When the Mood Strikes: Mare Behavior Studied
Mares have long carried a reputation for being more temperamental than geldings. Frequently, this perception is based on the estrous cycle. Is that fair, though? Do other influences, such as pain, training, or management, factor in?
To answer that question, a veterinarian at the University of Helsinki analyzed retrospective data from mares presented to a veterinary teaching hospital with estrus-related complaints. The goal was not only to better understand these cases but also to develop a diagnostic framework that could help clinicians determine the appropriate level of care.
Many horse owners attribute behavioral changes such as persistent or exaggerated estrous behavior, unexplained pain, poor performance, aggression, or recurrent colic to hormonal fluctuations. While reproductive disorders can influence a mare’s behavior, the researcher found that these assumptions often do not hold up under scrutiny.
The investigator reviewed medical records from 14,993 patients and focused on those specifically evaluated for estrus-related behavioral complaints. The medical records were then compared to the reported problems with physical examinations, stage of the estrous cycle, and final diagnoses.
One of the study’s most surprising findings was that behavioral problems, pain, and poor performance could not be consistently linked with estrus in any mare.
Even among mares presented for persistent or unusually strong estrous behavior, more than half (57%) were actually in diestrus, the stage of the reproductive cycle when mares are typically not in heat. This finding suggests that normal behavior may sometimes be misinterpreted as estrus-related.
The researchers also found that recurrent colic, nonspecific pain, and urinary tract-related signs were actually more common in geldings than in mares, further challenging the assumption that these problems are exclusive to cycling mares.
When underlying causes were identified, internal medicine disorders represented the most common diagnosis. Aggressive behavior, for example, was significantly associated with orthopedic disorders rather than reproductive disease.
Taken together, the findings emphasize the importance of avoiding premature conclusions when evaluating behavioral or performance problems in mares.
Instead of assuming hormones are responsible, the researcher recommended a systematic diagnostic approach that begins with a thorough reproductive examination but also considers other common causes of discomfort or behavioral change. Repeated reproductive exams, careful record-keeping throughout multiple estrous cycles, and appropriate orthopedic and internal medicine evaluations can help determine whether reproductive activity is truly contributing to a mare’s clinical signs.
The researcher also proposed a tiered diagnostic framework to help veterinarians prioritize testing while improving diagnostic accuracy and client compliance.
For horse owners, the message is straightforward: not every behavioral problem in a mare originates from the ovaries. Pain, musculoskeletal disease, and management factors should all be considered before attributing changes in behavior or performance solely to the estrous cycle.
*Kareskoski, A.M. 2026. Decoding moody mare syndrome: Retrospective study and tiered diagnostic framework. Journal of Equine Veterinary Science 160:105850.
