CARCASS AND EMPTY BODY COMPOSITION OF HEREFORD AND ANGUS BULLS FROM LINES SELECTED FOR RAPID GROWTH ON HIGH-ENERGY OR LOW-ENERGY DEITS

Abstract

Hereford and Angus bull calves, progeny of breeding lines selected for nearly six generations for rapid growth on a high-energy (80% concentrate: 20% forage) or a low-energy (100% forage) diet, were themselves given a diet of 70% concentrate: 30% forage from 50 kg liveweight until slaughter at 500 kg liveweight. Effects of breed and ancestral selection diet on the composition of the empty body and the carcass at slaughter were measured. The sole effect of differences in the energy content of the selection diet was that bulls from the high-energy selection lines had higher proportions of muscle and bone in the front quarter and lower proportions in the hind quarter than bulls from the low-energy selection lines. Differences were small and probably not of economic importance. Breed of bull influenced significantly a number of body composition variables. As a proportion of empty liveweight, Herefords had lighter carcasses, less kidney fat, and heavier hides, heads, and feet than Angus. In addition, the carcasses of Hereford bulls had a higher proportion of bone than did those of the Angus and this was associated with differences in live body dimensions that reflected a larger overall skeletal size. As a result of these differences in the distribution of weight among the various parts of the empty body, Angus were superior to the Herefords in terms of total yield of carcass muscle (642 vs. 616 g kg−1 of empty liveweight) and ratio of muscle to bone in the carcass (4.96 vs. 4.64). It was concluded that the various indices of empty body and carcass composition were little influenced by ancestral selection diet but were affected by breed. Key words: Carcass, empty body, composition, cattle, selection, growth rate