Ovarian Response to Injectable Deslorelin During Anestrus (AAEP 2010)

Most breeders meticulously plan out every detail of breeding a mare. But sometimes things don't go quite according to plan. Suppose, for example, as breeding season approaches, the clinically breeding-sound mare is anestrus (she doesn't show an estrous cycle and, thus, she's difficult to impregnate). What now?

According to Farhad Ghasemi, DVM, a resident in theriogenology at the University of Saskatchewan, injectable deslorelin (which is currently used to induce ovulation in mares during the breeding season) might be the answer to this problem. In a presentation at the 2010 American Association of Equine Practitioners convention, held Dec. 4-8 in Baltimore, Md., Ghasemi presented the results of his recent study, which aimed at determining what effect the drug had on anestrus mares.

Ghasemi and colleagues examined a group of 16 anestrus mares, aged 3 years to 20 years. The mares were considered anestrus after an ultrasound confirmed that no luteal tissue or ovarian follicles larger than 21 mm were present for more than two weeks (luteal tissue forms when the ovarian follicle converts into a structure called the corpus luteum after discharging an egg, and follicles become larger as they are getting ready to discharge an egg). The team divided the mares into two groups of eight: one group received water-soluble deslorelin twice daily for up to 14 days, and the other received a placebo. When a mare had a 35-mm follicle hCG (a hormone that helps stimulate ovulation in mares) was administered.

According to Ghasemi, seven of the eight mares in the deslorelin group developed follicles larger than 35 mm, and 50% ovulated, achieving pregnancy rates of 37.5%. No control mares developed large follicles or ovulated. He added that the average deslorelin treatment before mares developed larger follicles was 12 days.

Ghasemi added that after a mare is brought out of anestrus, there is a chance that she will return to anestrus if not pregnant. He also added that mares with naturally smaller follicles might be less likely to respond to deslorelin.

This treatment may be an option for mares' owners who want to breed their mares out of season, but do not want to use artificial lighting programs that take more than 60 days. More research may fine-tune the protocol and make it more successful, Ghasemi said.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.