The effect of passive immunization against oestrogens on the onset of parturition in the ewe.

Six ewes were treated twice daily with intravenous injections of antiserum to oestrogens and 3 ewes received normal sheep serum from Day 140 of gestation until parturition. All 9 ewes experienced normal parturitions and produced healthy active lambs after similar gestation lengths. Progesterone and prostaglandin F concentrations in maternal jugular venous plasma were similar in the immunized and control ewes, but total unconjugated oestrogen concentrations were significantly higher in the immunized ewes (P less than 0.005). It is concluded that immunization of the ewe against total unconjugated oestrogens did not affect the normal occurrence of parturition.