Risk factors for lamb mortality on UK sheep farms.

Data on neonatal-lamb mortality and flock history were recorded by veterinary students working on 108 sheep farms in the UK in Spring 1997. The mean reported mortality incidence risk was 10.0% (median 9%; inter-quartile range 5.9-12.3%). The outcomes were incidence risks of stillbirth, perinatal (within 24h of birth) mortality and postnatal (>24h after birth) mortality. Exposures were screened for univariable associations with mortality risk. Logistic binomial multiple regressions adjusted for confounding, with farm as a random effect. This study has raised hypotheses for management factors associated with lamb mortality that warrant further study. Intensive rearing systems appear to be associated with increased perinatal and postnatal mortality, although housing ewes at lambing was associated with a decreased risk of stillbirth. High perinatal mortality also was associated with poor mothering-pen hygiene, flocks that foster more lambs, and failure to provide appropriate nursing for sick lambs. Larger flocks, poor ewe condition at breeding, and flocks with higher ewe-replacement rates were associated with higher postnatal mortality.