Effects of forage sampling method on nutritive value of bahiagrass during the winter and spring

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Effects of forage sampling method on nutritive value of bahiagrass during the winter and spring
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2009 Florida Beef Report
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Hughes, Ashley
Hersom, Matt
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Institute of Food and Agricultural Sciences, University of Florida
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Effects of Forage Sampling Method on Nutritive Value of Bahiagrass During
the Winter and Spring

Ashley Hughes1
Matt Hersom



This study suggest that when adequate forage is available for grazing, steers will selectively graze
bahiagrass forage with greater nutritive value than hand-collected forage during the winter and spring.


Summary
A six-mo trial was conducted from December
2006 to May 2007 to evaluate the differences
between forage and masticate samples of
bahiagrass pastures at four research stations
across Florida (Ona, Brooksville, Santa Fe, and
Marianna) during the winter and spring. Eight
ruminally cannulated steers were used for
collection of masticate samples. Forage
samples were collected by cutting the grass
within a 0.8-ft2quadrat to approximately 1-in
from the soil surface. High and low forage
availabilities were designated to represent
differences in forage quantities at each location.
Forage mass, in vitro digestible organic matter,
and crude protein concentrations were
determined for each sample type. There were
differences in forage mass, digestible organic
matter, and crude protein between locations, as
well as the state mean.. Selection indices
indicated the opportunity for selection offorage
that was greater in digestibility and crude
protein compared to hand-collected forage
samples. The selection indices for digestibility
were similar at the four locations varying from 0
to 62%, while the selection indices for CP
differed more by location ranging from -4 to
68%. Overall, during the winter and spring,
steers were able to select a diet that was 31%
greater in digestibility and 21% greater in crude
protein compared to hand-collected forage
samples.

Introduction
Florida pastures are comprised primarily


of tropical and subtropical grasses, which are
typically high yielding, but low in quality.
Bahiagrass (Paspalum notatum) is the most
commonly utilized forage in pasture grazing
systems in Florida occupying approximately 2.5
million ac (Chambliss and Sollenberger, 1991),
but also extends into the Gulf Coast Region.
Currently, there is little published data dedicated
to classifying subtropical forages on a year-
round basis, whether by hand-sampling or
collection of masticate samples, with even less
data devoted to studying diet selection by cattle
grazing subtropical pastures.

Studies have shown that when adequate forage is
available for grazing, ruminants will selectively
graze within those situations (Weir and Torell,
1959; Schlegel et al., 2000). When attempting
to represent the diet of a grazing animal,
research has illustrated how hand-collected
forage samples are inaccurate in their
estimations of selected material (Coleman and
Barth, 1973; Russell et al., 2004). The objective
of this study was to characterize the nutritive
value of bahiagrass from four locations across
the state of Florida during the winter and spring
comparing sampling techniques, either by hand-
sampling or collection of masticate sample,
within pastures of varying levels of forage
availability (FA) with the ultimate goal of better
predicting available forage nutritive value and
subsequent supplementation needs to meet
Florida grazing cattle nutritional requirements.


2009 Florida BeefReport










Materials and Methods
Four locations were utilized for this project to
represent the variation in the Florida pasture
landscape, the locations included: Range Cattle
Research and Education Center, Ona; USDA-
Subtropical Agricultural Research Station,
Brooksville; Santa Fe River Ranch Beef Unit,
Alachua; and North Florida Research and
Education Center, Marianna. The pasture sizes
at each location were: 2.5 ac (Ona), 2.5 ac
(Brooksville), 2.0 ac (Alachua), and 3.7 ac
(Marianna). Bahiagrass (Paspalum notatum) was
the primary forage of interest for this trial.
However, there were different cultivars at each
location. At the Ona research site, the bahiagrass
cultivar used for the trial was Pensacola
(Paspalum notatum cv. Suarae Parodi), while
the cultivar found in Brooksville was primarily
Argentine bahiagrass, which is similar to
Pensacola, but may be more palatable. At the
Alachua research site, the bahiagrass cultivar
was Pensacola, while Marianna contained
Pensacola bahiagrass. The selected pastures
were managed at each location either by grazing
or mowing to allow for differences in available
forage mass. Pastures were not fertilized prior to
or during the trial.
Forage and masticate samples were collected
monthly (approximately every 30 d) from
December 2006 to May 2007. Eight ruminally
cannulated Angus or Brangus steers were used
for this experiment with two steers at each
location (one Angus and one Brangus) for
collection of masticate samples. Forage
availabilities were visually assigned to the
selected pastures, as either HIGH or LOW, at
each location to represent differences in forage
quantity. Within each pasture, two individuals
hand-clipped three forage samples each for a
total of six samples per pasture. Hand shears
were used to cut the forage within a 0.8-ft2
quadrat to an approximate height of 1-in from
the soil surface. Simultaneously, masticate
samples were collected from the fistulated steers
by initially emptying the rumen, allowing the
steers to graze either the HIGH or LOW FA
pasture for approximately one h, then removing
the selected material from the rumen. Forage
and masticate samples were analyzed for


