Interpreting Endocrine Diagnostics for Subfertile Mares

Hormone concentrations can help diagnose reproductive problems, determine pregnancy status, and more.

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Researchers are always looking for new ways to detect failed pregnancies, reproductive problems, or pregnancy loss in mares. Some of those indicators are tiny little molecules that we know better as hormones.

At the 2016 American Association of Equine Practitioners Convention, held Dec. 3-7 in Orlando, Florida, Alejandro Esteller-Vico, PhD, of the University of Kentucky Gluck Equine Research Center’s Equine Reproduction Laboratory, reviewed how veterinarians can use basic endocrine (hormone) tests to diagnose reproductive problems in mares. He discussed three useful hormones and groups of hormones: anti-Mullerian hormone, estrogen, and progestogens.

Anti-Mullerian Hormone (AMH)

Granulosa cells in ovarian follicles produce AMH, a measure of reproductive aging and an indication of the number of viable follicles a mare has in reserve. This hormone is also a marker for granulosa cell tumors (ovarian tumors), which could impair reproduction. Very low AMH concentrations could mean that a mare does not have many, if any, viable follicles left.


Estrogens are a group of hormones—the primary female sex hormones—synthesized by the ovary and placenta that serve as biomarkers for pregnancies. One form of estrogen—estrone sulfate (ES)—begins to increase around Days 35-40 of gestation and is a good indicator of pregnancy status, Esteller-Vico said. He cautioned that ES concentrations tend to be higher in Miniature Horses than in their larger counterparts; pregnancy might not be detectable by measuring ES until approximately 80 days of gestation in Minis. Other estrogens, such estradiol or estradiol sulfate, can be used during late gestation as biomarkers for placentitis (infection of the placenta), he added

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Written by:

Nettie Liburt, MS, PhD, PAS, is an equine nutritionist based on Long Island, New York. She is a graduate of Rutgers University, where she studied equine exercise physiology and nutrition. Liburt is a member of the Equine Science Society.

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