New Zealand Journal of Agricultural Research abstracts
Carcass composition and growth in Angus cattle genetically selected
for differences in pubertal traits
C. A. Morris
N. C. Amyes
N. G. Cullen
S. M. Hickey
AgResearch
Ruakura Research Centre
Private Bag 3123
Hamilton, New Zealand
Abstract A selection experiment to change
reproductive traits in Angus cattle was established in New Zealand in
1984/85. Alongside an unselected control line, three lines were set up,
selected for increased age at puberty in heifers (AGE+ line), reduced
age at puberty in heifers (AGE– line), or increased scrotal
circumference (SC line), with the last two lines being merged at the
1992 matings (forming a new AGE– line, with continued heifer
puberty selection). The heritability of the direct response (age at
puberty) through to 2004 was 0.27 ± 0.04. The purpose of the
present study was to investigate correlated responses in carcass
composition and growth traits, in response to pubertal selection.
Traits measured included weaning, yearling, and breeding-cow weights,
carcass weight, dressing percentage, the weights of pericardial,
omental and kidney fats, and the percentages of meat, bone, and trimmed
fat. The carcass study included selection-line and control animals (n
= 185; calf crops born in 1997–2002), and also back-crosses to both
lines (n = 294; calf crops born in 2000–02). The divergence in
age at puberty in heifers from the AGE+ and AGE– lines was 62 days (16%
of the mean). For carcass traits, the only consistent line effects
across both the AGE+ and AGE– lines and the back-cross lines were in
pericardial fat weights of post-pubertal bulls (P < 0.05).
However, where significant line differences in kidney fat weight or
fore-quarter fat trim percentage occurred, they were also in the same
direction as for pericardial fat (AGE+ animals fatter than AGE–
animals). For heifers and steers, none of the line contrasts for fat
traits was significant. The selection-line effects for weaning,
yearling, and pre-calving mature cow weights (AGE+ minus AGE– means)
were 2.5 ± 2.1, –7.3 ± 3.0 (P < 0.05), and 8.2
± 3.7 kg (P < 0.05), 1.5, –2.7, and 1.8% of their
respective means. The interpretation of these results was that earlier
sexual maturity in heifers (AGE– line) was associated with a steeper
juvenile growth curve through puberty, but ultimately the cows were
lighter than in the AGE+ line and not different in fatness. Earlier
sexual maturity in bulls was also associated with a steeper growth
curve, but there was the suggestion from some fatness traits that the
AGE– line were leaner than the AGE+ line when compared at the same age.
Keywords Angus; puberty; weight; genetics;
correlation; carcass; fat
A05009; Received 18 March 2005; accepted 21 October 2005; Online
publication date 28 February 2006
New Zealand Journal of Agricultural
Research, 2006, Vol. 49: 1–11
0028–8233/06/4901–0011 © The Royal Society of New Zealand 2006
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