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Relationship of feedlot feed efficiency, performance, and feeding behavior with metabolic rate, methane production, and energy partitioning in beef cattle

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Residual feed intake (RFI) is the differ- ence between the actual and expected feed intake of an animal based on its BW and growth rate over a specified period. The biological mechanisms underlying the vari- ation in feed efficiency in animals with similar BW and growth rate are not well understood. This study determined the relationship of feedlot feed efficiency, performance, and feeding behavior with digestion and energy partitioning of 27 steers. The steers were se- lected from a total of 306 animals based on their RFI following feedlot tests at the University of Alberta Kinsella Research Station. Selected steers were ranked into high RFI (RFI >0.5 SD above the mean, n = 11), medium RFI (RFI ± 0.5 SD above and below the mean, n = 8), and low RFI (RFI of steers was correlated with DE (r = −0.41; P < 0.05), ME (r = −0.44; P < 0.05), heat production (HP; r = 0.68; P < 0.001), and retained energy (RE; r = −0.67; P < 0.001; energy values are expressed in kcal/kg of BW0.75). Feedlot partial efficiency of growth was correlated (P < 0.01) with methane production (r = −0.55), DE (r = 0.46), ME (r = 0.49), HP (r = −0.50), and RE (r = 0.62). With the exception of HP (r = 0.37; P < 0.05), feed conversion ratio was unrelated to the traits considered in the study. Feeding duration was correlated (P < 0.01) with appar- ent digestibility of DM (r = −0.55), CP (r = −0.47), meth- ane production (r = 0.51), DE (r = −0.52), ME (r = −0.55), and RE (r = −0.60). These results have practical implica- tions for the selection of animals that eat less at a similar BW and growth rate and for the environmental sustainability of beef production.
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Z. Wang and S. S. Moore
J. D. Nkrumah, E. K. Okine, G. W. Mathison, K. Schmid, C. Li, J. A. Basarab, M. A. Price,
metabolic rate, methane production, and energy partitioning in beef cattle
Relationships of feedlot feed efficiency, performance, and feeding behavior with
2006. 84:145-153. J Anim Sci
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Relationships of feedlot feed efficiency, performance, and feeding behavior
with metabolic rate, methane production, and energy partitioning in beef cattle
1
J. D. Nkrumah,* E. K. Okine,* G. W. Mathison,* K. Schmid,* C. Li,* J. A. Basarab,†
M. A. Price,* Z. Wang,* and S. S. Moore*
2
*Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton,
AB, T6G 2P5 Canada; and †Alberta Agriculture, Food and Rural Development,
Lacombe Research Centre, Lacombe, AB, T4L 1W1 Canada
ABSTRACT: Residual feed intake (RFI) is the differ-
ence between the actual and expected feed intake of an
animal based on its BW and growth rate over a specified
period. The biological mechanisms underlying the vari-
ation in feed efficiency in animals with similar BW
and growth rate are not well understood. This study
determined the relationship of feedlot feed efficiency,
performance, and feeding behavior with digestion and
energy partitioning of 27 steers. The steers were se-
lected from a total of 306 animals based on their RFI
following feedlot tests at the University of Alberta
Kinsella Research Station. Selected steers were ranked
into high RFI (RFI >0.5 SD above the mean, n = 11),
medium RFI (RFI ± 0.5 SD above and below the mean,
n = 8), and low RFI (RFI <−0.5 SD below the mean, n =
8). The respective BW ± SD for the RFI groups were
495.6 ± 12.7, 529.1 ± 18.6, and 501.2 ± 15.5 kg. Digest-
ibility and calorimetry trials were performed on a corn-
or barley-based concentrate diet in yr 1 and 2, respec-
tively, at 2.5 × maintenance requirements. Mean DMI
(g/kg of BW
0.75
) during the measurements for high-,
medium-, and low-RFI groups, respectively, were 82.7
± 2.0, 78.8 ± 2.6, and 81.8 ± 2.5 and did not differ (P >
Key words: beef cattle, energy partitioning, feed efficiency, methane production
2006 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2006. 84:145–153
INTRODUCTION
The high cost of feeding in beef cattle production
means that profitability depends on the efficient and
1
This work was supported through Grant #ACC-99AB343, #ASRA
AARI 2002L030R, #BCRC 2002L030R, and ABP/ACC awarded to
S. S. Moore through the Canada/Alberta Beef Industry Dev. Fund,
Alberta Agric. Res. Inst., Beef Cattle Res. Council, Alberta Beef Pro-
ducers, and Alberta Cattle Commission. The authors acknowledge
the technical assistance of the manager and staff of the Univ. Alberta
metabolic research unit.
2
Corresponding author: stephen.moore@ualberta.ca
Received February 9, 2005.
Accepted August 18, 2005.
145
0.10). Residual feed intake was correlated with daily
methane production and energy lost as methane (r =
0.44; P < 0.05). Methane production was 28 and 24%
less in low-RFI animals compared with high- and me-
dium-RFI animals, respectively. Residual feed intake
tended to be associated (P < 0.10) with apparent digest-
ibilities of DM (r = 0.33) and CP (r = 0.34). The RFI
of steers was correlated with DE (r = 0.41; P < 0.05),
ME (r = 0.44; P < 0.05), heat production (HP; r = 0.68;
P < 0.001), and retained energy (RE; r = 0.67; P <
0.001; energy values are expressed in kcal/kg of BW
0.75
).
