Systemic treatment with high dose of flunixin-meglumine is able to block ovulation in mares by inducing hemorrhage and luteinisation of follicles.

The research conducted studied the effects of systemic administration with high doses of flunixin-meglumine (FM) on ovulation in mares. The researchers found that this treatment method resulted in ovulatory failure and subsequent development of luteinised unruptured follicles in the majority (83%) of the mares.

Objective and Methodology of the Study

• The primary objective of the study was to determine whether a high dose of FM, administered systemically to mares during the periovulatory period (around the time of ovulation), could block ovulation. A secondary aim was to analyze the ultrasound characteristics of the follicles in the treated mares.
• In this study, six mares were used over two consecutive estrous cycles (periods of sexual receptivity in female mammals). Each mare received a treatment consisting of 2 mg FM per kg administered intravenously twice a day, beginning at the time of treatment with human chorionic gonadotropin (hCG), a hormone that triggers ovulation, and continuing until the time of actual ovulation.
• The same process was repeated in the later cycle, known as the control cycle, but in this case, the mares did not receive FM.

Observations and Conclusions

• During the FM treatment cycle, five out of six mares failed to ovulate, even though the preovulatory follicles did not collapse, and small, bright reflections (echoic specks) were detected in the follicles.
• Instead of discharging the ovum or egg (ovulating), the mares’ follicles continued to grow until reaching an average diameter of 55 mm. After reaching this size, the follicles’ contents became more structured and luteinised. Luteinisation is the process where the follicle turns into a corpus luteum, a structure that produces progesterone, a hormone crucial for pregnancy.
• All mares in the control cycle, which did not receive FM, ovulated as expected.
• The researchers concluded that when mares were treated with FM, they demonstrated a significantly higher incidence of ovulatory failure (the inability to release an egg from the ovaries). As a result, the follicles became luteinised but remained unruptured (83%, P = 0.015) compared to untreated mares.