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EFFECTS OF ENERGY INTAKE ON ENERGETIC EFFICIENCY
AND BODY COMPOSITION OF BEEF STEERS DIFFERING
IN SIZE AT MATURITY
C. A. Old and W. N. Garrett
University o f California, Davis 95616
ABSTRACT
Hereford and Charolais steers were fed at three levels of feed intake (low, medium or ad libitum)
to similar weights within breed groups to evaluate effects of energy intake on energetic efficiency
and body composition. Two methods were employed to partition metabolizable energy intake into
use for maintenance and gain. Method one used an assumed daily fasting heat production of 77
kcal/weight (W) "Is ; method two estimated fasting heat production from the regression of log daily
heat production against metabolizable energy intake (keal/W "Ts). Net energy for gain (NEIz) was
determined in method one by regressing retained energy (kcal/W "is ) against feed intake (g/W "Ts).
For method two, the estimated maintenance requirement of feed was subtracted from total feed
intake and retained energy was regressed against feed intake above maintenance to estimate NEg.
Conclusions regarding feed energy utilization for maintenance and gain were the same by either
method of energy partitioning. Charolais steers used feed energy less efficiently for gain than
Hereford steers, and ad libitum steers used feed energy less efficiently for gain than steers at lower
intakes (P<.05). Charolais steers made leaner (P<.05) gains than Hereford steers. Although steers
consuming the lowest level of feed made gains containing a lower percentage of fat and a higher
percentage of protein (P<.05) than steers at higher intakes, body composition within a breed was
not altered by level of energy intake when animals, within breeds, were slaughtered at similar end
weights.
(Key Words: Hereford, Charolais, Body Composition, Energy Metabolism.)
Introduction
Literature reports on the effects of energy
intake on b o d y c o m p o s i t i o n are n u m e r o u s and
interpretations of the findings are variable. Reid
et al. (1968) and Preston (1971) r e p o r t e d variations in b o d y c o m p o s i t i o n are largely explained
by variations in b o d y weight. M o u l t o n et al.
(1922), Prior et al. (1977) and Ferrell et al.
(1978) f o u n d level of energy intake to influence b o d y composition.
Several m e t h o d s
exist for partitioning
metabolizable energy intakes into net energy
for m a i n t e n a n c e and gain. Lofgreen and Garrett
(1968) use an e x p e r i m e n t a l l y derived value of
77 kcal/weight (W) .Ts as the daily fasting h e a t
production. There is variability associated with
this m e a s u r e m e n t ; it is n o t the same for all
breeds of cattle, and it is essential for evaluating energetic efficiency. Fasting heat production can be estimated for a particular experim e n t by regression procedures, (Lofgreen and
Received October 27, 1986.
Accepted May 12, 1987.
Garrett, 1968) if several increments of energy
intake (preferably one level near the maintenance requirement) are included. This research
was u n d e r t a k e n to evaluate energetic efficiency
and b o d y c o m p o s i t i o n of Hereford and Charolais steers fed f o u r intakes to similar end
weights within breeds.
