Fa. Rodriguezalmeida et al., ESTIMATION OF NONADDITIVE GENETIC VARIANCES IN 3 SYNTHETIC LINES OF BEEF-CATTLE USING AN ANIMAL-MODEL, Journal of animal science, 73(4), 1995, pp. 1002-1011
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.