Effect of residual feed intake, gender, and breed composition on plasma urea nitrogen concentration in an Angus-Brahman ...

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Effect of residual feed intake, gender, and breed composition on plasma urea nitrogen concentration in an Angus-Brahman multibreed herd
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Myer, Bob
Elzo, Mauricio
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University of Florida
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Gainesville, Fla.

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Effect of Residual Feed Intake, Gender, and Breed Composition on Plasma
Urea Nitrogen Concentration in an Angus-Brahman Multibreed Herd

Bob Myer1
Mauricio Elzo2



Feed efficient beef cattle appear to more efficiently utilize absorbed diet protein than feed inefficient
beef cattle.


Summary
Plasma urea nitrogen can be used as an
indicator of N use and excretion by an animal.
The objective of this research was to assess the
effect of residual feed intake (RFI) on plasma
concentration of urea N (PUN) in 188 bulls,
heifers, and steers (mean body weight 652 lb,
SD 82 lb) ranging from 100% Angus to 100%
Brahman. Calves were assigned to pens in a
GrowSafe feeding facility by sire group and sex,
and self-fed a total mixed ration (corn,
cottonseed hulls, chopped grass hay, cottonseed
meal, molasses, and mineral-vitamin
supplement; 90% dry matter (DM), 14% crude
protein (CP), 0.7 Mcal/lb DM of NEm, and 0.4
Mcal/lb DM of NEg). The pre-trial adjustment
period lasted 21 d. Individual daily feed intake
was collected during the 70-d feeding trial; body
weights were recorded every 2 wk. Blood
(jugular) was drawn on d 56for PUN. Residual
feed intake was computed as the difference
between actual and expected feed intakes. The
RFI groups were high (RFI > mean + 0.5
standard deviation (SD)), medium (RFI between
S0.5 SD), and low (RFI < mean -0.5 SD; SD
4.4 lb DM/d). Data (PUN) were analyzed using
a mixed model. Fixed effects were sex of calf,
RFI group, and Brahman fraction of calf; daily
feed intake was a covariate. Random effects
were sire and residual. Overall ADG was 2.74
0.55 lb/d. Brahman PUN concentration was
greater than Angus (P<0.01). Sex affected PUN
(P<0.01) concentration with bulls having the
lowest and heifers the highest. PUN
concentration was related to RFI (P=0.02),


indicating that more feed efficient animals also
had lower PUN.

Introduction
Analyzing plasma urea nitrogen (PUN)
concentration is a useful indicator of protein
status within a group of animals, and can be
used to predict nitrogen (N) utilization and
excretion (Kohn et al., 2005). Nitrogen is a
component of protein and urea is a waste
product of protein utilization and metabolism.
With similarly fed and managed animals, high
PUN levels would indicate inefficient utilization
of absorbed protein for growth and other animal
functions, and conversely, low levels would
indicate efficient utilization.

Canadian researchers have reported that the
digestibility of diet crude protein (CP) was
moderately positively related to feed efficiency
in growing beef cattle (Nkrumah et al., 2006).
However, the relationship between utilization of
absorbed protein and N and feed efficiency has
not been investigated using the advanced feed
intake technology now available such as the
GrowSafeTM system. The GrowSafe system
allows the measurement of individual animal
feed intake for cattle reared in groups. We
hypothesize that feed efficient beef cattle will
also be more efficient in the utilization of
absorbed protein and resulting in less N loss to
the environment. Thus, the objective of this
initial study was to determine the effect of
residual feed intake (RFI) on PUN
concentration in growing bulls, heifers, and


'North Florida Research and Education Center, University of Florida, Marianna, FL
2Department of Animal Sciences; University of Florida, Gainesville, FL










steers ranging from 100% Angus to 100%
Brahman.

Residual feed intake was used as the measure of
feed efficiency as it is phenotypically
independent of average daily weight gain (ADG)
and has become the preferred measure of
efficiency of feed utilization (Koch et al., 1963;
Archer et al., 1997). Residual feed intake is
defined as the difference between actual and
expected feed intake, therefore the lower the
RFI, the better the feed efficiency.

