Breed prenatal, breed postnatal and heterosis effects for postweaning traits in swine

Crossfostering techniques were used to evaluate breed prenatal, breed postnatal and heterosis effects in Duroc and Yorkshire swine. Traits analyzed for these effects were: age adjusted to 104 kg (DAYS), backfat adjusted to 104 kg (AJBF), average daily gain (ADG), weight/day of age (WDA), unadjusted backfat (BF) and weight at 154 d (WT154). Breed prenatal (genetics and prenatal maternal) effects were important for BF and WT154 (P less than .10). Pigs gestated by Duroc dams tended to be fatter and weigh more at 154 d than pigs from Yorkshire dams. Breed postnatal effects were important only for AJBF (P less than .05). Pigs reared by Duroc nurses were fatter than pigs reared by Yorkshire nurses. Prenatal dam x postnatal nurse interaction effects were important for BF (P less than .10) and AJBF (P less than .05). Heterosis values were -10.2, 8.0, 13.7, 13.6, 14.1 and 7.7% for DAYS, AJBF, ADG, WDA, WT154 and BF, respectively. Differences between purebred and crossbred pigs were larger when purebred and crossbred pigs were reared in the same litter than when reared separately. These data suggest that intra-litter competition between purebred and crossbred pigs may have a detrimental effect on postweaning growth for purebred pigs.