forage mass, in vitro digestible organic matter
(IVDOM), and crude protein (CP). The
selection index (SI) for chemical composition
was also calculated using the following
equation, SI = {[(Masticate concentration -
hand-collected forage concentration) / hand-
collected forage concentration] 100} + 100.

Data were analyzed as a split plot design with
the whole plot completely randomized using the
MIXED procedure of SAS. The experimental
unit was steer or person for sample collection.
Fixed effects in the model included FA, month,
sampling type (masticate or hand-collection),
and their interactions. Repetition (steer or
person) within each FA was used for the
repeated measures and random effect. The least
squares means were determined. Means were
separated using the P-diff option when protected
by a significant F-value (P<0.05).

Results
Ona
At Ona, there was a month effect (Table 1;
P<0.001), whereas there was only a tendency for
a FA effect (P=0.09). Ona had significantly
greater forage mass in comparison to the other
locations. The high FA decreased steadily
during the winter months until a 4,500 lb/ac
increase in May, whereas the low FA remained
fairly similar during the winter until a 4,000
lb/ac increase in May. The IVDOM
concentration of masticate samples (Table 2)
were greater (P<0.001) than hand-collected
forage samples during the winter and spring.
Month also affected IVDOM concentration
(P<0.001) of forage and masticate samples, as
both sample types steadily increased in IVDOM
concentration during the winter. Likewise, the
CP concentration of masticate samples (Table 3)
was greater (P<0.001) compared to hand-
collected forage samples with exception of
March, which likely caused the type x month
effect (P<0.001). The mean SI at Ona (Table 4)
indicated that the steers were selecting forage
31% greater in IVDOM concentration and 21%
greater in CP concentration compared to hand-
collected forage samples during the winter and
spring months.


2009 Florida BeefReport










Brooksville
There were no differences in forage mass at
Brooksville (Table 1) between FA (P=0.23) or
month (P=0.15) during the winter and spring.
While the IVDOM concentration of both sample
types (Table 2) increased from December to
May (P<0.001), masticate samples averaged
13% greater IVDOM concentration (P<0.001)
compared to hand-collected forage samples.
Similarly, the CP concentration of masticate
samples (Table 3) was greater (P<0.001) than
the hand-collected samples during the winter
and spring. The similarity of the forage and
masticate CP concentrations in March led to a
type x month (P<0.001) effect. At Brooksville,
the steers were able to select forage that was
32% greater in IVDOM and CP compared to
hand-collected forage samples (Table 4).

Santa Fe
There was no LOW FA sample taken at Santa Fe
during January due to sampling difficulty, thus
forage and masticate samples were not analyzed
for IVDOM and CP during January. There was
a month effect (P=0.04) for forage mass from
December to May, which was likely due to the
sharp increase in forage mass in May with only a
tendency (P=0.09) for a difference between FA
(Table 1). Throughout the winter and spring,
IVDOM concentration (Table 2) was greater
(P<0.001) for masticate compared to hand-
collected samples. Month also affected IVDOM
concentration of both sample types (P<0.001)
from December to May. The variation between
sample type and month led to type x month
(P=0.01) interaction for IVDOM concentration.
During the winter and spring, CP concentration
(Table 3) varied between month (P<0.001).
While there was no sample type effect (P=0.18)
on CP concentration, masticate samples had
greater CP concentration than hand-collected
forage samples with the exception of March.
February had the greatest SI (Table 4) for
IVDOM concentration (P<0.05) indicating the
opportunity for steer selection of forage 62%
greater in IVDOM concentration compared to
hand-collected forage samples with other
months eliciting less of a selection response
(mean= 14%). During January and February,
the steers were able to select forage that was


greater in CP concentration (36% and 22%,
respectively) with other months eliciting less of
a selection response.

