Effect of periovulatory prostaglandin F-2 alpha on pregnancy rates and luteal function in the mare

The objective of this study was to determine whether periovulatory treatmen ts with PGF(2 alpha) affects the development of the CL, and whether the tre atment was detrimental to the establishment of pregnancy. Reproductively so und mares were assigned randomly to one of the following treatment groups d uring consecutive estrus cycles: 1. 3,000 IU hCG within 24 hours before art ificial insemination and 500 mug cloprostenol (PGF(2 alpha) analogue) on Da ys 0, 1, and 2 after ovulation (n=8); 2. 2 mt sterile water injection withi n 24 hours before artificial insemination and 500 mug cloprostenol on Days 0, 1, and 2 after ovulation (n=8); 3. 3,000 TU hCG within 24 hours before a rtificial insemination and 500 mug cloprostenol on Day 2 after ovulation (n =8); or 4. 3,000 IU hCG within 24 hours before artificial insemination and 2 mt of sterile water on Days 0, 1, and 2 after ovulation (controls; n=8). Blood samples were collected from the jugular vein on Days 0, 1, 2, 5, 8, 1 1, and 14 after ovulation. Plasma progesterone concentrations were determin ed by the use of a solid phase 12,1 radioimmunoassay. All mares were examin ed for pregnancy by the use of transrectal ultrasonography at 14 days after ovulation. Mares in Group 1 and 2 had lower plasma progesterone concentrat ions at Day 2 and 5, compared to mares in the control group (P < 0.001). No difference was detected between group 1 and 2. Plasma progesterone concent rations in group 3 were similar to the control group until the day of treat ment, but decreased after treatment and were significantly lower than the c ontrol group at Day 5 (P < 0.001). Plasma progesterone concentrations incre ased in all treatment groups after Day 5, and were comparable among all gro ups at Day 14 after ovulation. Cloprostenol treatment had a significant eff ect on pregnancy rates (P < 0.01). The pregnancy rate was 12.5% in Group 1, 25% in Group 2, 38% in Group 3, and 62.5% in Group 4. It was concluded tha t periovulatory treatment with PGF2a has a detrimental effect on early lute al function and pregnancy. (C) 2001 by Elsevier Science Inc.