Introduction
Current feeding systems calculate heat production (HP) and energy requirements for a given level of production or feed intake from the sum of maintenance energy and energy used for gain. Changes in body composition are calculated from fixed, empirically-derived, relationships between fat and protein gain relative to degree of maturity and body condition (Freer et al., 2007). However, these fixed relationships may not be able to capture the variation in body protein and fat as animals respond to nutritional changes, nor the effects of compensatory growth on body composition.