Materials and Methods
Weaned beef cattle (n = 188; 7 to 8 mo of age;
average initial body weight of 652 lb) were
evaluated in a 70-d feed intake study. There
were 11 bulls, 93 heifers and 84 steers from 6
breed groups: Angus (A; n = 25), Brahman (B; n
= 28), 34 A '4 B (n = 36), Brangus (5/8 A 3/8 B;
n = 31),2 A '2B (n = 43), and 4A % B (n =
25). After weaning (August or early September),
the calves grazed on bahiagrass (Paspalum
notatum) and received a preconditioning diet for
3 to 6 wk in preparation for their feed intake trial
at the Feed Efficiency Facility at the UF North
Florida Research and Education Center in
Marianna. This facility is equipped with
GrowSafeTM technology to measure individual
feed intake in cattle housed in groups. The
calves were assigned to pens of 15 or 16 head of
either heifers or steers, or bulls and steers by
sire, body weight and breed group. After
assignment, the calves were self-fed a total
mixed ration (corn, cottonseed hulls, chopped
grass hay, cottonseed meal, molasses, and
mineral-vitamin supplement; 90% DM, 14% CP,
0.7 Mcal/lb DM NEm, and 0.4 Mcal/lb DM
NEg) for the duration of the study. The pre-trial
adjustment period lasted 21 d. Individual daily
feed intake was collected during the 70-d
feeding trial; calf body weight was recorded
every 2 wk. Blood (jugular) was drawn on d 56
into heparin-containing tubes; plasma was
separated and analyzed for urea N (Coulombe
and Favrean, 1963). The study started mid-
October and ended in mid-December of 2007.


Residual feed intake was computed as the
difference between actual and expected intakes.
Expected feed intake was estimated as a linear
regression of average daily feed intake on
average daily gain and metabolic mid-weight.
The RFI groups were high (RFI > mean + 0.5
SD), medium (RFI between 0.5 SD), and low
(RFI < mean 0.5 SD; SD = 4.4 lb DM/d).

Data (PUN) were analyzed using a mixed
model. Fixed effects were sex of calf, RFI
group, and Brahman fraction of calf; daily feed
intake was a covariate. Random effects were sire
and residual.

Results and Discussion
In this study, daily feed intake was used as a
covariate for PUN statistical analysis as feed
intake in itself can influence PUN concentration
(Eggum, 1970). Day 56 was chosen for blood
sampling as it is well into the 70-d feeding
period and still be at the time of year in which
climatic conditions would be comfortable for the
cattle.

Overall cattle performance and PUN
concentration are summarized in Table 1.
Growth performance and feed intake were as
expected given the age and size of the calves,
the diet composition, and the climatic
conditions. Mean RFI equaled 0 by design and
varied plus or minus by 4.4 lb (one standard
deviation). Calves with a negative RFI ate less
feed than predicted for a given weight gain (feed
efficient animals) whereas those with a positive
RFI ate more for a given weight gain (inefficient
animals).

Feed efficiency and average daily feed intake
were affected by RFI grouping (P < 0.01; Figure
1). As expected, average daily gain was not
affected by RFI grouping (P > 0.10) indicating
that RFI was independent of this parameter.

Concentration of PUN was affected by RFI
grouping, in that feed efficient cattle had lower
PUN concentrations than feed inefficient cattle
(P =0.02; Figure 2). This finding indicated that










feed efficient animals were more efficient in the
utilization of absorbed protein for growth and
other body functions than inefficient cattle.
Another benefit would be less urea-N excreted
via urine in the efficient animals as compared to
the inefficient animals.

Sex of calf affected PUN concentration (P <
0.01; Figure 3). This effect was expected due to
differences in hormone types and
concentrations. Androgens increase utilization
of protein-N by the animal to a greater extent
than estrogen.

Breed grouping also affected PUN concentration
(P < 0.01; Figure 4). In general, as the Brahman
fraction increased from 0 to 100%, PUN
concentration increased. This would indicate
that Brahman cattle are not as efficient in the
utilization of absorbed protein as Angus cattle.
This effect may be due to the greater feed intake
and poorer feed efficiency in Brahman versus
Angus cattle noted in a companion study (Elzo
et al., 2009).

