Tracking a mare's cycle means recording one row per day, per mare, from the start of the season to the end, with four things on it: the date, her teasing score, anything you observed without a teaser, and any veterinary finding. The point is not the chart. The point is that a teasing score of three or more is the published trigger for a veterinary palpation or ultrasound, per Extension Horses, and a chart is what tells you that today's three is the third day of a rising pattern rather than a one-off. The Merck Veterinary Manual gives the underlying rhythm as a regular 21-day interovulatory cycle with 2 to 8 days of behavioral estrus. Your record is what turns that average into your mare's actual calendar.
This piece covers what to record, how a season actually behaves month by month, and the moment the record becomes a booking decision.
Mare heat cycle tracking: the four columns, and why each exists
| Column | What goes in it | Why it earns its place |
|---|---|---|
| Date | Every day, including the days nothing happened | Blank days are data. A gap in the record is not the same as a recorded zero, and only one of those lets you count an interval |
| Teasing score | The published 1 to 5 scale (Extension Horses), or the simpler 0 to 4 scale used by breeding operations such as Iron Spring Farm | Turns a subjective impression into a number you can compare across days. Score 1 is obvious hostility, score 5 is strong interest with frequent urination, winking and squatting |
| Observed without a teaser | Winking, squatting, urinating in small amounts, restlessness, tail carriage, behavior under saddle | The weakest evidence, but free, and it is all you have on days you cannot tease |
| Veterinary findings | Follicle size and side, uterine edema, ovulation confirmed, anything your vet tells you on the day | The only column that contains facts rather than inferences. Merck notes the dominant follicle usually ovulates at 30 mm or larger |
Add two more if you are breeding: a notes column for anything unusual (weather, transport, a new horse in the field, illness), and the date the stallion or shipment was booked. Extension Horses flags lactating mares, aged mares, mares on steroids, transported mares and mares in extreme weather as ones whose behavior needs special interpretation, and you will not remember three months later that she was hauled the week her scores went strange.
How often to record, and how often to tease
Every day for the observation column. It costs nothing and takes thirty seconds.
For teasing, Extension Horses says mares are ideally teased daily and can be carefully teased every other day while still providing adequate information for breeding. Their operational rule is the one to build the chart around: mares scoring three or more are checked by rectal palpation or ultrasound.
That rule is worth restating as a workflow, because it is the whole reason to keep the chart at all:
- Tease and score daily, or every other day.
- When a score hits 3 or more, call the vet for an exam.
- Record what the exam found on that same row.
- Use the confirmed ovulation date as the anchor for counting the next cycle.
Merck notes that if pregnancy is not established, luteolysis occurs at 14 days post-ovulation. So a confirmed ovulation is not just a breeding date, it is the reference point that lets you predict the next heat instead of waiting to be surprised by it.
What a whole season actually looks like
This is the part the chart explainers skip. The 21-day cycle is not 21 days all year.
Winter (short daylight). Mares are seasonally polyestrous and cycle when daylight is long, per Merck. Over winter most are in anestrus. Records here are near-empty and that is correct.
Vernal transition (roughly February to April). This is where owners lose their minds. Merck describes transition as involving 3 or 4 prolonged intervals of estrus lasting 7 to 14 days each, during which ovulation does not occur. A mare can therefore score 4s and 5s for two straight weeks and be nowhere near a useful breeding. If your chart in March shows a heat that will not end, that is very probably transition and it is normal. It is also the single most common reason a first shipment of semen gets wasted.
Established season (roughly late April or early May through August, with the normal cycling period often given as March through September by Oklahoma State University Extension). Now the 21-day interovulatory cycle is regular. Estrus runs 2 to 8 days per Merck, longer early in the season and as short as 2 to 3 days around the summer solstice. Ovulation typically occurs 24 to 48 hours before the end of behavioral estrus, which is why the last day of a heat is a bad day to be starting to organize anything.
End of season. Daylight shortens, cycles become irregular again, and mares return to anestrus.
Two practical consequences fall straight out of that. First, a long heat in March means something different from a long heat in June, so date every row and never analyze the record without the month in front of you. Second, the shortening estrus around midsummer means the window for getting shipped semen to arrive at the right moment is narrower in July than in May.