Feedlot partial efficiency of growth was correlated (P <
0.01) with methane production (r = 0.55), DE (r = 0.46),
ME (r = 0.49), HP (r = 0.50), and RE (r = 0.62). With
the exception of HP (r = 0.37; P < 0.05), feed conversion
ratio was unrelated to the traits considered in the study.
Feeding duration was correlated (P < 0.01) with appar-
ent digestibility of DM (r = 0.55), CP (r = 0.47), meth-
ane production (r = 0.51), DE (r = 0.52), ME (r = 0.55),
and RE (r = 0.60). These results have practical implica-
tions for the selection of animals that eat less at a
similar BW and growth rate and for the environmental
sustainability of beef production.
productive use of feed for maintenance and growth with
minimal excesses and losses. There is considerable phe-
notypic and genetic variation in measures of beef cattle
feed efficiency, such as feed conversion ratio (FCR),
residual feed intake (RFI), and partial efficiency of
growth (PEFFG; Archer et al., 1999; Arthur et al.,
2001). Thus, improvements in feed efficiency would lead
to cost reduction and better overall production system
efficiency. Residual feed intake is the difference be-
tween an animal’s actual feed intake and its expected
intake based on BW and growth rate over a specified
period.
Considerable research progress has been made in de-
fining the variation in RFI using different biological
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Nkrumah et al.146
types of cattle; however, the biological reasons underly-
ing the observed variations are generally unknown, al-
though several physiological mechanisms have been
proposed. Johnson et al. (2003) and Richardson and
Herd (2004) suggested that sources that may contribute
to the variation in RFI are feed intake, digestion of
feed, heat increment, protein turnover and overall tis-
sue metabolism, feeding behavior and activity, body
composition and rate of gain, BW, prolificacy, and sev-
eral other presently unknown factors.
In a recent study, Richardson et al. (2004) reported
significant metabolic differences in Angus steers diver-
gently selected for RFI. Generally, there is considerable
variation among cattle in energy use and partitioning.
This variation is mainly related to differences in dietary
energy losses (fecal, methane, and urinary), heat pro-
duction (HP), and energy retention (Delfino and Mathi-
son, 1991; Saama and Mao, 1995; Basarab et al., 2003).
The current study examined the relationship of feedlot
feed efficiency, performance, and feeding behavior with
metabolic rate, digestion, and energy partitioning in
beef cattle ranked by RFI.
MATERIALS AND METHODS
Animals and Diets
Twenty-seven Continental × British hybrid beef
steers sired by Angus or Charolais bulls were used in
the study. Postweaning feedlot performance and feed
efficiency tests using the GrowSafe automated feeding
system (GrowSafe Systems Ltd., Airdrie, Alberta, Can-
ada) were carried out for a total of 306 animals over 2
yr (2 test groups per year with approximately 80 ani-
mals per test) at the University of Alberta Kinsella
Research Station. Details of the procedures for the feed-
lot test were given by Nkrumah et al. (2004). At the
end of each feedlot test, steers were ranked by their
RFI and selected to be halter-trained for use in the
metabolic and digestion trials at the University of Al-
berta Metabolic Research Center, Edmonton. Standard
deviations above and below the mean RFI were used
to group the selected steers into high RFI (RFI >0.5 SD
above the mean; n = 11), medium RFI (RFI ± 0.5 SD
above and below the mean; n = 8), and low RFI (RFI
<−0.5 SD below the mean; n = 8). Respective BW ±
SD for the high-RFI, medium-RFI, and low-RFI groups
during the measurements were 495.6 ± 12.7, 529.1 ±
18.6, and 501.2 ± 15.5 kg.
The feedlot test diets for the 2 yr are shown in Table
1. In each year, the same feedlot test diet was used in
subsequent metabolic and digestion trials. Corn was
used in yr 1 instead of barley and oats because of a feed
barley shortage that particular year; however, the diets
used in both years were formulated to contain similar
levels of ME. At the Metabolic Research Center in Ed-
monton, animals were housed individually in adjacent
holding pens in a climate-controlled thermoneutral en-
vironment and adapted to individual metabolism crates
Table 1. Ingredients and composition of experimental
diets
Diet ingredient, % (as-fed basis) Yr 1 Yr 2
Dry-rolled corn 80.00
Barley grain 64.50
Oat grain 20.00
Alfalfa hay 13.50 9.00
Beef feedlot supplement
1
5.00 5.00
Canola oil 1.50 1.50
DM, % 90.50 88.90
Composition (DM basis)
ME, Mcal/kg 2.90 2.91
CP, % 12.50 14.00
NDF, % 18.30 21.49
ADF, % 5.61 9.50
1
Contained 440 mg of monensin/kg, 5.5% Ca, 0.28% P, 0.64% K,
1.98% Na, 0.15% S, 0.31% Mg, 16 mg of I/kg, 28 mg of Fe/kg, 1.6 mg
of Se/kg, 160 mg of Cu/kg, 432 mg of Mn/kg, 432 mg of Zn/kg, 4.2
mg of Co/kg, and a minimum of 80,000 IU of vitamin A/kg 8,000 IU
of vitamin D/kg, and 1,111 IU of vitamin E/kg.
and confinement-type respiration calorimetry stan-
chions. Each experimental period consisted of a 14-d
adaptation period, during which steers were acclimated
(or re-acclimated if previously used in a trial), gentled,
and gradually brought to the specific feeding level. All
steers in the study were cared for according to the guide-
lines of the Canadian Council on Animal Care
(CCAC, 1993).
