Heritability estimates and genetic and phenotypic correlations of lamb production parameters with hogget liveweight and fleece traits in Western Australian Merino sheep

Heritability estimates (h(2)) for weight of lamb weaned and number of lambs weaned totalled over 3 reproduction opportunities were estimated in a multi-bloodline Western Australian medium wool resource flock. These traits were defined to give an indication of lifetime lamb production (the ewes were retained in the breeding flock for a maximum of 4 lambing opportunities). Both reproduction traits were highly variable, as suggested by coefficients of variation of approximately 50%. The between-bloodline variance ratio was significant (P <0.05), but failed to exceed 5% of the total across-bloodline phenotypic variation. Within-bloodline h(2) (+/- s.e.) was estimated at 0.154 +/- 0.040 for total weight of lamb weaned, and at 0.141 +/- 0.040 for total number of lambs weaned. Within-bloodline genetic correlations of both traits with hogget liveweight were positive and significant (P < 0.05; 0.58 +/- 0.11 and 0.26 +/- 0.13, respectively). Within-bloodline genetic correlations of the reproduction traits with wool production were generally positive, being 0.26 +/- 0.11 for the correlation between total weight of lamb weaned and clean fleece weight, and 0.29 +/- 0.15 for the correlation between total number of lambs weaned and clean fleece weight. Clean yield was genetically unrelated to both measures of reproductivity. The genetic correlation of total weight of lamb weaned per breeding ewe with fibre diameter was positive in sign, but smaller than twice its standard error (0.17 +/- 0.10). The corresponding estimate for total number of lambs weaned was 0.16 +/- 0.12. It was concluded that the reproduction traits investigated would respond to selection in Western Australian Merinos if it should form part of a breeding strategy. Genetic correlations with hogget liveweight and wool traits were generally favourable.