Impact of Maternal Effects on Ranking of Animal Models in Genetic Parameter Estimation for 18-Month Weight in Tuli Cattle of Zimbabwe

Direct and maternal effects have been reported using different animal models for post weaning growth traits in some cattle breeds. 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 for 18-months weight records of Tuli cattle of Zimbabwe. All models included a random direct genetic effect, but different combinations of random maternal genetic and permanent environmental effects as well as for direct-maternal genetic covariance. The direct heritability (h2a) was constant (0.10) when the maternal genetic effects were included in the model, while (h2a) estimates were higher (0.22) and (0.63) when maternal effects were excluded. The maternal heritability (h2m) was (0.23) and higher than the direct heritability (0.10) when only maternal genetic effects were included in the model and did not change even when the permanent environmental effects of the dam was added. The permanent environmental effects of the dam were negligible and a strong positive correlation between direct and maternal genetic effects (?2am) was observed. The strong positive genetic correlation between direct and maternal genetic effects would not limit the effective response to selection if individual performance of animals is used in selection for post weaning growth in Tuli cattle.