Marianna
Marianna had the lowest forage mass (Table 1)
compared with other locations, with variation
between months (P=0.04), but not between FA
(P=0.12). Masticate sample IVDOM
concentration (Table 2) was greater (P<0.001)
compared to hand-collected forage samples with
variation between months (P<0.001). With the
exception of January (35.0% IVDOM
concentration), hand-collected forage samples
varied by less than 5% IVDOM (mean= 53.0%).
Similarly, IVDOM concentration of masticate
samples only varied by 9% during the winter
and spring (mean= 64.3%) with the exception of
January (54.5%). The differences between
sample type and month resulted in a type x
month (P=0.03) effect for IVDOM
concentration during the winter and spring.
Masticate sample CP concentrations (Table 3)
were greater (P<0.001) than hand-collected
forage samples from December to May. CP
concentrations were also affected by month
(P<0.001) with only a tendency for a type x
month interaction (P=0.08), which was likely
due to the similarity in value between masticate
and hand-collected forage samples during
March. The greatest opportunity for selection of
forage with greater IVDOM concentration
compared to hand-collected forage (Table 4;
P<0.05) was in January (55.4%) and February
(37.3%). The mean SI for CP concentration
indicated the opportunity for selection of forage
material that was 17% greater in CP
concentration compared to hand-collected forage
during the winter and spring.

State Mean
Month affected the overall state mean forage
mass (Table 1; P<0.001), while there only
tended to be a difference between FA (P=0.10)
at all locations. The forage mass of the HIGH
FA decreased from December to April until
increasing in May, while the LOW FA remained
fairly constant during the winter until increasing
by approximately 1,400 lb/ac in May. Masticate


2009 Florida BeefReport










samples were consistently greater (mean=
59.2%) in IVDOM concentration (Table 2;
P<0.001) compared to hand-collected forage
samples (mean= 45.8%). Month also affected
IVDOM concentration of masticate and hand-
collected forage samples (P<0.001) during the
winter and spring likely due to changing
environmental factors at each location. The
sample type and month effects led to a type x
month interaction (P<0.001) for IVDOM
concentration. Similarly, CP concentrations
(Table 3) were affected by month (P<0.001)
with masticate samples consistently greater than
the hand-collected forage samples with the
exception of March, thus influencing a type x
month interaction (P=0.02). The SI for IVDOM
concentration (Table 4) varied by month
(P<0.05) with the greatest opportunity for
selection in January and February (51%), while
the remaining months indicated the steers
selected forage that was 19% greater in IVDOM
concentration compared to hand-collected forage
samples. The SI for the overall mean CP
concentration (P<0.05) was greatest in
December (37%), followed by January and
February (30%), and least in March, April and
May (10%) indicating less of an opportunity for
selection of forage as the winter and spring
seasons progressed.


Conclusions and Implications
The results of this study indicate that during the
winter and spring when bahiagrass forage mass
is most limiting and nutritive value is low,
grazing steers will select forage material with
greater IVDOM and CP concentrations
compared to hand-collected forage values,
which are normally gathered for estimation of
available forage quality. The data collected in
this study imply that forage samples collected by
hand may under-estimate the nutritive value of
the actual selected forage by cattle. The
implications of this study indicate the
opportunity to more closely match cow
requirements with forage resources, based on
available bahiagrass nutritive value and cow
selection within those forage opportunities. If
energy and protein supplementation can be more
closely matched to cow requirements, then less
N and other nutrient inputs would be added to
the environment thus improving land and water
quality, which is an important concern for
Florida cattle producers.


SAshley Hughes, Former Graduate Student; Matt Hersom, Assistant Professor, UF-IFAS, Animal
Sciences, Gainesville, FL


2009 Florida BeefReport


Literature Cited
Chambliss, C. G. and L. E. Sollenberger. 1991. Proc. 40th Annual Florida Beef Cattle Short Course, pp 74-
80.
Coleman, S. W. and K. M. Barth. 1973. J. Anim. Sci. 36: 754-761.
Russell, J. R. et al. 2004. J. Anim. Sci. 82(Suppl 2): 93.
Schlegel, M. L. et al. 2000. J. Anim. Sci. 78: 2202-2208.
Weir, W. C. and D. T. Torell. 1959. J. Anim. Sci. 18:641-649.












