder tissue

than LC and SC heifers; however, the total number of adipocytes in the

udder was not affected (P>.58) by creep treatment. The LC heifers had

larger (P>.04) udder and subcutaneous adipocytes than NC heifers (166.0

and 166.7 pm vs 152.7 and 148.8 Pm, respectively). The SC heifers

tended (P>.15) to have larger udder and subcutaneous adipocytes than NC

heifers. Subcutaneous adipocyte number/g of tissue was not affected (P>

.49) by creep treatment. Figure 2 illustrates the size distribution of

adipocytes by creep treatment. The LC and SC heifers had higher (P<

.10) percentages of total adipccyte volume composed of adipocytes

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had the highest (P<.05) percentage of total adipocyte volume made up of

adipocytes less than 129 Pm in diameter.

Data reported by Hood and Allen (1973), Allen (1976) and

Garbutt et al. (1979) indicate that adiposity in cattle may be

influenced by nutritional treatment during periods of growth and

development. Allen (1976) stated that changes in bovine cellular

hypertrophy and hyperplasia are dependent on the location of the fat

depot. He indicated that intramuscular lipid accumulation is more

dependent on cellular hyperplasia than are subcutaneous depots. The

results of this study would indicate that cellular hypertrophy had

occurred in the udder and subcutaneous fat depots of creep-fed

heifers. Therefore, any increase in lipid accumulation in these fat

depot areas would be due primarily to adipocyte hypertrophy rather than

hyperplasia.

Zeranol implants did not affect (P>.98) udder weight. Percent

udder lipid was lower (P<.02) in heifers implanted with zeranol;

however, total udder lipid was not affected (P>.68). Implanted heifers

had more (P<.07) adipocytes/g of udder tissue and tended (P>.14) to

have smaller udder adipocytes than non-implanted heifers. Total udder

adipocytes did not differ (P>.22) between implanted and non-implanted

heifers (8.55 and 7.06 x 10 respectively). Zeranol treatment did not

affect (P>.65) number of subcutaneous adipocytes/g of tissue; however,

implanted heifers had smaller (P<.10) subcutaneous adipocytes than

non-implanted heifers. Size distribution of udder and subcutaneous

adipocytes by zeranol treatment is shown in figure 3.

Heifers out of Angus dams had smaller (P<.08) udders and less

(P<.10) total fat in the udder than those out of F1 dams (2.91 vs 3.49







































































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kg and 2.37 vs 2.86 kg). This difference in udder size was not

detected from visual estimates presented in the first study. Breed of

dam did not affect (P>.44) percent lipid in the udder. Total udder

adipocytes and udder adipocytes/g of tissue were not affected (P>.35)

by breed of dam. Heifers out of F1 dams tended (P<.12) to have larger

udder adipocytes than those produced by Angus dams. Subcutaneous

adipocyte size anc number were unaffected (P>.61) by breed of dam.

Brahman-sired heifers had heavier (P<.001) udders (3.85 vs

2.55 kg) and more total fat in their udders (3.15 vs 2.08 kg) than

Romana Red-sired heifers. Percent lipid in the udder, however, was

unaffected (P>.78) by breed of sire. Number of udder adipccytes/g of

tissue was not affected (P>.31) by breed of sire. But as a result of

more total fat in the udder, Brahman-sired heifers had more (P<.004)

total adipocytes than those sired by Romana Red bulls. Romana

Red-sired heifers, however, tended (P>.14) to have larger udder

adipocytes than Brahman-sired heifers. In addition, Romana Red-sired

heifers had fewer (P<.08) adipocytes/g of subcutaneous adipose tissue

but larger (P<.09) subcutaneous adipocytes than those sired by Brahman

bulls.

Breed type has been used to provide an explanation for

differences in adiposity in several studies; however, there have been

few studies specifically designed to investigate variations in

adipocyte size and number among breeds. Hood and Allen (1973, 1975)

reported that perirenal and subcutaneous adipose tissue in 14-mo old

Hereford x Angus steers contained larger cells than the respective

tissues from Holstein steers of similar age and live weight. In

addition, they observed that a higher percentage of the total adipocyte










volume for Hereford x Angus steers was in larger cell diameter ranges

than for the same tissues from Holstein steers. Figures 4 and 5

illustrate the distribution of udder and subcutaneous adipocytes for

breed of sire and breed of dam.

