Breed Prenatal, Breed Postnatal and Heterosis Effects for Preweaning Traits in Swine2

Crossfostering techniques were used to evaluate breed prenatal, breed postnatal and heterosis effects in Duroc and Yorkshire swine. Survival rate, individual weights at 0, 21 and 42 d, and weight gains from 0 to 21, 0 to 42, and 21 to 42 d were analyzed. When crossbred pigs were produced, prenatal effects were larger for Durocs for survival (P<.01) and all weight traits (P<.10). When purebred pigs were produced, Durocs had significantly larger breed prenatal effects for birth weight (P<.05). Yorkshires, rearing crossbred pigs, had larger (P<.10) breed postnatal effects than Durocs for all preweaning traits except survival and birth weight. When rearing purebred pigs, breed postnatal effects for Yorkshires were larger (P>.10) for all traits except birth weight. This suggests that crossbred pigs may provide a suckling stimulus or a demand to which a Yorkshire nurse is more responsive than a Duroc nurse. Heterosis values ranged from 5.6% for birth weight to 16.9% for 21-to 42-d wt gain. Yorkshires had larger breed postnatal effects than Durocs for 0 to 21-d litter gain (P<.10), 42-d litter wt (P<.05) and 0 to 42-d litter gain (P<.05). However, breed postnatal effects were not significantly different for 21-d litter weight. This suggests that 21-d litter wt may not be the best estimate of postnatal maternal performance.