Materials and Methods
N i n e t y - f o u r grade British breed steers
( p r e d o m i n a n t l y H e r e f o r d breeding) and 94
Charolais steers were purchased f r o m commercial sources for use in a comparative slaughter feeding trial. Seventy-two steers of each
breed were r a n d o m l y assigned to a 2 • 3 X 3
factorial experiment. The factors were breed,
crude protein level in the diet and level o f feed
intake. There were three feed intake levels in
the factorial experiment, ad libitum (AL),
m e d i u m (85 AL) and low (70 AL). Intakes
were adjusted periodically so that steers at the
t w o lower intakes (70 A L and 85 AL) w o u l d
gain at a p p r o x i m a t e l y 70 and 85% of the rate
o f A L steers o f the same breed. Crude protein
levels were 8.9, 11.0 and 12.9%. In addition to
the factorial e x p e r i m e n t , 12 steers of each
1371
J. Anita. Sci. 1987.65:1371-1380
1372
OLD AND GARRETT
TABLE 1. COMPOSITION OF DIETS a
Protein level
Item
8.9%
Ingredient b
Cracked corn, %
Wheat straw, %
Molasses, %
Cottonseed meal, %
Oystershell flour, %
Trace mineral salt, %
Nutrient composition c
DE, Mcal/kgd
ME, Mcal/kg d
Crude protein, %
ADIN, % total N
76.6
16.1
4.5
1.3
1.0
.5
11.0%
12.9%
68.1
64.2
15.5
5.5
12.8
.5
.5
17.7
5.5
7.4
.5
.5
3.11 • .05
2.69 • .04
8.9
4.8
3.15 + .05
2.72 -+ .04
11.0
3.8
3.19 • .05
2.76 -+ .04
12.9
3.6
avitamin A, 2200 1.U. per kg, was added to all diets.
bAs-fed basis.
CDry matter basis. DF is digestible energy; ME is metabolizable energy; ADIN is acid insoluble nitrogen.
dActual determination from eight steers.
breed were assigned to a m a i n t e n a n c e level of
intake, f o u r steers of each breed per protein
level. Ad libitum-fed steers were pen-fed (eight
head per pen), while t h o s e on lower intakes
(maintenance, 70 A L and 85 AL) were individually housed. Steers were n o t i m p l a n t e d with
any anabolic agent and did n o t receive any nonnutritive feed additives. Ingredients used to
f o r m u l a t e the diets are s h o w n o n a percentage
basis (as fed) in table 1.
Steers were weighed every 28 d after overnight (16 to 18 h) removal o f feed and water
(shrunk weights). Feed offered to 70 A L and
85 A L steers was adjusted at this time. F e e d
c o n s u m p t i o n s o f steers assigned to the lower
feeding levels (maintenance, 70 A L and 85 AL)
are actual individual feed intakes. Individual
feed intakes for group-fed (AL) steers were
estimated f r o m the measured feed c o n s u m p t i o n
for each group using m e t h o d D of Old and
Garrett (1981):
F F M i = .077Wi "Ts/NE m X DOF,
n
FFG=FI--]~
FFMi,
i=l
F F G i = G i / G p • F F G and
FI i = F F M i + F F G i,
where:
FFMi =
Wi =
NEro =
DOF =
FFG
FI
FFGi
Gi
=
=
=
=
Gp =
FIi =
individual feed r e q u i r e d for maintenance;
mean e m p t y b o d y weight;
net energy for m a i n t e n a n c e (feed,
Mcal/kg);
days on feed;
pen feed intake above m a i n t e n a n c e ;
t o t a l pen f e e d intake;
feed available for gain, individual;
individual gain, kg e m p t y b o d y ;
pen gain, kg e m p t y b o d y and
individual feed intake (kg).
All steers were slaughtered c o m m e r c i a l l y and
b o d y c o m p o s i t i o n was estimated f r o m carcass
density. Estimating equations for Hereford
steers were those of Garrett and H i n m a n
(1969). Separate equations (table 2) were used
for Charolais steers (Garrett et al., 1978).
Initial b o d y c o m p o s i t i o n was d e t e r m i n e d
f r o m 10 steers of each breed. A d libitum and
m a i n t e n a n c e steers were slaughtered after 189 d
on feed (at this time it was estimated, by visual
appraisal, that the full-fed Hereford steers
w o u l d grade a p p r o x i m a t e l y l o w Choice).
Shrunk weights for ad libitum-fed cattle were
435 and 501 kg for H e r e f o r d and Charolais
steers, respectively. Steers at the 85 A L and 70
ENERGETIC EFFICIENCY OF STEERS
AL intakes were slaughtered when they attained
similar weights.
Metabolizable energy concentrations of the
diets were determined in a digestion trial by
total collection of urine and feces from four
Hereford and four Charolais steers. Each diet
was offered at three levels: maintenance, 1.75
times maintenance and 2.5 times maintenance.
