Thermochemical Efficiency of Growth

Abstract

THE term ‘gross efficiency of growth’ has usually been meant to denote the ratio of the increase in body-weight during a given period of time to the amount of food ingested during this period. It had been shown previously¹, using the albino rat as the experimental animal, that the gross efficiency of growth can be fitted quite satisfactorily to a logarithmic function, the actual efficiency E_t at time t being represented by where E₀ is the efficiency at weaning and A is a constant. This function decreases rapidly, and on the thirtieth day of post-weaning life the gross efficiency is only about one-third of the value at weaning. In subsequent publications² it was pointed out, however, that the thermochemical significance of weight increments varies with age, as do the proportions of water retained and of protein and fats synthesized, so that consideration of gross efficiency does not adequately represent the energetics of growth, any more than the weight curve does.