Co-product and rumen degradable protein supplementation of beef steers fed bahiagrass forage

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Co-product and rumen degradable protein supplementation of beef steers fed bahiagrass forage
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2009 Florida Beef Report
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Wahrmund, Jacqueline
Hersom, Matt
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Co-product and Rumen Degradable Protein Supplementation of Beef Steers
Fed Bahiagrass Forage

Jacqueline Wahrmund1
Matt Hersom



Growing beef cattle consuming bahiagrass hay require supplemental dietary crude protein to maintain
performance and promote ADG. Supplements of dried distillers grains or soybeans hulls can may be
useful supplements. Additional degradable protein may not be beneficial.


Summary
An experiment was conducted to evaluate the
effects of feeding co-products with Optigen II
on animal performance and blood metabolites in
growing beef calves. Angus steers were allowed
ad libitum access to bahiagrass hay and were
supplemented for 42 d via Calan gates.
Treatments included 1) dried distillers grains; 2)
dried distillers grains + Optigen; 3) soybean
hulls; 4) soybean hulls + Optigen. Amounts of
dried distillers grains and soybean hulls were
formulated to be isonitrogenous. On d 42, there
were no treatment differences for steer
'ii I, i. rilt (BW), average daily gain (ADG), or
blood glucose concentrations. Across all days,
steers offered only dried distillers grains had
greater plasma urea nitrogen concentrations
than steers offered soybean hulls. On d 14, 28,
and 42, Opimg i-sull'li li,,l steers had
greater plasma urea nitrogen concentrations
compared to those that were not. Beef cattle
consuming bahiagrass hay require additional
dietary crude protein to maintain performance
and promote ADG. However, when sources of
natural protein are fed, additional rumen
degradable protein may not be necessary.

Introduction
Bahiagrass is the most common type of forage
utilized in Florida (Chambliss and Sollenberger,
1991); however, cattle are not able to consume
enough bahiagrass to meet their nutrient
requirements at certain points of the production
cycle. Therefore, supplementation programs
must be developed to optimize beef cattle


performance. Bahiagrass in Florida generally
does not contain enough protein to meet growing
cattle requirements. This makes growing calves
particularly susceptible to protein deficiencies
on low-quality forage-based diets, because they
require high levels of protein to support tissue
growth, are.

Dried distillers grains (DDG) are a co-product of
the corn-derived ethanol fuel industry. As
ethanol fuel production continues to increase in
the United States, DDG will become more
available to cattle producers for animal
consumption. Dried distiller grains are high in
crude protein (CP) but relatively low in rumen
degradable protein (RDP; 31.6% CP, 27.9%
RDP, as a % CP). Soybean hulls (SBH) are
another co-product which are relatively low in
total RDP (12.6% CP, 58% RDP, as a % CP).
For growing cattle a small amount of additional
RDP may optimize performance when added to
co-product supplements. Optigen II (Opt;
Alltech, Inc., Nicholasville, KY) is a urea
product which has slow-release properties that
should result in N availability from urea that is
better synchronized with the energy availability
provided by forage or supplements. A trial was
conducted to evaluate the use of DDG or SBH
with or without additional RDP to background
growing beef steers.

Materials and Methods
Animals and Diets
Fifty-six Angus steers were blocked by


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bodyweight (BW; mean = 544 57 lb) and
randomly assigned to one of four treatments and
one of seven pens. Treatments included: 1)
DDG (2.62 lb of DM); 2) DDG+Opt (2.62 lb of
DDG, 0.10 lb Optigen II); 3) SBH (5.79 lb of
DM); 4) SBH+Opt (5.79 lb of SBH, 0.10 lb
Optigen II). Basal supplements (DDG and
SBH) were formulated to be isonitrogenous
(0.80 lb CP); the addition of Optigen II
provided 0.10 lb of supplemental RDP. Steers
were offered basal supplements daily beginning
five d prior to the initiation of the experiment.
Bahiagrass hay was offered in each pen, ad
libitum, as large round bales. Fresh bales were
offered each wk, and each bale was weighed and
core-sampled for analysis of chemical
composition. Steers were individually
supplemented at approximately 0700 via a Calan
gate system. Approximately 0.13 lb of a
vitamin/mineral supplement was included in the
daily supplements.

