ESTIMATES OF DISPERSION PARAMETERS AND OF GENETIC AND ENVIRONMENTAL TRENDS FOR WEANING WEIGHT IN ANGUS CATTLE USING A MATERNAL ANIMAL-MODELWITH GENETIC GROUPING

Variance components for additive direct, additive maternal, maternal e nvironmental and direct environmental effects, and the covariance betw een additive direct and maternal effects were estimated by restricted maximum likelihood from 935 weaning weights of Angus calves. An animal model including genetic grouping, with the same grouping criterion fo r direct and maternal effects, was employed. Estimates of (co)variance components in the model including genetic groups did not differ very much from those obtained when genetic groups were excluded. Estimates of heritability for direct and maternal effects, and of the correlatio n between direct and maternal effects (r(G)) were 0.11, 0.03 and - 0.3 1, respectively. The estimated genetic trend for direct effects was po sitive whereas the estimated additive trend was close to zero. Estimat es of environmental trends were positive for direct effects and null f or maternal effects. The value of r(G) did not affect estimates of gen etic trends for direct effects. The estimate of the genetic maternal t rend was slightly sensitive to variation in the value and sip of r(G), and tended to increase as this correlation increased, but was not sig nificantly different from zero for any of the values of r(G) considere d.