Why Does Selection for Liveweight Gain Increase Fat Deposition? A Model

Abstract

SummarySince selection for growth-rate has been found to increase appetite and decrease maintenance requirements, it will lead to an increase in the excess of intake over maintenance. It is proposed that weight gain, both lean and fat, is directly related to a positive energy balance, but that the lean:fat partition coefficient is a decreasing physiological function of the excess of intake over maintenance. On this model the effect of selection for gain on fat deposition would therefore be twofold: (1) a direct effect tending to increase lean deposition at the expense of fat, and (2) an indirect physiological effect, mediated by way of the excess of intake over maintenance, tending to increased fat deposition at the expense of lean. The latter effect apparently predominates in determining the net overall effect of selection for gain on fat deposition.