Sampling and Analysis
Steers were fed for 42 d, unshrunk BW were
taken on two consecutive days at the initiation (d
-1, 0) and termination of the trial (d 42, 43).
Interim BW were obtained on d 14 and 28. The
two-d mean of BW was utilized to determine
initial and final BW and to determine ADG.
Blood samples were collected for analysis of
plasma urea nitrogen (PUN) and glucose
concentrations. On each of the sampling dates,
spot urine samples were obtained from steers
and creatinine concentrations were determined.
Creatinine concentrations were used to
determine total daily urine output based on the
principle that cattle excrete 883 imol of
creatinine *(kg BW075)-' d-1 (Chen et al., 1992).
Bodyweight measurements, blood, and urine
samples were obtained approximately two h
after supplements were offered.

Weekly hay samples were collected from each
pen and composite for analysis of chemical
composition. Hay and supplement total
digestible nutrients (TDN) concentrations were
determined using the equation (Fike et al.,
2002):
%TDN = [(% IVDMD 0.59) + 32.2] *
organic matter concentration.


Because hay was fed as large round bales within
each pen, mean daily hay dry matter intake
(DMI) was calculated using the NRC (2000)
equation:
SBW = 13.91 REO9116 EQSBW-06837
where:
SBW = shrunk body weight
RE = retained energy
EQSBW = equivalent shrunk body
weight,
assuming a 4% shrink, and that RE is
equal to net energy for gain (NEg).

Statistical analysis.
The experiment was designed as a completely
randomized design, with supplement treatment
as the fixed effect (Littell et al., 2006), steer
within treatment as the random effect and
individual steer was the experimental unit. Data
were analyzed using the Mixed procedure of
SAS v9.1. Means were calculated using least
squares means, and means were separated using
the P-diff option when the overall F-value was
<0.10.

Results
Steer performance and intake.
At the initiation of the trial, steer BW averaged
521 lb (Table 1), with no differences (P=0.97)
among treatments. No differences were
observed in ADG during any two-wk sampling
period (P>0.14). While the addition of Optigen
II had no effect on overall ADG (P=0.30), steers
offered SBH gained approximately 0.15 lb/d
more (P=0.05) compared to steers offered DDG.

The changes observed in steer BW from d 0 to
14 were approximately 2.4 times greater
compared to the period between d 14 and 28.
The dramatic decline in ADG between the first
two collection periods was likely due to
compensatory gain observed during the first 14
d. Two wk prior to the initiation of the trial,
steers consumed a restricted diet consisting of
only limited amounts of a grain-based feed with
molasses. The purpose of this diet was to induce
hunger to enhance the steers' willingness to
learn to use the Calan gates. During the two wk
training period, steer BW gain was minimal,
with some steers losing BW. The ADG of all


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steers was 0.20 lb/d during the three weeks prior
to d 0. The ADG from d -22 to 14 (restriction
through compensation) was nearly equal to the
BW gains observed through the remainder of the
trial (d 14 42) for each treatment, indicating
that the steers likely compensated for the lack of
BW gain during the period of feed restriction.

Forty-two day estimated mean daily hay DMI
(Table 1) was calculated based on shrunk BW
gain and net energy values of the feedstuffs.
Based on the estimations, co-product type
affected voluntary hay DMI (P<0.001), but not
the addition of Optigen II (P=0.62). Steers
consuming DDG or DDG+Opt had 62% greater
(P<0.05) estimated daily hay DMI compared to
steers offered SBH or SBH+Opt. The
differences in estimated mean hay DMI resulted
in 18% greater (P<0.001) total DMI for steers
consuming the DDG supplements compared to
steers receiving SBH. The addition of Optigen
II had no effect (P=0.52) on total DMI.