Digestion Trial Procedure
Steers were individually fed in metabolic crates after
acclimation and achievement of full feeding level [2.5 ×
estimated NRC (1996) maintenance requirement (0.077
Mcal NE
m
/BW
0.75
)]. Animals were weighed twice during
the acclimation period, and the average BW was used
to determine the 2.5 times the NE
m
feeding level. The
metabolic crates permitted steers to lie down or stand
during the trial. The digestibility trial consisted of a 5-
d period during which a total collection of feces and
urine was made. Aliquots of feed, orts, feces (10%), and
pre-acidified urine (5%) were collected daily (after thor-
ough mixing) and stored at 20°C for later processing
and analyses. Feed, orts, and fecal samples were dried
in a forced-air oven at 60°C for 72 h and ground in a
Wiley mill (Arthur H. Thomas, Philadelphia, PA) to
pass a 1-mm screen.
Dry matter contents of the feed, orts, and feces were
determined by oven drying at 100°C to a constant
weight. A standard macro-Kjeldahl procedure (AOAC,
1980) was used to determine N in feed, orts, feces, and
urine samples. Gross energy contents of feed, feces,
orts, and urine were determined in an automatically
controlled Parr adiabatic oxygen bomb calorimeter
(Parr Instrument Co., Inc., Moline, IL). Neutral deter-
gent fiber was determined according to the procedure
of Van Soest et al. (1991). Acid detergent fiber was
determined according to AOAC (1997). These analyses
were determined in the ANKOM 200 fiber analyzer
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Residual feed intake and energy partitioning 147
(Ankom Technology Corp., Fairport, NY). The NDF and
ADF analyses were carried out in triplicate; the intra-
sample CV for fiber determination was <5% in 95%
of samples.
Indirect Calorimetry Procedure
Oxygen consumption and methane production were
measured in a 4-chamber, open-circuit, indirect calo-
rimetry system (Delfino et al., 1988). The calorimetry
system is designed for individual animals to stand or
lie down in stanchions with their heads in hoods. The
hoods were located in a climate-controlled thermoneu-
tral environment, and animals were allocated randomly
to the calorimetry hoods after acclimation. The calorim-
etry system was designed such that air could be drawn
from the hoods at a mean oxygen concentration of 20%.
Respired air was passed through Drierite (W. A. Ham-
mond Drierite Co., Ltd, Xenia, OH) to remove water
vapor before passing through a paramagnetic oxygen
analyzer (Servomex Inc., Sussex, UK) or methane ana-
lyzer (Model 880A Infrared Analyzer, Rosemount Ana-
lytical, Orville, OH). A Foxboro 823 IFO integral flow
orifice with cell transmitter (Invensys Systems, Inc.,
Foxboro, MA) was used to measure airflow rate. Pres-
sure was measured with a Foxboro 821AL absolute
pressure transmitter (Invensys Systems, Inc.). Temper-
ature and relative humidity also were measured by
cellular temperature and relative humidity transmit-
ters (General Eastern, Fairfield, CT).
The system also allowed measurement of the concen-
tration of ambient oxygen. The calorimetry system was
calibrated by the N injection method (by releasing a
weighed amount of N
2
gas into the system) as described
by Young et al. (1984). Two 16-h measurements at 3-d
intervals were obtained from each steer at the esti-
mated (NRC, 1996) 2.5 times maintenance requirement
feeding level after the digestion trial. To estimate heat
increment of feeding (HIF), oxygen consumption also
was measured at 1.2 times maintenance feeding level.
To remove residual feed caused by the higher feeding
level from the gut, steers were kept on the 1.2 times
maintenance feeding level for 5 d before measurements
were made.
Calculations and Statistical Analyses
Procedures for obtaining the measures of feedlot per-
formance and feed efficiency have been described pre-
viously (Nkrumah et al., 2004). Each animal’s ADG
during the feedlot test was computed as the coefficient
of the linear regression of BW (kg) on time (d) using
the regression procedure of SAS (SAS Inst., Inc., Cary,
NC; Version 9.1). The metabolic BW of each animal over
the feedlot test period was computed as the midpoint
BW
0.75
of a 70-d test. The total feed intake of each
animal over a 70-d test period was used to compute the
daily DMI. Residual feed intake was computed for each
animal as the difference between actual DMI and pre-
dicted expected daily DMI based on the ADG and meta-
bolic BW over the test period using procedures de-
scribed by Arthur et al. (2001). The PEFFG (i.e., ener-
getic efficiency for ADG) above maintenance of each
animal was computed as the ratio of ADG to the differ-
ence between average daily DMI and expected DMI for
maintenance (Arthur et al., 2001) in which DMI for
maintenance was computed according to NRC (1996).
Feed conversion ratio was computed as the ratio of DMI
to ADG on test.
Feedlot behavior traits studied were daily feed bunk
attendance and daily feeding duration (FD). Procedures
for determining feeding behavior from the GrowSafe
System have previously been described (Basarab et al.,
2003). Daily feed bunk attendance in this study was
defined as the number of independent visits or atten-
dances in a day by a particular animal to a feed bunk,
irrespective of the duration of the visit. Daily FD was
computed as the sum of the difference between feeding
event end times and start times per day for each animal.
It was equal to the total number of minutes each day
spent in feeding-related activities (prehension, chew-
ing, backing away from the bunk and chewing, socializ-
ing, scratching, or licking) at the feed bunk.
