Effects of single injections of stilboestrol at various stages in the oestous cycle on behavioural oestrus and ovarian function in Romney ewes

Abstract

Mature Romney ewes were injected with either 10, 100, or 1000 ¦g stilboestrol on days 5,10,14, or 15 of the oestrous cycle (oestrus = day 1) and then observed twice daily for oestrus. The day 5 ewes were subjected to a laparotomy and then slaughtered 1 day after their next natural oestrus, the day 10 ewes were slaughtered 1 day after their next oestrus, and the day 14 and 15 animals slaughtered 2 days after oestrus. None of the ewes receiving stilboestrol on days 5 or 10 ovulated in response to the administration but animals receiving the highest dose often showed induced oestrus. Injections of 1000 or 100 ¦g stilboestrol given on days 5 and 10 were luteolytic in the present experiment. Some ewes receiving stilboestrol on days 14 and 15 showed induced oestrus and, of the ewes not displaying an induced oestrus, most experienced longer cycles after treatment.