Maternal Effects on Preweaning Growth Rate in Cattle

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Abstract
Records from a Brahman herd and from a crossbred foundation herd of Brahman-Shorthorn breeding were evaluated for genetic influence on the pre-weaning growth rate of calves. The theoretical genetic and environmental components for growth and for maternal effects were estimated by equating variances and covariances obtained from the date to their theoretical genetic and environmental components. The components estimated included the variances for additive genotypes for growth and for maternal effects; the covariance between additive genotype for growth and for maternal effect; the variance of dominance deviations for growth; the variance of permanent environmental influences on maternal effects and nonpermanent environmental variance. The respective values for these components, expressed as a percent of total phenotypic variance, were for the Brahman herd: 18, 15, 0, 0, 8 and 59; and for the crossbred herd, 40, 46, -30, 0, 7 and 38. The estimate for total heritability, including both maternal and nonmaternal effects and their covariance, was .25 for the Brahman, but dropped to .17 in the crossbred herd due to the estimated negative covariance of additive genotype for growth and maternal effect.

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