Date of this Version
Individual heterosis and direct and maternal breed effects for postweaning average daily gain (ADG), off-test age (AGE) and probed backfat thickness (BF) were estimated from data on 1,664 pigs produced in a complete diallel mating system involving the Duroc, Yorkshire, Landrace and Spotted breeds. The same genetic parameters were estimated for various carcass traits by analyses of data collected on 269 barrow carcasses. Significant breed x environment (i.e., year-season farrowed, parity and sex) interactions were found for ADG, AGE and BF. Specific heterosis estimates for ADG and AGE were all highly significant and reasonably consistent among crosses. Overall heterosis for BF was significant, although specific estimates were not. Overall heterosis estimates were .07 kg/d (10.5%) for ADG, -14 d (7.5%) for AGE and .83 mm (3.2%) for BF. Of 72 specific heterosis estimates for carcass traits, only seven were significantly different from zero, apparently at random. Duroc- and Spotted-sired pigs grew faster and were younger off-test than Yorkshire- and Landrace-sired pigs. Landrace-sired pigs had higher BF and Duroc-sired pigs lower BF than Spotted- or Yorkshire-sired pigs. Breed-of-dam effects for ADG were similar to breed-of-sire effects. Significant breed-of-sire effects for carcass traits reflected the superiority of Duroc-sired pigs for carcass backfat, loin muscle area, lean cuts yield and muscle quality (marbling and firmness). Maternal effects were important for carcass composition in crosses involving the Duroc. Such crosses produced leaner, more heavily muscled carcasses where the Yorkshire, Landrace and Spotted were used as the dam breed.