Abstract

Data from seven commercial New Zealand sheep flocks were analysed to quantify the extent to which lamb survival in New Zealand sheep is influenced by genetic factors. Estimates of direct and maternal genetic variance components, and the effects of inbreeding in either the lamb or the dam on lamb survival, were found to vary significantly across flocks. Direct heritability estimates ranged from 0.008 to 0.070, while maternal heritability estimates ranged from 0.002 to 0.075. Inbreeding in the lamb showed a statistically significant (P<0.05) effect on survival in three of the seven flocks, ranging in value from -0.17 to -0.29% reduction in lamb survival for a 1% increase in inbreeding coefficient. Inbreeding of the lamb’s dam had a statistically significant effect (P<0.05) on survival in two of the seven flocks, taking values of -0.32 to -0.71% reduction in lamb survival for a 1% increase in the dam’s inbreeding coefficient. It is recommended that lamb survival records be transformed to a constant variance within flock and year prior to estimation of breeding values, but that no transformation to either a logit or probit scale within the statistical analysis is required. Inbreeding coefficients for both the lamb and the lamb’s dam should be included as linear covariates in the mixedmodel analysis of lamb survival breeding values.

PR, Amer, and NB Jopson

Proceedings of the New Zealand Society of Animal Production, Volume 63, Queenstown, 201-203, 2003