Mare in Heat Behavior: Signs, Mood Changes, and When It’s a Problem

Introduction

A mare in heat, also called estrus, may act noticeably different for a few days. Many mares become more interested in other horses, especially stallions or geldings, and may raise the tail, squat, urinate more often in social situations, or "wink" the vulva. Others seem clingy, distracted, sensitive around the flanks, or less willing to work. During the breeding season, mares typically cycle about every 21 days, with estrus lasting roughly 2 to 8 days.

Not every behavior change is caused by hormones alone. Some mares show only subtle signs, while others become irritable, squealy, kicky toward other horses, or uncomfortable under saddle. Seasonal transition in spring can also make behavior look erratic because mares may show heat-like signs before they settle into regular ovulatory cycles.

What matters most is the pattern. Mild, predictable changes that come and go with the cycle are often normal. But sudden aggression, persistent pain, marked performance decline, continuous heat behavior, or stallion-like behavior can point to a medical issue such as ovarian disease, urinary or reproductive tract discomfort, back pain, or ulcers. If your mare's behavior is intense, new, or unsafe, your vet can help sort out whether this is normal cycling or a problem worth working up.

What normal heat behavior looks like

Normal estrus behavior is mostly about receptivity. A mare may lift the tail, squat, urinate in small amounts when near other horses, and evert the vulvar lips. Some become more social, more distractible, or more sensitive to touch around the hindquarters and belly.

Under saddle, normal heat can look like mild crankiness, reduced focus, tail swishing, or reluctance with leg pressure. These signs should still be intermittent and manageable, not severe enough to make the mare dangerous or miserable.

Mood changes pet parents and riders often notice

Common mood changes include irritability, squealing, pinned ears toward nearby horses, clinginess, restlessness, and a shorter attention span. Some mares seem uncomfortable during grooming, saddling, or collection work. Others barely change at all.

A useful clue is timing. If the same behavior appears for a few days, improves, and then returns about three weeks later during the breeding season, hormones may be part of the picture. Keeping a calendar of behavior, riding quality, and any physical signs can help your vet see the pattern.

When heat behavior may be a problem

Call your vet if your mare has continuous or unusually prolonged heat behavior, seems painful, becomes newly aggressive, loses weight, develops vaginal discharge, or shows a major drop in performance. Behavior that is blamed on being "mareish" can sometimes be linked to back pain, gastric ulcers, lameness, urinary discomfort, or reproductive disease.

One important reproductive cause is a granulosa-theca cell tumor, the most common ovarian tumor in mares. These mares may show persistent estrus, stop cycling, or even develop stallion-like behavior. Your vet may recommend a reproductive exam, ultrasound, and hormone testing if the history fits.

How your vet may evaluate the issue

A workup often starts with a history and physical exam, followed by a reproductive exam if needed. Depending on the mare, your vet may suggest transrectal palpation and ultrasound of the ovaries and uterus, vaginal or speculum exam, and blood tests such as anti-Müllerian hormone, inhibin, or testosterone when an ovarian tumor is a concern.

Typical US cost ranges in 2025-2026 vary by region and whether the visit is farm-based or hospital-based. A focused exam for behavior concerns may run about $150-$350, a reproductive ultrasound exam about $80-$250 per visit, and ovarian hormone testing roughly $70-$250 for the lab fee alone, with total visit costs often higher once collection, farm call, and interpretation are added.

Management options your vet may discuss

There is no single right answer for every mare. Some do well with management changes alone, such as tracking the cycle, adjusting training on harder days, reducing social stress, and checking saddle fit or pain triggers. Others benefit from a broader pain and performance workup.

For mares whose estrus behavior clearly affects comfort or performance, your vet may discuss hormonal management options. Merck notes that altrenogest can suppress estrous behavior in mares, but it should only be used under veterinary guidance because the right plan depends on the mare's breeding status, health history, handling safety, and goals.

Questions to Ask Your Vet

Bring these questions to your vet appointment to get the most out of your visit.

  1. Does this pattern sound like normal estrus, spring transition, pain, or something else?
  2. What signs make you worry about an ovarian problem such as a granulosa-theca cell tumor?
  3. Would a reproductive exam and ultrasound help in my mare's case?
  4. Are there non-reproductive causes, like ulcers, back pain, or lameness, that could be driving this behavior?
  5. Should I keep a cycle and behavior log, and what details would be most useful?
  6. What conservative, standard, and advanced management options fit my mare's job and temperament?
  7. If hormonal management is an option, what are the benefits, risks, handling precautions, and expected cost range?
  8. At what point would you recommend referral to an equine reproduction or surgery service?
Find a Vet Near You