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Components of Variance and Covariance for Reproductive Traits in Swine Estimated from Yorkshire Field Data¹

The University of Georgia, Athens 30602

Abstract

Genetic and phenotypic parameters were estimated for adjusted number born alive (NBA), number weaned at 21 d (NWN) and adjusted 21-d litter weight (LWT) using approximately 34,000 Yorkshire litter records recorded under the Sow Productivity Index program of the American Yorkshire Club. Genetic variances were estimated using an approximate quadratics procedure; covariances were estimated using traditional mixed model techniques from associations between paternal half-sib dams. Heritability estimates from this study were .13 ± .02 for NBA and .15 ± .02 for LWT. These estimates indicate that with proper selection programs genetic progress can be made in these traits. The genetic correlations between NBA and NWN (.58) and between NWN and LWT (.55) were found to be moderate and positive. A weak positive genetic correlation between NBA and LWT (.12) was found. Phenotypic and environmental correlations were similar in size and magnitude to the genetic correlations. All correlations indicate that simultaneous improvement could be achieved in the litter traits through multiple trait selection.

¹ This research was supported by State and Hatch funds allocated to the Georgia Agr. Exp. Sta.

² Anim. and Dairy Sci. Dept.

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