Genetic variances for liveweight and fleece traits in Merino, Dohne Merino and South African Meat Merino sheep

(Co) variance estimates for weaning weight, yearling liveweight, clean fleece weight and fibre diameter at yearling age were obtained for Merino, Dohne Merino and South African Meat Merino flocks maintained on the same property. Direct additive genetic variances for weaning weight [expressed as a ratio of the total phenotypic variance (h(2), direct heritability)] were estimated at 0.15 for Merinos, 0.21 for Dohne Merinos and 0.32 for South African Meat Merinos. Corresponding maternal variance ratios (m(2), including direct maternal variance and permanent environmental maternal variance) were estimated at 0.15, 0.30 and 0.24, respectively. The correlation between direct and maternal variance ratios was high and negative in Dohne Merinos and South African Meat Merinos (-0.72 and -0.53, respectively). Direct heritability estimates for yearling liveweight were 0.30 for Merinos, 0.33 for Dohne Merinos and 0.45 for South African Meat Merinos. Corresponding maternal variance ratios were only significant in the latter 2 breeds, amounting to 0.13 in Dohne Merinos and 0.12 in South African Meat Merinos. For yearling clean fleece weight, h(2) and m(2) were estimated at 0.28 and 0.12, respectively, for both Merinos and Dohne Merinos. In the case of South African Meat Merinos, only the h(2) estimate was significant, at 0.68. Maternal variance ratios for yearling fibre diameter were not significant in any of the breeds, while h(2) ranged from 0.58 in Merinos to 0.75 in South African Meat Merinos. Selection progress for yearling traits seems likely in all breeds, depending on the breeding objectives being strived for.