ESTIMATION OF NONADDITIVE GENETIC VARIANCES IN 3 SYNTHETIC LINES OF BEEF-CATTLE USING AN ANIMAL-MODEL

Dominance and additive x additive genetic variances were estimated for birth and weaning traits of calves from three synthetic lines of beef cattle differing in mature size. Data consisted of 3,992 and 2,877 re cords from lines of small-, medium-, and large-framed calves in each o f two research herds located at Rhodes and McNay, IA, respectively. Va riance components were estimated separately by herd and line for birth weight (BWT), birth hip height (BH), 205-d weight (WW), and 205-d hip height (WH) by derivative-free REML with an animal model. Model 1 inc luded fixed effects of year, sex, and age of dam. Random effects were additive direct (a) and additive maternal (m) genetic with covariance (a,m), maternal permanent environmental, and residual. Model 2 also in cluded dominance (d) and model 3 included dominance plus additive x ad ditive (a:a) effects. In general, only slight changes occurred in othe r variance components estimates when day was included in Model 2. Howe ver, large estimates of additive x additive genetic variances obtained with Model 3 for 4 out of 24 analyses were associated with reductions in estimates of direct additive variances. Direct(maternal) heritabil ity estimates averaged across herd-line combinations with Model 2 were .53(.11), .42(.04), .27(.12), and .35(.04) for BWT, BH, WW, and WH, r espectively. Corresponding covariance (a,m) estimates as fractions of phenotypic variance (sigma(p)(2)) were .00, .01, .01, and .06, respect ively. For maternal permanent environmental effects in Model 2, averag e estimates of variances as fractions of sigma(p)(2) across herd-line combinations were .03, .00, .05, and .02, for BW, BH, WW, and WH, resp ectively. Dominance effects explained, on average, 18, 26, 28, and 11% of total variance for BWT, BH, WW, and WH, respectively. Most of the estimates for additive x additive variances were negligible, except fo r one data set for BWT, two for BH, and one for WH, where the relative estimates of this component were high (.21 to .45). These results sug gest that most of the nonadditive genetic variance in the traits studi ed is accounted for by dominance genetic effects.