While breeders might try anything to get their mares into heat, some other mare owners will try anything to keep their mares out of heat. From aggressive behavior to performance problems, some mares can turn into different animals when they're in estrus. Fortunately, veterinarians have many options by which to keep mares out of heat. One common technique is to implant a glass marble in a mare's uterus, but this method isn't without its risks.
At the 2014 American Association of Equine Practitioners Convention, held Dec. 6-10 in Salt Lake City, Utah, Mariana Diel de Amorim, DVM, DVSc, Dipl. ACT, described some complications associated with long-term use of intrauterine glass marbles. Diel de Amorim is a PhD candidate and an assistant professor in the Department of Large Animal Clinical Sciences at the University of Saskatchewan's Western College of Veterinary Medicine (WCVM), in Saskatoon. She noted this study was carried out in collaboration between researchers at the WCVM and the University of Guelph, in Ontario, Canada.
"The effectiveness of intrauterine glass marbles for estrus suppression in mares varies in studies from 11 to 41.3%, but their use is still common practice," Diel de Amorim said.
Intrauterine marbles help suppress estrus by extending the mare's natural corpus luteum (the structure formed after the follicle releases the egg, or ovulates, and then produces progesterone) function. When veterinarians place a glass marble in the mare's uterus at the right time, a signal similar to pregnancy recognition occurs and estrus is suppressed due to the corpora lutea's persistent function. Mares return to estrus after the veterinarian removes the marble.