Lamb survival in Australian Merino sheep: a genetic analysis.

Direct and maternal components of variance for lamb survival to birth, 7 d, and weaning (110 d) were estimated by REML procedures in a flock of Australian Merino sheep. A total of 14,142 lambs, the progeny of 421 sires and 3,666 dams, born between 1975 and 1983 were available for analysis. The study has produced some of the most precise estimates of genetic parameters for lamb survival in the Australian Merino. Very low heritabilities for lamb viability (0.03) and the performance of the dam or ewe rearing ability (0.07) suggest that genetic solutions to lamb survival are unlikely to be significant. But, despite the low heritabilities, there is still potential for improvement through selective breeding. The estimated repeatability of at least 0.10 shows that multiple records on the rearing ability of a ewe over its lifetime can increase selection accuracy. More importantly, such repeatabilities indicate that current generation improvement can be achieved by culling ewes from the breeding flock with poor rearing ability. Despite maternal bond score and lamb birth weight being highly repeatable and moderately heritable traits, correlations with lamb survival were essentially zero. These traits therefore have no value as indirect selection criteria for Merino lamb survival.