Genetic, Sex and Diet Effects on Pig Carcass Traits1

Main and interaction effects of breed of dam, line and sex of pig and diet on traits related to body composition were studied in a balanced design. Duroc and Yorkshire parents were crossed reciprocally within low-fat lines and control lines from a previous long-term study in which selection was based on backfat thickness. Pigs were fed ad libitum one of three corn-soybean meal diets, 1, 2 or 3, containing, respectively, 12% (crude) protein, 16% protein or 12% protein, supplemented with lysine and methionine to approximate their levels in diet 2. Pigs were slaughtered at 100 kilograms. Crossbred pigs from Yorkshire dams had significantly leaner carcasses and deposited lean tissue faster than crosses from Duroc dams, giving evidence of an important maternal influence. Crossbred pigs of the low-fat line were significantly leaner at slaughter but did not exceed control line crosses in rate of deposition of lean tissue. Gilt carcasses were leaner than barrow carcasses but barrows deposited lean tissue faster. Pigs fed diets 2 and 3 produced significantly more lean tissue and at a faster rate than crossbred pigs fed diet 1. Further results also indicated that synthetic amino acids were highly effective in supplementing the basic 12% protein diet. For some body composition traits, differences between low-fat and control line crosses were larger in pigs fed diets 2 and 3 than in pigs fed diet 1, with implications for testing programs. Further results indicated that rate of deposition of lean tissue may be largely independent of body composition at slaughter.