The decreased DMI observed for steers
consuming the SBH treatments may be a result
of the greater amount of supplement offered
compared to DDG treatments. Supplements
were formulated to contain equal amounts of
CP. Dried distillers grains have a greater
concentration of CP compared to SBH, and as a
result, steers in the SBH treatment were offered
3.17 lb/d more supplement compared to steers in
the DDG treatment. However, the steers offered
the DDG treatment consumed an estimated
mean of 6.0 lb/d more hay; therefore, not all of
the differences in hay intake between
supplement types were the result of substitution
effects. Supplements were formulated to contain
equal concentrations of CP, and therefore, equal
concentrations of N. However, the greater hay
DMI observed in steers consuming DDG
resulted in 40% greater (P<0.001) N intake for
DDG-supplemented steers compared to SBH-
supplemented steers (Table 1). Similarly, steers
offered DDG+Opt consumed 35% greater
(P<0.001) amounts of N/d compared to steers
offered SBH+Opt.

Gain:feed (Table 1) was calculated using mean
estimated daily hay DMI and amount of
supplement offered. Co-product type affected


(P<0.001) gain efficiency, while the addition of
Optigen II did not (P=0.34). Steers offered
DDG-based supplements had a mean gain
efficiency of 0.10, however, steers offered SBH-
based supplements had mean gain efficiency of
0.13. Thus, steers consuming supplements
containing SBH were approximately 25% more
efficient at converting feed to BW compared to
steers offered DDG based supplements. The
differences in gain efficiency were mainly
driven by the differences observed in hay DMI.

Physiological response
As a result of the five-d acclimation period prior
to d 0, differences were observed in initial steer
PUN concentrations (Table 2). Plasma urea
nitrogen concentrations of steers consuming the
SBH and SBH-based supplement treatments
were 45% less (P<0.001) than steers consuming
DDG-based supplement treatments on d 0.
Optigen II was first included in the
supplements on d 0; therefore, resulting in
greater (P=0.05) initial PUN concentration in
steers offered Optigen. On d 14, the steers
consuming DDG-based supplements continued
to have greater (P<0.001) PUN concentrations
compared to steers consuming SBH-based
supplements. Additionally, the inclusion of
Optigen II increased steer PUN concentrations
by 31% (P<0.001) when included in
supplements containing DDG and by 84% in
supplements containing SBH (P<0.001). On d
28, the inclusion of Optigen II increased steer
PUN concentrations by 28.2% in DDG
supplements and by 38.0% in SBH supplements
(P<0.001) compared to steers not offered
Optigen II. Steers consuming DDG+Opt
maintained the greatest PUN concentrations, and
steers offered only SBH had the lowest PUN
concentrations. On d 42, steer PUN
concentrations were greatest (P<0.001) in steers
offered DDG+Opt, followed by the steers on the
DDG and SBH+Opt treatments, which were not
different (P>0.10), followed by SBH-
supplemented steers.

The greater level of N intake observed in steers
offered DDG likely contributed to greater PUN
concentrations compared to SBH. Plasma urea
nitrogen concentrations above 12 mg/dL are
associated with adequate dietary CP, and


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consequently, may indicate a potential for
performance improvement through energy
supplementation (Hammond et al., 1993).
Therefore, steers offered the DDG+Opt
treatment may have exhibited improved
performance with additional dietary energy.
Additionally, Hammond et al. (1993) stated that
cattle with PUN concentrations below 9 mg/dL
are most likely to respond to protein
supplementation when maintained on a
subtropical forage-based diet. The steers offered
the SBH supplement were the only group of
steers that consistently had PUN concentrations
below 9 mg/dL, indicating that these steers may
have benefited from additional protein
supplementation.

Plasma glucose concentrations (Table 2) were
not different (P=0.59) among supplement
treatments or Optigen (P=0.92) on any of the
four sampling dates. Mean glucose
concentration during the experiment was 68.34
mg/dL. While there were differences (P=0.06)
in estimated total TDN intake (Table 1), only
about 1.32 lb/d separated the group of steers that
consumed the greatest amount of TDN
compared to those that consumed the least.
These differences were likely not sufficient to
elicit any changes in plasma glucose
concentrations.

As a result of the acclimation period prior to d 0,
treatment differences as a result of co-product
supplementation (P<0.001) were observed in
initial daily urinary N excretion (Table 2). The


addition of Optigen II had no effect (P=0.12)
on initial urinary N excretion. However, steers
consuming DDG and DDG+Opt excreted 56.2 g
N/d more (P<0.001) compared to steers
consuming SBH and SBH+Opt on d 0. On d 14,
Optigen had no effect (P=0.80) on urinary N
excretion, steers offered DDG excreted
approximately 63% greater (P=0.05) amounts of
urinary N compared to steers offered the SBH
treatments. On d 28, co-product type and
addition of Optigen affected urinary-N excretion
(P=0.001 and 0.01, respectively). No treatment
differences (P>0.38) were observed for urinary
N excretion on d 42.

