Livestock Production Science 62 2000 143–153 www.elsevier.com locate livprodsci
Correlated responses in body composition and fat partitioning to divergent selection for yearling growth rate in Angus cattle
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Diana Perry , P.F. Arthur
NSW Agriculture , Agricultural Research Centre, Trangie, NSW 2823, Australia
Received 21 August 1998; received in revised form 7 April 1999; accepted 20 April 1999
Abstract
Body composition data were collected in a serial slaughter experiment on 91 Angus steers produced after 12 years of divergent selection for yearling growth rate. Steers born in 1986 and 1987 from lines selected for high High Line and low
Low Line growth rate from birth to weaning, and from an unselected line Control Line were slaughtered at 0 birth and circa 7, 12, 27, 35 and 45 months of age. Weights were obtained for dissected carcass muscle, bone, subcutaneous and
intermuscular fat, non-carcass fat depots, visceral organs, hide and head, tail and distal legs. At the same stage of maturity of empty body weight or total fat, body components and fat partitions were a similar proportion of their mean mature weights in
all three selection lines. At the same mean empty body weight of 360 kg, High Line steers had smaller proportions of carcass fat and a higher proportion of bone than steers from the other two lines, and the Low Line steers had a smaller proportion of
muscle relative to the other lines. Relative to the High Line, Control and Low Line steers required 85 and 175 additional days, respectively, to attain this carcass weight. Mean mature empty body weight body weight minus urine and gut contents
was 666617 standard error, S.E. kg, 588618 kg and 512616 kg for High, Control and Low Line steers, respectively. There were no significant P , 0.05 differences among the selection lines for the pattern of growth of the different body
components from birth to maturity. At maturity, no significant selection line differences were obtained in body composition. Relative growth rates indicated that, with respect to body weight, dissected fat was late developing and bone, muscle and
viscera early maturing, over the period from weaning to maturity. When compared at the same stage of maturity or level of fatness, steers from the line selected for fast growth rate would be heavier than unselected steers, but have the same body
composition.
2000 Elsevier Science B.V. All rights reserved.
Keywords : Beef cattle; Relative growth; Selection; Body composition, Fat partitioning
1. Introduction
Many beef cattle improvement schemes are based on some measure of growth. The perceived benefits
Corresponding author. Tel.: 1 61-2-6888-7404; fax: 1 61-2-
of selecting for faster growing cattle include the
6888-7201.
ability of stock to grow to market weights more
E-mail address : arthurpagric.nsw.gov.au P.F. Arthur
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quickly and to use feed more efficiently to attain
Present address: Meat Quality CRC, University of New England,
these weights. However there may be associated
Armidale, NSW 2351, Australia. 0301-6226 00 – see front matter
2000 Elsevier Science B.V. All rights reserved.
P I I : S 0 3 0 1 - 6 2 2 6 9 9 0 0 1 0 9 - 8
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.
