Performance testing several genotypes on one diet may impose nutritional constraints on the genetic merit for growth of particular genotypes. Use of the diet choice procedure may remove nutritional constraints on growth, if pigs can “choose” the appropriate combination of the diets to attain the growth determined by the animal's genotype. In a genetic improvement framework, the diet choice procedure could be used to identify animals of high genetic merit for a given selection objective.

There were 120 Large White pigs from the high, low and control lines, which had been selected for lean growth rate for seven generations in the Edinburgh lean growth selection experiment. In each selection line, there were 10 full-sib groups of four pigs. Pigs were performance tested from 30 to 85 kg, with individual penning and ad-libitum feeding. Within each full-sib group, one pig was allocated to each of the high (HP : 220 g crude protein (CP)/kg) or low (LP : 120 g CP/kg) protein diets.