Heritability of Type in Poland China Swine as Evaluated by Scoring

Abstract

Data on 731 Poland China pigs were analyzed to determine the relative importance of heredity and environment in determining type as measured by a scoring scheme used at the Beltsville Research Center. The intra-season variance in progeny scores due to differences between sires of the same type strain gave an estimate of 38 percent for the heritable part of the variance between pigs from different parents of the same strain. Because of the marked differences in scores between the small, intermediate, and large-type strains, the heritable portion of the intra-season variance between pigs in different strains was considerably higher, 92 percent. Differences in litter environment accounted for 5 percent and differences in environment peculiar to the individual for 57 percent of the intra-season variance in scores among pigs of the same type strain. Seasonal variation in environment was responsible for only 4 percent of the total variance among pigs of the same type strain. The heritability of type is apparently high enough for selection to be effective in changing the type of swine rather rapidly within individual herds. However, shifts in swine type can usually be made more rapidly by selecting breeding animals from herds in which type is more extreme in the desired direction than in a breeder's own herd. These conclusions are in harmony with the fact that in livestock history breeders have accomplished large changes in swine type rather quickly by selection for extremes in type. Copyright © . .