Placental production of progesterone in ovariectomized goats treated with a synthetic progestagen to maintain pregnancy.

Pregnant goats were ovariectomized or lutectomized and treated with medroxyprogesterone acetate. The circulating concentration of progesterone, which was reduced by 85% after ovariectomy or lutectomy, increased almost 3-fold between 120 and 140 days gestation, suggesting increased placental secretion. Measurement of veno-arterial differences across the uterus confirmed that an intrauterine organ was secreting progesterone at this time. Progesterone levels decreased (by 38%) in intact animals treated with medroxyprogesterone acetate alone. Concentrations of total unconjugated oestrogens were not altered by ovariectomy or lutectomy or by medroxyprogesterone acetate alone, but were related to the birth weight of the kids. Chronic treatment with medroxyprogesterone acetate reduced milk yield during lactation by up to 64%.