All energy intake and partitioning values during the
postfeedlot trial were expressed per unit of metabolic
BW (i.e., BW
0.75
). With the exception of HIF, which
by convention must be estimated using two different
feeding levels, all energy partitioning and digestibility
values reported in the study are measurements taken
at the 2.5 times maintenance feeding level. Digestible
energy was calculated by multiplying the daily intake
energy by the energy digestibility of the diet from each
animal. The energy lost as methane was calculated as
the total methane produced in liters per day at standard
temperature and pressure (STP) × 9.45 kcal/L
(Brouwer, 1965). Metabolizable energy (kcal/kg of
BW
0.75
) was calculated by subtracting energy losses
(kcal/kg of BW
0.75
) in urine and methane from DE (kcal/
kg of BW
0.75
). Heat production (kcal/kg of BW
0.75
) was
computed as (4.90 kcal/L of O
2
) × (volume of expired
air at STP) × (oxygen in exhaust air oxygen in inlet air
at STP). This approach has been shown to give accurate
estimates of HP (±1.2%; McLean and Tobin, 1990). Heat
increment of feeding was calculated as the change in
HP per unit change in ME intake for the same animal
(McDonald et al., 2002). Retained energy (RE; kcal/kg
of BW
0.75
) was calculated as the difference between ME
and HP (NRC, 1996) at 2.5 times maintenance re-
quirement.
Data were analyzed using the Mixed procedure of
SAS; the model included fixed effects of RFI group (high,
medium, and low), year (1 and 2), test group within
year (2 groups per year), and random effects of meta-
bolic crate or calorimetry chamber and sire of animal.
All interaction terms that were not significant for a
trait (P > 0.10) were dropped from the final model. There
was no RFI group × year interaction on any of the traits
considered. With the exception of the model for feedlot
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Nkrumah et al.148
Table 2. Relationship of residual feed intake (RFI, kg of DM/d) with measures of feedlot
performance, efficiency, and feeding behavior of steers used in the study (least squares
means ± SE)
RFI group
1
Trait High Medium Low P-value
2
No. of steers 11 8 8
RFI, kg/d 1.25 ± 0.13
c
0.08 ± 0.17
d
1.18 ± 0.16
e
<0.001
Feed conversion ratio, kg of DM/kg of gain 7.98 ± 0.23
c
7.04 ± 0.29
d
6.53 ± 0.30
e
0.01
Partial efficiency of growth 0.26 ± 0.01
c
0.31 ± 0.01
d
0.38 ± 0.01
e
<0.001
DMI, kg/d 11.62 ± 0.30
c
11.07 ± 0.39
d
9.62 ± 0.36
e
0.01
Metabolic BW, kg of BW
0.75
89.04 ± 2.57 92.21 ± 2.77 93.75 ± 2.87 0.48
ADG, kg/d 1.46 ± 0.20 1.51 ± 0.16 1.48 ± 0.16 0.39
Feeding duration, min/d 73.95 ± 4.34
c
65.03 ± 4.69
d
47.76 ± 4.85
e
0.006
Bunk attendance, events/d 35.58 ± 3.01
c
29.68 ± 3.38
d
18.07 ± 3.49
e
0.01
c–e
Within a row, means without a common superscript letter differ, P < 0.05.
1
Groups were defined as high = RFI >0.5 SD above the mean, medium = RFI ± 0.5 SD above and below
the mean, and low = RFI <−0.5 SD below the mean.
2
P-values from overall F-test.
DMI and post-feedlot GE intake (GEI), the model for all
other traits included feedlot DMI as a linear covariate
within treatments. Mean separation among RFI groups
for different test traits was carried out by least squares
using the PDIFF option in SAS. The PROC CORR of
SAS was used to obtain Pearson partial phenotypic cor-
relations adjusted for the linear effects of DMI and the
fixed effect of year.
RESULTS
There were differences among the different groups
of RFI steers selected for the study in PEFFG (P <
0.001), FCR (P = 0.01), DMI (P = 0.01), and the 2 mea-
sures of feeding behavior (P < 0.01), but not in metabolic
BW or ADG (P > 0.10; Table 2). These differences pro-
vided adequate variation among the animals for de-
termining the relationships of the different measures
of feed efficiency, performance, and behavior with the
measures of metabolic rate, digestion, and energy parti-
tioning considered in the study. Daily fecal DM, meth-
ane, orts, urine, urinary N excretion, and apparent di-
gestibility of dietary components are presented in Table
3. Table 4 shows the associations between RFI and
measures of daily energy partitioning. The phenotypic
correlations between the feedlot measures of perfor-
mance, efficiency, and feeding behavior with daily en-
ergy partitioning are presented in Table 5.
Daily DMI by the steers at 2.5 times feeding level
averaged 80.02 ± 7.78 g/kg of BW
0.75
, and this corres-
ponded to an average GEI of 375.2 ± 39.5 kcal/kg of
BW
0.75
. There were no differences in daily DMI or GEI
between the different RFI groups during the post-feed-
lot trial (P > 0.10). Of the mean daily GEI by the steers,
24.98 ± 8.39% was recovered in the feces, and 3.89 ±
1.22% and 2.67 ± 0.85% were recovered as methane gas
and in the urine, respectively. Thus, the mean DE and
ME in the study were approximately 75 and 68%, re-
spectively; the corresponding ME:DE was 0.91. Daily
HP averaged 149.0 ± 19.72 kcal/kg of BW
0.75
and formed
approximately 59% of the average daily ME; the corres-
ponding ME retention efficiency was 39%. Feedlot RFI
was correlated with daily methane production (P < 0.05)
and was approximately 28 and 24% less in low-RFI
animals than in high- or medium-RFI animals, respec-
tively. These differences were generally consistent over
the entire 16-h calorimetry period. Residual feed intake
also was negatively correlated with daily DE and ME
(P < 0.05). High-RFI steers recovered 9.7% less DE and
10.2% less ME from their daily feed consumed com-
pared with low-RFI steers.