Similar to PUN concentrations, urinary-N
excretion appears to have been related to
calculated mean daily N intake. Throughout
most of the experiment, urinary-N excretion was
greater for steers consuming DDG supplements
compared to steers consuming SBH. The
addition of Optigen II to the supplements of
beef steers generally did not affect urinary-N
excretion. This may suggest that despite the
additional dietary N, Optigen II did not
increase urinary-N excretion, possibly resulting
in greater N retention.

The SBH treatments were the most effective, as
these steers exhibited the greatest feed
efficiency. Supplemental RDP did not affect
steer performance. While Optigen II addition
increased PUN concentrations to more desirable
levels in SBH diets, it did not affect
performance.


Literature Cited
Chambliss and Sollenberger. 1991. Pages 74-80 in Proc. 40th Florida Beef Cattle Short Course.
Chen etal. 1992. Anim. Prod. 55:185.
Fike et al. 2002. J. Dairy Sci. 85:866.
Hammond et al. 1993. In: Proc. XVII Int. Grassl. Congr. p 1989.
Littell et al. 2006. SAS System for Mixed Models. 2nd ed.
NRC. 2000. Nutrient requirements of beef cattle. 7h rev. ed.


1 Jacqueline Wahrmund, Former Graduate Student, Matt Hersom, Assistant Professor, UF-IFAS,
Department of Animal Sciences, Gainesville, FL.


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Table 1. Effect of co-product source and Optigen" II supplementation on steer bodyweight (BW), BW gain
and intake.
Treatment P-Value
Item DDG DDG+Opt SBH SBH+Opt SEMb Co- Optigen
product
Initial BW, lb 522 522 524 515 15.6 0.88 0.71
BW gain, lb/d
d 0 14 2.80 3.00 2.91 3.19 0.22 0.46 0.29
d 14 28 0.99 1.01 1.54 1.34 0.31 0.14 0.78
d 28 42 1.74 1.67 1.45 1.81 0.24 0.77 0.54
d 0 -42 1.85 1.89 1.96 2.07 0.09 0.05 0.30

Mean hay DMI, lb/d 15.5d 15.9d 9.5e 9.8e 0.64 <0.001 0.62
Total DMI, lb/d 18.1d 18.6d 15.4e 15.7e 0.64 <0.001 0.52
N Intake, g/d" 165.65d 188.05e 118.02' 139.37g 3.93 <0.001 <0.001
TDN Intake, lb/dc 11.6de 11.8d 10.5f 10.7ef 0.39 0.007 0.62

Gain:Feed, lb:lb 0.10d 0.10d 0.12e 0.13e 0.003 <0.001 0.34
aLeast square means; Treatment: DDG, dried distillers grains; DDG+Opt, dried distillers grains plus
Optigen II, SBH, soybean hulls; SBH+Opt, soybean hulls plus Optigen II.
b Standard error of the mean, n=56.
c Estimated total dietary intake (hay and supplement).


Table 2. Effect of co-product source and Optigen II supplementation on steer plasma metabolite
concentrations and daily urinary excretion.
Treatment P-Value
Item DDG DDG+Opt SBH SBH+Opt SEMb Co- Optigen
product
PUN", mg/dL
dO 10.17 11.49 4.06 5.67 0.72 <0.001 0.05
d 14 10.70 14.02 5.51 10.12 0.82 <0.001 <0.001
d28 10.69 13.70 6.17 8.51 0.67 <0.001 <0.001
d 42 10.35 13.43 7.87 10.30 0.66 <0.001 <0.001

Mean glucose, 70.59 67.20 65.87 69.70 2.16 0.59 0.92
mg/dL

Urinary N, g/d
d 0 102.11 125.41 53.40 61.64 10.37 <0.001 0.12
d 14 162.11 144.62 77.74 110.33 33.70 0.05 0.80
d28 130.67 180.40 92.93 118.32 15.20 0.001 0.01
d42 113.01 110.05 112.77 141.78 22.32 0.38 0.47
aLeast square means; Treatment: DDG, dried distillers grains; DDG+Opt, dried distillers grains plus
Optigen II, SBH, soybean hulls; SBH+Opt, soybean hulls plus Optigen II.
b Standard error of the mean; n=56 for PUN and glucose, n=19, 23, 27, 22 for days 0, 14, 28, 42, respectively
for urinary N.
c Plasma urea nitrogen.


