Abstract
Two groups of barrows (23 Yorkshire-Chester White crossbreds and 23 Yorkshire-Duroc crossbreds) were used to study changes in body composition associated with increasing liveweight. Slaughter weight groups of 12 pigs at 23 kg., 12 pigs at 46 kg., 12 pigs at 68 kg. and 10 pigs at 91 kg. were established by random allotment. At slaughter, each animal was divided into carcass and non-carcass components. All carcasses were physically separated into muscle, fat and bone. Samples of muscle, fat and bone were analyzed for protein, ether-extractable constituents and water. The various physical separation and chemical estimates of body composition were subjected to the analysis of variance in order to estimate the importance of the effects of breed and weight group on body composition of the pig. Separable fat was found to be the most rapidly increasing component of the porcine body. Separable fat represented 10.2 and 6.7% of the carcass and liveweight, respectively, at 23 kg. liveweight. Similar values at 91 kg. liveweight were 32.6 and 24.3% of the carcass and liveweight, respectively. Percents of bone and muscle decreased with increasing liveweight. A significant breed effect was present in percentages of muscle, fat and bone in the carcass. Percent fat in the carcass exhibited significant linear and quadratic breed by weight group interaction effects. Carcass length, average backfat thickness and l. dorsi area increased as liveweight increased; while percents of ham, loin, lean cuts and primal cuts decreased slightly with increasing liveweight. All components except muscle exhibited a decrease in percent protein with increasing liveweight. Percent water decreased and percent ether-extract increased in all components. There were no breed effects on the chemical composition of the whole carcass. Chemical composition of the fat-free and fat-free dry components exhibited virtually no differences due to breed. Changes in chemical composition associated with weight groups were virtually eliminated by expression on fat-free or fat-free dry bases. Copyright © 1968. American Society of Animal Science . Copyright 1968 by American Society of Animal Science