Testing different pig genotypes on a single diet may constrain protein and lipid deposition or reduce the efficiency of nutrient utilisation by under- or over-supply of nutrients. If the ranking of genotypes is dependent on the diet used when performance testing animals, then genotype-specific nutritional regimes may be required by breeding companies to identify animals of high genetic merit and by producers to realise the benefits obtained by genetic improvement programmes. In the Edinburgh lean growth project, divergently selected lines for efficiency of lean growth (LFC), for rate of lean growth with animals performance tested on ad-libitum (LGA) or restricted (LGS) feeding or for daily food intake (DFI) have been established with seven generations of selection in a Large White population (Cameron, 1994). The selection lines provide an experimental resource to estimate the genotype with nutrition interaction for protein and lipid deposition rates as differences between selection lines will relate to the selection strategy since the lines were derived from the one base population.