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Full Text

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Co product and Rumen Degradable Protein Supplementation of Beef Steers Fed Bahiagrass Forage Jacqueline Wahrmund 1 Matt Hersom Summary An experiment was conducted to evaluate the effects of feeding co-products with Optigen II on animal performance and blood metabolites in growing beef calves. Angus steers were allowed ad libitum access to bahiagrass hay and were supplemented for 42 d via Calan gates. Treatments included 1) dried distillers grains; 2) dried distillers grains + Optigen; 3) soybean hulls; 4) soybean hulls + Optigen. Amounts of dried distillers grains and soybean hulls were formulated to be isonitrogenous. On d 42, there were no treatment differences for steer bodyweight (BW), average daily gain (ADG), or blood glucose concentrations. Across all days, steers offered only dried distillers grains had greater plasma urea nitrogen concentrations than steers offered soybean hulls. On d 14, 28, and 42, Optigen-supplemented steers had greater plasma urea nitrogen concentrations compared to those that were not. Beef cattle consuming bahiagrass hay require additional dietary crude protein to maintain performance and promote ADG. However, when sources of natural protein are fed, additional rumen degradable protein may not be necessary. Introduction Bahiagrass is the most common type of forage utilized in Florida (Chambliss and Sollenberger 1991); however, cattle are not able to consume enough bahiagrass to meet their nutrient requirements at certain points of the production cycle. Therefore, supplementation programs must be developed to optimize beef cattle performance. Bahiagrass in Florida generally does not contain enough protein to meet growing cattle requirements. This makes growing calves particularly susceptible to protein deficiencies on low-quality forage-based diets, because they require high levels of protein to support tissue growth, are. Dried distillers grains ( DDG) are a co-product of the corn-derived ethanol fuel industry. As ethanol fuel production continues to increase in the United States, DDG will become more available to cattle producers for animal consumption. Dried distiller grains are high in crude protein (CP ) but relatively low in rumen degradable protein (RDP; 31.6% CP, 27.9% RDP, as a % CP). Soybean hulls (SBH) are another co-product which are relatively low in total RDP (12.6% CP, 58% RDP, as a % CP). For growing cattle a small amount of additional RDP may optimize performance when added to co-product supplements. Optigen II (Opt; Alltech, Inc., Nicholasville, KY) is a urea product which has slow-release properties that should result in N availability from urea that is better synchronized with the energy availability provided by forage or supplements. A trial was conducted to evaluate the use of DDG or SBH with or without additional RDP to background growing beef steers. Materials and Methods Animals and Diets Fifty-six Angus steers were blocked by Growing beef cattle consuming bahiagrass hay require supplemental dietary crude protein to maintain performance and promote ADG. Supplements of dried distillers grains or soybeans hulls can may be useful supplements. Additional degradable protein may not be beneficial.

