Effects of Œstrogen on Fertility in Ewes

Abstract

IN a recent experiment¹ daily injection of 128 and 32 µg of stilbœstrol, prior to, and during, mating reduced fertility in Merino ewes almost to zero. Some circumstantial evidence also suggested that even 8 µg might result in reduced conception percentages and proportions of multiple births. Since intakes of plant œstrogens greater than the equivalent of 8 µg stilbœstrol (assayed by uterine weight in ovariectomized ewes) could be common in sheep-grazing pastures containing subterranean clover or red clover^2,3, it seemed to us important to assay the effects of such doses. Accordingly three groups of about 90 ewes were injected for six weeks, thrice weekly, with 1 ml. peanut oil containing the equivalent of 0, 8 µg and 16 µg stilbœstrol dipropionate (May and Baker) daily. Injections commenced on February 27, 1963. Rams were introduced on March 20 for three weeks. Vasectomized rams were kept with the ewes for a further three weeks. Matings were recorded with the aid of SIRE-SINE harness and crayon.