The main result of this initial study indicated
that more feed efficient cattle had lower PUN
indicating that they were more efficient in the
utilization of absorbed protein than inefficient
cattle. Further testing is needed to confirm this
initial finding.




Literature Cited
Archer et al. 1997. J. Anim. Sci. 75:2024.
Coulombe and Favrean. 1963. Clin. Chem. 9:102.
Eggum. 1970. Br. J. Nutr. 24:983.
Elzo et al. 2009. J Anim. Sci. 87:3877.
Koch et al. 1963. J. Anim. Sci. 22:486.
Kohn et al. 2005. J. Anim. Sci. 83:879.
Nkrumah et al. 2006. J. Anim. Sci. 84:145.


Acknowledgments
The assistance of Harvey Standland, Don Jones, Sergji Sennikov, Charles Nowell, Mary Maddox
and David Thomas is gratefully acknowledged.









Table 1. Overall summary of growth performance and plasma urea nitrogen concentrations in growing
beef cattle during the 70-d test feeding period
Trait Mean Standard deviation


Avg. daily feed intake, lb
Feed efficiency (feed:gain), lb/lb
Average daily gain, lb
Residual feed intake, lb/d
Plasma urea-N at d 56, mg/dL


23.5
9.0
2.74
0
11.9


4.6
2.5
0.55
4.4
2.9


Figure 1. Residual feed intake grouping for average daily weight gain (ADG), average daily feed
intake (ADFI), and average feed efficiency (Feed: gain) during the 70-d test feeding period (SE = 0.05
and P > 0.10 for ADG, SE = 0.5 and P < 0.01 for ADFI, and SE = 0.4 and P < 0.01 for F:G; least
square means).


ADG


5
4
"a3
2
1
0


Low RFI Med RFI High RFI
Residual feed intake


Feed:gain

12
10
8
6 -
4
2
0
LowRFI MedRFI High RFI
Residual feed intake


ADFI
40

30

2 20
10 -

0
Low RFI Med RFI High RFI
Residual feed intake


























Bulls Steers Heifers
Sex
Figure 3. Effect of calf sex on plasma urea nitrogen concentration at d 56 of the 70-d test feeding
period (SE = 0.2 and P<0.01; least square means).


0
Angus (A) 75 A: 25 B Brangus 50 A: 50 B 25 A: 75 B Brahman (B)

Breed

Figure 4. Effect of breed group on plasma urea nitrogen concentration at d 56 of the 70-d test
feeding period (SE= 0.6 and P<0.01; least square means).


I




Full Text

PAGE 1

Effect of R esidual F eed I ntake, G ender, and B reed C omposition on Plasma U rea N itrogen C oncentration in an Angus Brahman M ultibreed H erd Bob Myer 1 Mauricio Elzo 2 Summary Plasma urea nitrogen can be used as an indicator of N use and excretion by an animal. The objective of this research was to assess the effect of residual feed intake (RFI) on plasma concentration of urea N (PUN) in 188 bulls, heifers, and steers (mean body weigh t = 652 lb, SD = 82 lb) ranging from 100% Angus to 100% Brahman. Calves were assigned to pens in a GrowSafe feeding facility by sire group and sex, and self fed a total mixed ration (corn, cottonseed hulls, chopped grass hay, cottonseed meal, molasses, and mineral vitamin supplement; 90% dry matter ( DM ) 14% crude protein ( CP ) 0.7 Mcal/lb DM of NEm, and 0.4 Mcal/lb DM of NEg). The pre trial adjustment period lasted 21 d Individual daily feed intake was collected during the 70 d feeding trial; body weights were recorded every 2 wk. Blood (jugular) was drawn on d 5 6 for PUN. Residual feed intake was computed as the difference between actual and expected feed intakes. The RFI groups were high (RFI > mean + 0.5 standard deviation (SD)), medium (RFI between 0 .5 SD), and low (RFI < mean 0.5 SD; SD = 4.4 lb DM/d). Data (PUN) were analyzed using a mixed model. Fixed effects were sex of calf, RFI group, and Brahman fraction of calf; daily feed intake was a covariate. Random effects were sire and residual. Overa ll ADG was 2.74 0.55 lb/d. Brahman PUN concentration was greater than Angus (P<0.01). Sex affected PUN (P<0.01) concentration with bulls having the lowest and heifers the highest. PUN concentration was r elated to RFI (P=0.02), indicating that more feed efficient animals also had lower PUN. Introduction Analyzing plasma urea nitrogen ( P UN) concentration is a useful indicator of protein status within a group of animals, and can be used to predict nitrogen (N) utilization and excretion (Kohn et al., 2005). Nitrogen is a component of protein and urea is a waste product of protein utilizatio n and metabolism. With similarly fed and managed animals, high P UN levels would indicate inefficient utilization of absorbed protein for growth and other animal functions, and conversely, low levels would indicate efficient utilization. Canadian researche rs have reported that the digestibility of diet crude protein (CP) was moderately positively related to feed efficiency in growing beef cattle (Nkrumah et al., 2006). However, the relationship between utilization of absorbed protein and N and feed efficien cy has not been investigated using the advanced feed intake technology now available such as the GrowSafe TM system. The GrowSafe system allows the measurement of individual animal feed intake for cattle reared in groups. We hypothesize that feed efficient beef cattle will also be more efficient in the utilization of absorbed protein and resulting in less N loss to the environment. Thus, the objective of this initial study was to determine the effect of residual feed intake (RFI) on PUN concentration in grow ing bulls, heifers, and Feed efficient beef cattle appear to more efficiently utilize absorbed diet protein than feed inefficient beef cattle. 1 North Florida Research and Education Center, University of Florida Marianna FL 2 Department of Animal Sciences; University of Florida, Gainesville FL

