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.
Proceedings of the New Zealand Society of Animal Production, Volume 55, , 91-93, 1995
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