Genetic parameters and trends for lamb survival following long-term divergent selection for number of lambs weaned in the Elsenburg Merino flock

Context Mortality of new-born lambs is well known to have important implications for both animal production and welfare. Improving survival rates by genetic selection very desirable, but the low heritability traits challenges prospect useful gain. Aim This study aimed derive environmental parameters lamb in Elsenburg Merino resource flock. It also investigated correlations possible indicator birthweight birth coat score reported progress breeding values following 33 years divergent selection. Methods The flock was divergently selected number weaned separated High (positive) Low (negative) groups. pedigree file identified 8138 as progeny 273 sires 2062 dams. considered total from weaning (Tsv) that partitioned into perinatal 3 days age, remaining period. Variance components were derived linear mixed models using ASREML® program. Genetic trends predicting mean groups within each year evaluated fitting broken-stick regression models. Results Predicted Tsv H-line (0.81 ± 0.01) higher (P < than L-line (0.68 0.01). Heritability significant (0.03–0.07), moderate (0.16) high (0.54). trended traits, a changepoint trend suggested reached plateau 19–22 Preceding this period, rate change equalled ~1% Tsv. Conclusions Despite survival, contradicted premise not worthwhile method reduce incidences mortality. Implications recommended phenotypes should be recorded incorporated indices individually where possible, composite are viable alternative.