D . Perry, P.F. Arthur Livestock Production Science 62 2000 143 –153
147
P , 0.01, year P , 0.001, log total fat P , significant P . 0.05 terms for year and line and
0.001 and the interaction between year and log total significant terms for log scaled total fat weight P ,
fat P , 0.001. 0.001 and the interactions between year and line
To determine growth relative to stage of maturity, P , 0.05 and year by log total fat P , 0.001.
weights of each component, and of empty body weight, were scaled by their mean mature weight
within year and selection line, and then transformed
3. Results
to log base 10. Using this data from the 79 steers a multivariate allometric analysis, as described above,
3.1. Proportional body composition at maturity was used to determine the growth of dissected
muscle, bone, visceral mass and total fat relative to There was a symmetrical divergence in mature
stage of maturity of empty body weight, and of all empty body weight between the lines, with the High
the dissected fat partitions relative to stage of Line steers being 78 kg heavier than Control Line
maturity of total fat. Once again, non-significant steers whilst the Low Line steers were a further 76
P . 0.05 interactions were sequentially deleted kg lighter Table 2. Despite the differences in
from the models. For growth relative to stage of mature weight, the multivariate analysis indicated
maturity of empty body weight the final model that these animals had similar P . 0.05 mean
contained non-significant P . 0.05 terms for line proportions of muscle, bone, visceral mass and total
and year, and significant terms for log scaled empty fat Table 2. Year of birth had an effect P , 0.01
body weight P , 0.001 and the year by log scaled on proportional distribution, with steers from the first
empty body weight interaction P . 0.01. For calving having a higher proportion of bone than
growth of the fat partitions relative to stage of those from the second year. Within the mature group
maturity of total fat the final model contained non- of steers there was no change in proportional com-
Table 2 Means for liveweight 6SD, empty body weight 6S.E. and dissectible components expressed as percentages of empty body weight
6S.E. in mature steers from lines selected for divergent growth rate Trait
Selection line High Line
Control Line Low Line
Number of animals 10
9 11
Liveweight kg 730647
644658 558656
a b
c
Empty body weight kg 666617
588618 512616
A
Dissected components
B
Muscle Y1
32.261.12 34.161.12
34.061.12 Y2
33.860.91 33.761.00
31.460.84 Bone
Y1 8.760.47
8.860.47 9.260.47
Y2 8.460.38
8.260.42 7.560.35
C
Total fat Y1
36.761.66 34.861.66
32.561.66 Y2
34.061.35 32.661.48
34.961.25 Total viscera
Y1 7.560.29
7.560.29 7.860.29
Y2 7.960.24
8.560.26 8.360.22
a,b,c
Means with different superscripts are significantly different P , 0.05 within row.
A
Other components of empty body weight such as hide, head and tail are not presented.
B
Y1, Y2: consecutive birth years.
C
Total fat 5 subcutaneous 1 intermuscular 1 all non-carcass fat partitions.
148 D
. Perry, P.F. Arthur Livestock Production Science 62 2000 143 –153
position with age, indicating that the animals had had a higher P , 0.05 growth impetus b coeffi-
achieved their mature composition. cient, Table 4 and was a lesser P , 0.05 propor-
tion of empty body weight a coefficient, Table 4 at 3.2. Fat partitioning at maturity
the same body weight than in steers from the second year. Line P , 0.01 affected the proportions of
Table 3 shows the mean total dissected fat weight, components at the same empty body weight a
and the proportion of this total fat made up by each coefficients, Table 4. At the same weight the Low
of the fat partitions, for mature steers from the three Line had relatively more fat and less bone than the
selection lines, adjusted for birth year. The mean Control Line, which in turn had more fat and less
proportion of total fat weight made up by the various bone than the High Line. The Low Line also had less
partitions was not affected P . 0.05 by line or birth muscle than the High Line. Table 5 shows predicted
year when examined by multivariate analysis. How- values for component weights at 360 kg empty body
ever examination of the univariate coefficients indi- weight, which is equivalent to comparison at 240 kg
cated that the Low Line had less omental fat as a carcass weight suitable for the heavy domestic
proportion of total fat than did the High Line Table Australian trade. Multivariate allometric analysis of
3. There was no effect of age on partitioning of fat scaled data indicated no difference P . 0.05 among
within the mature group of steers. selection line or birth year in growth rates b
coefficients relative to stage of maturity of empty 3.3. Growth to maturity
body weight. The difference in composition among the selection lines evident when compared at the
The multivariate allometric analysis indicated that same empty body weight was not apparent P .
