The effects of clomiphene citrate on reproductive parameters in the mare.

Clomiphene citrate (CC) is a longstanding human fertility drug that has yet to be investigated in horses. The objective was to evaluate effects of CC on mare reproduction. After follicle ablation on Day 0, treatment mares (n=5) received 2 grams of CC intravenously on Days 1-5 while control mares (n=4) received no treatment. Transrectal ultrasonography was performed on Days 1-5 and 8, and transvaginal oocyte aspiration occurred on Day 8. Hormones were analyzed on Days 0-5, 8, 11, and 15. Mares receiving CC exhibited higher uterine edema grades compared to control mares (P=0.009). Antral follicle count and size of largest follicle did not differ between groups (P>0.05). Treated mares had higher luteinizing hormone (LH, P=0.04) and anti-müllerian hormone (AMH, P=0.05) compared to control mares. While CC treated mares had higher uterine edema and serum LH and AMH, significant changes in follicle stimulating hormone, estradiol, and follicular development were not demonstrated.