PAGE 2

bodyweight ( BW ; mean = 544 57 lb) and randomly assigned to one of four treatments and one of seven pens. Treatments included: 1) DDG (2.62 lb of DM); 2) DDG+Opt (2.62 lb of DDG, 0.10 lb Optigen II); 3) SBH (5.79 lb of DM); 4) SBH+Opt (5.79 lb of SBH, 0.10 lb Optigen II). Basal supplements (DDG and SBH) were formulated to be isonitrogenous (0.80 lb CP); the addition of Optigen II provided 0.10 lb of supplemental RDP. Steers were offered basal supplements daily beginning five d prior to the initiation of the experiment. Bahiagrass hay was offered in each pen, ad libitum, as large round bales. Fresh bales were offered each wk, and each bale was weighed and core-sampled for analysis of chemical composition. Steers were individually supplemented at approximately 0700 via a Calan gate system. Approximately 0.13 lb of a vitamin/mineral supplement was included in the daily supplements. Sampling and Analysis Steers were fed for 42 d, unshrunk BW were taken on two consecutive days at the initiation (d -1, 0) and termination of the trial (d 42, 43). Interim BW were obtained on d 14 and 28. The two-d mean of BW was utilized to determine initial and final BW and to determine ADG. Blood samples were collected for analysis of plasma urea nitrogen (PUN) and glucose concentrations. On each of the sampling dates, spot urine samples were obtained from steers and creatinine concentrations were determined. Creatinine concentrations were used to determine total daily urine output based on the principle that cattle excrete 883 mol of 0.75 ) -1 -1 (Chen et al., 1992). Bodyweight measurements, blood, and urine samples were obtained approximately two h after supplements were offered. Weekly hay samples were collected from each pen and composited for analysis of chemical composition. Hay and supplement total digestible nutrients (TDN) concentrations were determined using the equation (Fike et al., 2002): %TDN = [(% IVDMD 0.59) + 32.2] organic matter concentration. Because hay was fed as large round bales within each pen, mean daily hay dry matter intake (DMI) was calculated using the NRC (2000) equation: SBW = 13.91 RE 0.9116 EQSBW -0.6837 where: SBW = shrunk body weight RE = retained energy EQSBW = equivalent shrunk body weight, assuming a 4% shrink, and that RE is equal to net energy for gain (NE g ). Statistical analysis. The experiment was designed as a completely randomized design, with supplement treatment as the fixed effect (Littell et al., 2006), steer within treatment as the random effect and individual steer was the experimental unit. Data were analyzed using the Mixed procedure of SAS v9.1. Means were calculated using least squares means, and means were separated using the P-diff option when the overall F-value was <0.10. Results Steer performance and intake. At the initiation of the trial, steer BW averaged 521 lb (Table 1), with no differences ( P =0.97) among treatments. No differences were observed in ADG during any twowk sampling period ( P >0.14). While the addition of Optigen II had no effect on overall ADG ( P =0.30), steers offered SBH gained approximately 0.15 lb/d more ( P =0.05) compared to steers offered DDG. The changes observed in steer BW from d 0 to 14 were approximately 2.4 times greater compared to the period between d 14 and 28. The dramatic decline in ADG between the first two collection periods was likely due to compensatory gain observed during the first 14 d. Two wk prior to the initiation of the trial, steers consumed a restricted diet consisting of only limited amounts of a grain-based feed with molasses. The purpose of this diet was to induce learn to use the Calan gates. During the two wk training period, steer BW gain was minimal, with some steers losing BW. The ADG of all

