Feed requirements for maintenance of mature rams and ewes from
lines selected for differences in body composition
A.J. Ball, J.M. Thompson, G.N. Hinch, P.F. Fennessy, A.R. Blakely
Department of Animal Science, University of New England, Armidale,
Australia
Proceedings of the New Zealand Society of Animal Production. 1995,
55: 133-136
A total of 24 mature rams and ewes (>2.5 yrs) from a line selected for
high backfat thickness and an unselected control line were used to investigate
the relationship between maintenance efficiency and body composition in
mature sheep. Over a 6 week period the sheep were fed daily a pelleted
ration at levels to maintain liveweight. At the end of this period the weights
of total fat, carcass lean, viscera and of the empty body (fleece free) were
estimated from X-ray computed tomographic images. After adjustment for
empty body weight the control line required 5% more feed to maintain
liveweight (P<0.05) than sheep from the fat line and males required 19%
more feed (P0.05) than females. After adjustment for differences in either
total fat or carcass lean weight, there were no significant difference (P>0.05)
in feed requirements between the lines. This indicated that although a
genetic change in body composition did alter maintenance feed requirements
at maturity, the efficiency of maintaining a unit weight of either fat or carcass
lean remained the same. After adjustment for differences in total fat and
carcass lean weight, rams still required 11% more feed than ewes to maintain
liveweight. Adjusting for visceral weight had no effect on feed requirements
to maintain the mature sheep. It was proposed that differences in the
turnover rates of adipose tissue or carcass lean contributes to the higher
maintenance feed cost observed for the mature ram.
Keywords: NZSAPAB;
body composition; maintenance requirements; sex; sheep
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Last Updated 25-01-1997
