Submitted to: World Congress of Genetics Applied in Livestock Production
Publication Type: Proceedings
Publication Acceptance Date: January 11, 1998
Publication Date: N/A
Interpretive Summary: The genotypic model of inheritance includes additive, dominance, and epistatic effects. Because models for calculating genetic evaluations currently ignore effects other than additive, evaluations are less accurate than they could be. This study quantified how dominance affects additive evaluations that ignore the effect of dominance and estimated how much variation in genetic merit of dairy cattle, beef cattle, and swine vary is the result of dominance. Changes in additive evaluations after considering dominance were found to be important for selected traits of dairy and beef cattle and of swine. The absence of a dominance effect leads to biases in evaluations for some animals. Although genetic gains realized through use of dominance information by breeders would not be large, they would outweigh the expenditure needed to derive the information.
Potential gains from including the dominance effect in genetic evaluations include "purification" of additive values and the availability of specific combining abilities for each pair of prospective parents. The magnitude of such gains was tested for dairy and beef cattle and for swine by estimating variance components for several traits and by analyzing changes in additive evaluations when the dominance effect was added to the model. Estimates of dominance variance for dairy and beef cattle and for swine were up to 10.3% of phenotypic variance; estimates were larger for growth traits. As a percentage of additive variance, estimates of dominance variance reached 78% for 21-day litter weight of swine and 47% for postweaning weight of beef cattle. Changes in additive evaluations after considering dominance are largest for dams of a single large family. These changes were found to be important for dairy cattle, especially for dams of full-sibs, but less important for swine.