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steers was 0.20 lb/d during the three weeks prior to d 0. The ADG from d -22 to 14 (restriction through compensation) was nearly equal to the BW gains observed through the remainder of the trial (d 14 42) for each treatment, indicating that the steers likely compensated for the lack of BW gain during the period of feed restriction. Forty-two day estimated mean daily hay DMI (Table 1) was calculated based on shrunk BW gain and net energy values of the feedstuffs. Based on the estimations, co-product type af fected voluntary hay DMI ( P <0.001), but not the addition of Optigen II ( P =0.62). Steers consuming DDG or DDG+Opt had 62% greater ( P <0.05) estimated daily hay DMI compared to steers offered SBH or SBH+Opt. The differences in estimated mean hay DMI resulted in 18% greater ( P <0.001) total DMI for steers consuming the DDG supplements compared to steers receiving SBH. The addition of Optigen II had no effect ( P =0.52) on total DMI. The decreased DMI observed for steers consuming the SBH treatments may be a result of the greater amount of supplement offered compared to DDG treatments. Supplements were formulated to contain equal amounts of CP. Dried distillers grains have a greater concentration of CP compared to SBH, and as a result, steers in the SBH treatment were offered 3.17 lb/d more supplement compared to steers in the DDG treatment. However, the steers offered the DDG treatment consumed an estimated mean of 6.0 lb/d more hay; therefore, not all of the differences in hay intake between supplement types were the result of substitution effects. Supplements were formulated to contain equal concentrations of CP, and therefore, equal concentrations of N. However, the greater hay DMI observed in steers consuming DDG resulted in 40% greater ( P <0.001) N intake for DDG -supplemented steers compared to SBHsupplemented steers (Table 1). Similarly, steers offered DDG+Opt consumed 35% greater ( P <0.001) amounts of N/d compared to steers offered SBH+Opt. Gain:feed (Table 1) was calculated using mean estimated daily hay DMI and amount of supplement offered. Co-product type affected ( P<0.001) gain efficiency, while the addition of Optigen II did not ( P =0.34). Steers offered DDG -based supplements had a mean gain efficiency of 0.10, however, steers offered SBHbased supplements had mean gain efficiency of 0.13. Thus, steers consuming supplements containing SBH were approximately 25% more efficient at converting feed to BW compared to steers offered DDG based supplements. The differences in gain efficiency were mainly driven by the differences observed in hay DMI. Physiological response As a result of the five-d acclimation period prior to d 0, differences were observed in initial steer PUN concentrations (Table 2). Plasma urea nitrogen concentrations of steers consuming the SBH and SBH-based supplement treatments were 45% less ( P <0.001) than steers consuming DDG -based supplement treatments on d 0. Optigen II was first included in the supplements on d 0; therefore, resulting in greater ( P =0.05) initial PUN concentration in steers offered Optigen. On d 14, the steers consuming DDG-based supplements continued to have greater ( P <0.001) PUN concentrations compared to steers consuming SBH-based supplements. Additionally, the inclusion of Optigen II increased steer PUN concentrations by 31% ( P <0.001) when included in supplements containing DDG and by 84% in supplements containing SBH ( P<0.001). On d 28, the inclusion of Optigen II increased steer PUN concentrations by 28.2% in DDG supplements and by 38.0% in SBH supplements ( P<0.001) compared to steers not offered Optigen II. Steers consuming DDG+Opt maintained the greatest PUN concentrations, and steers offered only SBH had the lowest PUN concentrations. On d 42, steer PUN concentrations were greatest ( P<0.001) in steers offered DDG+Opt, followed by the steers on the DDG and SBH+Opt treatments, which were not different ( P >0.10), followed by SBHsupplemented steers. The greater level of N intake observed in steers offered DDG likely contributed to greater PUN concentrations compared to SBH. Plasma urea nitrogen concentrations above 12 mg/dL are associated with adequate dietary CP, and

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consequently, may indicate a potential for performance improvement through energy supplementation (Hammond et al., 1993). Therefore, steers offered the DDG+Opt treatment may have exhibited improved performance with additional dietary energy. Additionally, Hammond et al. (1993) stated that cattle with PUN concentrations below 9 mg/dL are most likely to respond to protein supplementation when maintained on a subtropical forage-based diet. The steers offered the SBH supplement were the only group of steers that consistently had PUN concentrations below 9 mg/dL, indicating that these steers may have benefited from additional protein supplementation. Plasma glucose concentrations (Table 2) were not different ( P =0.59) among supplement treatments or Optigen ( P =0.92) on any of the four sampling dates. Mean glucose concentration during the experiment was 68.34 mg/dL. While there were differences ( P =0.06) in estimated total TDN intake (Table 1), only about 1.32 lb/d separated the group of steers that consumed the greatest amount of TDN compared to those that consumed the least. These differences were likely not sufficient to elicit any changes in plasma glucose concentrations. As a result of the acclimation period prior to d 0, treatment differences as a result of co-product supplementation ( P <0.001) were observed in initial daily urinary N excretion (Table 2). The addition of Optigen II had no effect ( P =0.12) on initial urinary N excretion. However, steers consuming DDG and DDG+Opt excreted 56.2 g N/d more ( P <0.001) compared to steers consuming SBH and SBH+Opt on d 0. On d 14, Optigen had no effect ( P =0.80) on urinary N excretion, steers offered DDG excreted approximately 63% greater ( P =0.05) amounts of urinary N compared to steers offered the SBH treatments. On d 28, co-product type and addition of Optigen affected urinary-N excretion ( P=0.001 and 0.01, respectively). No treatment differences ( P >0.38) were observed for urinary N excretion on d 42. Similar to PUN concentrations, urinaryN excretion appears to have been related to calculated mean daily N intake. Throughout most of the experiment, urinary-N excretion was greater for steers consuming DDG supplements compared to steers consuming SBH. The addition of Optigen II to the supplements of beef steers generally did not affect urinaryN excretion. This may suggest that despite the additional dietary N, Optigen II did not increase urinary-N excretion, possibly resulting in greater N retention. The SBH treatments were the most effective, as these steers exhibited the greatest feed efficiency. Supplemental RDP did not affect steer performance. While Optigen II addition increased PUN concentrations to more desirable levels in SBH diets, it did not affect performance. Literature Cited Chambliss and Sollenberger. 1991. Pages 74 80 in Proc. 40 th Florida Beef Cattle Short Course. Chen et al. 1992. Anim. Prod. 55:185. Fike et al. 2002. J. Dairy Sci. 85:866. Hammond et al. 1993. In: Proc. XVII Int. Grassl. Congr. p 1989. Litt ell et al. 2006. SAS System for Mixed Models. 2 nd ed. NRC. 2000. Nutrient requirements of beef cattle. 7 th rev. ed. 1 Jacqueline Wahrmund, Former Graduate Student, Matt Hersom, Assistant Professor, UF IFAS, Department of Animal Sciences, Gainesville, FL.