there was no difference among the selection lines in 0.05 at the same stage of maturity of empty body
the rate of growth b coefficients, Table 4 for any of weight. All components for each of the lines were a
the body components relative to empty body weight, similar proportion of their mature weight at the same
nor was there any significant line by year interaction stage of maturity of empty body weight. Table 5
P . 0.05. In steers from the first year of birth, bone compares these proportions at 0.67 maturity of
empty body weight the mean for this data group. b coefficients for all scaled log components were
similar to those obtained using log component
Table 3
weights.
Means for total dissectible fat 6S.E. and dissectible fat com-
Relative growth coefficients derived from the
ponents expressed as percentages of total fat weight 6S.E. in
allometric analysis Table 4 indicated that total fat
mature steers from lines selected for divergent growth rate, adjusted for year of birth
was late developing relative to body weight. That is, as the animal matured, fat made up an increasing
Selection line
proportion of empty body weight. Dissected muscle,
High Line Control Line
Low Line
bone and total visceral mass grew at a slower rate
Number of animals 10
9 11
than body weight i.e., developed early relative to
a a,b
b
Total fat kg 235610
198611 175610
body weight for the period from weaning to maturi- ty.
Carcass depots
Multivariate allometric analysis indicated that
Subcutaneous fat 39.961.55
39.161.62 40.961.49
Intermuscular tissue 35.160.96
36.361.01 36.560.92
there was no difference P . 0.05 among the selec- tion lines in the growth rate of any of the fat
Non-carcass depots
partitions relative to weight of total dissected fat, but
Kidney channel 7.460.56
8.160.59 7.160.54
there was a difference among years P , 0.001, with
Omental 7.460.53
7.560.56 6.760.51
scrotal and kidney channel fat being later developing
Mesenteric 5.360.33
4.660.35 4.260.32
Scrotal 4.860.22
4.460.23 4.660.21
relative to total fat, in the first year of the experiment
a
compared to the second Table 6. Steers from the
Means within a row with different superscripts are different P , 0.05.
first year of the experiment also had less scrotal P
D . Perry, P.F. Arthur Livestock Production Science 62 2000 143 –153
149 Table 4
Proportional a 6S.E. and growth b 6S.E. coefficients relative to empty body weight for dissected components in steers selected for divergent growth rate based on allometric log–log regression
Trait a coefficient
b coefficient
a,b a,c
a
Coefficient Line effect
Year effect Coefficient
Year effect Muscle
0.2201 H 0.0029
Y1 2 0.0317 0.8783
Y1 0.0053 60.0790
C 0.0076 Y2 0.0317
60.0141 Y2 2 0.0053
L 2 0.0104
60.0770 60.0138
60.0043 Bone
0.4098 H 0.0195
Y1 2 0.2537 0.7398
Y1 0.0476
60.1090
C 0.0036 Y2 0.2537
60.0195
Y2 2 0.0476 L 2 0.0232
60.1066 60.0190
60.0060 Total fat
2 4.2580 H 2 0.0219
Y1 2 0.0573 1.6838
Y1 0.0117 60.1423
C 2 0.0064 Y2 0.0573
60.0254 Y2 2 0.0117
L 0.0283
60.1390 60.0248
60.0078 Viscera
0.9371 H 0.0074
Y1 0.1749 0.6451
Y1 2 0.0321 60.1007
C 2 0.0003 Y2 2 0.1749
60.0180 Y2 0.0321
L 2 0.0072 60.0984
60.0176 60.0055
a
Coefficients in bold are significantly different within class P , 0.05.
