ESTIMATION OF VARIANCE-COMPONENTS WITH DOMINANCE AND INBREEDING IN DAIRY-CATTLE

The five variance components in the genetic (co)variance among inbred relatives for a quantitative trait with additive and dominance genetic variation were estimated by equating variances among and within diffe rent types of families of inbred cows to their expectations. The data used were milk and fat yields of 85,433 U.S. Holstein cows with inbree ding coefficients of 6.25 % or higher. When all five parameters were e stimated, unrealistic results were obtained. If all quantitative trait loci are biallelic, genetic (co)variance depends on only four paramet ers. More realistic estimates were obtained under this assumption. The re was a substantial negative covariance among breeding values and dom inance effects under inbreeding, and the dominance variance in inbred cows was larger than the dominance variance in the noninbred base popu lation.