Almost every published sign that a mare is about to foal has a window measured in days or weeks. The birth itself takes 10 to 30 minutes. That mismatch is why owners lose sleep for a two weeks and then miss the actual event. Udder development starts two to six weeks before delivery, and teats wax within hours to a few days before foaling, per Merck Animal Health's broodmare labor guidance. Only one sign starts a clock you must act on: when the water breaks and second-stage labor begins, Merck's stated normal is 10 to 30 minutes to a delivered foal, and their instruction is to call your veterinarian immediately if 30 to 45 minutes pass without the foal being delivered. Everything before that is a probability. That is a timing, and it is the one to memorize.
This piece separates the two, sign by sign, with the published window attached to each.
The short version, in order
- Two to six weeks out: the udder starts filling (Merck Animal Health). Mammary development ramps up two to three weeks before foaling, per Dr. Ellerbrock in The Horse.
- Two to three weeks out: the muscles around the tail head relax, and a hollow appears on either side of the tail root (Ranvet). This is gradual and not visible on every mare.
- Hours to a few days out: teats wax, meaning small waxy yellowish beads of thickened colostrum form at the teat ends. Secretions turn opaque and sticky (Merck Animal Health).
- Roughly 24 to 48 hours out: milk chemistry shifts, which is what the calcium test kits measure. See the numbers below.
- 1 to 5 hours out: first-stage labor. Restlessness, mild contractions, colicky signs, tail switching, circling, sweating (Merck Animal Health).
- 10 to 30 minutes: second-stage labor, from the water breaking to a delivered foal (Merck Animal Health).
- Within 3 hours after: the placenta should be expelled (Merck Animal Health).
Signs a mare is about to foal: the window table nobody publishes
Here is every common sign with its published window, side by side. Read the right-hand column and the whole "is something wrong?" panic dissolves.
| Sign | Published window before foaling | Source |
|---|---|---|
| Udder fills | 2 to 6 weeks | Merck Animal Health |
| Mammary development accelerates | 2 to 3 weeks | Dr. Ellerbrock, via The Horse |
| Pelvic ligaments relax, hollow beside tail head | 2 to 3 weeks | Ranvet |
| Waxing | "hours to a few days" | Merck Animal Health |
| Waxing | typically 24 to 48 hours; about 90% foal in that window, but some mares wax for several days | Dr. Tibary, via The Horse |
| Waxing (wider reported range) | commonly 12 to 36 hours, occasionally up to a month out | Mad Barn |
| Milk calcium reaches 200 ppm | 50% foal within 24h, 85% within 48h, 95% within 72h | Dr. Tibary, via The Horse |
| Milk pH drops to 6.5 or lower | high likelihood within 24 hours | Dr. Tibary, via The Horse |
| First-stage labor | 1 to 5 hours | Merck Animal Health |
| Second-stage labor (water broken to foal out) | 10 to 30 minutes | Merck Animal Health |
Notice that the most-quoted sign, waxing, is the one where the sources disagree most. That is not sloppy sourcing. It is the actual biology: waxing is a genuine indicator with a genuinely wide spread, and any article that gives you a single confident number for it is hiding the spread from you.
"She waxed four days ago and nothing is happening"
This is the most common 3am search in the whole topic, so here is the direct answer.
Waxing four days ago and no foal is within the reported range. Dr. Tibary's figure in The Horse is that about 90% of mares foal within 24 to 48 hours of waxing, while explicitly acknowledging that some mares wax for several days. Mad Barn's coverage puts the outer end of the range at as much as a month, with up to two weeks more common than most owners expect. So a four-day gap does not by itself mean anything is wrong.
What would change that answer is anything abnormal alongside it: any discharge that is not the normal colostrum, premature udder development well ahead of the expected date, a mare who is unwell, or a mare with a history of placentitis. Dr. Tibary also notes that mares under stress or with placentitis do not give reliable test results, and that the response is more visual monitoring, not more testing. If any of that describes your mare, the answer is not "wait a bit longer," it is a call to your vet with the specifics.
The other honest reason nothing is happening: Merck notes most deliveries occur in the evening hours. Mares foal when the barn is quiet. A watched mare is a mare who waits.
The only clock that requires you to act
Everything above is prediction. This is the part that is not optional.
