A mare in heat typically winks (rhythmic opening and closing of the vulva), squats, raises her tail, urinates frequently in small amounts, and shows interest rather than hostility toward a stallion. Extension Horses lists the positive teasing response as "obvious interest in the stallion, vulval winking, squatting, tail raising and urination," and the negative response as "kicking, biting, striking, laying the ear back and an overall hostile attitude toward the stallion." Behavioral estrus lasts 2 to 8 days inside a roughly 21-day cycle, per the Merck Veterinary Manual.
Here is the part that decides whether you can trust any of that: behavior and ovarian activity do not always agree, and they disagree in both directions. Some mares are cycling and show nothing. Others show everything and are not in estrus at all. If a breeding decision or a stallion booking depends on the answer, the answer comes from your vet's palpation and ultrasound, not from your eyes.
How to tell if a mare is in heat: the signs, ranked by weight
| Sign | What it means | How much weight to give it |
|---|---|---|
| Winking at the vulva | Extension Horses lists vulval winking as a core positive teasing response, and it is described as almost always associated with estrus | High, especially with squatting and urination together |
| Squatting and tail raising | Classic estrus posture in response to a stallion | High, in a teasing context |
| Frequent small urinations | Commonly reported alongside winking | Moderate to high in combination |
| Leaning toward or approaching a stallion | Extension Horses: "obvious interest in the stallion" | High, but requires a stallion or teaser to observe |
| Increased vocalizing | Reported in mares in season | Low on its own |
| Restlessness, pacing, general anxiety | Reported in mares in season | Low on its own, since a dozen other things cause it |
| Sensitivity to brushing around belly and flanks | Reported in mares in season | Low on its own |
| Kicking, biting, striking, ears back at a stallion | Extension Horses lists this as the diestrus (not in heat) response | High, as a negative |
The pattern in that table is the useful bit: the signs that carry real weight are the ones that appear in response to a stallion or teaser. The signs owners most often try to read from a mare standing alone in a field (moodiness, sensitivity, restlessness) are the weakest evidence available, and the reason people spend a whole season unsure.
The four cases, because behavior and ovaries do not always agree
This is the thing the "12 signs your mare is in heat" articles leave out, and it comes straight from primary sources.
| Actually in estrus | Not in estrus | |
|---|---|---|
| Shows heat signs | The straightforward case | False heat. Extension Horses notes maiden mares and transported mares "will frequently show signs of heat when they are actually not in estrus" |
| Shows no heat signs | Silent heat. Merck notes some mares with foals at side may not exhibit estrous behavior despite follicular development, and that nervousness or inexperience can mask receptivity even with a dominant follicle present | The straightforward case |
Two of those four boxes are wrong answers you can reach by careful observation. That is not a failure of your stockmanship. It is a documented property of the species.
Merck states the standard directly: "The mare's behavior when teased should be consistent with the findings on examination of the genital tract." The word doing the work is should. When it is not consistent, the genital tract is the fact and the behavior is the opinion.
Extension Horses also flags lactating mares, aged mares, mares on steroids, and mares in extreme weather as needing special attention for exactly this reason.
Silent heat, specifically
"Silent heat" means the mare is cycling and ovulating without displaying the behavioral signs. It is not a disorder in itself and it is not rare enough to ignore.
The populations most associated with it in the sources above are mares with a foal at side (whose maternal behavior overrides receptivity), nervous or inexperienced maiden mares, and aged mares. A mare who has been moved recently, or who is at the bottom of a herd hierarchy and unwilling to display in company, may also show nothing useful.
The resolution is not a better observation technique. It is a transrectal palpation and ultrasound examination of the ovaries by your veterinarian, which shows follicular development directly. Merck notes that one follicle usually becomes dominant and ovulates at 30 mm or larger in diameter. No amount of watching from the gate gives you that number.
Teasing, and the score that actually triggers a vet visit
If you are breeding, teasing is the practical system, and it comes with a published scoring scale. Extension Horses describes a five-point scale running from score 1 (obvious hostility toward the stallion) to score 5 (strong interest with frequent urination, winking and squatting). Their operational rule is the useful part: mares receiving a teasing score of three or more are checked by rectal palpation or ultrasound.
