The Occurrence of Estrus in Pregnant Ewes

Abstract

About 22% of a band of 103 Western ewes was observed to mate one or more times during early pregnancy, pregnancy being verified at autopsy. Fifteen of 24 pregnant Rambouillet ewes, all of which later lambed, mated during late stages of pregnancy, four of them mating four to six days before parturition. The intervals between heats during pregnancy ranged from 4 to 113 days and averaged 21.3 days. These heats were observed during the normal breeding season of non-pregnant sheep and none occurred outside it. Heats during pregnancy were not accompanied by ovulation in those ewes which were killed. This observation is restricted to the first one-third of gestation. There was no difference in the number of lambs produced or the number of conceptions found between ewes which did and those which did not mate during pregnancy. In ewes in which lambs were removed shortly after parturition, post-partum heats occurred 1 to 61 days after parturition averaging 23.9 days. Ewes which continue to mate after exposure to fertile rams may be culled after conception because they are supposed barren. There was a significant increase in follicle number and follicle size from early pregnancy (3–8 days after mating) to about the 25th day of gestation. During the remainder of pregnancy follicle number remained constant but follicle size decreased significantly.