Table 1. Effect of forage availability and month on overall mean forage mass (lb/ac)
Month P-value
Location FAa Dec Jan Feb Mar Apr May SEMd FA Month FA*Month
Ona Hb 5,184 3,429 3,156 2,653 1,840 6,258 592 0.09 <0.001 0.17
L' 1,858 1,195 1,257 1,341 978 4,017
Brooksville H 2,093 1,277 2,251 1,974 1,329 1,788 356 0.23 0.15 0.50
L 1,431 833 951 1,366 1,114 1,259
SantaFe H 1,626 1,000 1,345 1,311 1,170 3,549 383 0.09 0.02 0.19
L 939 na 867 930 946 1,466
Marianna H 1,128 1,616 889 730 927 1,872 275 0.12 0.04 0.42
L 406 478 672 703 519 1,386
St. Mean H 2,508 2,832 1,911 1,085 889 2,032 414 0.10 0.001 0.73
L 1,159 836 937 1,376 1,316 2,700
aFA= Forage availability.
bH = High forage availability.
CL= Low forage availability.
dSEM= Standard error of the mean.


Table 2. Effect of sampling type and month on in vitro digestible organic matter (IVDOM, %)
Month P-value
Location Typea Dec Jan Feb Mar Apr May SEMd Type Month Type*Month
Ona Fb 38.56 34.94 39.09 42.83 43.70 51.29 2.05 <0.001 <0.001 <0.001
M" 47.80 51.17 58.41 56.45 65.25 58.72
Brooksville F 40.43 39.69 38.73 44.36 50.26 50.10 1.42 <0.001 <0.001 <0.001
M 52.44 60.08 58.78 56.62 57.89 57.78
SantaFe F 43.66 na 39.32 55.84 51.81 50.42 2.62 <0.001 <0.001 0.01
M 51.46 na 63.27 63.63 57.08 61.57
Marianna F 54.68 35.04 50.80 54.88 54.49 50.19 2.23 <0.001 <0.001 0.06
M 66.34 54.56 69.51 61.99 60.15 63.65
St. Mean F 44.21 37.51 42.24 49.62 50.81 50.52 1.98 <0.001 <0.001 <0.001
M 55.63 56.32 62.62 60.63 59.84 60.53
aType= Forage sampling type.
bF= Hand-collected forage.
CM= Masticate.
dSEM= Standard error of the mean, n=48.


2009 Florida BeefReport












Table 3. Effect of sampling type and month on crude protein (CP, %)
Month P-value
Location Typea Dec Jan Feb Mar Apr May SEMd Type Month Type*Month
Ona Fb 7.57 9.22 10.93 12.05 11.70 10.84 0.62 <0.001 <0.001 <0.001
Me 9.57 10.56 13.49 11.92 15.72 12.24
Brooksville F 6.78 8.02 8.06 10.20 10.06 10.89 0.49 <0.001 <0.001 <0.001
M 10.19 12.90 11.47 10.39 11.63 11.63
Santa Fe F 7.70 na 11.91 15.20 13.75 13.27 0.89 0.18 <0.001 0.43
M 9.83 na 14.56 14.72 15.07 13.55
Marianna F 9.03 9.75 12.16 10.36 11.47 9.83 0.56 <0.001 <0.001 0.08
M 12.00 11.70 14.24 10.57 11.89 12.61
St. Mean F 7.81 9.53 10.82 11.92 11.72 11.31 0.58 <0.001 <0.001 0.02
M 10.62 11.94 13.44 11.93 13.64 12.52
aType= Forage sampling type.
bF= Hand-collected forage.
CM= Masticate.
dSEM= Standard error of the mean, n=48.


Table 4. Effect of month on steer selection index" of bahiagrass forage.
Location Analysis Month
Dec Jan Feb Mar Apr May SEMd P-value
Ona IVDOMb 122.73 146.45 153.78 129.85 149.22 115.12 18.96 0.65
CPc 124.98 118.66 134.53 99.91 136.43 112.88 24.93 0.89
Brooksville IVDOM 129.68 151.72 151.79 127.67 115.74 116.70 6.72 0.04
CP 150.24 167.84 147.56 101.84 115.55 106.71 19.55 0.24
Santa Fe IVDOM 108.78 na 161.63 114.36 110.47 122.25 6.18 0.02
CP 136.06 na 122.17 96.84 109.80 102.08 21.34 0.79
Marianna IVDOM 121.72 155.43 137.30 112.87 104.30 126.98 8.11 0.05
CP 134.69 118.00 116.28 102.07 103.91 129.38 8.96 0.21
St. Mean IVDOM 120.71g 151.82ef 151.11e 121.23g 119.92g 120.34g 5.73 <0.001
CP 136.52f 131.03f 130.12f 100.24e 116.44ef 112.82ef 8.59 0.03
a {[(Masticate concentration forage concentration) / forage concentration] 100} + 100.
bIVDOM= In vitro digestible organic matter.
cCP= Crude protein.
dSEM= Standard error of the mean, n=12.
e,"gwithin a row, means with a different superscript differ, P<0.05