b
H, High Line; C, Control Line; L, Low Line.
c
Y1, Y2; consecutive years of experiment. Table 5
, 0.001 and kidney channel fat P , 0.05 when
Least-squares mean 6S.E. for age, and predicted values for body components in steers from lines selected for divergent growth rate,
compared at the same weight of total fat than did
when compared at an empty body weight of 360 kg weight
steers from the second year a coefficients, Table 6.
constant and at 0.67 stage of maturity of empty body weight
Line significantly P , 0.01 affected the proportion
maturity constant
of total fat made up by the different partitions at the
Selection line
same weight of total fat a coefficients, Table 6. The
High Line Control Line
Low Line
Low Line had more subcutaneous fat than the Control and High Lines, whilst the High Line had
Weight constant
a b
c
Age days 544628
629628 719629
more mesenteric fat than the Control Line, which in
a a
b
Muscle 126.8
128.1 122.9
turn had more than the Low Line. When compared at
a b
c
Bone 34.6
33.4 31.4
the same stage of maturity of total fat, using scaled
a ab
b
Viscera 33.8
33.2 32.7
a a
b
log data, multivariate analysis showed no effect of
Total fat 86.5
89.6 97.1
line on the maturing rate of the different fat parti-
d
Maturity constant
tions P . 0.05, although there was a difference in
Muscle 0.70
0.70 0.71
maturing rate between the two years P , 0.001.
Bone 0.75
0.73 0.74
There was also a significant interaction between line
Viscera 0.76
0.75 0.77
and year on the a coefficients P , 0.05. Subcuta-
Total fat 0.53
0.53 0.52
neous and omental fat in the Low Line steers were a
Empty body weight 446
394 343
lesser proportion of their mature weight, and mesen-
a
Means within a row with different superscripts are different
teric and kidney channel fat a greater proportion of
P , 0.05.
d
their mature weight, in year 1 relative to year 2,
As proportion of mean mature component weights.
150 D
. Perry, P.F. Arthur Livestock Production Science 62 2000 143 –153 Table 6
Proportional a 6S.E. and growth b 6S.E. coefficients relative to total dissected fat for dissected fat partitions in steers selected for divergent growth rate based on allometric log–log regression
Trait a coefficient
b coefficient
a,b a,c
a
Coefficient Line effect
Year effect Coefficient
Year effect Subcutaneous fat
2 2.0045 H 2 0.0185
Y1 0.1128 1.3007
Y1 2 0.0210 60.0849
C 2 0.0062 Y2 2 0.1128
60.0169 Y2 0.0210
L 0.0247
60.0838 60.0166
60.0086 Intermuscular fat
0.5087 H 2 0.0014
Y1 0.0669 0.8215
Y1 2 0.0131 60.0485
C 0.0037 Y2 2 0.0669
60.0096 Y2 0.0131
L 2 0.0051 60.0479
60.0095 60.0049
Mesenteric fat 0.0745
H 0.0484 Y1 0.1271
0.7351 Y1 2 0.0230
60.1435
C 0.0068 Y2 2 0.1271
60.0285 Y2 0.0230
L 2 0.0552
60.1417 60.0281
60.0145 Omental fat
2 0.7544 H 0.0160
Y1 2 0.2316 0.9284
Y1 0.0470 60.1403
C 0.0107 Y2 0.2316
60.0279 Y2 2 0.0470
L 2 0.0266 60.1386
60.0275 60.0142
Kidney channel fat 2 1.6233
H 2 0.0170 Y1 2 0.3415
1.0928 Y1 0.0652
60.1417 C 0.0266
Y2 0.3415
60.0281
Y2 2 0.0652 L 2 0.0096
60.1399 60.0279
60.0143 Scrotal fat
2 2.0100 H 0.0096
Y1 2 1.0921 1.1277
Y1 0.2056
60.1455 C 2 0.0306
Y2 1.0921
60.0289
Y2 2 0.2056 L 0.0209
60.1438 60.0285
60.0147
a
Coefficients in bold are significantly different within class P , 0.05.
b
H, High Line; C, Control Line; L, Low Line.
