Effect of coumestans on reproduction in the ewe

Abstract

In an experiment to study the effect of the ingestion of coumestans on reproductive variables in the ewe, pelleted feed containing c. 1000 ppm coumestans was given to nulliparous Merino ewes for varying periods (6.5 and 19.5 days) during their oestrous cycle. In a second experiment a similar diet was given to mature Merino ewes over days 12–18 of their oestrous cycle. Only 17% (12/69) of the total number of ewes on this diet came into oestrus, compared with 92% (35/38) of ewes given a phyto-oestrogen-free diet. Of the ewes given coumestan-rich feed that were detected in oestrus, 58% (7/12) did not have a recently formed corpus luteum at laparotomy. Injection of 25 µg oestradiol benzoate on day 16 of the oestrous cycle induced oestrus but not ovulation in ewes on the coumestan-rich diet. Follicular abnormalities indicative of strong oestrogenic stimulation were detected in the ovaries of ewes ingesting coumestans. It was suggested that coumestans inhibit oestrus through inhibiting the production of endogenous oestrogen.