Antiluteogenesis effects of prostaglandin F2-alpha (PGF) in cyclic mares

A series of experiments were conducted to investigate the effects of PGF in cycling mares when administered during the early post-ovulatory period. We hypothesized that administration of PGF during the early post-ovulatory period would prevent the establishment of luteal function as denoted by low concentrations of plasma progesterone. We further hypothesized that prevention of luteal function would result in induction of an ovulatory estrus followed by a normal diestrus. Further, treated mares would have normal potential for fertility when artificially inseminated during the induced estrus following PGF (dinoprost tromethamine) treatments. Cycling mares (n 1⁄4 25) followed during 50 estrous cycles were subjected to the following experimental groups: 1) Group 1(n1⁄410), no PGF treatment; Group 2 (n 1⁄410), mares were treated with a single i.m. injection of PGF (10 mg dinoprost) 10 days post ovulation (ovulation 1⁄4 day 0); Group 3 (n 1⁄4 10), mares were treated with 2.5 mg PGF twice daily for 3 days beginning within 24 hours from ovulation detection; Group 4 (n 1⁄4 10), mares were treated with 10 mg PGF twice daily for 3 days beginning within 24 hours from ovulation; Group 5 (n1⁄4 10 ), mares were treated with 10 mg PGF twice daily for 3 days beginning within 12 hours from ovulation, followed by once daily injections on days 3 and 4 following ovulation. Only mares in Groups 2 and 5 were artificially inseminated.