c
Y1, Y2; consecutive years of experiment.
when compared at the same stage of maturity of total 4. Discussion
fat. b coefficients for all scaled log components were almost identical to those obtained using log com-
This study was started 12 years after selection for ponent weights.
yearling growth rate commenced. Therefore any The allometric growth coefficients indicated that
differences observed among the selection lines repre- subcutaneous and kidney channel fat were late de-
sent approximately 3.5 generations of selection Par- veloping relative to the growth of total fat Table 6,
nell et al., 1997. Arthur et al. 1997 have already whereas intermuscular, omental and mesenteric fat
reported that selection for yearling growth rate grew relatively slower than total fat from weaning to
resulted in changes in size of the cattle as yearlings, maturity. The relative growth coefficient for scrotal
with no change in shape of the animals. Archer et al. fat differed between years, being late developing in
1998 reported that in cows and steers, selection for the first year, and early developing in the second
yearling growth rate resulted in a correlated response Table 6.
in liveweight and height at all ages up to maturity,
D . Perry, P.F. Arthur Livestock Production Science 62 2000 143 –153
151
but rate of maturation in the two traits did not differ carcass fat relative to carcass weight Robelin et al.,
significantly among the selection lines. 1978 were greater than 1. That is, fat is a late
In this study there was no correlated response in developing component of the body. Relative growth
mature body composition and in the growth of the coefficients for muscle reported in the literature are
major body components, to divergent selection for not as consistent, although most suggest approxi-
yearling growth rate. Most reports on cattle slaug- mately isometric growth relative to the body measure
htered prior to maturity indicate that correlated to which they are being compared. Robelin et al.
responses in proportional carcass composition to 1978 and Morris et al. 1993 reported coefficients
selection for growth rate or size are either non not significantly different from 1 for muscle relative
significant or very small Andersen et al., 1974; to carcass weight and for saleable meat relative to
Koch, 1978. Comparable information on body carcass weight. In this study the relative growth
composition at maturity is limited. Morris et al. coefficient from weaning to maturity for muscle was
1993 found no difference in the growth of saleable less than 1. The coefficients reported by Fortin et al.
meat, bone or fat trim relative to carcass weight 1980 for muscle growth relative to body weight
between bulls from a weight-selected and an un- ranged from 0.85 to 1.159 depending on breed and
selected line, and no difference between the herds in level of feed intake, and Shahin et al. 1993
the proportions of saleable meat and fat trim. This reported values of less than 1 for muscle relative to
suggests that there would also have been no differ- side weight. This inconsistency could be due to
ence at maturity, although they reported that, when varying nutritional treatments, or to the range of
adjusted for differences in body weight, the selected weights over which the study was done. The non-
line had slightly more bone than unselected animals. linearity of birth data for log muscle in our study
Averaged over the two years of the experiment when plotted against log empty body weight illus-
there was no difference in mature body composition trates the possibility of different patterns of growth
between the lines. As maturing rate of body com- being reported if studies are conducted at different
ponents also did not differ between lines, animals stages of maturity. Bone is considered to be an early
from the three growth rate selection lines would have developing component in the body, as indicated by
the same proportional composition if compared at the the growth coefficients of less than 1 obtained in this
same stage of maturity of body weight. In fact, when study, and in the studies by Morris et al. 1993 and
compared at 0.67 maturity of empty body weight Shahin et al. 1993. Fig. 2, which plots the main
each component had attained a similar proportion of body components, as a percentage of empty body
its mean mature weight in each line Table 5. At the weight, against age, illustrates the patterns of growth
same body weight, however, animals from the High described here.
