And maternal (co)variance components and heritability estimates for body weight at different ages and fleece traits in Afrino sheep

Data, consisting of 4325 lamb records, the progeny of 146 sires and 946 darns, collected on the Carnarvon Afrino flock over the period 1975 to 1992, were used for this study. Variance components resulting from direct additive genetic effects, maternal additive genetic effects, maternal permanent environmental effects, as well as the relationship between direct and maternal effects for birth weight, monthly body weight from weaning at 4 months to 12 months of age, 18 month body weight, 16 month clean fleece weight and 16 month mean fibre diameter were estimated by REML procedures. By ignoring or including maternal genetic or environmental effects, five different models of analysis were fitted in order to determine the most effective model for each trait. The direct heritability estimate for body weight increased from birth (0.22+/-0.04) up to 8 months of age (0.59+/-0.06), where it seemed to stabilise. Maternal heritability estimates for body weight, on the other hand, increased from birth (0.09+/-0.04) to 5 months of age (0.17+/-0.02), whereafter it decreased gradually. The maternal permanent environmental effect was significant only for birth weight (0.12+/-0.03). Direct heritability estimates of 0.62+/-0.04 and 0.73+/-0.03 were obtained for clean fleece weight and mean fibre diameter, respectively. Maternal effects had no significant influence on clean fleece weight or mean fibre diameter.