144 D
. Perry, P.F. Arthur Livestock Production Science 62 2000 143 –153
changes in body composition that could affect the and sire, with calves born to cows two years of age
value of the carcass. or greater than eight years of age being excluded
Selection for growth results in a difference in where possible. Twin born and hand reared calves
mature size, with consequent difficulties in interpre- were also excluded. Calves nursed their dams on
tation when doing comparative studies, as it is pasture throughout the preweaning period. The
possible that much of the difference reported be- calves were castrated at about three months of age.
tween genotypes may be related to differences in the After weaning at about seven months of age, the
stage of maturity at which the comparison takes steers were fed by an automatic feeding system
place Webster, 1980. Thus any comparative work described by Herd 1991. They were fed a high
that is done between animals selected for measures quality pelleted diet which supplied 10.9 MJ ME kg
of growth should encompass differences in the dry matter. They had access to this feed 24 h a day,
mature size of the animals when interpreting differ- although the feeding system was programmed to feed
ences in body composition. an animal only if it had not been fed in the previous
This experiment was part of the evaluation of a half hour. There was thus the potential for each
research project investigating the effect of divergent animal to be fed 48 times each day. The weight of
selection for growth rate to yearling age yearling feed offered each time was approximately 1 kg.
growth rate on growth, feed efficiency and body Three 1987 born steers which did not adapt to the
composition. Following 12 years of selection the feeding system were dropped from the experiment. A
divergence in growth between the lines selected for further 12 nine 1986 born, three 1987 born steers
increased and decreased growth rate to yearling age died from bloat or other gastro–intestinal conditions.
exceeded 25 for both males and females Parnell et Data on dissected composition were collected in a
al., 1997. This paper reports the effect of divergent serial slaughter experiment. For each of the two
selection for yearling growth rate on body com- years, two steers per selection line were slaughtered
position in steers, and the growth of these body at 0 birth and at circa 7, 12, 27 and 35 months of
components to maturity, in a serial slaughter experi- age three 1986 Control Line steers were slaughtered
ment involving steers from 0 to 47 months of age. at 12 months. The remainder 12 from the 1986
calving, 18 from the 1987 calving were grown until they were considered to be mature and then slaug-
2. Materials and methods htered in batches as quickly as facilities would allow.
Steers were considered to be mature when their 2.1. Animals and design
growth curves, based on weekly liveweight measure- ments, showed that they had effectively stopped
Steers were derived from the three selection lines growing. Age at mature slaughter ranged from 44 to
of Angus cattle at the Agricultural Research Centre, 47 months. Animals were randomly selected for each
Trangie, New South Wales, Australia. These selec- slaughter. A schematic diagram of the slaughter
tion lines were established in 1974 using 220 cow schedule is presented in Fig. 1. There were slaughter
Angus breeding herd at the Centre. Firstly, 50 cows data available from a total of 91 steers.
were randomly chosen to form a Control Line, then the remainder of the cows was divided into a High
2.2. Measurements Line and a Low Line, based on their own growth rate
from birth to yearling age. The lines remained closed The steers were fasted for 24 h, weighed and then
from 1974, with animals from each line being run slaughtered. After slaughter the components of the
together throughout the year, except during mating. gastro–intestinal tract were emptied of remaining
Parnell et al. 1997 reported details on the establish- contents, and omental and mesenteric fat removed.
ment and maintenance of these selection lines. All non-carcass components were weighed separately
A total of 106 animals born in 1986 and 1987 and also bulked into four depots. These were viscera
were used in the study. The steers were selected all organs plus thoracic fat, non-carcass fat omen-
systematically after being stratified by selection line tal, mesenteric, kidney-channel and testicular, other
D . Perry, P.F. Arthur Livestock Production Science 62 2000 143 –153
145
Fig. 1. Schematic diagram of the slaughter schedule within each of the 1986 and 1987 born groups. S indicates slaughter points and numbers in parentheses indicate mean number of steers slaughtered per selection line per year born group.
non-carcass components head, tail and the non- effect of line, age, year of birth and all first order
carcass portions of the legs, and hide. Non carcass interactions was examined on proportional body
fat partitions were according to those defined by composition in mature animals using a multivariate
Thompson et al. 1987. The carcasses were halved model which analysed all components simultaneous-
and each half then weighed. All components were ly. Non-significant P . 0.05 interactions and the
frozen at 2 208C until required for analysis. age effect were sequentially omitted from the model
The right side of each carcass was subsequently until the final model was obtained. The final multi-
thawed, divided into commercial cuts, and then variate model contained terms only for the fixed
dissected into muscle, bone, subcutaneous fat as effects of selection line P . 0.05 and year of birth
define by Thompson et al. 1987 and intermuscular P , 0.01.
