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Estimates of Maternal and Grandmaternal Influences on Weights and Gains of Pigs¹

University of Wisconsin, Madison 53706

Abstract

A study on 1,904 early-weaned (4-week-old), spring-farrowed pigs was undertaken to determine the importance of direct, maternal and grandmaternal variances and of their covariances and some environmental variances in the phenotypic variation of weights and gains. Weights were taken at birth, 3, 8, 12, 16 and 20 weeks of age on swine weaned at 4 weeks of age. The gains were those between adjacent ages. The data were adjusted by least squares for the effects of breeding group (Yorkshire, Poland China and reciprocal crosses), parity of dam (first and second), sex of individual (boars, barrows and gilts), farrow (early or late spring), year (5 years), five interaction effects and the regression of weight on age at weighing. These adjusted data were used in the calculations of the covariances of paternal half-sibs, full-sibs within sire, offspring-dam, maternal aunt (uncle)-niece (nephew), maternal half aunt (uncle)-niece (nephew), maternal single first-cousins and half single first-cousins whose dams were paternal half-sibs and the variances within full-sibs. These were equated to their expected biological components.

The direct additive genetic variance estimates were as expected from the literature. There was little evidence for additive maternal or additive grandmaternal variance in weights at birth, 3 and 8 weeks of age and gains from 1 day to 3 weeks, 3 to 8 weeks and 16 to 20 weeks of age and because of this it was felt that their covariances could not be important sources of variation for the weights and gains at these stages of development. There was some indication of additive maternal variance in weights at 12, 16 and 20 weeks of age, and gains from 8 to 12 weeks and 12 to 16 weeks of age. However, there was little evidence of any additive grandmaternal influence for these weights and gains. The possibility of having direct and maternal dominance deviation variance and their covariance in these traits was not excluded as these components were not estimated in this study. It was concluded that selection for weights at 8, 12, 16 and 20 weeks of age and gains from 3 to 8, 8 to 12 and 12 to 16 weeks of age in pigs should be effective.

¹ This work was done under a cooperative agreement between die Research Division of the College of Agricultural and Life Sciences, University of Wisconsin, and the Animal Sciences Research Division, A.R.S., U.S.D.A., and supported by Cooperative U.S.D.A.-C.S.R.S. Grants No. 816-15-20 and 916-15-20, and in cooperation with the late Regional Swine Breeding Laboratory, A.S.R.D., A.R.S., U.S.D.A Paper No. 1751 from the Laboratory of Genetics and No. 643 from the Department of Meat and Animal Science.

² Present address: Department of Animal Science, 239 Kildee Hall, Iowa State University, Ames 50011.