Second-stage labor begins when the membranes rupture and allantoic fluid passes. From that moment, Merck Animal Health's stated normal is 10 to 30 minutes to a delivered foal, and the foal should present with both forelimbs extended (one slightly ahead of the other) followed by the outstretched head, all inside the white amnion.
Merck lists four situations as immediate calls to your veterinarian:
- Labor exceeds 30 to 45 minutes without the foal delivered.
- The foal is in an abnormal position: only one forelimb showing, no head appearing, or hind limbs first.
- The placenta has not passed within three hours.
- A "red bag" delivery: a red chorioallantoic membrane presenting at the vulva instead of the white amnion.
Number four is the one where you cannot wait for the vet at all, because the foal has stopped receiving oxygen. We have set the sequence out separately in red bag delivery in horses, and it should be read before your mare is due, not on the night.
For the other three, the correct action is a phone call, made early rather than late. No vet has ever complained about a foaling call that turned out to be nothing. Plenty of foals have been lost to an owner deciding to give it another twenty minutes.
What the pre-foaling signs cannot tell you
They cannot tell you the night. They give you a probability distribution, not an appointment.
They also cannot distinguish first-stage labor from colic on their own, because the signs overlap almost completely: restlessness, sweating, flank-watching, kicking at the belly and getting up and down look the same either way. That is a genuinely dangerous ambiguity in a pregnant mare and it deserves its own treatment, which we have given it in pre-foaling restlessness or colic.
And they cannot substitute for having the kit and the plan ready two weeks before the earliest plausible date, because the signs will not give you two weeks of notice on the night. Our mare foaling kit checklist sorts what you actually use from what the vet uses.
The practical monitoring plan
- Know the breeding date and therefore the approximate due date. Average gestation is around 340 days, and The Horse notes mares may foal three weeks either side of that. Treat the average as the middle of a six-week window, not a date.
- Start checking the udder daily from about six weeks out. You are looking for change, not for a threshold.
- Start milk testing when the udder is clearly developing, and read the results as probabilities in the table above.
- Have your vet's after-hours number posted physically at the stall, and know your actual drive time from their clinic.
- When first-stage signs appear, note the time. Everything that follows is measured from it.
If you are earlier in this process than any of that, the decision piece is should you breed your mare.
FAQ
How long after waxing will a mare foal?
Most foal within 24 to 48 hours of waxing, with Dr. Tibary putting that figure at about 90% in The Horse, but some mares wax for several days and Mad Barn reports outliers up to a month out. Waxing narrows the window, it does not set a date.
What is the most reliable sign a mare will foal tonight?
Milk chemistry is the most quantified. Dr. Tibary's figures via The Horse: at 200 ppm mammary calcium there is a 50% chance of foaling within 24 hours, 85% within 48, and 95% within 72; a milk pH of 6.5 or lower indicates a high likelihood within 24 hours. None of that is a guarantee, and it is unreliable in stressed mares and mares with placentitis.
How long should foaling take once the water breaks?
Merck Animal Health gives second-stage labor as 10 to 30 minutes. Their instruction is to call your veterinarian immediately if 30 to 45 minutes pass without the foal being delivered.
My mare has been showing signs for two weeks. Is something wrong?
Not necessarily. Udder development starts two to six weeks out and pelvic relaxation two to three weeks out, so a two weeks of signs is normal. What is not normal is abnormal discharge, a mare who seems unwell, or premature udder development well before her date. Any of those is a call to your vet.
Should I be in the stall with her?
Merck notes most deliveries occur in the evening hours, and mares are widely observed to prefer quiet and privacy. Monitoring from a distance, by camera or a quiet check, disturbs her less than standing in the stall. What matters is that you see the transition into second-stage labor and can time it.
Sources: Merck Animal Health USA's broodmare labor guidance (stages, durations and the four immediate-call triggers); Dr. Ahmed Tibary and Dr. Sarah Ellerbrock via The Horse, "How to Predict Foaling" (milk calcium and pH figures, waxing timing); Ranvet (pelvic relaxation); Mad Barn (waxing range). Horsetin is written by a hobbyist owner and breeder, not a veterinarian. This page describes what to observe and when to call. It is not a manual for assisting a delivery, and nothing here replaces your own vet's instructions for your own mare.