Analysis of lamb survival in Australian Merinos.

Lamb survival from a Merino flock (13,163 records) and a crossbred flock (15,569 records) were analysed by both animal and sire model to estimate genetic parameters for lamb survival on the normal and logit transformed scales. Average survival rates were 77.5% in crossbred and 72.7% in Merino flock. The estimated direct heritabilities from animal model in the crossbred flock were 0.013 and 0.001 on normal and logit scales respectively and in the Merino flock 0.026 and 0.006. Maternal heritability was 0.007 and 0.013 on normal and logit scales in the crossbred flock and 0.026 and 0.031 in the Merino flock. The estimated direct and maternal heritabilities from sire model on normal and logit scales were similar within each flock, as well as and heritability estimates from animal and sire model on normal scale. However heritability estimates on the logit scale from animal model were seriously underestimated. The results suggest that selection for lamb survival will have limited impact in Merinos.