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Effect of Breed and Mating Season on Reproductive Performance of Sheep

U. S. Department of Agriculture, Clay Center, Nebraska 68933

Abstract

The effects of mating season and breed on interval to first estrus and conception, gestation length, lambing rate and lambing percent were evaluated in a study conducted during 1968 on 975 ewes. Approximately one-third of the ewes in each breed were mated during seasons corresponding to early (August 19 to October 1), intermediate (October 2 to November 12) and late (November 14 to December 18) in the normal breeding season. Ewes from the Suffolk, Hampshire, Rambouillet, Targhee, Corriedale, Coarse Wool and Navajo breeds were evaluated. Main effects of age of ewe and sires within breeds were also considered in analysis of the data.

Season had significant effects on interval to first estrus (P<.01), interval to conception (P<.01), and lambing rate (P<.01), but not on lambing percent. Intervals to first estrus and conception were longest during the August breeding season. Lambing rate was maximum during the October breeding season. Rambouillet and Navajo ewes tended to exhibit estrus and conceive earlier than other breeds in the early breeding season. Gestation length was longest in the Rambouillet breed (150.7 days) and shortest in the Suffolk (145.4 days) and Hampshire (144.9 days) breeds. Lambing percents were higher (P<.01) in the Suffolk, Hampshire, Targhee and Coarse Wool breeds than in the Rambouillet, Corriedale and Navajo breeds. Ewes bearing triplets had longer average gestation lengths than those bearing singles or twins. Both lambing rates and lambing percents were lower for yearling and 2-year-old ewes than for ewes from 3 to 6 years of age.

¹ U. S. Meat Animal Research Center, A.R.S.

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