A compounded drug has shown considerable promise in treating anestrus mares–those that are not cycling and thus are difficult to impregnate. Walter Zent, DVM, of Hagyard Equine Medical Institute, described his experience using Buserelin in mares at the Hagyard Bluegrass Equine Symposium, held Oct. 18-21 in Lexington, Ky. He cautions, however, that this method hasn’t yet stood the test of time.

Buserelin is a synthetic gonadotropin-releasing hormone (GnRH) analogue that is designed to alter hormone levels. It is not currently labeled for the horse in the United States. “We got our pharmacy to compound some for us–we compounded a 25 microgram/cc (concentration),” said Zent. In the first treatment protocol Zent used, he gave 12 micrograms of the drug per day until ovulation occured. “It usually takes about 13 days, and mares that don’t begin to respond by 10 days usually will not respond.”

A second protocol used 25 micrograms of Buserelin once a day for two days. “Most responded in eight to nine days,” he said, citing that one Central Kentucky Thoroughbred farm has had “pretty good results. It works as good or better than other things we’ve tried, and it’s not a terribly long procedure.”

Zent noted that Hagyard veterinarians have used these protocols only on mares that have been under lights (to manipulate their estrous cycles), have had time to cycle, and have not responded. They have not used Buserelin on mares in winter anestrus