2009 Florida BeefReport




Full Text

PAGE 1

Effects of Forage Sampling Method on Nutritive Value of Bahiagrass During the Winter and Spring Ashley Hughes 1 Matt Hersom Summary A six-mo trial was conducted from December 2006 to May 2007 to evaluate the differences between forage and masticate samples of bahiagrass pastures at four research stations across Florida (Ona, Brooksville, Santa Fe, and Marianna) during the winter and spring. Eight ruminally cannulated steers were used for collection of masticate samples. Forage samples were collected by cutting the gras s within a 0.8ft 2 quadrat to approximately 1-in from the soil surface. High and low forage availabilities were designated to represent differences in forage quantities at each location. Forage mass, in vitro digestible organic matter, and crude protein concentrations were determined for each sample type. There were differences in forage mass, digestible organic matter, and crude protein between locations, as well as the state mean.. Selection indices indicated the opportunity for selection of forage that was greater in digestibility and crude protein compared to hand-collected forage samples. The selection indices for digestibility were similar at the four locations varying from 0 to 62%, while the selection indices for CP differed more by location ranging from -4 to 68%. Overall, during the winter and spring, steers were able to select a diet that was 31% greater in digestibility and 21% greater in crude protein compared to hand-collected forage samples. Introduction Florida pastures are comprised primarily of tropical and subtropical grasses, which are typically high yielding, but low in quality. Bahiagrass ( Paspalum notatum) is the most commonly utilized forage in pasture grazing systems in Florida occupying approximately 2.5 million ac (Chambliss and Sollenberger, 1991), but also extends into the Gulf Coast Region. Currently, there is little published data dedicated to classifying subtropical forages on a yearround basis, whether by hand-sampling or collection of masticate samples, with even less data devoted to studying diet selection by cattle grazing subtropical pastures. Studies have shown that when adequate forage is available for grazing, ruminants will selectively graze within those situations (Weir and Torell, 1959; Schlegel et al., 2000). When attempting to represent the diet of a grazing animal, research has illustrated how hand-collected forage samples are inaccurate in their estimations of selected material (Coleman and Barth, 1973; Russell et al., 2004). The objective of this study was to characterize the nutritive value of bahiagrass from four locations across the state of Florida during the winter and spring comparing sampling techniques, either by handsampling or collection of masticate sample, within pastures of varying levels of forage availability (FA) with the ultimate goal of better predicting available forage nutritive value and subsequent supplementation needs to meet Florida grazing cattle nutritional requirements. This study suggest that when adequate forage is available for grazing, steers will selectively graze bahiagrass forage with greater nutritive value than hand collected forage during the winter and spring.

