Genetic parameters for weaning weight of Zimbabwean Nguni cattle accounting for direct-maternal genetic covariances

Abstract

Five models were fitted to weaning weight data of indigenous Nguni cattle to investigate their suitability for evaluation of breeding values. The animal models were ranked using a simple Mallows statistic. Variance components for additive direct, additive maternal, permanent environmental maternal effects, the covariance between additive direct and maternal effects were estimated by restricted maximum likelihood, fitting five animal models from 1278 weaning weight records of indigenous Nguni cattle collected over a period of 10 years (1989- 1999). All investigated models included a random direct effect, but different combinations of random maternal genetic and permanent environmental effects as well as for direct-maternal genetic covariance. The direct heritability (h 2 a ) ranged from 0.0 to 0.25 when the maternal genetic effects were included in the model, while h 2 a estimates were 0.21 and 0.68 when maternal effects were excluded. The maternal heritability (h 2 m ) was lower (0.04) than h 2 a (0.09) when only maternal genetic effects were included in the model, and were 0.13 and 0.17 when the permanent environmental effects of the dam was fitted. The permanent environmental effects of the dam were not important. A large and negative covariance (σ 2 am ) between direct and maternal genetic effects was observed. Using Mallows statistic test Model 5 could be the best for genetic evaluation of weaning weight and this could maximize genetic response.