Fecal and urinary collection periods were for 7
d after a 7-d adaptation period. Gross energy
determinations were made on samples of feed,
feces and urine by adiabatic b o m b calorimetry.
Methane energy losses were estimated from
digestible carbohydrates (Bratzler and Forbes,
1940). Nitrogen determinations on feed, feces
and urine were made b y a macro-Kjeldhl
technique (AOAC, 1970).
Metabolizable energy intake (MEI) was
partitioned into energy used for maintenance
and gain b y two procedures. Calculation of net
energy for maintenance (NE m) by method one
used a daily fasting heat production (FHP) of
77 kcallW -Ts (Lofgreen and Garrett, 1968); for
m e t h o d two, FHP was estimated by use of the
following relationships:
HP = MEI -- RE and log HP = a + b (MEI),
where:
HP
MEI
RE
a
-- daily heat production (kcal/W "Ts ),
= daily ME intake (kcal/W "Ts),
= daily energy retention (kcal/W "Ts ) and
= estimate of log daily FHP (kcal/W '~s ).
1373
or metabolizable energy for maintenance,
MEm) and using the following relationship:
FHP = NE m
ME m ME
Method one net energy for gain (NEg) values
were obtained by the classical method of linear
regression of retained energy (RE) per W "Ts on
feed intake per W g s . In method two, the estimate of feed required for maintenance (which
was different than the method one maintenance
value) was subtracted from total feed intake.
Retained energy was then regressed against
feed intake above maintenance. Efficiency of
ME use for gain (kg) was estimated by regression of daily retained energy (kcal/W "Ts)
against daily ME consumed ( k c a l / k g "Ts) above
the maintenance requirement.
When different treatment means were indicated by a significant F-statistics, Duncan's
multiple-range test was applied. A step-wise
polynomial regression technique (BMDP, 1977)
was used to determine relationships between
e m p t y b o d y (EB) weight or average daily EB
gain and the fat, protein, water and energy
components of the final e m p t y body. This technique was also used to determine the relationship between retained energy and ME intake. A
multiple regression technique was used to obtain standardized regression coefficients for the
relationship between EB fat and average daily
EB gain and EB weight.
Results and Discussion
Net energy for maintenance values are obtained
by iteration to HP = MEI (maintenance point
Digestion trial data are summarized in table
1. Neither intake level nor protein level affected
TABLE 2. REGRESSION EQUATIONS TO ESTIMATE CHAROLAIS
BODY COMPOSITION FROM CARCASS DENSITY
Item
Regression
equation
n
r
SE
EBa water, %
EB protein, %
EB fat, %
Kcal/kg EB
EB weight
449.109CD b -- 422.123
90.928CD -- 79.581
621.593 -- 562.272CD
53.290 - 47.139CD
1.316WCWc + 32.287
25
25
25
25
25
.92
.90
.95
.94
.998
1.6
.37
1.5
.14
6.4
aEB = empty body.
bCD = carcass density.
CWCW= warm carcass weight.
1374
OLD AND GARRETT
digestibility o f t h e diets. Digestible e n e r g y a n d
m e t a b o l i z a b l e energy (ME) c o n c e n t r a t i o n s were
3.15 + .05 a n d 2.72 + .04 kcal/g, respectively.
No significant i n t e r a c t i o n s were f o u n d f o r
any o f t h e f a c t o r s e x a m i n e d regarding f e e d l o t
p e r f o r m a n c e data (table 3). Charolais steers
w e r e heavier initially (244 vs 230 kg) a n d
finally (440 vs 398 kg) t h a n H e r e f o r d steers
( P < . 0 5 ) . M e t a b o l i z a b l e e n e r g y intakes scaled b y
W "Ts were d i f f e r e n t ( P < . 0 5 ) a m o n g intake
groups b u t w e r e n o t d i f f e r e n t f o r ad l i b i t u m - f e d
Charolais steers c o m p a r e d w i t h H e r e f o r d s .
