COVARIANCE COMPONENTS AND PREDICTION FOR ADDITIVE AND NONADDITIVE PREWEANING GROWTH GENETIC-EFFECTS IN AN ANGUS-BRAHMAN MULTIBREED HERD

Estimates of covariances and sire expected progeny differences of addi tive and nonadditive direct and maternal genetic effects for birth and weaning weights were obtained using records from 1,581 straightbred a nd crossbred calves from the Angus-Brahman multibreed herd at the Univ ersity of Florida. Covariances were estimated by Restricted Maximum Li kelihood, using a Generalized Expectation-Maximization algorithm appli ed to multibreed populations. Estimates of heritabilities and additive genetic correlations for straightbred and crossbred groups were withi n the ranges of values found in the literature for these traits. Maxim um values of interactibilities (ratios of nonadditive genetic variance s to phenotypic variances) and nonadditive correlations were somewhat smaller than heritabilities and additive genetic correlations. Sire ad ditive and total direct and maternal genetic predictions for birth and weaning weight tended to increase with the fraction of Brahman allele s, whereas nonadditive direct and maternal genetic predictions were si milar for shes of all Angus and Brahman fractions. These results showe d that it is feasible to evaluate sires far additive and nonadditive g enetic effects in a structured multibreed population. Data from purebr ed breeders and commercial producers will be needed to accomplish the same goal. at a national level.