Line would be less mature than animals from the The pattern of growth for subcutaneous and
Control Line, which in turn would be less mature intermuscular fat, relative to total fat, was similar to
than Low Line animals. This was evident when the that reported by numerous studies, as reviewed by
lines were compared at the same empty body weight Kempster 1981. All studies showed that as total fat
Table 5, the High Line steers displaying the less or total carcass fat increased the proportion of
mature pattern of higher bone and lower fat per- intermuscular fat decreased and that of subcutaneous
centages. Market specifications for carcasses are fat increased. Truscott et al. 1983 reported growth
usually based on ranges of weight and fatness. The coefficients relative to total fat of 1.14 for subcuta-
results imply that relative to the Control Line, High neous and 0.83 to 0.90 for intermuscular fat, which
Line cattle will need to be raised to slightly heavier are similar to those obtained in this study. The
weights to achieve the required level of fatness while growth of kidney and channel fat is more variable.
the opposite applies to Low Line cattle. Truscott et al. 1983 found it to be late developing
The pattern of growth reported here is similar to b 5 1.13 whereas Johnson et al. 1972 found it be
that reported in other cattle experiments. The growth early developing, decreasing as a proportion of total
coefficients for dissected carcass fat relative to side carcass fat over the range of carcass weights studied.
weight Shahin et al., 1993 and for the growth of Over the range of breeds and feeding systems studied
152 D
. Perry, P.F. Arthur Livestock Production Science 62 2000 143 –153
maturity. However, meat animals are usually slaug- htered to particular market specifications or at a
particular age. When slaughtered to attain a particular carcass weight, steers selected for high growth rate
will be younger, less mature, and will thus have higher bone weights, lower levels of fat, and similar
levels of muscle than will unselected animals. Where degree of fatness is an important market considera-
tion, steers from a line selected for fast growth rate will be heavier at the same level of fatness than will
unselected steers. This also applies where animals are slaughtered at a set age.
Acknowledgements
Fig. 2. Dissected body components as percentages of empty body weight at different ages.
Meat and Livestock Australia formerly Meat Research Corporation funded this study. We thank
R. Barlow, who was instrumental in the design of the by Kempster et al. 1976 the growth of kidney
selection experiment, our colleagues P.F. Parnell and channel fat relative to total carcass fat differed
R.M. Herd and J.M. Thompson of the University of markedly between groups, being early developing in
New England for advice throughout, and the staff of some and late in others. They found scrotal fat to
the cattle section at the Agricultural Research Centre, vary in this manner also. The pattern of development
Trangie, in particular C. Brennan, D. Mula and R. of fat partitions between this study and that of
Snelgar, who cared for the animals and did the major Truscott et al. 1983 was similar except for omental
part of slaughters and dissections. fat, which we found to be early developing relative
to total fat and they found to be late developing b 5 1.08 to 1.22. In both this study and for the
Hereford steers studied by Truscott et al. 1983
References
subcutaneous fat was a greater proportion of total fat than was intermuscular fat in older animals. This
Andersen, B.B., Fredeen, H.T., Weiss, G.M., 1974. Correlated
differs from other studies Johnson et al., 1972;
response in birth weight, growth rate and carcass merit under single-trait selection for yearling weight in beef Shorthorn
Kempster et al., 1976 and from the Friesian steers
cattle. Can. J. Anim. Sci. 54, 117–125.
of Truscott et al. 1983, where intermuscular fat
Archer, J.A., Herd, R.M., Arthur, P.F., Parnell, P.F., 1998.
was a higher proportion of total carcass fat at all
Correlated responses in rate of maturation and mature size of
carcass weights. Fat is a tissue that can vary in
cows and steers to divergent selection for yearling growth rate
development and site of deposition more readily than
in Angus cattle. Livest. Prod. Sci. 54, 183–192. Arthur, P.F., Parnell, P.F., Richardson, E.C., 1997. Correlated
other tissues Berg and Butterfield, 1974, and can
responses in calf body weight and size to divergent selection
thus vary with nutrition. However the increasing
for yearling growth rate in Angus cattle. Livest. Prod. Sci. 49,
proportion of total fat in the carcass fat partitions as
305–312.
an animal increases in body weight seems standard.
Berg, R.T., Butterfield, R.M., 1974. Growth of meat animals. In: Cole, D.J.A., Lawrie, R.A. Eds., Proceedings of the 21st
Easter School in Agricultural Science, University of Notting- ham, Meat, Butterworths, London.
5. Conclusion
