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


Persistent or Irregular Heat Behavior in Mare


In the northern Hemisphere, most mares experience estrus cycles between April and October. In the southern hemisphere, between October and April. This season may begin earlier or end later depending on where the mare lives. During breeding season, average mares experience a 21 day heat cycle, with 15 days out of heat and 6 days in heat.

Signs that a mare is showing heat can include irritability, lack of focus, reluctance to work, sensitivity to touch, aggressive (kicking and biting), elevating the tail and opening and closing the vulvar lips (winking), and/or excessive squatting and urination. This is usually accentuated when mares are around stallions and some geldings.

Hormonal changes are believed to cause these behavioral changes. Discomfort from ovulation may also affect behavior at the end of estrus. Abnormal and irregular heat cycles or heat-related behavior can arise from a variety of problems, including ovarian abnormalities and uterine infections.

  • Code Orange

    Call Your Vet at Their First Available Office Hours
    • If the behavior seems extreme, or the horse seems to be in distress.
  • Code Yellow

    Contact Your Vet at Your Convenience for an Appointment
    • If you want to rule out any physical issue being a factor in the behavior.
    • You are interested in pursuing treatment for the behavior.

your role


What To Do

Try to track and record the frequency and duration of the abnormal behavior, and share this information with your vet.

What Not To Do

Do not ignore this behavior because it could indicate conditions that, if left untreated, can cause chronic infertility.

your vet's role

Since perceived abnormal behavior does not always coincide with a real heat cycle, your vet will need to perform a thorough exam to determine the underlying cause. This exam typically includes evaluation of the reproductive tract, and potentially hormone profiles.

Managing this problem may be very important to the mare's future fertility and use as a riding horse.
Questions Your Vet Might Ask:
  • When did you first notice this?
  • What is the mare's reproductive history?
  • Do you see a pattern to the changes in behavior?
  • What is the horse's age, sex, breed and history?
  • Have you noticed vaginal discharge?
  • Are you interested in breeding the mare in the future?
  • What are the results of the Whole Horse Exam (WHE)?

Diagnoses Your Vet May Consider

The cause of the problem. These are conditions or ailments that are the cause of the observations you make.

Very Common
Less Common
more diagnoses

Author: Doug Thal DVM Dipl. ABVP