PAGE 2

steers ranging from 100% Angus to 100% Brahman. Residual feed intake was used as the measure of feed efficiency as it is phenotypically independent of average daily weight gain (ADG) and has become the preferred measure of efficien cy of feed utilization (Koch et al., 1963; Archer et al., 1997). Residual feed intake is defined as the difference between actual and expected feed intake, therefore the lower the RFI, the better the feed efficiency. Materials and Methods Weaned beef cattl e (n = 188; 7 to 8 mo of age; average initial body weight of 652 lb) were evaluated in a 70 d feed intake study. There were 11 bulls, 93 heifers and 84 steers from 6 breed groups: Angus (A; n = 25), Brahman (B; n = 28), A B (n = 36), Brangus (5/8 A 3/8 B; n = 31), A B (n = 43), and A B (n = 25). After weaning (August or early September), the calves grazed on bahiagrass ( Paspalum notatum ) and received a preconditioning diet for 3 to 6 wk in preparation for their feed intake trial at the Feed Effi ciency Facility at the UF North Florida Research and Education Center in Marianna. This facility is equipped with GrowSafe TM technology to measure individual feed intake in cattle housed in groups. The calves were assigned to pens of 15 or 16 head of eithe r heifers or steers, or bulls and steers by sire, body weight and breed group. After assignment, the calves were self fed a total mixed ration (corn, cottonseed hulls, chopped grass hay, cottonseed meal, molasses, and mineral vitamin supplement; 90% DM, 14 % CP 0.7 Mcal/lb DM NEm, and 0.4 Mcal/lb DM NEg) for the duration of the study. The pre trial adjustment period lasted 21 d. Individual daily feed intake was collected during the 70 d feeding trial; calf body weight was recorded every 2 wk. Blood (jugular ) was drawn on d 56 into heparin containing tubes; plasma was separated and analyzed for urea N (Coulombe and Favrean, 1963). The study started mid October and ended in mid December of 2007. Residual feed intake was computed as the difference between actual and expected intakes. Expected feed intake was estimated as a linear regression of average daily feed intake on average daily gain and metabolic mid weight. The RFI groups were high (RFI > mean + 0.5 SD), medium (RFI between 0.5 SD), and low (RFI < mean 0.5 SD; SD = 4.4 lb DM/d). Data (PUN) were analyzed using a mixed model. Fixed effects were sex of calf, RFI group, and Brahman fraction of calf; daily feed intake was a covariate. Rando m effects were sire and residual. Results and Discussion In this study, daily feed intake was used as a covariate for PUN statistical analysis as feed intake in itself can influence PU N concentration (Eggum 1970). Day 56 was chosen for blood sampling as it is well into the 70 d feeding period and still be at the time of year in which climatic conditions would be comfortable for the cattle. Overall cattle performance and PUN concentration are summarized in T able 1. G rowth performance and feed intake were as expected given the age and size of the calves, the diet composition, and the climatic conditions. Mean RFI equaled 0 by design and varied plus or minus by 4.4 lb (one standard deviation). Calves with a neg ative RFI ate less feed than predicted for a given weight gain (feed efficient animals) whereas those with a positive RFI ate more for a given weight gain (inefficient animals). Feed efficiency and average daily feed intake were affected by RFI grouping ( P < 0.01; Figure 1). As expected, average daily gain was not affected by RFI grouping ( P > 0.10) indicating that RFI was independent of this parameter. Concentration of PUN was affected by RFI grouping, in that feed efficient cattle had lower PUN concentrations than feed i nefficient cattle ( P = 0.02; Figure 2). This finding indicated that