Ferrell et al. (1978) r e p o r t e d ad l i b i t u m ME int a k e s per W "Ts t o b e similar b e t w e e n British a n d
e x o t i c cattle. C o a d y et al. (1979) i n d i c a t e d increased intakes f o r H e r e f o r d steers relative t o
Charolais steers. Average daily gains were differe n t a m o n g intake g r o u p s (AL > 85 A L > 70
AL) a n d w e r e also higher f o r Charolais steers
t h a n f o r H e r e f o r d steers ( P < . 0 5 ) . Crude prot e i n intakes (g/d) w e r e 680, 820 a n d 930 averaged over t h e t h r e e levels o f f e e d i n g f o r t h e 8.9,
11.0 a n d 12.9% diets, respectively. Level o f
p r o t e i n did n o t i n f l u e n c e daily gains, final
weights, MEI/W "Ts or b o d y c o m p o s i t i o n . T h e
l o w e s t p r o t e i n i n t a k e is a b o u t 10% b e l o w t h e
level r e c o m m e n d e d f o r similar p e r f o r m a n c e o f
cattle o f this t y p e (NRC, 1984) b u t o t h e r
i n t a k e s are well w i t h i n t h e r e c o m m e n d a t i o n s .
In all cases significant regressions, t h a t is slopes
greater t h a n zero, w e r e a t t a i n e d f o r t h e relationship b e t w e e n log HP and MEI (figures 1 a n d 2).
E s t i m a t e s o f F H P were l o w e r ( P < . 0 5 ) b y m e t h o d t w o ( m a i n t e n a n c e steers i n c l u d e d ) t h a n t h e
77 kcal/W "Ts u s e d in m e t h o d o n e ( m a i n t e n a n c e
g r o u p n o t used). E s i m a t e s o f ME m were also
less b y m e t h o d t w o t h a n b y m e t h o d o n e
( P < . 0 5 ) ; t h e s e w e r e 104 and 122 kcal/W "Ts,
TABLE 3. FEEDLOT PERFORMANCE AS INFLUENCED BY BREED AND LEVEL OF INTAKE
Item a
Initial EB wt, kg
Final EB wt, kg
ME intake W"as , Mcal
Daily feed intake, kg/DM
ADG EB, kg
Days on feed
Breed
Intake
level b
Hereford
Charolais
Mean c
70 AL
84 AL
AL
Mean c
70 AL
85 AL
AL
Mean
70 AL
85 AL
AL
Mean
70 AL
85 AL
AL
Mean
70 AL
85 AL
AL
Mean
70 AL
85 AL
AL
Mean
223
236
230
230
• 2.7
393
398
402
398
-+ 3.6
218
241
314
258
• 5.4
5.85
6.62
8.67
7.04-+ .16
.62
.75
.91
.76 + .02
273
217
189
226
240
241
250
244
441
435
443
440
228
257
319
268
6.61
7.42
9.43
7.82
.74
.84
1.03
.87
273
231
189
231
231
239
240
-+ 3.6
-+ 2.8
+- 3.4
417
416
423
+ 5.0
• 5.1
+ 6.0
223
249
317
• 1.8 e
• 2.2 f
-+ 3.9g
+_2.5 d
• 3.6 d
_ 5.0
6.23 • .06 e
7.02 -+ .07 f
9.05 • .17g
•
.16 d
.68 • .02 e
.79 • .02 f
.97 + .02g
•
.02 d
273
224
189
aEB is empty body basis; ME is metabolizable energy; DM is dry matter.
bMaintenance-fed animals gained empty body weight slowly (33 • 15 and 25 • 12 g/d for Herefords and
Charolais, respectively) and were in positive energy balance (see figure 3).
CWhere applicable, row and column means are shown with standard error of the mean.
dMeans for breeds differ (P<.05).
e'f'gvalues in mean column within an item with different superscripts differ (P<.05).