PAGE 2

Materials and Methods Four locations were utilized for this project to represent the variation in the Florida pasture landscape, the locations included: Range Cattle Research and Education Center, Ona; USDASubtropical Agricultural Research Station, Brooksville; Santa Fe River Ranch Beef Unit, Alachua; and North Florida Research and Education Center, Marianna. The pasture sizes at each location were: 2.5 ac (Ona), 2.5 ac (Brooksville), 2.0 ac (Alachua), and 3.7 ac (Marianna). Bahiagrass ( Paspalum notatum) was the primary forage of interest for this trial. However, there were different cultivars at each location. At the Ona research site, the bahiagrass cultivar used for the trial was Pensacola ( Paspalum notatum cv. Suarae Parodi), while the cultivar found in Brooksville was primarily Argentine bahiagrass, which is similar to Pensacola, but may be more palatable. At the Alachua research site, the bahiagrass cultivar was Pensacola, while Marianna contained Pensacola bahiagrass. The selected pastures were managed at each location either by grazing or mowing to allow for differences in available forage mass. Pastures were not fertilized prior to or during the trial. Forage and masticate samples were collected monthly (approximately every 30 d) from December 2006 to May 2007. Eight ruminally cannulated Angus or Brangus steers were used for this experiment with two steers at each location (one Angus and one Brangus) for collection of masticate samples. Forage availabilities were visually assigned to the selected pastures, as either HIGH or LOW, at each location to represent differences in forage quantity. Within each pasture, two individuals hand-clipped three forage samples each for a total of six samples per pasture. Hand shears were used to cut the forage within a 0.8ft 2 quadrat to an approximate height of 1-in from the soil surface. Simultaneously, masticate samples were collected from the fistulated steers by initially emptying the rumen, allowing the steers to graze either the HIGH or LOW F A pasture for approximately one h, then removing the selected material from the rumen. Forage and masticate samples were analyzed for forage mass, in vitro digestible organic matter (IVDOM), and crude protein (CP). The selection index (SI) for chemical composition was also calculated using the following equation, SI = {[(Masticate concentration hand-collected forage concentration) / handcollected forage concentration] 100} + 100 Data were analyzed as a split plot design with the whole plot completely randomized using the MIXED procedure of SAS. The experimental unit was steer or person for sample collection. Fixed effects in the model included FA, month, sampling type (masticate or hand-collection), and their interactions. Repetition (steer or person) within each FA was used for the repeated measures and random effect. The least squares means were determined. Means were separated using the P-diff option when protected by a significant F-value ( P <0.05). Results Ona At Ona, there was a month effect (Table 1; P <0.001), whereas there was only a tendency for a FA effect ( P =0.09). Ona had significantly greater forage mass in comparison to the other locations. The high FA decreased steadily during the winter months until a 4,500 lb/ac increase in May, whereas the low FA remained fairly similar during the winter until a 4,000 lb/ac increase in May. The IVDOM concentration of masticate samples (Table 2) were greater ( P <0.001) than hand-collected forage samples during the winter and spring. Month also affected IVDOM concentration ( P<0.001) of forage and masticate samples, as both sample types steadily increased in IVDOM concentration during the winter. Likewise, the CP concentration of masticate samples (Table 3) was greater ( P <0.001) compared to handcollected forage samples with exception of March, which likely caused the type x month effect ( P <0.001). The mean SI at Ona (Table 4) indicated that the steers were selecting forage 31% greater in IVDOM concentration and 21% greater in CP concentration compared to handcollected forage samples during the winter and spring months.

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Brooksville There were no differences in forage mass at Brooksville (Table 1) between FA ( P =0.23) or month ( P =0.15) during the winter and spring. While the IVDOM concentration of both sample types (Table 2) increased from December to May ( P <0.001), masticate samples averaged 13% greater IVDOM concentration ( P <0.001) compared to hand-collected forage samples. Similarly, the CP concentration of masticate samples (Table 3) was greater ( P <0.001) than the hand-collected samples during the winter and spring. The similarity of the forage and masticate CP concentrations in March led to a type x month ( P <0.001) effect. At Brooksville, the steers were able to select forage that was 32% greater in IVDOM and CP compared to hand-collected forage samples (Table 4). Santa Fe There was no LOW FA sample taken at Santa Fe during January due to sampling difficulty, thus forage and masticate samples were not analyzed for IVDOM and CP during January. There was a month effect ( P =0.04) for forage mass from December to May, which was likely due to the sharp increase in forage mass in May with only a tendency ( P =0.09) for a difference between FA (Table 1). Throughout the winter and spring, IVDOM concentration (Table 2) was greater ( P <0.001) for masticate compared to handcollected samples Month also affected IVDOM concentration of both sample types ( P <0.001) from December to May The variation between sample type and month led to type x month ( P =0.01) interaction for IVDOM concentration. During the winter and spring, CP concentration (Table 3) varied between month ( P <0.001). While there was no sample type effect ( P =0.18) on CP concentration, masticate samples had greater CP concentration than hand-collected forage samples with the exception of March. February had the greatest SI (Table 4) for IVDOM concentration ( P <0.05) indicating the opportunity for steer selection of forage 62% greater in IVDOM concentration compared to hand-collected forage samples with other months eliciting less of a selection response (mean= 14%). During January and February, the steers were able to select forage that was greater in CP concentration (36% and 22%, respectively) with other months eliciting less of a selection response. Marianna Marianna had the lowest forage mass (Table 1) compared with other locations, with variation between months ( P =0.04), but not between FA ( P=0.12). Masticate sample IVDOM concentration (Table 2) was greater ( P <0.001) compared to hand-collected forage samples with variation between months ( P <0.001). With the exception of January (35.0% IVDOM concentration), hand-collected forage samples varied by less than 5% IVDOM (mean= 53.0%). Similarly, IVDOM concentration of masticate samples only varied by 9% during the winter and spring (mean= 64.3%) with the exception o f January (54.5%). The differences between sample type and month resulted in a type x month ( P =0.03) effect for IVDOM concentration during the winter and spring. Masticate sample CP concentrations (Table 3) were greater ( P <0.001) than hand-collected forage samples from December to May. CP concentrations were also affected by month ( P<0.001) with only a tendency for a type x month interaction ( P =0.08), which was likely due to the similarity in value between masticate and hand-collected forage samples during March. The greatest opportunity for selection of forage with greater IVDOM concentration compared to hand-collected forage (Table 4; P <0.05) was in January (55.4%) and February (37.3%). The mean SI for CP concentration indicated the opportunity for selection of forage material that was 17% greater in CP concentration compared to hand-collected forage during the winter and spring. State Mean Month affected the overall state mean forage mass (Table 1; P <0.001), while there only tended to be a difference between FA ( P =0.10) at all locations. The forage mass of the HIGH FA decreased from December to April until increasing in May, while the LOW FA remained fairly constant during the winter until increasing by approximately 1,400 lb/ac in May. Masticate

