Perinatal lamb mortality remains a major welfare and economic concern for the sheep farming industry. The vitality and teat-seeking abilities of the newborn lamb are fundamental to its survival and are likely to be greatly influenced by its physical characteristics and ease of birth. The following experiment used embryo-transfer techniques to distinguish between maternal and foetal genotype and environmental factors affecting gestation length, lambing ease and postnatal growth in two breeds of sheep with differing ewe and lamb liveweights.

Thirty-eight Scottish Blackface (BF; mean liveweight (±s.e.m.) at lambing=54.25 kg ±1.03) and 41 Suffolk ewes (S; 80.33 kg ± 1.52) were given single purebred embryos obtained from 17 donor ewes and 10 sires. Embryos were transferred between ewes in a balanced design such that the following combinations were obtained: 18 BF ewes with BF lambs; 20 BF ewes with S lambs; 20 S ewes with BF lambs; 21 S ewes with S lambs.