ENERGETIC EFFICIENCY OF STEERS
METHODONET=I.BBB5+.OOIBOX
R2=.99 SEI=.05
--METHOD
TNO T=I.8435+.OOI79X
R2--.96 S E I = . 0 1
~ . ~"
1375
j
m
:
:
:
:
~
50
:
:
:
:
l:
:
:
:
I
;
~
=
~
I
D
I
I
I
I
,
I
iO0
150
200
250
ME INTAKE {KCAL/N .Ts *DAY)
I
t
I
:
300
:
:
:
1
350
Figure 1. Relationship of heat production (HP) to metabolizable energy (ME) intake as estimated by two
methods for Hereford steers.
(,D
METHODONET=1.B865+.OOIB2X
R2=.99 SEI=.05
--METHOD TWOT=1.B5316+.OO179X
R2=.97 SEx=.04
>.-(I
Wc c~
L/3
__.I
cm~
(_J
xc--
rl
-r-
o
(_.bc~
(22)
._.I
/
:::::::::::::::::::::::::::::::::::::
50
100
150
200
250
300
350
ME INTAKE(KCAL/14 .?s *DAY)
Figure 2. Relationship of heat production (HP) to metabolizable energy (ME) intake as estimated by two
methods for Charolais steers.
1376
OLD A N D GARRETq"
respectively. The lower estimate of FHP obtained using method two may be due to the
fact that the FHP estimate of Lofgreen and
G a r r e t t ( 1 9 6 8 ) is f o r s t e e r s i m p l a n t e d w i t h
a n a b o l i c a g e n t s ; s t e e r s in t h i s s t u d y w e r e n o t
i m p l a n t e d . A l s o , as i n d i c a t e d b y t h e s t a n d a r d
error of estimate (5.4) for the data of Lofgreen
a n d G a r r e t t ( 1 9 6 8 ) , t h e r e is v a r i a b i l i t y a s s o c i ated with this measurement. Given the relationships determined for this experiment, a lower
e s t i m a t e o f F H P ( M E I = 0 ) will r e d u c e t h e e s t i -
mate of MEre. However, since the ratio of FHP/
ME m was very nearly the same for method one
and two, values obtained for NE m were similar
for each method.
NEm
values were not
different between breeds nor among intake
groups.
Both methods showed that Charolais steers
had lower efficiency of feed energy utilization
f o r g a i n (kg) t h a n H e r e f o r d s t e e r s ( P < . 0 5 ) . N e t
energy for gain (NEg) values (table 4) for Charolais s t e e r s w e r e 1 . 0 1 a n d . 8 9 ; H e r e f o r d s t e e r s
TABLE 4. ENERGY U T I L I Z A T I O N AS INFLUENCED BY BREED AND LEVEL OF INTAKE
Item
Maintenance
Method one bc, Kcal, NE/W "Ts
Method two bc, Kcal, ME/W 'Ts
NEmd
Method one b, Mcal/kg
Method two b, Mcal/kg
NEg e
M e t h o d one b, Mcal/kg
Method two b, Mca!/kg
Estimated fasting h e a t production, kcal/W "Ts
kg f
Intake
level
70 AL
85 AL
AL
Mean a
70 AL
85 AL
AL
Mean a
70 AL
85 AL
AL
Mean a
70 AL
85 AL
AL
Mean a
70AL
85 AL
AL
Mean a
70 A L
85 AL
AL
Mean a
70 AL
85 AL
AL
Mean a
70 AL
85 AL
AL
Mean a
Breed
Hereford
Charolais
Mean a
123
121
121
122
• .6
101
101
104
102
• 5.1
1.70
1.73
1.73
1.72 +- .01
1.68
1.72
124
122
123
123
104
105
108
106
1.69
1.71
1.71
1.70
1.68
1.72
1.75
1.72
1.12
1.07
.84
1.01
.94
.95
.78
.89
64
66
69
66
.32
.33
.27
.31
123
122
122
•
•
•
102
103
106
• 3.9
• 4.5
+ 5.7
1.77
1.72
1.18
1.15
.90
1.08
.95
.97
.83
.92
62
64
68
65
.33
.33
,30
.32
•
.03
+ .02
•
.01
+- 3.1
•
.01
•
.7
.8
.7
.6
~ 4.7
1.70
•
1.72
•
1.72 •
.01
.01
.01
1.68 •
1.72 •
1.76 •
.04
.03
.04
1.15 •
1.11 •
.87 •
.02
.03
.02
.95 •
.02
.02
.01g
_+ .01
•
.02
_+ .02g
.96 •
.80 •
•
.01g
63
65
69
-+ 2.4
• 2.9
• 3.1
• 2.6
.33 •
.33 •
,29•
•
.O1
.O1
.01g
.02
aRow and c o l u m n m e a n s are s h o w n with standard error of the m e a n except m a i n t e n a n c e m e t h o d two. which
shows -+ .95% confidence interval.
