The effect of treatment with flunixin meglumine at different times relative to hCG administration on ovulation failure and luteal function in mares.

This research investigates how administering flunixin meglumine (a mediator of ovulation) at different times relative to the treatment with a hormone (hCG) affects ovulation failure and the functioning of the corpus luteum (luteal function) in horses. They found that early and repeated flunixin meglumine (FM) treatments resulted in more ovulation failure and lowered progesterone levels, but follicles still carried out luteinization.

Research Methodology

• The study used mature female horses (mares) in their reproductive cycle (estrus) that had a follicle size of 32 to 38 mm.
• The selected mares were treated with 1.7 mg/kg of FM via intravenous injection at different time intervals after a given dose (1500 IU) of the hormone hCG.
• The time intervals for FM treatment were zero, 12, 24 and 36 hours for the first group; 24 and 36 hours for the second; 28 and 36 hours for the third; only 24 hours for the fourth; and only 30 hours for the fifth. There was also a control group that didn’t receive any FM treatment.
• Progesterone concentrations were determined by using a radioimmunoassay (RIA), a common scientific method used to measure substances in the blood.

Key Findings

• Mares treated with FM between 0-36 hours and 24-36 hours showed a significantly high incidence of ovulatory failure (83% and 80% respectively) compared to the other groups. This suggests the timing of FM treatment significantly affects ovulation.
• Despite failing to ovulate, the mares still underwent luteinization, a process where the ovarian follicles turn into the corpus luteum and produce progesterone.
• The concentration of progesterone was lower in mares treated with FM between 0-36 hours and 24-36 hours post hCG administration compared to the other groups. This suggests that FM treatment might influence the hormonal balance of the mares.

Conclusion

• The administration of FM was found to effectively block ovulation, but this was only the case when it was given no later than 24 hours after hCG treatment and then every 12 hours up to a minimum of 36 hours.
• The follicles of mares that did not ovulate as a result of FM treatment underwent luteinization and were actively producing progesterone, although the levels were lower for those that received their first FM treatment within 24 hours of hCG administration.