Losses may be attributed to the lamb or to the behaviour of the dam.
Maternal effects are environmental for the offspring but are at least partly genetic for the dam.
The genetic evaluation of survival is complicated by the fact that this trait has a binomial distribution whereas most analytical procedures assume normality. Records of survival were from 25,874 lambs born over the period 1989 to 1995 in a prolific Romney flock representing the progeny of 218 sires and 6,771 dams. The model included fixed effects of sex, year, litter size at birth and age of dam and the random effects for direct genetic, maternal genetic and maternal environmental influences. The estimates of heritability on the logit scale were 0.01, 0.03 and 0.04 for direct, maternal and total genetic effects, respectively. The proportion of total variance explained by maternal environmental influences was 0.09.