Energy and growth

Abstract

In this review we explore the relation between energy needs and growth. In the normal animal, we assume there are fixed values for the efficiency with which protein and fat are deposited. However, through modern technology, growth is increasingly being altered, either through the use of hormones, vaccines, or genetic manipulations. By examining the effects of such treatments (including different levels of feeding and the use of protein, steroid and catecholamine growth promoters), on the relation between protein and fat deposition, we attempt to determine how these treatments affect the efficiency of growth. What emerges from this review, is that each type of treatment (and in some cases individual compounds within a class) has a different spectrum of activity with respect to effects on food intake, the efficiency of protein and fat deposition, and the maintenance requirements of the animal. Moreover, the degree of variation in the efficiency with which available energy is used to deposit tissue, particularly protein, is shown to be marked. Whereas the size of this variation suggests that there is considerable scope for further improvements in domestic animal productivity through 'growth engineering', to make this progress, the cause of this variation needs to be better understood. Steps towards this understanding can be made by further studies on the mechanisms of action of available anabolic and catabolic hormones, and on their interactions with the sympathetic nervous system.