Horse Side Vet Guide ®

Equine Health Resource

Hormone Influenced Performance Problem (in Mare)

Hormonal changes in mare can cause changes in behavior. This is a primary reason for people to prefer geldings. Some mares show more changes than others while in estrus.

Be aware of mare’s cycles when interpreting their behavior. Mares are on a 21 day cycle during the breeding season, 7 days of which are “in heat” and 14 days of which are “out of heat”.

During the winter (November through March for horses in northern hemisphere), most mares are not cycling and so should not show estrus behavior.

Prognosis & Relevant Factors

Most mares can be "trained through" their hormonal issues with clear and firm communication. For those in which hormonal cycles are interfering, there are medical treatments that may help. Discuss those treatment possibilities with your vet.


Good training and handling techniques solve many of these problems. For the rest of them, estrus suppression using medications may be needed.
Author: Doug Thal DVM Dipl. ABVP


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