The effects of severe feed restriction on bulls and steers. II.* Carcass composition

Abstract

The effects of a substantial liveweight loss on the carcass composition of nine half-sib Hereford bulls and steers of similar weight but different fatness have been studied by a serial slaughter technique. Bulls had a significantly (P < 0.01) greater percentage of muscle and bone and lower percentage of fat in the three-rib cut. Weight loss resulted in a significant increase in the proportion of bone (P < 0.001) and of muscle (P < 0.05), and a significant (P < 0.01) decrease in the proportion of fat, in the three-rib cuts of the steers. In terms of estimated absolute weight change in the carcass, bone loss was small in both 'sexes', and muscle loss was 32% greater than fat loss in the bulls, and 25% less than fat loss in the steers during the same period. The proportions of some commercial cuts in the carcass differed both between 'sexes' and among liveweights. An hypothesis (homeomyosis) is advanced, to explain the regulation of individual tissue weight changes during periods of liveweight change. The hypothesis indicates that it may be possible to develop greater muscularity (e.g. by the application of external loads) in cattle, and to change the distribution of muscle weight in the carcass. ________________ *Part I, Aust. J. Agric. Res., 28: 521 (1977).