Coumestans in lucerne and ovulation in ewes

Abstract Four trials with a total of 1750 Perendale ewes were conducted to determine the effect of feeding lucerne on ovulation rate and lambing performance. Levels of up to 600 ppm coumestans in lucerne leaf, associated with fungal infection, depressed ovnlation rate and lambing by 34% and 14.6% respectively. In the absence of fungal infestation no coumestans were found and stage of regrowth had 110 effect on lambing performance. A negative linear relationship between coumestan ccntent of the diet (x) and ovulation rate (y) was determined (y = 1.382 - O.004x). Levels of coumestans as low as 25 ppm in the diet depressed the ovulation rate of ewes fed lucerne pellets for 35 days. The depression in ovulation rate of ewes fed a high (100 ppm) level of coumestans was overcome by treatment with pregnant mare's serum gonadotrophin. It is suggested that coumestans exert their effect by interference with the release of follicle stimulating hormone from the pituitary gland.