Growth rate effects on the chemical composition of the carcase and muscle tissue of sheep

Abstract

A study was conducted of the effects of a high (H), low (L), or high growth rate with an intermittent period of liveweight maintenance (HMH) on the chemical composition of both the whole half carcase and the standard muscle groups (SMG's) (Butterfield 1963). Animals in the three treatments were killed at common liveweights of 25, 30, 35 and 40 kg and compositional data compared by regression using analysis of covariance and the logarithmic transformation of the allometric equation. Significant differences were found in the regression slopes relating carcase water (HMH > H), protein (L > H, HMH) and chemical fat (H > HMH, L) to carcase weight indicating differential treatment effects on composition with increasing carcase weight. These differences could not be explained by corresponding differences in carcase muscle composition, which was similar in the three treatments except for protein (H > HMH). Chemical analyses of the SMG's showed that muscle group protein was greater in the H than in the HMH treatment for all groups, although significantly so only for SMG's 3, 4, 6, 8 and 9. Except for this difference in protein content, relatively minor treatment differences were found in muscle group composition. The similarity of muscle group composition in the H and L treatments provides a theoretical basis for the prediction of total muscular composition from that of a single muscle group in carcases from continuously grown animals.