Daily HP and energy retention were highly signifi-
cantly associated with feedlot RFI (P < 0.001). Heat
production was 21 and 10% less by low-RFI steers than
by steers with high or medium RFI, respectively. Con-
sistent with this result was the lower RE (44 and 23%)
in high- and medium-RFI steers, respectively, com-
pared with low-RFI steers. Simple regression analyses
showed that differences in feedlot DMI, post-feedlot HP,
and post-feedlot ME (kcal/d), respectively, accounted
for 20, 48, and 16% of the variation in feedlot RFI among
the animals. The regression equation was feedlot RFI =
6.52 + 0.320 × DMI (kg/d; feedlot) + 0.031 × HP (kcal/
kg of BW
0.75
; post-feedlot) 0.005 × ME (kcal/kg of
BW
0.75
; post-feedlot). The differences in metabolizabil-
ity were mainly attributable to the observed differences
in DE (kcal/d) and methane production.
No significant differences were observed among the
RFI groups in HIF, measured at 2 different feeding
levels above maintenance (P > 0.20), although low-RFI
steers had 32.6% lower HIF. There was a tendency for
a negative association between RFI and digestibility of
dietary CP (r = 0.34; P < 0.10) and DM (r = 0.33; P
< 0.10). Daily fecal DM production was 15.5 and 8.1%
greater in high- and medium-RFI steers, respectively,
compared with low-RFI steers, although these differ-
ences were not significant (P > 0.10). The results for
NDF and ADF indicated that NDF digestibility was
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Residual feed intake and energy partitioning 149
Table 3. Relationship of feedlot residual feed intake (RFI, kg of DM/d) with fecal DM,
urine and methane production, and digestion in beef cattle fed at 2.5 times their estimated
(NRC, 1996) maintenance requirements (least squares means ± SE)
RFI group
1
Trait High Medium Low P-value
2
No. of steers 11 8 8
Metabolic BW, kg of BW
0.75
105.01 ± 2.00 110.22 ± 2.94 105.75 ± 2.45 0.32
DMI, g/kg of BW
0.75
82.66 ± 2.03 78.77 ± 2.62 81.75 ± 2.69 0.35
Orts, % of DM offered 10.31 ± 2.11 17.77 ± 3.16 14.04 ± 3.21 0.14
Fecal DM production, g/kg of DMI 272.13 ± 13.0 249.72 ± 16.79 234.22 ± 17.16 0.24
Methane, L/kg of BW
0.75
1.71 ± 0.11
c
1.68 ± 0.14
c
1.28 ± 0.14
d
0.04
Urine production, g/kg of BW
0.75
56.27 ± 4.62 49.62 ± 5.61 45.49 ± 5.47 0.25
Urine N, g/kg of DMI 8.60 ± 0.60 8.92 ± 0.72 7.13 ± 0.74 0.19
Apparent digestibility
%
DM 70.87 ± 1.97
d
73.40 ± 2.12
cd
75.33 ± 2.10
c
0.10
CP 69.76 ± 2.17
d
73.52 ± 2.32
cd
74.70 ± 2.29
c
0.09
NDF 17.29 ± 8.24 28.25 ± 8.51 31.49 ± 8.31 0.19
ADF 3.26 ± 8.94 10.07 ± 9.24 14.67 ± 9.03 0.43
c,d
Within a row, means without a common superscript letter differ, P < 0.05.
1
Groups were defined as high = RFI > 0.5 SD above the mean, medium = RFI ±0.5 SD above and below
the mean, and low = RFI <−0.5 SD below the mean.
2
P-value from overall F-test.
generally less in high-RFI compared with low-RFI
steers, although differences were not significant. Corre-
lations of NDF and ADF digestibility with RFI did not
differ from zero (P > 0.10). Urinary N excretion was
17% greater in the urine of high-RFI steers compared
with low-RFI steers, although these differences, as well
as that of daily urine production, were not significant
(P > 0.10).
