Variance components for lambing ease and gestation length in sheep

Lambing ease (LE) and gestation length (GL) are two important factors which influence Australian lamb production. Records for both these traits were available from the Sheep Genetic Australia terminal sire database. Lambing ease was scored from 0 to 5, with 0 being not observed and 5 being (other) special assistance such as veterinary intervention. Variance components were estimated with all traits treated as traits of the lamb with maternal genetic and permanent environment due to the dam effects included. Lambing ease had low estimates of direct and maternal heritability of 0.06 and 0.04 respectively. There was however a large permanent environment effect due to dam of 0.24. Gestation length was highly heritable (0.53) with high maternal genetic and permanent environment effects (0.16 and 0.25 respectively). Lambing ease and gestation length were positively genetically correlated with birth, weaning and post weaning weight and negatively correlated with number of lambs weaned. Lambing ease was not significantly correlated with gestation length. Lambing ease and gestation length could be included in the SGA analysis to provide estimated breeding values which could be used to improve lamb survival.