REGULATION OF MUSCLE PROTEIN-METABOLISM IN SHEEP AND LAMBS - NUTRITIONAL, ENDOCRINE AND GENETIC-ASPECTS

Muscle protein accretion, as with the body in general, increases with feed intake. Protein balance across hind limb muscles occurs at energy intakes less than energy balance in the animal as a whole. There is considerable between-sheep variation in muscle protein accretion, and in the relative rates of protein synthesis and degradation, which are in part due to inherent differences in growth potential. Lambs selected for high weight at weaning deposit proportionately more nitrogen in the body than those selected for low weight at weaning. Inherently faster growing lambs have lower rates of protein breakdown in muscle and whole body than those which exhibit slower growth. Differences in sensitivity to insulin and plasma concentration of insulin-like growth factor-1 (IGF-1) indicate that the inherent differences in growth are associated with differences in responsiveness of muscle to hormones, and possible direct effects of IGF-1. Arteriovenous difference methodology, and isotope dilution, have been important tools in improving our understanding of the regulation of muscle protein metabolism.