The relationship of PEFFG with the various test
traits consistently followed those with RFI. There were
Table 4. Relationship of feedlot residual feed intake (RFI, kg of DM/d) with post-feedlot
daily dietary energy flows in beef cattle fed at 2.5 times their estimated (NRC, 1996)
maintenance requirements (least squares means ± SE)
RFI group
1
Trait High Medium Low P-value
2
No. of steers 11 8 8
Intake energy, kcal/kg of BW
0.75
384.77 ± 7.90 382.24 ± 6.26 387.98 ± 6.03 0.39
Fecal energy, kcal/kg of BW
0.75
104.41 ± 4.89 96.02 ± 6.44 88.22 ± 6.65 0.16
DE, kcal/kg of BW
0.75
265.18 ± 5.20
d
288.11 ± 7.07
c
293.78 ± 6.84
c
0.05
Methane energy, kcal/kg of BW
0.75
16.08 ± 1.01
c
15.90 ± 1.30
cd
12.09 ± 1.28
d
0.04
Urinary energy, kcal/kg of BW
0.75
10.88 ± 0.64 9.36 ± 0.84 10.00 ± 0.81 0.35
ME, kcal/kg of BW
0.75
238.54 ± 5.41
e
248.73 ± 7.13
d
265.73 ± 7.36
c
0.02
Heat production, kcal/kg of BW
0.75
163.97 ± 4.17
c
143.00 ± 5.54
d
129.32 ± 5.46
e
<0.001
Retained energy, kcal/kg of BW
0.75
75.34 ± 7.22
e
104.30 ± 9.51
d
135.23 ± 9.82
c
<0.001
Heat increment, kcal/kcal of ME 53.60 ± 10.54 53.18 ± 13.88 36.08 ± 14.35 0.58
Energy loss % of GE intake
Methane 4.28 ± 0.26
c
4.25 ± 0.35
c
3.19 ± 0.34
d
0.04
Urine 2.55 ± 0.28 2.32 ± 0.30 2.47 ± 0.28 0.74
Feces 28.80 ± 1.77 26.39 ± 2.01 24.18 ± 2.02 0.14
ME:DE 0.90 ± 0.01 0.91 ± 0.01 0.92 ± 0.01 0.16
c–e
Within a row, means without a common superscript letter differ, P < 0.05.
1
Groups were defined as high = RFI > 0.5 SD above the mean, medium = RFI ±0.5 SD above and below
the mean, and low = RFI <−0.5 SD below the mean.
2
P-value from overall F-test.
significant correlations (P < 0.01) between PEFFG with
DE, ME, HP, RE, and methane production. Similarly,
the PEFFG of the steers tended to be related to fecal
output and digestibility of dietary components (P <
0.10). With the exception of daily HP (P < 0.05), feedlot
FCR of the steers was generally unrelated to any of the
metabolic rate and energy partitioning traits consid-
ered in the study. Feedlot DMI showed positive associa-
tions with methane production (P < 0.05) and energy
lost through urine (P < 0.01), but it was negatively
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Nkrumah et al.150
Table 5. Relationship of feedlot growth, feed intake, feed efficiency, and feeding behavior
with measures of postfeedlot digestibility and energy partitioning of steers
1
Trait
2
DFO DMP DDE DME DHP DRE DMD CPD NDF ADF
RFI 0.33† 0.44* 0.41* 0.44* 0.68*** 0.67*** 0.33† 0.34† 0.005 0.11
FCR 0.02 0.19 0.06 0.09 0.37* 0.24 0.02 0.09 0.04 0.07
PEFFG 0.35† 0.55** 0.45* 0.49** 0.50** 0.62*** 0.35† 0.32† 0.20 0.28†
DMI 0.32† 0.38* 0.46** 0.48** 0.31† 0.53** 0.32† 0.16 0.13 0.20
ADG 0.23 0.05 0.28† 0.27† 0.09 0.18 0.23 0.04 0.04 0.06
MBW 0.005 0.03 0.08 0.10 0.36† 0.07 0.005 0.19 0.32† 0.30†
DFA 0.23 0.14 0.22 0.22 0.42* 0.004 0.25 0.06 0.48** 0.46**
FD 0.54** 0.51** 0.52** 0.55** 0.25 0.60** 0.55** 0.47* 0.23 0.36†
1
Traits in columns were measured during the feedlot trial, and those in rows were measured during the
post-feedlot animal house experiment.
2
DFO = daily fecal DM output, DMP = daily methane production, DDE = daily DE, DME = daily ME,
DHP = daily heat production, DRE = daily retained energy, DMD = apparent DM digestibility, CPD =
apparent CP digestibility, NDF = NDF digestibility, RFI = residual feed intake, FCR = feed conversion
ratio, PEFFG = partial efficiency of growth, MBW = metabolic BW, DFA = daily feed bunk attendance, and
FD = daily feeding duration.
P < 0.10; *P < 0.05; **P < 0.01; ***P < 0.001.
correlated with daily DE (P < 0.05), ME (P < 0.01), and
RE (P < 0.01). There also was a tendency for feedlot DMI
to affect fecal DM production (positive association), HP,
and DM digestibility (negative association; P < 0.10).
Daily feed bunk attendance of steers was positively
related to HP and negatively related to NDF and ADF
digestibility (P < 0.05), but it was unrelated to other
traits considered in the study (P > 0.10). Daily FD
showed significant correlations with fecal DM and
methane production (P < 0.01; positive associations)
and with daily DE, ME, RE, and apparent digestibility
of CP and DM (P < 0.01; negative associations). Feedlot
ADG was generally unrelated to the traits considered in
the study, except for a weak trend toward an association
with daily DE and ME (P = 0.12). With the exception
of daily urinary energy (P < 0.05), HP, NDF, and ADF
digestibility (P < 0.10), feedlot metabolic BW was gener-
ally not related to the traits considered in the study.
The use of either corn or barley and oats in yr 1 or 2
did not result in any interactions between RFI and
year in the analyses (P > 0.10); however, energy lost as
methane (percentage of GEI) was less (P < 0.01) for the
diet in yr 1 (corn-based diet; 3.25 ± 0.23%) than for yr 2
(barley-based diet; 4.59 ± 0.30%). Additionally, dietary
and fecal NDF and ADF levels were lower (P < 0.05)
for the corn-based diet compared with the barley-
based diet.
