Do hormones cause mares to misbehave?

Researchers found no connection between abnormal behavior in mares and increased ovarian hormones.

A new study from the University of California, Davis, challenges the common assumption that misbehavior in mares is often linked to “elevated ovarian hormones.”

Case histories

The California researchers reviewed 2,914 hormonal profiles of mares referred to the UC Davis Clinical Endocrinology Laboratory and the Equine Reproduction Service with case histories that contained the terms “behave,” “behavior” or “behaving.” They then analyzed the data for any association between reported abnormal behaviors and concentrations of testosterone and other hormones produced by the ovaries.

Hormones and misbehavior

The researchers found that abnormal behaviors (misbehavior) were associated with elevated hormone concentrations in less than 10 percent of the study samples. They report that only stallion-like behavior was correlated to elevated hormone levels. That behavior was defined as vocalizations, biting and/or mounting other horses. In contrast, simple aggression and other abnormal behaviors were significantly less likely to be associated with elevated hormone levels.

Abnormal behaviors were associated with elevated hormone concentrations in less than 10 percent of the mares in a recent study.

Mare behavior: It’s complicated

Ultimately, say the researchers, “These results highlight the assumption about the involvement of ovarian hormones in ‘abnormal behaviors’ of mares.” But, they conclude, “abnormal behaviors among mares… were not associated with increased ovarian hormones.”

Reference: “Abnormal mare behavior Is not often associated with changes in hormonal markers of granulosa cell tumors: A retrospective study.” 68th Annual American Association of Equine Practitioners Convention Proceedings, November 2022

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