 Lambs belonging to small breeds, such as Scottish Blackface, are more vulnerable than larger breeds, such as Merino.Twins may be more vulnerable to foxes than singlets, as ewes cannot effectively defend both simultaneously.Crossbreeding small, upland ewes with larger, lowland rams can cause difficult and prolonged labour for ewes due to the heaviness of the resulting offspring, thus making the lambs more at risk to fox predation.