Breed variation in lambing performance and lamb mortality in commercial sheep flocks

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Abstract
SUMMARY Two surveys were conducted on commercial farms in England, Wales and Scotland to ascertain whether breeding contributed to variation in the number of lambs born per ewe, in lamb mortality and in the number of lambs remaining to be weaned per ewe. Each flock comprised two or more breed groups, but within flocks differences in breed were often quite small. In one survey of 74 flocks (average size 198 ewes, comprising 175 breed groups) the lambing percentage averaged around 150% and the lamb deaths to weaning (including stillbirths) around 9%. Within flocks there were statistically significant differences in the number of lambs born and weaned per ewe attributable to the breed of lamb and of its dam and sire. Crossbreeding was associated with a higher weaning percentage. Lamb mortality differed significantly among breeds and crosses of lamb. Lambing performance varied with type of farm. The second survey was a comparison of different crossbred types of dam, themselves the offspring of three breeds of sire and seven of ewe. Thirty flocks participated, providing 29 sets of records for 1-yearold females producing on average 120% lambs and losing through death (including stillbirths) 25 % of lambs born, and 10 sets at 2 years old, with 176 lambs per 100 ewes lambing and 11 % of the lambs born dying before 8 weeks old. Variation attributable to the crossbred type of the dam and to the breed of the dam's sire was significant for lambing and weaning percentage and the incidence of lamb mortality.