Carcass Characteristics and Composition. Least-squares means

for carcass characteristics and composition are shown in tables 11, 12

and 13. The LC heifers had heavier (P<.005) empty body weights and

less (P<.02) gastrointestinal tract (GIT) fill than NC heifers. The LC

heifers also had heavier (P<.002) hot carcass weights and higher (P<

.02) dressing percentages than NC heifers. The LC heifers had heavier

(P<.10) empty body and hot carcass weights than SC heifers, but there

was no difference (P>.21) in GIT fill or dressing percent between

heifers of the two creep treatments. The SC heifers did not differ (P<

.10) frcm NC heifers for empty body weight, GIT fill, hot carcass

weight or dressing percentage.

Yield grade was not affected by creep treatment; however,

carcasses from LC heifers had more (P<.05) KPH fat, greater (P<.003)

fat thicknesses and larger (P<.04) ribeyes than NC and SC heifers.

Carcasses from SC and NC heifers did not differ (P>.17) for KPH fat,

fat thickness cr ribeye area. When expressed on a per 100 kg of hot

carcass basis, ribeye area was not influenced (P>.84) by creep

treatment. Creep treatment did not affect (P>.47) marbling sccre,

carcass maturity, lean color or fat color. Similar effects of

long-term creep feeding on the carcass characteristics of weanling

calves were reported by Scarth et al. (1968), Corah and Bishop (1975)

and Martin et al. (1980). Rouquette et al. (1983), on the other hand,




























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found no differences in carcass characteristics between long-term and

noncreep-fed calves.

Carcasses from LC heifers had a lower percent edible protein
(P< .05) than carcasses from NC and SC heifers (table 13). Creep

treatment did not affect (P>.26) percent edible fat or moisture in the

carcass. The LC heifers had a higher (P<.04) percent separable fat and

tended (P <.1) to have a lower percent separable lean content of the

carcass than SC and NC heifers. Carcasses from SC heifers had a higher

(P<03) percent bone than carcasses from LC heifers, but did not differ

(P>.17) from those of NC heifers. Contrary to the above, Corah and

Bishop (1975) reported no difference in percent protein of carcasses

between noncreep-fed and creep-fed heifers slaughtered at weaning.

Furthermore, they observed that carcasses from noncreep-fed heifers had

a higher percent bone than those from creep-fed heifers.

The SC heifers sacrificed in this study were probably not
completely representative of the SC treatment group. SC and NC heifers

did not differ (P<.11) with respect to any carcass trait including

slaughter height and hot carcass weight. However, in the population

from which these heifers were chosen, SC calves were heavier (P<.001)

at 210-d of age than NC calves.

Zeranol implants did not affect (P>.20) empty body weight, GIT

fill, hot carcass weight or dressing percent. Implanted heifers had

higher (P>.02) cutability carcasses (lower yield grade number) than

non-implanted heifers. Percent KPH and fat thickness were not affected

(P>.20) by zeranol treatment, but ribeye areas were larger (P<.06) in

the implanted heifers. The larger ribeye accounted for the lower yield

grade number of the carcasses from implanted heifers. Marbling score








and fat color were not affected (P>.41) by zeranol treatment. However,

zeranol implants increased lean color (P<.05) and maturity (P<.006),

and overall maturity (P<07). Bone maturity was not affected (P>.17)

by zeranol.

These results indicate that zeranol affects carcass traits

associated with body weight, and may increase maturity rate, as

measured by characteristics of the muscle. Gregory and Ford (1983),

using late maturing bull calves, concluded that zeranol treatment

effects on carcass characteristics were of little consequence other

than through increases in body weight.

Estimated edible fat, protein and moisture in the carcass were

not affected (P>30) by zeranol implants. Zeranol, however, did cause

a decrease in the percent separable fat (P<.09) and an increase (P<

.008) in the percent separable lean in the carcass. Percent separable

bone was not affected (P>.23) by zeranol treatment. Similar results

for estimated carcass components, using yearling steers, were reported

by Sharp and Dyer (1971).

Breed of dam did not affect (P>.23) empty body weight, GIT

fill, hot carcass weight or dressing percent. Carcasses from heifers

out of Angus dams had more (P<.08) ribeye area per 100 kg of hot

carcass and tended (P.11) to have less KPH fat than those out of F1

dams. This resulted in a tendency for carcasses from heifers out of

Angus dams to be higher (P<.12) yielding than those out of F1 dams.

Carcass fat thickness, maturity, lean color and fat color were

unaffected (P>48) by breed of dam. Estimated edible and separable

carcass components were not affected (P>.19) by breed of dam.








