Estimates of genetic and environmental (co)variances for live weight and fleece traits in yearling South African Mutton Merino sheep

Abstract

Yearling live weight and fleece trait data were obtained from between 2214 and 2270 yearling SA Mutton Merino progeny of the Elsenburg flock during a 20-year period from 1983 to 2002. Information of (co)variances for these traits in SA Mutton Merinos is exceedingly scarce in the literature. Estimates of (co)variance components and ratios were thus obtained from these data, using an Animal Model. Coefficients of variation, for live weight as well as greasy and clean fleece weight were above 18%. Corresponding values for clean yield and fibre diameter were below 9%. Estimates of heritability were 0.23 for yearling live weight, 0.38 for greasy fleece weight, 0.39 for clean fleece weight, 0.59 for clean yield and 0.67 for fibre diameter. Maternal permanent environmental variance ratios were only significant for live weight, greasy fleece weight and clean fleece weight, amounting to 0.09, 0.06 and 0.06, respectively. Genetic correlations between yearling live weight and wool weight were positive but low (0.14 for greasy fleece weight and 0.13 for clean fleece weight). Those of live weight with clean yield and fibre diameter were zero and 0.22, respectively. The genetic correlation between greasy fleece weight and clean fleece weight was 0.87. The genetic correlations of greasy fleece weight with clean yield and fibre diameter were –0.07 and 0.21, respectively. Corresponding correlations with clean fleece weight were 0.43 and 0.38, respectively. The genetic correlation of clean yield with fibre diameter amounted to 0.33. In most cases, the derived values were in agreement with those derived from Merino data sets.