Selection of sires with high growth rates may unintentionally reduce lamb survival due to dystocia. Australian Sheep Breeding Values (ASBVs), including birthweight, lambing ease and gestation length, can be used as selection criteria to genetically increase lamb survival. However, lamb survival is likely to vary between birth types. Commercial producers with a high proportion of single born lambs and evidence of lambing ease problems should consider placing an upper limit on BWT ASBVs. Producers with more fecund flocks can afford to select rams with higher BWT ASBVs, because average lamb birth weight is lower in twin litters, and there is a positive relationship between higher birth weight and lamb survival.