Brahman-sired heifers had heavier empty body (P< .009) and hot

carcass (P <.02) weights than Romana Red-sired heifers. Breed of sire

did not affect (P>.18) GIT fill, dressing percent, quality and yield

grade components, or estimated carcass composition. These results are

in agreement with Koch et al. (1982) who mated Angus and Hereford cows

to various breeds of bulls and reported no differences in carcass

characteristics between Brahman and Sahiwal-sired steers, other than

Brahman-sired steers had heavier carcass weights.

These data indicate that an increase of subcutaneous fat in

long-term creep-fed heifers is due primarily to adipocyte hypertrophy.

Creep feeding also increases adipocyte size in the udder. Heifers

implanted preweaning with zeranol have a Icwer percent lipid in the

udder and smaller udder and subcutaneous adipocytes than non-implanted

heifers. Zeranol implants increase ribeye area and percent separable

lean and decrease percent separable fat in the carcasses of weanling

heifers.

Summary

Effects of preweaning creep feeding and zeranol implants on

reproductive tract development, udder and subcutaneous fat deposition,

and carcass composition were studied in 24 weanling heifers sired by

Brahman and Romana Red bulls and out of Angus and FI Angus x Brown

Swiss reciprocal crossbred cows. Creep treatment did not affect (P>

.19) ovarian weight, ovarian size, uterine horn diameter or follicle

number. Heifers from the three creep treatments did not differ (P >.25)

in udder weight or percent lipid and total lipid in the udder. The

noncreep-fed (NC) heifers had a greater (P<.02) number of adipocytes/g

of udder tissue than long-term creep fed (LC) and short-term








creep-fed (SC) heifers. The LC heifers had significantly larger udder

(166.G vs 152.7 um) and subcutaneous adipocytes (166.7 vs 148.8 um)

than NC heifers. The LC heifers had heavier (P<.10) empty body and hot

carcass weights than SC and NC heifers. Carcasses from LC heifers had

m re (P<.04) separable fat, less (P<.11) separable lean and less (P<

.05) edible protein than carcasses from SC and NC heifers. Heifers

implanted with zeranol had a greater (P<.03) uterine horn diameter and

heavier (P<.02) uterine weight than no -implanted heifers. Percent

lipid was lower (P<.02) in heifers implanted with zeranol. Total udder

adipocytes did not differ (P>.22) between implanted and non-implanted

heifers; however, implanted heifers had smaller (P<.10) subcutaneous

adipocytes than non-implanted heifers. Implanted heifers had higher (P<

.02) cutability carcasses (lower yield grade number) than non-implanted

heifers. Zeranol implants increased carcass lean color (P<.05) and

maturity (P<.006) and overall maturity (P<.07). Zeranol decreased (P<

.09) percent separable fat and increased (P<.008) separable lean in the

carcass. Breed of dam did not have an effect (P>.17) on development of

the reproductive tract of weanling heifers. Heifers out of Angus dams

had smaller (P<.08) udders and less (P<.10) total fat in the udder than

those out of I dams. Heifers out of F1 dams tended (P<.12) to have

larger udder adipocytes than heifers produced by Angus dams. Estimated

edible and separable carcass components were unaffected (P>.19) by

breed of dam. Brahman-sired heifers had a greater ovarian weight (P<

.04) and size (P<.02) than Romana Red-sired heifers. Brahman-sired

heifers had mcre (P<.004) total udder adipccytes; whereas, Romana

Red-sired heifers tended (P>.14) to have larger udder adipocytes.

Breed of sire did not affect (P>.18) estimated carcass composition or

quality and yield traits.













SUMMARY AND CONCLUSIONS


A 2-year study was initiated to evaluate the effects of creep

feeding, preweaning zeranol implants and breed type on calf and cow

performance and on weanling heifer development and composition. Two

hundred calves sired by Brahman and Romana Red bulls and out of Angus

and F, Angus x Brown Swiss reciprocal crossbred (F1) cows were

stratified by breed type and sex to the following creep treatments: no

creep feed (NC); long-term creep (LC), creep-fed from 56 d of age to

weaning (210 d); and short-term creep (SC), creep-fed from 146 d of age

to weaning. Half of the steer and heifer calves within each breed and

creep treatment were implanted with 36 mg of zeranol at 56 and 146 d of

age. Twenty-four of the weanling heifers were sacrificed to evaluate

the effects of creep feeding, zeranol implants, and breed on

reproductive tract development, udder and subcutaneous fat deposition

and carcass composition.

