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

Flunixin meglumine (FM), a prostaglandin synthetase inhibitor, causes ovulatory failure in the mare. However, the effect of the FM treatment relative to the time of hCG administration on the ovulation failure has not been determined nor has its effect on the luteal function of treated mares. Estrous mares with a follicle ≥32 mm (range of 32–38 mm) were treated with 1.7 mg/kg b.w. of FM iv at zero, 12, 24 and 36 h (n = 6), at 24 and 36 h (n = 6), at 28 and 36 h (n = 6), at 24 h (n = 6) or at 30 h (n = 6) after treatment with 1500 IU hCG. One group received no FM (control, n = 6). Progesterone concentrations were determined using RIA. Mares treated with FM 0–36 h and 24–36 h had higher (P < 0.05) incidence of ovulatory failure (83 and 80%, respectively) than mares treated twice at 28 and 36 h, or once at 24 or at 30 h after hCG (16.7, 0 and 0%, respectively). The anovulatory follicles of FM treated mares luteinized and produced progesterone (>2 ng/ml). The progesterone concentration was lower in mares treated with FM at zero to 36 h and at 24–36 h after hCG than in the other groups. In conclusion, the FM administration was effective in blocking ovulation only when the treatment began ≤24 h after hCG and was continued every 12 h until ≥36 h. In addition, the FM-induced anovulatory follicles underwent luteinization of follicular cells with active production of progesterone.