New IUD for Suppressing Estrus in Mares

Researchers successfully tested a drug- and hormone-free approach for suppressing estrus in mares they say is safe, easy, and doesn’t affect future fertility.

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suppressing estrus in mares
Gradil designed the new IUD with safety in mind: Composed of three shatter-proof magnetic beads, the device self-assembles into a ring upon insertion with an applicator into the mare’s uterus. | Photo: Courtesy Dr. Carlos Gradil

Owners of marish mares are always on the hunt for ways to suppress undesirable estrus-related behaviors in these horses. While many methods exist, some are more effective, practical, and even safe than others. A researcher at the University of Massachusetts has devised a new drug-free approach for suppressing estrus in mares—one that could help manage performance mares and more.

Carlos Gradil, DVM, PhD, Dipl. ACT, professor in the school’s Department of Veterinary and Animal Sciences, in Amherst, and adjunct associate professor at Tufts University’s Cummings School of Veterinary Medicine, in North Grafton, described how to use the magnetic intrauterine device (IUD) and reported on its efficacy at the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.

Existing techniques for suppressing estrus in mares include administering progesterone or progestins (the estrous cycle’s dominant hormones), the hormone oxytocin, or a gonadotropin-releasing hormone vaccine (not approved for use in the United States); and inserting IUDs that mimic pregnancy. Historically, IUDs such as marbles have been problematic, causing inflammation and infection, breaking, adhering to the endometrium (the uterine lining), and being unintentionally left in the mare for years—all of which can compromise her fertility

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Alexandra Beckstett, a native of Houston, Texas, is a lifelong horse owner who has shown successfully on the national hunter/jumper circuit and dabbled in hunter breeding. After graduating from Duke University, she joined Blood-Horse Publications as assistant editor of its book division, Eclipse Press, before joining The Horse. She was the managing editor of The Horse for nearly 14 years and is now editorial director of EquiManagement and My New Horse, sister publications of The Horse.

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