PAGE 3

feed efficient animals were more efficient in the utilization of absorbed protein for growth and other body functions than inefficient cattle. Anot her benefit would be less urea N excreted via urine in the efficient animals as compared to the inefficient animals. Sex of calf affected PUN concentration ( P < 0.01; Figure 3). This effect was expected due to differences in hormone types and concentrations. Androgens increase utilization of protei n N by the animal to a greater extent than estrogen. Breed grouping also affected PUN concentration ( P < 0.01; Figure 4). In general, as the Brahman fraction increase d from 0 to 100%, PUN concentration increased. This would indicate that Brahman cattle are not as efficient in the utilization of absorbed protein as Angus cattle. This effect may be due to the greater feed intake and poorer feed efficiency in Brahman versu s Angus cattle noted in a companion study (Elzo et al., 2009). The main result of this initial study indicated that more feed efficient cattle had lower PUN indicating that they were more efficient in the utilization of absorbed protein than inefficient cattle. Further testing is needed to confirm this initial finding. Acknowledgments The assistance of Harvey Standland, Don Jones, Sergji Sennikov, Charles Nowell, Mary Maddox and David Thomas is gratefully acknowledged. Literature C ited Archer et al. 1997. J. Anim. Sci. 75:2024 Coulombe and Favrean. 1963. Clin. Chem. 9:102. Eggum. 1970. Br. J. Nutr. 24:983. Elzo et al. 2009. J Anim. Sci. 87:3877. Koch et al. 1963. J. Anim. Sci. 22:486. Kohn et al. 2005. J. Anim. Sci. 83:879. Nkrumah et al. 2006. J. Anim. Sci. 84:145.

PAGE 4

0 1 2 3 4 5 Low RFI Med RFI High RFI lb/d Residual feed intake ADG 0 10 20 30 40 Low RFI Med RFI High RFI lb/d Residual feed intake ADFI 0 2 4 6 8 10 12 Low RFI Med RFI High RFI lb/lb Residual feed intake Feed:gain Table 1. Overall summary of growth performance and plasma urea nitrogen concentrations in growing beef cattle during the 70 d test feeding period Trait Mean Standard deviation Avg. daily feed intake, lb 23.5 4.6 Feed efficiency (feed:gain), lb/lb 9.0 2.5 Average daily gain, lb 2.74 0.55 Residual feed intake, lb/d 0 4.4 Plasma urea N at d 56, mg/dL 11.9 2.9 Figure 1 Residual feed intake grouping for average daily weight gain (ADG), average daily feed intake (ADFI) and average feed efficiency (Feed: gain) during the 70 d test feeding period (SE = 0.05 and P > 0.10 for ADG, SE = 0.5 and P < 0.01 for ADFI, and SE = 0.4 and P < 0.01 for F:G; least square mean s).

PAGE 5

Figure 4. Effect of b reed group on plasma urea nitrogen concentration at d 56 of the 70 d test feeding period (SE= 0.6 and P <0.01; least square means). Figure 3. Effect of calf sex on plasma urea nitrogen concentration at d 56 of the 70 d test feeding period (SE = 0.2 and P <0.01; least square means).