Active immunization of ewes against prostaglandin F2 alpha to control ovarian function

The hypothesis that pregnancy success could be improved in early postpartum ewes by prolonging the lifespan of the corpus luteum via active immunization against prostaglandin F2 alpha (PGF2 alpha) was tested. Further experiments in ewes immunized against PGF2 alpha investigated the effects of exogenous PGF2 alpha on the preovulatory follicle and the effects of PGF2 alpha and oestradiol benzoate on corpus luteum function. Four weeks pre-partum, 39 ewes bred to lamb during seasonal anoestrus received either 5 mg PGF2 alpha-ovalbumin conjugate (n = 20; immunized) or ovalbumin (n = 19; control) in Freund's complete adjuvant. Treatments were repeated on day 5 post-partum with reagents emulsified in Freund's incomplete adjuvant. On day 17 post-partum, ewes received 500 iu pregnant mares' serum gonadotrophin (PMSG) and 48 h later 50 micrograms gonadotrophin-releasing hormone (GnRH). Laparoscopy was performed 36 h after GnRH to assess ovarian activity and ewes with recent ovulations were inseminated into the uterus. No immunized ewes had ovulated, but ten had follicles that luteinized and secreted progesterone during the 8 weeks studied. Eighteen of 19 control ewes ovulated and 15 of 18 had increased progesterone concentration for at least 21 days. By day 70 post partum, progesterone had returned to basal values in all control ewes. In a second study, 24 immunized ewes bearing persistent corpora lutea, and for which the interval from the previous parturition was greater than 90 days, received 15 mg PGF2 alpha and 500 iu PMSG followed 48 h later by 50 micrograms GnRH. PGF2 alpha induced corpus luteum regression in all ewes.(ABSTRACT TRUNCATED AT 250 WORDS)