Production in Some Pure Breeds of Sheep and Their Crosses. I. Reproductive Efficiency in Ewes

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Abstract
Differences in fertility, prolificacy and livability were studied with Hampshire, Columbia-Southdale, Targhee, Suffolk and Dorset breeds of sheep and their crosses. The study includes 4 years (1965 through 1968) with a total of 1,893 ewes bred, 1,378 ewes lambing, 2,228 lambs born and 2,030 lambs weaned. The traits studied were: fertility, measured by percent of ewes lambing of ewes bred; prolificacy, measured by percent of lambs born of ewes lambing; lamb livability, measured by percent of lambs born alive of total lambs born and percent of lambs weaned of lambs born alive; and the overall measure of reproductive ability defined as the percent lambs weaned of ewes bred. Age of dam had a significant effect only upon prolificacy and overall reproduction. Single lambs survived better from birth to weaning than twin lambs. Type of birth did not have a significant effect on whether the lamb was born dead or alive. Years had an important effect on fertility, percent of lambs born alive of total lambs born and on overall reproduction. For the purebred matings the Targhee ewes were most fertile and the Columbia-Southdale most prolific. Fewer Targhee lambs were born dead than in any other breed, while more Dorset lambs lived to be weaned. The Targhee ewes had the highest overall reproductive rate, followed by the Columbia-Southdale and Suffolk ewes. Fertility, prolificacy, lamb livability and overall reproductive efficiency were generally higher for crossbred than for purebred matings. For fertility, 15 out of 20 crosses showed some positive hybrid vigor. Fourteen out of 20 crosses showed some positive hybrid vigor for prolificacy. In percent of lambs born alive of total lambs born, 13 crosses showed some positive hybrid vigor while for percent of lambs of live lambs born all crosses except one showed some degree of superiority over the purebreds. All crosses except three showed considerable improvement over the purebreds for overall reproduction. For percent of lambs weaned of ewes bred the overall crossbred average was 94.0% compared to 78.8% for the average of the purebreds. Copyright © 1971. American Society of Animal Science. Copyright 1971 by American Society of Animal Science.

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