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Table 1. Effect of co product source and Optigen II supplementation on steer bodyweight (BW), BW gain and intake. Treatment a P Value Item DDG DDG+Opt SBH SBH+Opt SEM b Co product Optigen Initial BW, lb 522 522 524 515 15.6 0.88 0.71 BW gain, lb/d d 0 14 2.80 3.00 2.91 3.19 0.22 0.46 0.29 d 14 28 0.99 1.01 1.54 1.34 0.31 0.14 0.78 d 28 42 1.74 1.67 1.45 1.81 0.24 0.77 0.54 d 0 42 1.85 1.89 1.96 2.07 0.09 0.05 0.30 Mean hay DMI, lb/d 15.5 d 15.9 d 9.5 e 9.8 e 0.64 <0.001 0.62 Total DMI, lb/d 18.1 d 18.6 d 15.4 e 15.7 e 0.64 <0.001 0.52 N Intake, g/d c 165.65 d 188.05 e 118.02 f 139.37 g 3.93 <0.001 <0.001 TDN Intake, lb/d c 11.6 de 11.8 d 10.5 f 10.7 ef 0.39 0.007 0.62 Gain:Feed, lb:lb 0.10 d 0.10 d 0.12 e 0.13 e 0.003 <0.001 0.34 a Least square means; Treatment: DDG, dried distillers grains; DDG+Opt, dried distillers grains plus Optigen II, SBH, soybean hulls; SBH+Opt, soybean hulls plus Optigen II. b Standard error of the mean, n=56. c Estimated total dietary intake (hay and supplement). Table 2. Effect of co product source and Optigen II supplementation on steer plasma metabolite concentrations and daily urinary excretion. Treatment a P Value Item DDG DDG+Opt SBH SBH+Opt SEM b Co product Optigen PUN c mg/dL d 0 10.17 11.49 4.06 5.67 0.72 <0.001 0.05 d 14 10.70 14.02 5.51 10.12 0.82 <0.001 <0.001 d 28 10.69 13.70 6.17 8.51 0.67 <0.001 <0.001 d 42 10.35 13.43 7.87 10.30 0.66 <0.001 <0.001 Mean glucose, mg/dL 70.59 67.20 65.87 69.70 2.16 0.59 0.92 Urinary N, g/d d 0 102.11 125.41 53.40 61.64 10.37 <0.001 0.12 d 14 162.11 144.62 77.74 110.33 33.70 0.05 0.80 d 28 130.67 180.40 92.93 118.32 15.20 0.001 0.01 d 42 113.01 110.05 112.77 141.78 22.32 0.38 0.47 a Least square means; Treatment: DDG, dried distillers grains; DDG+Opt, dried distillers grains plus Optigen II, SBH, soybean hulls; SBH+Opt, soybean hulls plus Optigen II. b Standard error of the mean; n=56 for PUN and glucose, n=19, 23, 27, 22 for days 0, 14, 28, 42, respectively for urinary N. c Plasma urea nitrogen.