Heritability estimates, genetic and phenotypic correlations of total weight of lamb weaned with hogget liveweight and fleece traits in Western Australian Merinos

The heritability (h(2)) of weight of lamb weaned totalled over 3 reproduction opportunities (TWW) was estimated in a multi-bloodline, medium wool resource flock in Western Australia. TWW was defined to give an indication of lifetime lamb production (the ewes were retained in the breeding flock for a maximum of 4 lambing opportunities). The trait was highly variable, as suggested by a coefficient of variation of 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 TWW. Within bloodline genetic correlations of TWW with hogget live weight was positive (0.58 +/- 0.11) and significant (i.e larger than double its standard error). The within bloodline genetic correlation of TWW with wool production were generally positive, being 0.26 +/- 0.11 for the genetic correlation with clean fleece weight. Clean yield was genetically unrelated TWW. The genetic correlation of TWW with fibre diameter was positive in sign, but smaller than twice its standard error (0.17 +/- 0.10). It was concluded that TWW 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.