Direct and maternal genetic (co)variances for hogget liveweight and fleece traits in Western Australian Merino sheep

Abstract

(Co)variance estimates for hogget liveweight, greasy fleece weight, clean fleece weight, clean yield, fibre diameter, and the coefficient of variation of fibre diameter were obtained for a Western Australian Merino resource flock. The flock encompassed 16 medium wool bloodlines and data were available for the period 1982–93. Direct additive genetic variances (h²) — expressed as a ratio of the total phenotypic variance within bloodlines — were estimated at 0.52 for hogget liveweight, 0.44 for greasy fleece weight, 0.42 for clean fleece weight, 0.63 for clean yield, 0.71 for fibre diameter, and 0.62 for coefficient of variation of fibre diameter. Maternal genetic variance estimates were significant (P < 0.05) only in hogget liveweight and fibre diameter, but components within bloodlines were low (0.05 for liveweight and 0.02 for fibre diameter). Direct within-bloodline genetic correlations of hogget liveweight as well as greasy and clean fleece weight with fibre diameter were positive (0.17, 0.31, and 0.31, respectively), suggesting that selection for bigger and heavier cutting sheep would generally lead to a broader fibre diameter. Liveweight was unrelated to clean yield and negatively related to coefficient of variation of fibre diameter (–0.17). Greasy fleece weight was negatively related to clean yield (–0.20). The genetic correlation of clean fleece weight with clean yield was positive (0.37). Wool quantity was, in general, positively related to coefficient of variation of fibre diameter, although the estimated genetic correlations were low (0.12 for greasy fleece weight and 0.07 for clean fleece weight). The genetic correlation between fibre diameter and coefficient of variation of fibre diameter was negative, and fairly low (–0.10). These results are discussed with reference to sheep breeding.