The LC and SC calves had higher 210-d weights than NC calves

(264 and 256 vs 231 kg). The LC calves had higher 146-d weights,

higher average daily gains from 118 to 210-d of age, and higher

condition scores at 146 and 210-d than NC calves. Frame score was not

affected by creep treatment. Cows with creep-fed calves gained more

weight during the breeding sea on than cows with noncreep-fed calves,

but pregnancy rate was not affected by creep treatment. Zeranol

implants increased both 46 and 210-d weights (184 vs 175 and 259 vs







243 kg) and average daily gains during all periods to weaning. Cow

weight gain, condition score and pregnancy rate were not affected by

zeranol treatment of calves. Brahman-sired calves had higher 146 and

210-d weights and frame scores than RomEna Red-sired calves. Calves

out of Angus dams had lower 146 and 210-d weights, frame scores and

average daily gains from 56 to 46 and 210 d of age, but higher 210-d

condition scores than calves out of F1 dams. The F1 cows gained more

weight during the breeding season, had a lower condition score, and a

higher pregnancy rate (96.6 vs 86.8%) than the Angus cows. Cows

nursing heifer calves had a higher pregnancy rate than those nursing

steer calves.

Creep treatment did not affect (P>.19) ovarian weight, ovarian

size, uterine horn diameter or follicle number. Heifers from the three

creep treatments did not differ (P >.25) in udder weights or percent

lipid and total lipid in the udder. The NC heifers had a greater (P <

.02) number of adipocytes/g of udder tissue than LC and SC heifers. The

LC heifers had significantly larger udder (166.0 vs 152.7 um) and

subcutaneous adipocytes (166.7 vs 148.8 um) than NC heifers. The LC

heifers had heavier (P <.10) empty body and hot carcass weights than SC

and NC heifers. Carcasses from LC heifers had mcre (P<.04) separable

fat, less (P <.11) separable lean and less (P<.05) edible protein than

carcasses from SC and NC heifers. Heifers implanted with zeranol had a

greater (P <.03) uterine horn diameter and heavier (P <.02) uterine

weight than non-implanted heifers. Percent lipid was lower (P <.02) in

heifers implanted with zeranol. Total udder adipocytes did not differ

(P >.22) between implanted and non-implanted heifers; however,

implanted heifers had smaller (P <.10) subcutaneous adipocytes than






77

non-implanted heifers. Implanted heifers had higher (P< .02) cutability

carcasses (lower yield grade number) than non-implanted heifers.

Zeranol implants increased carcass lean color (P< .05) and maturity (P

.006) and overall maturity (P <07). Zeranol decreased (P <09) percent

separable fat and increased (P< .008) separable lean in the carcass.

Breed of dam did riot have an effect (P >.17) on development of the

reproductive tract of weanling heifers. Heifers out of Angus dams had

smaller (P< .08) udders and less (P< .10) total fat in the udder than

those out of F1 dams. Heifers out of F1 dams tended (P< .12) to have

larger udder adipocytes than heifers produced by Angus dams. Estimated

edible and separable carcass components were unaffected (P> .19) by

breed of dam. Brahman-sired heifers had a greater ovarian weight (P>

.04) and size (P<.02) than Romana Red-sired heifers. Brahman-sired

heifers had more (P <004) total udder adipocytes; whereas, Romana

Red-sired heifers tended (P> .14) to have larger udder adipocytes.

Breed of sire did not affect (P> .18) estimated carcass composition or

quality and yield traits.

It can be concluded that calves receive very little benefit

from creep feed prior to 120 d of age. Creep feeding calves from about

5 mo of age to weaning results in more efficient utilization of creep

feed and almost as much increase in weight gain as creep feeding from 2

mo of age. The effect of creep feed intake on preweaning weight gain

may be additive with milk intake in calves with above average growth

potential. Increased levels of nutrition, from creep feed and milk, may

result in increased growth response to zeranol. Little benefit, in

terms of increased pregnancy of the cow herd, is obtained from creep
feeding when cows have adequate nutrition during the breeding season.








The increase of subcutaneous fat in long-term creep-fed

heifers is due primarily to adipocyte hypertrophy. Creep feeding also

increases adipocyte size in the udder. Heifers implanted preweaning

with zeranol have a lower percent lipid in the udder and smaller udder

and subcutaneous adipocytes than non-implanted heifers. Zeranol

implants increase ribeye area and percent separable lean and decrease

percent separable fat in the carcasses of weanling heifers.

Work is continuing on the long-term effects of preweaning

creep feed and zeranol treatments on the future productivity of beef

heifers.













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