DISCUSSION
The identification of the metabolic and physiological
reasons underlying the variation in feed efficiency in
cattle that are similar in BW and growth is a well-
recognized prerequisite for the effective planning of
breeding strategies to select animals that are more effi-
cient. In the current study, we considered several poten-
tial metabolic and physiological pathways that may in-
fluence feed efficiency. These include pathways that
are generally related to variations in the efficiency of
conversion of GE into ME (because of differences in
digestibility, generation of gases during ruminal fer-
mentation, absorption of nutrients, waste excretion,
and HP) and the subsequent efficiency of ME conversion
to RE for maintenance and growth. The relationship of
feedlot RFI with metabolic BW, ADG, DMI, FCR, and
PEFFG of the animals selected for the post-feedlot
study were consistent with those reported in the litera-
ture (Arthur et al., 2001; Basarab et al., 2003).
The current study identified significant differences
in methane emission among animals differing in RFI,
which represents the first experimental evidence dem-
onstrating associations between RFI and methane pro-
duction. Previous evidence (Herd et al., 2002; Okine et
al., 2003) relating RFI to methane production was based
only on estimates derived from the relationship be-
tween RFI and DMI and resulted in approximately 5%
difference between low-RFI and high-RFI animals in
methane production. Data from the current study indi-
cated that methane production was 28 and 24% less in
low-RFI animals than in high- or medium-RFI animals,
respectively. Although feedlot DMI was also correlated
with daily methane production from steers, the differ-
ences observed among RFI groups were still evident
following covariate adjustment for feedlot DMI. These
differences correspond to approximately 16,100 L/yr
less methane in low-RFI animals compared with high-
RFI animals.
The mechanisms behind the observed differences
among animals in methane emission, independent of
intake, are unknown, but they may be related to differ-
ences in metabolizability as well as possible individual
animal differences in methane production. Methane
production has been shown to be heritable (h
2
= 0.42)
in humans (Flatz et al., 1985). According to Hackstein
et al. (1996), there is a genetic link between methano-
gens and their hosts such that the presence of methano-
genic bacteria in an animal requires a quality of the
host that is under phylogenetic rather than dietary con-
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Residual feed intake and energy partitioning 151
straint. Whether this link has any effects on the type
of methanogens that are dominant in the rumen of
individual animals is unknown.
Any inherent differences in animals that may lead to
ecological changes in the ruminal microbial ecosystem
may translate into differences in methane production.
Increased methane production by high-RFI animals not
only represents significant decreases in energetic effi-
ciency, but it also has implications for the environmen-
tal sustainability of beef cattle production because of
the significant contributions to atmospheric methane
emissions. Agriculture in Canada contributes approxi-
mately 10% of the total Canadian green house gas emis-
sions (Environment Canada, 2004), of which 2.6% is
methane. The current study also identified a tendency
toward differences in daily fecal DM production per
unit of DMI, an observation consistent with previous
estimates by Okine et al. (2003).
The current study also indicated a trend toward asso-
ciations between RFI and apparent digestibilities of
dietary DM and CP. These differences in apparent di-
gestibilities between RFI groups reported in the current
study were consistent with the results of Richardson
et al. (1996), who reported greater DM digestibility by
low-RFI steers than by high-RFI steers and concluded
that small differences in digestibility can result in large
differences in feed efficiency. The differences in appar-
ent digestibility observed in the current study between
high-RFI and low-RFI animals were, however, weak
(approximately 5%). A recent study by Channon et al.
(2004) demonstrated significant genetic and phenotypic
associations between RFI and traits that are indicative
of the extent of starch digestion in the gastrointestinal
tract of cattle. Russell and Gahr (2000) indicated that
individual animal variation in factors such as the mech-
anism of digestion and absorption, ruminal retention
time, and feeding behavior might contribute to varia-
tion between individual animals in diet digestibility.
Variation in ruminal retention time among animals
has been reported in cattle (Ørskov et al., 1988), and it
might be associated with differences in DMI or feeding
behavior. Significant differences in feedlot DMI among
animals differing in RFI have been demonstrated in
several studies (Arthur et al., 2001; Basarab et al., 2003;
Nkrumah et al., 2004). In addition, considerable differ-
ences in FD were observed among the animals in the
different RFI groups in the current study. The differ-
ences in FD in the current study were associated posi-
tively with differences in fecal and methane production
and associated negatively with DM and CP digestibil-
ity. These associations also translated into differences
in daily DE and ME among the steers differing in RFI.
Significant differences in DE, ME, and RE among the
animals of the different RFI groups also were demon-
strated in the current study. Part of the variation in
efficiency of energy retention has been attributed,
among other factors, to a decrease in metabolizability
of the diet and to an increase in the HIF at high levels of
intake above maintenance (Ferrell and Jenkins, 1998).
The results of the current study are generally in
agreement with these suggestions; the differences in
feedlot DMI also were associated with significant de-
creases in DE, ME, and RE. Nonetheless, to evaluate
whether differences in daily DE, ME, or RE were due
to inherent differences in the different RFI steers, inde-
pendent of the level of intake-associated effects pro-
posed by Ferrell and Jenkins (1998), we included feedlot
DMI as a linear covariate in the statistical models of
analyses. This did not eliminate the relationships of
the given traits with RFI, which demonstrated that
part of the variation in the different RFI steers in DE,
ME, and RE might be independent of the level of intake.
