Genetic parameters for fitness and neonatal behavior traits in sheep.

Poor neonatal survival constrains productivity and good welfare. The heritability of survival in sheep is very low, suggesting that genetic progress will be slow. Previously we have shown that a difficult birth and low neonatal lamb vigor are important predictors of future survival. In this study we investigated the heritability of these traits, and their relationship to production traits, as an alternative indirect route to improve lamb survival. Neonatal lamb data from 11,092 animals were collected over 2 years from 290 commercial sheep flocks, using previously developed methods to rapidly assess three traits (birth assistance, lamb vigor, sucking ability) on farm. Heritabilities for neonatal traits were moderate: birth assistance (mean ± standard error; 0.26 ± 0.03), lamb vigor (0.40 ± 0.04) and sucking ability (0.32 ± 0.03). Genetic correlations between neonatal traits were moderate to high, and positive. Heritabilities for production traits were also moderate: 8-week weight (0.27 ± 0.06), 20-week weight (0.39 ± 0.07), ultrasound muscle depth (0.37 ± 0.06). Genetic and phenotypic correlations between the neonatal traits and production traits were not significantly different from zero. However, lambs that were scored as of poor vigor at birth were less likely to be recorded at 8 or 20 weeks, indicating that they may have died. The data demonstrate that the neonatal survival traits of birth assistance, lamb vigor and sucking assistance are moderately heritable when treated as a lamb trait, indicating that selection to target these lamb traits would successfully, and efficiently, improve survival without influencing productivity.