bMethod one used daily fasting heat production of 77 Kcal/W "~s. Method tWO used estimate of fasting heat
production obtained by regressing log heat production/W "~s on metabolizable energy intake/W "7s .
CME/W.TS = Metabolizable energy intake/W "Ts .
d N E m = Net energy for m a i n t e n a n c e of feed.
eNeg = Net energy for gain of feed.
fkg = t h e slope of daily retained energy (kcal/W "*s ) vs daily metabolizable energy intake (kcal/W "Ts).
g v a l u e s in m e a n rows and c o l u m n s with different superscripts are different (P<.05),
1377
ENERGETIC EFFICIENCY OF STEERS
were 1.08 and .92 by methods one and two,
respectively. Differences are due to a lower
ME m and higher HP/MEI for method two. Garrett (1971), comparing Hereford and Holstein
steers, and FerreU and Jenkins (1985), comparing Hereford and Simmental males and females, reported similar results. Webster (1978)
has indicated that it is energetically more efficient to gain fat than protein. Previously published data from this trial (Old and Garrett,
1985) showed a much greater efficiency of ME
use for fat gain (.58) than for protein gain (.11).
Multiple regression technqiues as used by Old
and Garrett (1985) or Thorbek (1980) have
shown that fat deposition is energetically more
efficient than protein deposition. This finding
is not necessarily at odds with theoretical estimates (Baldwin and Smith, 1979; Van Es,
1980), which indicate that protein synthesis
is most efficient. Synthesis and deposition are
not synonymous and protein turnover may
account for at least part of the discrepancy
between the theoretical and experimental resuhs. Ad libitum-fed steers (gains higher in fat
content) had lower NEg values than did 70 AL
or 85 AL steers (P<.05), by either method.
Method one estimates of NEg were .87, 1.11
and 1.15 Mcal/kg; by method two, 82, .96 and
.95 Mcal/kg for the AL, 85 AL and 70 AL intakes, respectively. Efficiency of ME use for
gain (kg) was also less (P<.05) for AL steers
(.29) than for 85 AL (.33) or 70 AL (.33). Bestfit polynomial regressions of retained energy
(kcal/W "?s) vs MEI (kcal/W "?s ) showed a curvilinear relationship between these factors (figure 3). Blaxter (1956) has shown a similar relationship between gross energy intake and retained energy. However, other reports (Lofgreen and Garrett, 1968; Webster et al., 1976)
have found little effect of intake on kg.
0
HEREFORD
Y=-40.24744+.45935X-.OOO39X
R 2---a 8 4
-
Lt3
2
-CHAROLAIS
Y=-46.12747+.51416X-.OOO54X
"~
C~
2
R 2-- - . 85
._J
CE
(_J
=
Z
,
j~.~,~.
*
9
H
rlm
*
9
",~..~
m'*
*
c_b
>.._
c_b
OC
W
Z
W
9 =Z~*
al, *
...;.