The results of the current study indicate that the
greater DMI by animals with high RFI might be partly
related to the low metabolizability of consumed feed and
the accompanying increased need to attain the levels of
energy intake required for maintaining BW and sup-
porting body protein and fat accretion. According to the
present results, the lowered metabolizability of feed in
high-RFI steers in itself might be attributable, at least
in part, to the decreased digestibility and increased
fecal DM production and methane production but is
less related to energy lost through urine. The current
study, however, failed to demonstrate significant differ-
ences among RFI groups in HIF above maintenance,
partly because of high within-RFI group variation in
HIF.
The mean of ME:DE observed in the current study
(0.91) is indeed greater than the 0.82 suggested by the
beef cattle NRC (1996). Values similar to those reported
in the present study have been reported for other stud-
ies (Rikhardsson et al., 1991). For feedlot steers on high-
grain diets that also may contain vegetable fats or iono-
phores such as monensin, the proportion of intake en-
ergy lost through urine and methane is considerably
less than for high-roughage diets (Van der Honing and
Steg, 1990). The practice of adding vegetable oils and
ionophores to high-grain feedlot diets to decrease ex-
treme cases of bloat has been shown to decrease ruminal
methanogenesis considerably (Mathison, 1997; McGinn
et al., 2004), and this might have contributed to the
high ME:DE observed in the current study.
The considerably greater HP in high-RFI steers com-
pared with low-RFI steers observed in the current
study, despite the lack of differences in GEI, might be
attributable to variation in metabolic efficiency. Varia-
tion in energy expenditure related to differences in the
size of visceral organs, for instance, has been proposed
as contributing significantly to the differences in HP
between animals with different RFI (Basarab et al.,
2003). Residual feed intake is positively correlated with
DMI, and it has been demonstrated that increased DMI
in cattle is generally accompanied by significant in-
creases in the size of visceral organs (Ferrell and Jen-
kins, 1998). Indeed, a study by Basarab et al. (2003),
which indicated a greater HP from high-RFI animals
compared with low-RFI animals, also indicated signifi-
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Nkrumah et al.152
cantly greater visceral organ weights in high-RFI steers
than in low-RFI steers.
According to Reynolds (2002), differences in visceral
organ size contribute significantly to the variation in
total oxygen consumption, and thereby HP, accounting
for 40 to 50% of daily HP. In addition, Webster (1980)
indicated that there is a strong linear relationship be-
tween protein synthesis and HP and that marked differ-
ences in metabolic rate could be explained almost en-
tirely by differences in protein synthesis. Not surpris-
ingly, the greatest proportion of the protein synthesis
and associated HP takes place in visceral tissues such
as the gastrointestinal tract and the liver, which are
not normally associated directly with growth and meat
production (Webster, 1980; Reynolds, 2002).
An evaluation of the differences in expression of
genes involved in protein turnover and associated HP
in certain metabolically active tissues, such as the liver
and gastrointestinal tract, may help to explain part
of the molecular mechanisms leading to variations in
energy expenditure in cattle with similar BW and ADG.
This may be even more important in ruminants because
of the comparatively large size of the viscera in relation
to the whole body.
IMPLICATIONS
This study provided experimental evidence indicat-
ing significant associations between feedlot residual
feed intake with methane production and measures of
metabolic rate and dietary energy partitioning in beef
cattle. The results show that differences in metaboliz-
ability (mainly digestibility and methane production),
heat production, and energy retention are responsible
for a major part of the variation among animals in
residual feed intake. These findings should provide a
basis for further research to better characterize the
biological sources of variation in energetic efficiency in
beef cattle. This will be useful for the efficient planning
of breeding strategies to select animals that eat consid-
erably less to achieve a similar growth rate and body
weight.
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... Thus, the use of tools like genetic improvement to improve reproduction and growth characteristics will lessen the environmental impacts of the beef production chain (ABY et al., 2013). Genetic improvement can also contribute directly to reducing the environmental impacts of beef production, through selection, by reducing methane emissions (PINARES-PATINO et al., 2013), or indirectly, through selection to improve feed efficiency, since more efficient animals produce less CH4 per kilo of body weight than less efficient animals (NKRUMAH et al., 2006). ...
... *Correspondence: lihui@neau.edu.cn reduce food consumption, saving the expenditure on livestock production and contributing to the sustained development of the environment [2,3]. Breeders have always focused on improving FE of broilers [4]. ...
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... Ruminants' importance as a source of human food (milk and meat) leads to the rapid growth of animal husbandry and higher production of greenhouse gases. This has contributed to the growing knowledge about the rumen microbiome to e.g., improve feed conversion efficiency [1], and animals' health [2], and mitigate methane emissions [3]. The ruminants microbiome's ability to digest plants with high fibre content resulted in a large number of metagenomic studies, given the interest of the biobased industries in discovering microorganisms and lignocellulolytic enzymes to apply to their industrial processes [4][5][6]. ...
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... In general, data in beef cattle show that eating rate is greater for inefficient animals (Kelly et al., 2010;Durunna et al., 2011;Fitzsimons et al., 2014). However, eating time is greater for inefficient beef cattle in some studies (Nkrumah et al., 2006;Durunna et al., 2011;Fitzsimons et al., 2014) but not in others (Kelly et al., 2010;McGee et al., 2014). Because eating rate is a function of DMI and eating time, the eating rate in these studies may have been influenced by the definition of eating time. ...
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Thesis
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Chapter
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