Anyone who rides a mare knows the days when a different horse suddenly seems to be standing in the stall: more sensitive, distracted, sometimes downright irritable. Usually that's a mare in heat (estrus) — a normal part of the cycle, not a problem to be fixed. Still, it's worth knowing what belongs to it and what doesn't: normal in-heat behavior mostly calls for understanding and planning, while extreme or painful behavior is a reason to call the vet. This guide lays out both sides.
What Being in Heat Means
Being in heat (estrus) is the fertile phase of the mare's cycle: the days when she's receptive to a stallion. The cycle is seasonal — mares cycle roughly through spring and summer, when the days are long, and many mares stop cycling during the winter months. As a rule of thumb, a full cycle lasts about three weeks, of which the mare is in heat for a few days. How long and how pronounced it is varies by mare and by point in the season: around the start and end of the cycling season, cycles are often more irregular and behavior more erratic.
Important to keep in mind: these are rules of thumb, not a timetable. One mare will barely show you anything, another is clearly dealing with it for a few days every three weeks. Both are normal.
Normal In-Heat Behavior
Being in heat shows up differently in each mare, but the recognizable list looks like this:
- Different social behavior — more affectionate and contact-seeking, or conversely more irritable toward people and stablemates.
- Tail raising and more frequent urination — often in small amounts, especially around other horses.
- Sensitive flanks and belly — grooming or girthing can produce more reaction on those days than usual.
- Distraction — more attention to other horses, less to the rider.
This behavior comes and goes with the cycle: it's there for a few days, and then the mare is herself again. That pattern — behavior that follows the rhythm of the cycle — is exactly what makes it normal.
Riding and Competing While a Mare Is in Heat
Most mares are perfectly rideable during their in-heat days, but concentration and sensitivity can be noticeably different. Exercises that require sharpness are harder to achieve, and aids that are otherwise neutral — a leg against a sensitive flank — can trigger a bigger reaction. Take that seriously without making a drama of it: ask for slightly less precision, choose work that does succeed on those days, and save the heavy training sessions for the week after if needed.
This is where a training log proves its worth. Anyone who tracks a few months' worth of off days often sees a pattern of roughly three weeks — and can plan around it. For competition riders, that's especially relevant: scheduling an important start outside the expected in-heat days saves frustration for both rider and horse. The log offers no guarantees, since cycles shift, but recognizing a pattern is already half the battle.
When It's More Than Just Being in Heat
Normal in-heat behavior is mild, predictable, and temporary. There's reason to look further when it falls outside that:
- Extreme behavior — the mare is unmanageable or unrideable during her heat, or the behavior gets more intense every cycle.
- Signs of pain — dipping away from the back, kicking at the belly, sharp resistance to touch on the flanks or girth.
- Behavior that doesn't fit the cycle — irritability or heat-like behavior that persists for weeks, including outside the season, or a mare whose temperament suddenly seems to change permanently.
In those cases, the vet is the right first step, not a different training approach. Extreme or atypical behavior can have a physical cause; the vet can, among other things, examine the ovaries and assess whether the behavior is really tied to the cycle at all. The general guidance on when to call and when it can wait is covered in when to call the vet — for behavioral change that persists, the rule is: call sooner rather than waiting.
Managing It or Accepting It
For mares whose in-heat behavior genuinely gets in the way of riding or welfare, there are options through the vet to hormonally support or suppress the cycle. That's a medical choice with pros and cons, made together with the vet based on examination — not something to arrange yourself based on a story from the stable. Also be cautious with supplements that promise calm or balance: the evidence for them is thin, and they can mask a real underlying cause.
For most mares, the healthiest approach is simply accepting that the cycle comes with the territory. Being in heat is normal behavior in a healthy horse, not a disorder. A few off days every three weeks are easily managed with some planning — and a mare who feels understood on those days is often a great partner the rest of the month. Keep the basics in order too: a mare who's in good shape in terms of weight and condition, gets enough turnout, and has social contact copes better with the fluctuations.
Misconceptions
Two stubborn ideas deserve a correction. The first: "she's just being difficult, that's her personality." Mares have a reputation for being strong-willed, but behavior that moves with the cycle is physiology, not a character flaw — and behavior that does not move with the cycle deserves investigation rather than a label.
The second misconception is the mirror image: using being in heat as an excuse for every training problem. A mare who consistently struggles with an exercise also struggles with it outside her in-heat days. Anyone who blames every bit of resistance on the cycle skips the real analysis — is it the riding technique, physical development, the saddle, the structure of the training? The log helps here too: it shows which problems track with the cycle and which stand apart from it.
In Short
- Being in heat is the fertile phase of the cycle: seasonal (roughly spring and summer), as a rule of thumb a cycle of about three weeks with a few days in heat.
- Normal behavior: more affectionate or irritable, tail raising, more frequent urination, sensitive flanks — it comes and goes with the cycle.
- Schedule heavy training and important competitions around the off days where possible; a training log makes the pattern visible.
- Extreme or painful in-heat behavior, or behavioral change that doesn't fit the cycle, is a reason to call the vet — who can, among other things, examine the ovaries.
- Hormonal support is available through the vet, but for most mares, acceptance is the healthiest route.
- Being in heat is neither a character flaw nor an excuse: persistent training problems deserve their own analysis.
See also: When to Call the Vet · Keeping a Horse Training Log · Assessing Your Horse's Weight and Condition · Jargon: vet / veterinarian · Level: Considering Your Own Horse