*=,
o
>-._J
(2E
0
! x/,~
50
lOO
150
200
DAILY ME INTAKE
300
250
.75 ]
(KCALII4
Figure 3. Effects of metabolizable energy (ME) intake on energy retention.
350
1378
OLD AND GARRETT
Byers (1980b) indicates that the method used
to partition energy intake can influence conclusions regarding energetic efficiency. Our conclusions regarding the influence of level of
feeding or breed on energy utilization for maintenance and gain are the same by either method
one or two. However, the lack of uniqueness
of solution for MEm and NEg between methods
one and two indicates that one or both may be
inadequately specified. Unfortunately the extent of current knowledge is insufficient to resolve this issue.
Initial body composition of the Hereford
and Charolais steers were similar (table 5 footnote c), which may indicate comparable physi:
ological ages at the start of the experiment.
However, gains made by Charolais (table 5) had
more protein, less fat and energy than Herefords
(P<.05). Barber et al. (1981) reported similar
results. Gain of the 70 AL group was leaner
than that of 85 AL and AL steers (P<.05).
Black (1974) has shown, in sheep, and Fortin et
al. (1981), in cattle, that as ME intake increases,
the proportion of energy partitioned to fat increases. Protein gains averaged 93 g /d for all
Hereford steers, 121 g / d for atl Charolais steers.
These amounts are similar to those indicated by
Byers and Rompala (1979), but are considerably
below (30 to 50%) daily protein deposition
found by Garrett (1979) or Ferrell and Jenkins
(1985) and those quoted in reviews by Geay
(1984) and Rohr and Daenicke (1984). It is
T A B L E 5. C O M P O S I T I O N O F E M P T Y B O D Y A N D E M P T Y B O D Y G A I N
A S I N F L U E N C E D BY B R E E D A N D L E V E L O F I N T A K E
Item
Water b in e m p t y b o d y , %
F a t b in e m p t y b o d y , %
P r o t e i n b in e m p t y b o d y , %
Mcal/kg empty body
Water in gain, %
F a t in gain, %
P r o t e i n in gain, %
M c a l / k g gain
Breed
Intake
level
Hereford
Charolais
Mean a
70 A L
85AL
AL
Mean a
70 AL
85 A L
AL
Mean a
70 A L
85 A L
AL
Mean
70 AL
85 A L
AL
70 A L
85 A L
AL
Mean
70 AL
85 A L
AL
Mean
70 AL
85 A L
AL
Mean
70 AL
85 A L
AL
Mean
54.2
54.0
52.6
53.6
25.7
26.0
27.9
26.5
16.4
16.3
15.9
16.2
3.31
3.34
3.50
40.7
38.6
36.6
38.6
43.5
46.2
48.9
46.2
12.9
12.3
11,8
12.3
4,82
5.04
5.27
5.04
55.0
53.4
54.5
54.3
24.3
26.2
24.8
25.2
17.0
16.7
16.9
16.9
3.21
3.38
3.26
42.0
37.7
40.3
40.0
40.5
45.9
42.7
43.0
14.4
13.5
14.0
14.0
4.58
5.03
4.76
4.79
54.6
53.7
53.6
+ .31
+ .38
+ .50
25.0
26.1
26.3
+- .40
-+ .49
+ .66
16.7
16.5
16.4
-+ .08
+ .08
+- .13
3.26
3.36
3.38
41.3
28.2
38.4
,+ .03
_+ .04
,+ .05
-+ .7 c
+- 1.0
+ 1.1
42.0
46.1
45.8
+- .9 e
+ 1.3
+ 1.4
13.6
12.9
12.9
+ .2 e
+- .2
+- .3
-+ .3
+ .4
+ .1
-+.8
+ 1.0
+
+
.2
.08
•
.3
-+ .4 c
-+ .1
,+ .8
+ 1.0 c
+- .2 c
4 . 7 0 +- .08
5.04 -+ .11
5.01 ,+ .12
+
.09 c
a R o w s a n d c o l u m n m e a n s are s h o w n w i t h s t a n d a r d e r r o r o f t h e m e a n .
b I n i t i a l b o d y c o m p o s i t i o n s w e r e : 6 4 . 5 a n d 6 5 . 6 % w a t e r ; 12.1 a n d 10.9% f a t a n d 19.0 a n d 19.2% p r o t e i n for
H e r e f o r d a n d C h a r o | a i s cattle, r e s p e c t i v e l y .
