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Crossbreeding in Swine: Genetic Effects on Litter Performance^1,2,

Iowa State University^,5, Ames 50011

Abstract

Offspring heterosis, maternal heterosis and breed effects were estimated from 137 purebred, 376 single cross, 248 paternal backcross and 304 maternal backcross litters produced from matings among the Chester White, Duroc, Hampshire and Yorkshire breeds. An effect of offspring heterosis on survival was evident, with a final advantage in 154-d litter size of 7.1% (P<.10). The heavier weights and superior survival combined to produce highly significant estimates of heterosis for total litter weight, ranging from 9.4% at 21 d to 17.6% at 154 d. Maternal heterosis estimates for litter size and litter weight were large and highly significant at birth (10.3 and 11.1%, respectively) but decreased by 154 d [7.1% (P<.15) and 6.2% (P<.25), respectively]. General combining ability was not a significant source of variation for any litter traits. Breed of maternal grandparent was a significant source of variation for all litter traits except 21-d litter weight. Significant differences among breeds for maternal ability were indicated for all traits. Specific combining ability and the residual purebred effect (breed interaction effects) were important (P<.10) sources of variation for litter size and litter weight postfarrowing. The presence of these two interactions indicated that variation among crosses was greater than that explained by general combining ability and maternal ability and also indicated variability in the relative amount of offspring heterosis expressed by the different crosses.

¹ Journal paper no. J-9721 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Project no. 1901.

² Contributing project to NC-103, Genetic Improvement of Efficiency in the Production of Quality Pork.

³ Present address: Babock Swine, Inc., Rochester, MN 55901.

⁴ Present address: Auburn Univ., Auburn, AL 36830.

⁵ Dept. of Anim. Sci.