Could Intrauterine Marbles Cause Pyometra in Mares?

Mares in estrus can be challenging—and even dangerous—to deal with. So some owners seek a veterinarians' help to control their mares' estrous cycles and reduce estrus-related behavior. One of those methods involves placing a marble in the mare's uterus, which essentially keeps the mare from cycling.

While veterinarians have noted no significant uterine problems during treatment with this technique in the past, they recently encountered what they believe to be a significant complication. Jessica Klabnik-Bradford, a veterinary student at the Kansas State University (K State) College of Veterinary Medicine; Maria Soledad Ferrer, DVM, MS, Dipl. ACT, clinical associate professor of theriogenology at K State; and a team of veterinarians from the college recently presented the case in a poster at the 2013 Society for Theriogenology Conference, held Aug. 7-10 in Louisville, Ky.

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, pregnancy recognition occurs and estrus is suppressed due to the corpora lutea's persistent function. Mares return to estrus after the marble is removed.

In the current case, a 16-year-old Appaloosa mare who had no reproductive history presented to K State with a foul-smelling suppurative (pus-producing) vulvar discharge, Klabnik-Bradford said. Suspecting pyometra (infection of the uterus), endometritis (inflammation of the uterine lining), or vaginitis (inflammation of the vagina), veterinarians performed transrectal ultrasound to further explore the problem.

On ultrasonic exam, veterinarians found a corpus luteum and a 34 millimeter round structure in the left uterine horn. The team confirmed pyometra and suspected that the hyperechoic (dense) structure was either a mummified fetus or an intrauterine marble. Uterine endoscopy confirmed the latter, and they removed the marble from the mare's uterus.

Veterinarians removed the intrauterine marble after they identified it via endoscopy.

Photo: Courtesy Jessica Klabnik-Bradford

"After questioning the owners, it was determined that the marble had been in place for at least two years," Klabnik-Bradford said. "This case suggests that pyometra may be a complication of using intrauterine marbles for estrus suppression in mares and stresses the importance of removing the marble once estrus suppression is no longer desired."

She also cautioned that pyometra could negatively impact mares' long-term fertility; however, veterinarians did not test the study mare's fertility post-marble removal.

Both Klabnik-Bradford and Ferrer recommended that only veterinarians skilled in equine reproduction place intrauterine marbles for estrus suppression.

"This will ensure the marble is placed at the right time of the estrous cycle and with no damage to the cervix or bacterial contamination to the uterus," Ferrer explained. "Cervical damage can lead to fibrosis or adhesions that can prevent uterine clearance and lead to pyometra should infection occur.

"Owners may also want to have their veterinarians remove the marble once estrus suppression is no longer desired," Ferrer added. "Since the marble acts by prolonging function of the corpus luteum, the treatment will not be effective in mares in winter anestrus or spring transition that are not ovulating and producing corpora lutea. Therefore, removal of the marble during winter may be recommended."

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

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