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samples were consistently greater (mean= 59.2%) in IVDOM concentration (Table 2 ; P <0.001) compared to hand-collected forage samples (mean= 45.8%). Month also affected IVDOM concentration of masticate and handcollected forage samples ( P<0.001) during the winter and spring likely due to changing environmental factors at each location. The sample type and month effects led to a type x month interaction ( P <0.001) for IVDOM concentration. Similarly, CP concentrations (Table 3) were affected by month ( P <0.001) with masticate samples consistently greater than the hand-collected forage samples with the exception of March, thus influencing a type x month interaction ( P =0.02). The SI for IVDOM concentration (Table 4) varied by month ( P <0.05) with the greatest opportunity for selection in January and February (51%), while the remaining months indicated the steers selected forage that was 19% greater in IVDOM concentration compared to hand-collected forage samples. The SI for the overall mean CP concentration ( P <0.05) was greatest in December (37%), followed by January and February (30%), and least in March, April and May (10%) indicating less of an opportunity for selection of forage as the winter and spring seasons progressed. Conclusions and Implications The results of this study indicate that during the winter and spring when bahiagrass forage mass is most limiting and nutritive value is low, grazing steers will select forage material with greater IVDOM and CP concentrations compared to hand-collected forage values, which are normally gathered for estimation of available forage quality. The data collected in this study imply that forage samples collected by hand may under-estimate the nutritive value of the actual selected forage by cattle. The implications of this study indicate the opportunity to more closely match cow requirements with forage resources, based on available bahiagrass nutritive value and cow selection within those forage opportunities. If energy and protein supplementation can be more closely matched to cow requirements, then less N and other nutrient inputs would be added to the environment thus improving land and water quality, which is an important concern for Florida cattle producers. Literature Cited Cham bliss, C. G. and L. E. Sollenberger. 1991. Proc. 40 th Annual Florida Beef Cattle Short Course, pp 74 80. Coleman, S. W. and K. M. Barth. 1973. J. Anim. Sci. 36: 754 761. Russell, J. R. et al. 2004. J. Anim. Sci. 82(Suppl 2): 93. Schlegel, M. L. et al. 2000 J. Anim. Sci. 78: 2202 2208. Weir, W. C. and D. T. Torell. 1959. J. Anim. Sci. 18:641 649. 1 Ashley Hughes, Former Graduate Student; Matt Hersom, Assistant Professor, UF IFAS, Animal Sciences, Gainesville, FL

