Optimizing Implant Therapy in Cycling Mares

Deslorelin acetate implants (Ovuplant from Fort Dodge Animal Health) have proven highly successful at inducing ovulation in mares. Implanted mares typically ovulate within 48 hours. Unfortunately, despite administration of prostaglandin during diestrus, a percentage of mares with implants, perhaps as many as 1 in 4, experience a prolonged interval to the next ovulation. Researchers from Colorado State University recently set out to determine if removal of deslorelin implants 48 hours after placement can sufficiently restore reproductive hormone concentrations and prevent a prolonged interovulatory interval.

Briefly, 24 cycling mares were divided into three groups. Group 1 was allowed to ovulate spontaneously. Group 2 mares were implanted with deslorelin acetate, which was not removed. Group 3 also received the implant, but in a shallow incision in the neck for easy removal two days after ovulation. Prostaglandin was administered to all mares 10 days after ovulation.

All mares in Groups 2 and 3 ovulated within 48 hours, while Group 1 mares ovulated within an average of four to five days. Ten days after ovulation, follicle stimulating hormone (FSH) concentrations were significantly lower in Group 2 mares compared to Group 1 or 3. As a result, size of ovarian follicles on Day 14 was significantly smaller in Group 2 mares. In addition, the interval to the next ovulation was prolonged, to roughly 26 days. In contrast, Group 1 and 3 mares had intervals of only 18-19 days.

Therefore, the authors concluded that removal of deslorelin implants after ovulation, approximately 48 hours after placement, will help prevent adverse effects on follicle development and prolonged interovulatory interval.

Farquhar, V.J.; McCue, P.M.; Carnevale, E.M.; et al. Equine Veterinary Journal, 34 (4), 417-420, 2002.

About the Author

Susan Piscopo, DVM, PhD

Susan Piscopo, DVM, PhD, is a free-lance writer in the biomedical sciences. She practiced veterinary medicine in North Carolina before accepting a fellowship to pursue a PhD in physiology at North Carolina State University. She lives in northern New Jersey with her husband and two sons.

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