What you see. The starting point for addressing any equine health related issue is your observation.


Estrus or Heat Behavior in Mare Interferes with Work


Mares experience estrus cycles between April through September (Northern Hemisphere), although this season may begin earlier or end later depending on where the mare lives. During breeding season, mares experience a heat cycle once every 18-23 days and will "show heat" on average of 5 days during each cycle.

Signs that a mare is showing heat include irritability, lack of focus, reluctance to work, sensitivity to touch, aggression (kicking and biting), elevating the tail and opening and closing the vulvar lips ("winking"), and/or excessive squatting and urination. Hormonal changes and pain (from ovulation) may be involved in causing these behavioral changes.

Individual mares are very different. Some show radical changes in mood and performance, while others are even tempered regardless of their cycle.

  • Code Orange

    Call Your Vet at Their First Available Office Hours
    • If this problem seems severe and has come on suddenly.
  • Code Yellow

    Contact Your Vet at Your Convenience for an Appointment
    • If this seems mild or occasional and the horse seems normal otherwise.
You also might be observing
Very Common
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your role


What To Do

Ideally, mares respect their handlers enough so that they are respectful and attentive, regardless of hormonal influence. Good, consistent and firm horsemanship goes a long way toward dealing with this problem. So this is always something to consider. If you are having difficulty, it might be wise to engage a trainer who knows how to help.

That said, some mares benefit from hormonal therapy, and occasionally, hormonal behavior can indicate serious ovarian abnormalities like hormonally active tumors.

Perform the Whole Horse Exam, paying particular attention to attitude, appetite, any vulvar discharge or changes in appearance of udder. Keep track of the mare's behavior on the calendar and consider seasonal variations in behavior. The timing of behavioral changes is helpful information for your vet.

your vet's role

There are veterinary treatments that can help manage the hormonal changes that affect behavior, including heat suppression. Generally, vets want to evaluate a mare's reproductive health before suppressing estrus with drugs and hormones. This might involve rectal palpation, ultrasound or more rarely hormonal profiles. In some cases, they may choose to perform a trial of a hormone that suppresses heat (oral progestin) to see how much difference it makes to the behavior. If it is very helpful, long term management options can be discussed.
Questions Your Vet Might Ask:
  • Do you see a pattern to the changes in behavior?
  • Can you identify when your mare is in heat versus not?
  • What are the specific behaviors the mare is showing?
  • Do you notice moodiness of your mare during the winter also?
  • What are the results of the Whole Horse Exam (WHE)?
  • Have you tried any treatments?

Author: Doug Thal DVM Dipl. ABVP