Abstract
Fertility, prolificacy, numbers of lambs weaned and marketed, and total weight of lamb weaned and marketed per ewe bred (exposed to rams) were studied with the Romnelet, Columbia, Suffolk, and North Country Cheviot breeds of sheep and their two-breed and three-breed crosses. During a period of 4 yr, there were 1,675 matings, which resulted in 1,138 lambings with 1,818 lambs at birth. Fertility was improved (P < 0.05) by crossbreeding but prolificacy was not. Survival ability of lambs was improved by crossbreeding. Number of lambs weaned (at 3-4 mo of age) per 100 ewes bred and percentage of lambs surviving to end of a 75-day postweaning feeding period were 83 and 75 for purebred lambs, 94 and 83 for two-breed, and 104 and 86 for three-breed crosses. In total weight of lamb marketed per ewe bred, the two-breed and three-breed crosses surpassed purebreds by 16.6 and 32.5%, respectively. Total weight of lamb weaned per ewe in the foundation purebred flocks during their lifetime averaged 149.5 kg for the Suffolk, 146.6 for Romnelet, 119.3 for Columbia, and 92.1 for N.C. Cheviot. Longevity of ewes was highest for the Romnelet and Columbia breeds and lowest for the N.C. Cheviot. At the end of 8½ yr of production, the percentages of ewes remaining in the Romnelet, Columbia, Suffolk, and N.C. Cheviot flocks were 22, 25, 5, and 0.
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