CValues in m e a n r o w s a n d c o l u m n s w i t h d i f f e r e n t s u p e r s c r i p t s are d i f f e r e n t ( P < . 0 5 ) .
ENERGETIC EFFICIENCY OF STEERS
i n t e r e s t i n g ( a n d n o e x p l a n a t i o n is a p p a r e n t )
t h a t t h e c o m p o s i t i o n o f gain m a d e b y A L
Charolais steers. A similar o c c u r r e n c e is a p p a r e n t
in t h e d a t a o f Prior et al. ( 1 9 7 7 ) f o r British
steers. F i n d i n g s in t h e l i t e r a t u r e o n e f f e c t s o f
e n e r g y i n t a k e o n b o d y c o m p o s i t i o n are variable. M u r r a y e t al. ( 1 9 7 4 ) a n d Jesse et al. ( 1 9 7 6 )
r e p o r t e d t h a t c a t t l e fed at d i f f e r e n t e n e r g y int a k e s were similar in c o m p o s i t i o n w h e n slaught e r e d at e q u i v a l e n t weights. T h e findings o f
this e x p e r i m e n t are c o n s i s t e n t w i t h t h e s e conclusions. Ferrell et al. ( 1 9 7 8 ) , Byers a n d R o m pala ( 1 9 7 9 ) , Byers ( 1 9 8 0 a ) a n d F o r t i n e t al.
( 1 9 8 0 ) i n d i c a t e d t h a t h i g h e r r a t e s o f gain prod u c e d f a t t e r a n i m a l s at similar weights.
S t e p w i s e p o l y n o m i a l regressions, EB f a t (kg)
vs average daily gain ( A D G : kg, EB basis) a n d
EB f a t vs EB weight, i n d i c a t e d t h a t a b e s t fit t o
t h e d a t a was linear. T h e s e analyses f o u n d EB
f a t t o b e highly c o r r e l a t e d w i t h A D G a n d EB
w e i g h t ; f o r Charolais steers R 2 values were .69
a n d .77, f o r H e r e f o r d steers .77 a n d .86. E m p t y
b o d y f a t was m o r e highly c o r r e l a t e d w i t h b o d y
w e i g h t t h a n w i t h r a t e o f gain (gain a l t e r e d b y
r e d u c i n g feed i n t a k e ) . M u l t i p l e regressions o f
EB f a t o n A D G (EB) a n d EB w e i g h t indic a t e d t h a t m u c h m o r e o f t h e v a r i a t i o n in EB f a t
is e x p l a i n e d b y changes in w e i g h t r a t h e r t h a n
changes in rate o f gain. T h e s t a n d a r d i z e d coefficients were .71 a n d .25 ( H e r e f o r d steers)
a n d .73 a n d . 17 (Charolais steers) for EB w e i g h t
a n d A D G (EB), respectively. This analysis supp o r t s t h e g e n e r a l i z a t i o n (similar to G a r r e t t ,
1 9 8 0 ) t h a t " w i t h i n t h e usual e c o n o m i c res t r a i n t s .... n u t r i t i o n a l m a n i p u l a t i o n s have a relatively small i n f l u e n c e o n p r o t e i n p r o d u c t i o n p e r
a n i m a l c o m p a r e d w i t h t h a t w h i c h can b e o b t a i n e d b y selecting t h e m o s t a p p r o p r i a t e g e n o o
t y p e .... ".
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