Compensatory growth in immature sheep: II. Some changes in the physical and chemical composition of sheep half-carcass following feed restriction and realimentation

Abstract

SUMMARYExperimental conditions and design were described in part I. Separable lean and fat were highly correlated with the carcass and whole body components of protein and ether extract. The carcasses of refed sheep at 45 kg empty body weight (EBW) had about 1 kg less fat and more lean than carcasses from sheep of similar weight which had been continuously fed. Restricting feed intake to 70% ad libitum gave carcasses that had more protein than those from sheep fed ad libitum both during continuous growth and after realimentation.Sheep that had lost 25% EBW to 26 kg and then were refed to 31 kg EBW had 34% less separable carcass fat than sheep which had been continuously fed to EBW of 36 kg and then had lost weight from that level to 31 kg EBW, and the separable fat was higher in water content than during normal growth (an effect shown consistently in realimented sheep).Severe underfeeding rapidly reduced bone water but bone ether extract continued to accumulate. After a period of refeeding, bone fat was rapidly mobilized and bone water quickly returned to normal. During early weight loss following food intake reduction, there was a larger decrease in carcass water than expected, and most of the discrepancy could be accounted for by the disproportionately large loss of water from bone and separable fat.It is concluded that during early regrowth there is a marked stimulus of lean tissue growth and depressed fat synthesis. After this initial period, growth rate of carcass tissues is not greatly different from that found in continuously growing sheep although there is some evidence of a small positive rate of protein growth effect following through to 45 kg EBW in the refed animals. The ratio of muscle gain to fat gain from 30 to 40 kg EBW was 2·23 in realimented sheep and 1·08 during normal growth.