The effect of systemic administration of cloprostenol on ovulation in mares treated with a prostaglandin synthetase inhibitor.

This research paper explores the impact of a prostaglandin synthetase inhibitor (Flunixin Meglumine or FM) and a prostaglandin F2 alpha analogue (cloprostenol) on ovulation in mares. The study found that the administration of FM during the periovulatory period blocks ovulation, while the administration of cloprostenol does not restore ovulation in mares previously treated with FM.

Study Design and Procedure

• Two groups of mares were treated with FM at different intervals (0, 12, 24 and 36 hours) after a human chorionic gonadotropin (hCG) treatment to induce experimentally luteinized unruptured follicles (LUF), while a control group was left untreated.
• In addition to the FM treatment, cloprostenol was administered intravenously at specific times (either 33, 35 and 36 hours or 48, 49 and 50 hours) after the administration of hCG.
• The effect on ovulation rate, follicular diameter, and progesterone concentration in these mares were then observed and compared.

Key Findings

• The rate of ovulation within 48 hours of treatment was found to be significantly higher in the control group than in the groups treated with FM and cloprostenol.
• All but one mare treated with FM developed LUF within 48 hours of treatment, suggesting that FM effectively blocks ovulation.
• The experiment also found that two LUF collapsed between 48-60 hours and 72-84 hours in one mare from the FM-control group and from the cloprostenol grouped at 33 hours respectively.
• Progesterone concentration from 5 to 13 days after hCG treatment was markedly higher in control mares compared to FM-treated mares, implying that FM treatment significantly reduces progesterone levels, which are necessary for successful ovulation and pregnancy.

Conclusion

• The administration of FM during the periovulatory period successfully blocked ovulation in mares.
• Contrarily, the administration of cloprostenol in mares previously treated with FM was not successful in restoring ovulation, suggesting that this prostaglandin analogue’s effects could not reverse the impact of FM.