tissue fat, plus connective, vascular, nervous and Fat in the carcass subcutaneous and intermuscu-
lymphatic tissue. These components were then lar and non-carcass omental, mesenteric, kidney
weighed. Muscles were cleaned of intermuscular and channel and scrotal fat depots was expressed as
tissue and trimmed of any tendinous tissue at right a proportion of total dissectible fat in the body.
angles to the muscle fibres at the last vestige of Using a multivariate model the effect of line, age,
muscle tissue, before being weighed. Bones were year of birth and all first order interactions on fat
cleaned of all tissues except the periosteum. partitioning was examined. To avoid singularity,
scrotal fat was first excluded from the analysis. As 2.3. Statistical analysis
before non-significant P . 0.05 interactions and the age effect were sequentially omitted until the final
For both mature and immature animals the dissec- model was obtained. The analysis was then repeated
ted weights of muscle, bone, subcutaneous fat and with scrotal fat included and kidney channel fat
intermuscular tissue in the carcass were multiplied excluded. In both cases the final multivariate model
by two. Total body fat was calculated as the sum of contained non-significant terms for selection line and
subcutaneous, intermuscular, omental, mesenteric, year of birth P . 0.05.
kidney and channel fat and scrotal fat. Empty body weight was calculated as the liveweight immediately
2.3.2. Relative growth pattern of body tissues prior to slaughter, minus the weight of urine and
The weights of body components and empty body digesta.
weight were transformed to log base 10 values for allometric analysis. Plots of log component weight
2.3.1. Proportional body composition and fat against log empty body weight showed that the birth
partitioning in mature animals data deviated from linearity. Accordingly data from
For the 30 steers slaughtered at maturity, dissected those animals killed at birth day 1 were omitted
weights of muscle, bone, viscera and total fat were from all allometric analyses. Unadjusted means for
expressed as proportions of empty body weight. The weights 6standard deviation, SD at birth are
146 D
. Perry, P.F. Arthur Livestock Production Science 62 2000 143 –153 Table 1
Unadjusted means for body and component weights 6SD at one day of age for male calves from lines selected for divergent growth rate Selection line
High Line Control Line
Low Line No. of animals
4 4
4 Liveweight kg
33.265.0 30.960.4
24.262.7 Empty body weight kg
31.564.9 29.660.4
22.962.5
a
Dissected components kg Muscle
10.862.71 9.761.50
7.561.24 Bone
4.961.02 4.160.80
3.560.49
b
Total fat 2.560.45
2.160.11 1.760.22
Total viscera 3.060.37
2.860.26 2.460.24
Fat partitions kg Subcutaneous
0.360.1 0.360.06
0.360.04 Intermuscular
1.660.33 1.460.10
1.160.18 Kidney channel
0.260.05 0.260.03
0.160.01 Omental
0.0760.01 0.0760.005
0.0560.007 Mesenteric
0.260.02 0.260.03
0.160.02 Scrotal
0.0460.01 0.0460.02
0.0360.01
a
Other components of empty body weight such as hide, head and tail are not presented.
b
Total fat 5 subcutaneous 1 intermuscular 1 all non-carcass fat partitions.
shown in Table 1. Using data from the remaining 79 and growth coefficients for log weights of muscle,
animals weaning to maturity the growth of dissec- bone, viscera and total fat relative to log empty body
ted body components relative to the growth of the weight was examined using a multivariate allometric
body as a whole, and of fat partitions relative to total analysis.
Non-significant P . 0.05
interactions fat, was examined using the allometric equation,
were sequentially deleted from the model. The final
b
y 5 ax which was computed in the linear form as model for log body component weights included
log y 5 log a 1 b log x 1 error, where y was the significant terms for selection line P , 0.01, year
weight of the component and x the weight of the P , 0.05, log empty body weight P , 0.001 and
‘‘whole’’. The terms a and b are coefficients, a the the interaction between year and log empty body
proportionality coefficient being the value of y weight P , 0.05. Predicted means for the trans-
when x is equal to 1.0, and b the growth rate of y formed data were converted to the original scale by
2
relative to x . Thus the relative growth patterns for
taking the antilogarithm of log 10 y 1 1.1513s ,
2
tissues were estimated from the growth coefficient b, where s
is the sample variance of log y Johnson and multiplicative difference in distribution of the
and Kotz, 1970. components from the coefficient a. Components
The growth of the dissectible fat partitions sub- which had a growth coefficient equal to 1.0 changed
cutaneous, intermuscular, omental, mesenteric, kid- at the same rate as the whole and were defined as
ney channel and scrotal relative to the growth of having an average growth impetus. Components with
total dissectible fat was also determined by multi- a growth coefficient greater or less than 1.0 had a
variate analysis of the log transformed allometric higher or lower growth impetus, respectively, com-
model, where x was total dissectible fat. The effect pared with the whole.
of selection line and year on the proportionality and The effect of line, year, log empty body weight
growth coefficients was tested as above. The final and all first order interactions on the proportionality
model included significant terms for selection line
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
