Influence of rams on ovarian activity and oestrus in Merino ewes in the spring and early summer

Abstract

The occurrence of oestrus and ovulation and the changes in the vaglnal contents were studied in Merino ewes following the introduction of vasectomized rams at various times during the spring and early summer. The ewes were in an anoestrous state when the observations were commenced. Except in occasional ewes oestrus did not appear until early December. It had occurred in all except a few ewes by early January. In most ewes among which rams were introduced on October 26 or November 18, it occurred about a week earlier than in ewes among which rams mere not introduced until December 8, and ewes among which rams had been running continuously. In at least 80 per cent, of animals in which both were studied, oestrus was accompanied by massive desquamation of the vaginal epithelium and it was preceded by one or more periods of massive desquamation. Between December 8 and December 14, masses of desquamated epithelial cells were present in the vaginal contents in few only of the ewes which were held separate from rams, but in almost all ewes among which rams were introduced on December 8 (group 4), and in most of the em7es which were running continuously with rams (group 6). They first appeared in the ewes of group 4 between December 11 and December 14, 3-6 days after the introduction of the rams, whereas they were already present in almost all of the ewes of group 6 by December 11.Corpora lutea compatible with ovulation shortly after December 8 were present in most ewes among which rams were introduced on that day, and in few ewes which were held separate from rams. The significance of these results is discussed.