Plasma coumestrol levels and cervical mucus responses in ewes ingesting coumestan-rich feeds

Abstract

The concentrations of free and conjugated coumestrol in plasma drawn from the jugular vein of ovariectomized ewes were measured during 17 days of feeding on two coumestan-rich diets. Average daily intakes (± SE) of coumestans for ewes fed on diets A and B were 952 ± 30 mg and 514 ± 1 mg respectively. There was no change in the concentration of free coumestrol in the plasma during the period of feeding of the two diets, except for the last day when the diets were interchanged. The concentration of free coumestrol appeared to be related to the amount of coumestans ingested—81 v. 37 ng/l0 ml plasma (P < 0.01) for ewes fed on diets A and B respectively. The effects of length of feeding and diet on the concentration of conjugated coumestrol were less well defined but showed similar trends.

Despite the significant amounts of coumestrol in the plasma after 16 days of feeding on the two diets, the production of cervical mucus remained at basal levels. It was concluded that for the cervical mucus bioassay, ewes become refractory to coumestrol over prolonged periods of exposure.