Genotype with nutrition interactions for carcass composition and meat quality in pig genotypes selected for components of efficient lean growth rate

Genotype with nutrition interactions in carcass composition and meat qualit y traits were examined by testing pigs from four selection lines and a cont rol line on isoenergetic diets, which differed in lysine : energy content. The selected lines resulted from seven generations of selection for high da ily food intake, lean food conversion ratio (LFC) and lean growth rate on a d-libitum or restricted (LGS) feeding regimes in a Large White population. There were 128 pigs in the study, with 24 pigs per selection line and 32 pi gs from a control line. During performance test, 30 to 90 kg, pigs were off ered one of three isoenergetic diets, 14.0 MJ digestible energy (DE) per kg dry matter, which differed in ileal digestible lysine : digestible energy (A : 0.40, C: 0.76 and E : 2.12 g lysine per MJ DE) on ad-libitum or restri cted (0.75 g/g ad-libitum daily food intake) feeding regimes. For the majority of performance test, carcass composition and meat quality traits there tons no evidence of a genotype with diet or genotype with feed ing regime interaction. The selection line with feeding regime interactions for average daily gain, daily food intake and rates of lean and subcutaneo us fat deposition were primarily due to no feeding regime effect for the LF C selection line. Selection for high LFC had reduced ad-libitum daily food intake to such an extent that if was not significantly different from daily food intake on a restricted feeding regime, unlike other selection lines i n the study. A selection line with feeding regime interaction was detected for muscle pH(24h) and muscle reflectance, which resulted from the LGS sele ction line. LGS pigs offered food ad libitum had higher muscle pH(24h) and lower muscle reflectance than LGS pigs given food at a restricted level, wh ile there was no effect of feeding regime for the other selection lines. The general absence of genotype with nutrition interactions for traits meas ured in the study indicated that the ranking of genotypes for performance t est traits, carcass composition and meat quality traits will not be depende nt on diet or feeding regime. Genotype specific nutritional inputs will als o not be required for identification of pigs of high genetic merit, within a genotype. However, diet and feeding regime had significant effects on car cass composition and meat quality traits, such that the estimated mean valu e of a genotype will be dependent on the diet or feeding regime used to eva luate the genotype.