INFLUENCE OF DOMINANCE RELATIONSHIPS ON THE ESTIMATION OF DOMINANCE VARIANCE WITH SIRE-DAM SUBCLASS EFFECTS

Two data sets from the USDA Livestock and Range Research Laboratory me re analyzed to study dominance variance and the influence of dominance relationships. The first consisted of 4,155 birth weight (3,884 weani ng weight) records of inbred USDA Line 1 Herefords. The second consist ed of 8,065 birth weight (7,380 weaning weight) records from a line-cr oss experiment with five lines. Two models were used. Both included fi xed effects of year-sex of calf and age of dam, and covariates for cal ving date, inbreeding of animal, and inbreeding of dam. For the second set, additional covariates were line composition and heterozygosity c oefficients. Random effects were direct and maternal additive genetic, maternal permanent environment, sire-dam subclass, and residual. Mode l 1 considered sire-dam subclasses unrelated. Model 2 related sire-dam subclasses with a parental dominance relationship matrix. Variance co mponents were estimated using REML. Differences between estimates with Model 1 and 2 were unimportant except for dominance variance. For the first data set, estimates with Model 2 of relative genetic direct and maternal variances, direct-maternal correlation, permanent environmen t, and dominance variances for birth weight were .35, .13, -.02, .03, and .25, respectively, and they were .39, .11, .04, .06 and .14 for th e second data set. For weaning weight, the first data set estimates we re .20, .15, -.37, .19, and .11, respectively, and they were .16, .20, -.07, .18, and .18 for the second data set. Changes, decreases and in creases, in estimates of dominance variances may be due to increased i nformation from relationships and family types other than full-sibs. T he assumption of unrelated sire-dam subclasses might not be appropriat e for estimation of dominance variance in populations with many domina nce relationships among siredam classes.