Turning the chart into a booking decision
The chart's job is to answer one question: when do I commit money?
The costs that repeat every cycle are the ones the record protects you from repeating. Collection, shipping, insemination and veterinary breeding management are all per attempt, and we set the published ranges out in the real cost of breeding a horse. Extension Horses also reports that only about one half of all mares bred will become pregnant and foal the next year, which is the honest backdrop to every booking decision you will make.
A record that supports a booking looks like this:
- At least one confirmed ovulation date from your vet, so you have a real anchor rather than an assumed one.
- Two or three cycles of scores showing the shape of her heat: how many days it runs, whether it builds or starts strong, whether she is a reliable shower at all.
- The month, because of everything in the section above.
- Any noted disruption (transport, illness, weather, a foal at side) that might have distorted the pattern.
If your chart has none of that yet, the correct move is to spend a season building it before you commit to a stallion, not to book on hope. That is a genuinely unpopular recommendation and it is the cheapest one on this page.
When the chart contradicts itself
It will. Merck's standard is that "the mare's behavior when teased should be consistent with the findings on examination of the genital tract," and it also notes the cases where it is not: mares with foals at side may not show estrous behavior despite follicular development, and nervousness or inexperience can mask receptivity even with a dominant follicle present. Extension Horses notes the reverse, that maiden and transported mares frequently show heat signs when they are not in estrus.
So when the columns disagree, the veterinary column wins. The behavior columns are a scheduling tool for deciding when to pay for the veterinary column, not an alternative to it. We covered the four ways behavior and ovaries can disagree, including silent heat, in how to tell if a mare is in heat.
What tracking cannot do
It cannot make a mare cycle, and nothing on this site will tell you how to. Hormonal manipulation of the estrous cycle is a prescription matter for your veterinarian, and Horsetin is written by a hobbyist owner and breeder, not a vet.
It also cannot tell you whether to breed at all. That decision comes first and it is a different set of questions, covered in should you breed your mare. And if the season goes to plan, the record does not stop at conception: the breeding date is what gives you a due date, and the due date is what makes the signs your mare is about to foal readable eleven months later.
FAQ
How long is a mare's heat cycle?
The Merck Veterinary Manual gives a regular 21-day interovulatory cycle once the season is established, with behavioral estrus lasting 2 to 8 days, longer early in the season and as short as 2 to 3 days around the summer solstice. Other published sources describe it as roughly 22 days with 5 to 7 days of estrus.
What should I record when tracking a mare's cycle?
Date, teasing score, anything observed without a teaser, and any veterinary findings, with a notes column for disruptions like transport, illness or weather. Record every day, including days with nothing to report, because blank days and recorded zeros are not the same thing.
What teasing score means I should call the vet?
Extension Horses uses a 1 to 5 scale and checks mares scoring three or more by rectal palpation or ultrasound. Some operations use a simpler 0 to 4 scale. Either way, the score is a trigger for an exam, not a breeding decision on its own.
Why does my mare seem to be in heat for weeks in early spring?
That is very likely vernal transition. Merck describes 3 or 4 prolonged estrus intervals of 7 to 14 days each during that period, in which ovulation does not occur. It is normal, and it is why breeding on the first apparent heat of the year often wastes a shipment.
How do I know when to book the stallion?
When you have at least one veterinarian-confirmed ovulation as an anchor, two or three cycles of scores showing the shape of her heat, and no unexplained disruption in the record. Ovulation typically occurs 24 to 48 hours before the end of behavioral estrus, so the timing conversation belongs with your vet, working from your chart.
Sources: Merck Veterinary Manual, "The Reproductive Cycle of Horses" (21-day cycle, 2 to 8 day estrus, vernal transition, 30 mm dominant follicle, luteolysis at 14 days post-ovulation, behavior versus genital tract findings); Extension Horses, "Heat Detection and Teasing Systems for Mares" (five-point teasing scale, score-of-three rule, teasing frequency, mares needing special interpretation, and the roughly one-in-two figure for mares bred that foal the next year); Oklahoma State University Extension (approximate March to September cycling period and ovulation 24 to 48 hours before the end of estrus); Iron Spring Farm (0 to 4 practical grading scale). Horsetin is written by a hobbyist owner and breeder, not a veterinarian. No hormone protocol is described here.