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Table 1. Effect of forage a vailability and month on overall mean forage mass (lb/ac) Month P value Location FA a Dec Jan Feb Mar Apr May SEM d FA Month FA*Month Ona H b 5,184 3,429 3,156 2,653 1,840 6,258 592 0.09 <0.001 0.17 L c 1,858 1,195 1,257 1,341 978 4,017 Brooksville H 2,093 1,277 2,251 1,974 1,329 1,788 356 0.23 0.15 0.50 L 1,431 833 951 1,366 1,114 1,259 Santa Fe H 1,626 1,000 1,345 1,311 1,170 3,549 383 0.09 0.02 0.19 L 939 na 867 930 946 1,466 Marianna H 1,128 1,616 889 730 927 1,872 275 0.12 0.04 0.42 L 406 478 672 703 519 1,386 St. Mean H 2,508 2,832 1,911 1,085 889 2,032 414 0.10 0.001 0.73 L 1,159 836 937 1,376 1,316 2,700 a FA= Forage availability. b H = High forage availability. c L= Low forage availability. d SEM= Standard error of the mean. Table 2. Effect of sampling type and month on in vitro digestible organic matter (IVDOM, %) Month P value Location Type a Dec Jan Feb Mar Apr May SEM d Type Month Type*Month Ona F b 38.56 34.94 39.09 42.83 43.70 51.29 2.05 <0.001 <0.001 <0.001 M c 47.80 51.17 58.41 56.45 65.25 58.72 Brooksville F 40.43 39.69 38.73 44.36 50.26 50.10 1.42 <0.001 <0.001 <0.001 M 52.44 60.08 58.78 56.62 57.89 57.78 Santa Fe F 43.66 na 39.32 55.84 51.81 50.42 2.62 <0.001 < 0.001 0.01 M 51.46 na 63.27 63.63 57.08 61.57 Marianna F 54.68 35.04 50.80 54.88 54.49 50.19 2.23 <0.001 <0.001 0.06 M 66.34 54.56 69.51 61.99 60.15 63.65 St. Mean F 44.21 37.51 42.24 49.62 50.81 50.52 1.98 <0.001 <0.001 <0.001 M 55.63 56.32 62.62 60.63 59.84 60.53 a Type= Forage sampling type. b F= Hand collected forage. c M= Masticate. d SEM= Standard error of the mean, n=48.

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Table 3. Effect of sampling type and month on crude protein (CP, %) Month P value Location Type a Dec Jan Feb Mar Apr May SEM d Type Month Type*Month Ona F b 7.57 9.22 10.93 12.05 11.70 10.84 0.62 <0.001 <0.001 <0.001 M c 9.57 10.56 13.49 11.92 15.72 12.24 Brooksville F 6.78 8.02 8.06 10.20 10.06 10.89 0.49 < 0.001 <0.001 <0.001 M 10.19 12.90 11.47 10.39 11.63 11.63 Santa Fe F 7.70 na 11.91 15.20 13.75 13.27 0.89 0.18 <0.001 0.43 M 9.83 na 14.56 14.72 15.07 13.55 Marianna F 9.03 9.75 12.16 10.36 11.47 9.83 0.56 <0.001 <0.001 0.08 M 12.00 11.70 14.24 10.57 11.89 12.61 St. Mean F 7.81 9.53 10.82 11.92 11.72 11.31 0.58 <0.001 <0.001 0.02 M 10.62 11.94 13.44 11.93 13.64 12.52 a Type= Forage sampling type. b F= Hand collected forage. c M= Masticate. d SEM= Standard error of the mean, n=48. Table 4. Effect of month on steer selection index a of bahiagrass forage. Location Analysis Month Dec Jan Feb Mar Apr May SEM d P value Ona IVDOM b 122.73 146.45 153.78 129.85 149.22 115.12 18.96 0.65 CP c 124.98 118.66 134.53 99.91 136.43 112.88 24.93 0.89 Brooksville IVDOM 129.68 151.72 151.79 127.67 115.74 116.70 6.72 0.04 CP 150.24 167.84 147.56 101.84 115.55 106.71 19.55 0.24 Santa Fe IVDOM 108.78 na 161.63 114.36 110.47 122.25 6.18 0.02 CP 136.06 na 122.17 96.84 109.80 102.08 21.34 0.79 Marianna IVDOM 121.72 155.43 137.30 112.87 104.30 126.98 8.11 0.05 CP 134.69 118.00 116.28 102.07 103.91 129.38 8.96 0.21 St. Mean IVDOM 120.71 g 151.82 ef 151.11 e 121.23 g 119.92 g 120.34 g 5.73 <0.001 CP 136.52 f 131.03 f 130.12 f 100.24 e 116.44 ef 112.82 ef 8.59 0.03 a {[(Masticate concentration forage concentration) / forage concentration] 100} + 100. b IVDOM= In vitro digestible organic matter. c CP= Crude protein. d SEM= Standard error of the mean, n=12. e,f,g Within a row, means with a different superscript differ, P <0.05