EXPECTED PHENOTYPIC RESPONSE IN WEANING WEIGHT OF BEEF CALVES FROM SELECTION FOR DIRECT AND MATERNAL GENETIC EFFECTS

An equation is derived to predict expected phenotypic response to selection when the trait under selection is influenced by both direct and maternal genetic effects. The expected phenotypic response after the i+lth generation of selection is Pi+1 = (i+l){Delta}D + i{Delta}M + {Delta}MC where {Delta}D and {Delta}M are the averages of the genetic selection differentials of the parents for the direct and maternal effects and {Delta}MC is the maternal genetic selection differential for selected females. An example, corresponding to published reports of genetic variances and covariance for direct and maternal effects on weaning weight, illustrates the importance of the covariance term in long term response. With a large negative covariance, selection of males for direct and females for maternal genetic value would give greater expected response in progeny after the first generation than selection of females for direct genetic value