Direct and maternal genetic effects for birth weight in dorper and mutton merino sheep in Zimbabwe
Variance components for birth (BWT) in Dorper and Mutton Merino sheep were estimated by Average Information Restricted Maximum Likelihood (AIREML). Animal model was fitted allowing for genetic maternal effects and a genetic covariance between direct and maternal effects. Estimates of heritability for direct genetic effects (h²A), maternal genetic effects (h²M), and the genetic covariance between direct and maternal effects as a proportion of the total variance (cAM) for birth weight were 0.23, 0.16, 0.85 and 0.26, 0.46, -0.25 for Dorper and Mutton Merino sheep, for Dorper sheep, respectively. Direct additive genetic variance was larger than maternal variance for Dorper sheep, and direct additive genetic variance was smaller than maternal variance for Mutton Merino sheep. The correlation between direct and maternal effects was negative implying
selection in Mutton Merino sheep should be directed at both components considering the maternal heritability estimate which was high. Common environmental maternal effects were important in both Dorper and Mutton Merino sheep.
Keywords: Variance component, AIREML, heriability, birth, dorper, mutton Merino