That is a workable decision rule for a small breeding operation. Tease, score, and let the score decide when you pay for a vet exam rather than guessing.
On frequency: mares are ideally teased daily, and Extension Horses notes they can be carefully teased every other day and still provide adequate information for breeding. The teasing systems they describe range from pasture teasing (low labor, real safety concerns) through pen, paddock, stall-door and rail teasing to teasing chutes and mills. For most owners with one or two mares, a safe barrier between mare and teaser is the whole design question, and a kicking mare over a bad fence is how people get hurt.
The sobering number from the same source, and the reason this is worth doing properly: only about one half of all mares bred will become pregnant and foal the next year. That statistic is also why the per-cycle costs in our cost of breeding a horse breakdown matter so much. Missed heats cost cycles, and cycles cost money.
Is she cycling at all? The seasonal answer
Before concluding a mare is silent, check the calendar. Mares are seasonally polyestrous and cycle when daylight is long, per Merck, going into anestrus over winter. Oklahoma State University Extension puts the normal cycling period at approximately March through September.
The transition into the season is its own trap. Merck describes vernal transition as involving 3 or 4 prolonged intervals of estrus lasting 7 to 14 days each, during which ovulation does not occur. A mare in transition can therefore look flamboyantly in heat for two solid weeks and be nowhere near ovulating. If your mare seems to have been in heat forever in early spring, that is very likely what you are watching, and it is normal.
We have set out how to record all of this across a season in tracking a mare's heat cycle.
The honest limits of this page
You cannot confirm ovulation by watching a mare. You cannot rule out estrus by watching a mare who has no reason to display. And you should not use behavior alone to book a stallion, because a wasted cycle costs collection, shipping and veterinary management again.
Horsetin is written by a hobbyist owner and breeder, not a veterinarian. What is on this page is observation and record-keeping. Anything involving hormones to bring a mare into or out of season is a prescription conversation with your vet, and we do not cover protocols or products here.
If you are earlier in the process, the decision piece is should you breed your mare, and if you are simply trying to work out what is normal for a horse you have just brought home, start with the first two weeks with a new horse.
FAQ
What are the clearest signs a mare is in heat?
Winking at the vulva, squatting, raising the tail, frequent small urinations, and obvious interest rather than hostility toward a stallion. Extension Horses lists those as the positive teasing response, and lists kicking, biting, striking and ears back as the not-in-heat response.
How long is a mare in heat, and how often?
The Merck Veterinary Manual gives behavioral estrus as 2 to 8 days inside a regular 21-day interovulatory cycle, with estrus longer early in the season and as short as 2 to 3 days around the summer solstice.
My mare shows no signs at all. Is she cycling?
Possibly, and this is common enough to have a name: silent heat. Merck notes mares with foals at side may not show estrous behavior despite follicular development, and that nervousness or inexperience can mask receptivity even with a dominant follicle. A veterinary palpation and ultrasound is the only way to know.
Can a mare show heat signs and not be in heat?
Yes. Extension Horses notes that maiden mares and transported mares will frequently show signs of heat when they are not actually in estrus. This is why teasing scores trigger a veterinary check rather than a breeding decision.
She has been in heat for two weeks. Is that normal?
In early spring, very likely yes. Merck describes vernal transition as 3 or 4 prolonged estrus intervals of 7 to 14 days each during which ovulation does not occur. Mention it to your vet, but a long early-season heat is a documented normal.
Sources: Extension Horses, "Heat Detection and Teasing Systems for Mares" (teasing responses, the five-point scale, the score-of-three rule, teasing frequency, false heat in maiden and transported mares, and the roughly one-in-two figure for mares bred that foal the next year); Merck Veterinary Manual, "The Reproductive Cycle of Horses" (21-day cycle, 2 to 8 day estrus, vernal transition, dominant follicle at 30 mm or larger, and behavior versus genital tract findings); Oklahoma State University Extension (approximate March to September cycling period). Horsetin is written by a hobbyist owner and breeder, not a veterinarian. No hormone protocol or product is described here; that is your vet's territory.