When is my mare going to foal?

Foaling season every year makes us second guess our ability to predict foaling, experienced breeder or newbie is always a bit of a guessing game with mares as to when they will foal. But while I can’t give you a 100% guarantee of predicting exactly when your mare will foal I will share here some tested methods for narrowing your guesses.

As usual: for those that want Cole’s note version of the longer article:

  • Mares have no due date- The AVERAGE gestation duration is between 320-350 days with an absolute average between 340-345 days.
  • There is no ONE clear signal that tells you that your mare is about to foal: it is rather a combination of clues and the progression over time that is key.
  • Milk testing will save you a lot of sleep.
  • Mares are sneaky by nature and technology can be your best ally in outsmarting millions of years of evolution.

The so-called due-date

If you are new to horses it is normal to think that a due date is a thing. After all, for humans being born too early or too late by even a week can mean that something is wrong. A lot of other mammals have the same narrow window of when they will deliver ( dogs, cats, goats, sheep, cows). Mares DO NOT have a due date.

Again for those in the back: MARES DO NOT HAVE A DUE DATE.

There is a wide range of when a mare can foal and everything be ok. In fact, for the most part, mares CAN foal too early but rarely can they go too long.

Let this statistic convince you:

Result of a survey done by equine-reproduction.com

So if you know when your mare was bred then you can set aside a period centred around the 340 days of gestation but be ready to adapt. If you can’t be available for that period it’s best to enlist some help or accept that you might not be there.

*For a variety of reasons it is strongly recommended that you attend the birth, but if you are here, reading this blog, I can assume you already know that!

The most obvious: the udder.

Signs that things are progressing normally:

The fleshiness of your mare’s udder will increase- gradually- over time.

If your mare is a maiden, you will start to see some slight definition to her udder, it’s like the skin is getting thicker in a way (its not, it just looks that way). That is simply the udder starting to awaken and get ready for milk production.  At this point if you can feel the udder it is flacid, easily manipulated but there is a crease between the two side. This is a good time to maybe start cleaning it regularly as that crease will be trapping dust and normal skin grease (aka smegma).  Also worth noting if your mare is in a thick coat (not too hairy) you will start to see the large milk veins get enlarged: those are large veins along the belly that you might not have noticed before but they might start to show up.

If your mare is not a maiden, and had foals before, you might not notice much at first but the udder will go from flabby and thin to fleshy and slightly thickened.

This progression should be slow and steady. If your mare is not quite at the 300 days mark and her udder goes from flabby to fleshy  and starts to leak milk  within a few days that is sign of trouble and you should be ready for her to potentially abort. If you can get the vet to come and run an ultrasound and evaluate the healthiness of the placenta and the foetus it would give you a chance to intervene and perhaps get a positive outcome.

As your mares body get ready to produce milk the udder will go from fleshy and thick to full and then on to turgid (tight).

Again watch for the progression: some mare will do this over a week or so others will sloooowly grow that udder over a month.

As the udder starts to get ready to make milk what will be particularly significant will be the change in the nipples and the temperature and look of the udder.

At first recessed and small, the teats will fill up and start to point and look full as delivery is impending.  Depending on your mare’s udder and teat’s conformation that might look like the udder  that looks like an upside down tent with the tip of the triangle the tip of the teats or it might be more “cow like” with the teat clearly defined but bulging and thick (like a swollen thumb).  The udder often will take a bit of a shine to it. Between the skin being a bit tight from the swelling of the glands to the increase heat of the activity within, I often find that the look of the skin of the udder changes in the last few days or hours before delivery.

Now as the udder starts to become active, or rather the glands start to become active, you might confuse edema of the udder with actually udder development. The key is that the edema will likely be in front and around the udder. Edema is not the same as udder development but often precedes it or is seen at the same time. Note the time of the day you see the maximum swelling. If the mare has a larger udder in the morning after a quiet period but the udder shrinks during the day or with activity: you are not looking at real udder development and simply seing some edema. When the udder is really prime for milk production its size will not fluctuate down, it will enlarge and stay enlarged and eventually reach the turgid state when it is full, tight, a bit tender, and shinny.

Flat teats- not losing any sleep yet.

So to summarize:

Thin and skin like–>flabby–>fleshy–>fleshy with bilateral enlargement (pouch stage)–>full–>full and tight (but teats are flat)–>tight, shinny and teats full.

Dont confuse edema with udder development per-say: if the udder goes down with exercise; judge its state post-activity.

Also in early spring I have found that often all mares (pregnant and not!) will get a bit of fleshy-ness in the udder- keep that in mind and watch if it progresses or not.

Watch for the rate of change. You should be checking twice a day from 250 days onward and note the progression or lack of. If the mare is past 300 days and the changes all happen within a week or two I would be on foal watch. If those changes are happening gradually; I personally will not be on foal watch until the nipples have started to fill.

Almost full teats this mare foaled ~48 hours after this picture.

The most discussed amongst breeders: udder secretions.

There are various fluids, with various compositions that are secreted by the mare’s udder leading to the foal’s first suckle. Those are other clues to add to the overall picture.

Initially, the udder will have some clear liquid of various shades. Some multiparous mare never completely dry out so that liquid might look like very pale milk but most of the time it’s mostly clear, cloudy clear, yellow-ish, watery and thin.

There is not much point testing the secretion until the udder is clearly full. The only reason would be to get your mare used to getting a little bit of milk expressed -some object, most don’t care if they are well handled and  if you have already been cleaning their udder once in a while.

If the teats are not full, it can be a bit hard to express milk, and that is a good sign that maybe you dont need to. But if you want the practice: all you need is to pinch the teat from top to bottom and collect the secretion in the palm of your hand.

Calcium and Ph testing can be useful to detect key changes in the state of readiness of the mare to produce milk. There are milk testing kits out there that will explain all that in detail. After a while and experience pool strips are just as useful and frankly even those become a bit irrelevant once you have seen enough pre-foaling milk.

If you want to use the cheap pool testing strip (pick a brand that goes as low as possible on the Ph scale, if the lowest it shows is 7 or 6.8 it’s not sensitive enough for your needs) and focus on the drop of Ph as your indicator: you need to dilute your milk with distilled water (available in pharmacy). The ratio is 1:6 or one ml of milk for 6 ml of water. You will need a tiny graduated dropper or a small graduated cylinder to measure.

The important point I want to make here is that there is not much point in testing the “milk” too early on: the results will not be useful until you are talking about milk- real milk.

Ok, so the progression:

Clear and watery, slightly yellow–> clear and watery with a shift toward white–> skim milk like–> thicker milky white–>pure milk (mare’s milk is very rich in fat and can have a slight amber tinge to it).

Basic milk testing supplies.

Now the colour is one thing, the texture and feels between your fingers is important also: early watery secretions can be a bit greasy, skim milk stage is very thin but as the colostrum starts to be produced the milk leaves a sticky residue on your fingers, before foaling. I find that the milk, regardless of how thick and white it is (in fact good colostrum doesn’t quite look like normal milk) is extremely sticky, it leaves a sticky honey-like feel on your finger and in the palm of your hands.

When I  have either real opaque white milk or really sticky pale milk on almost full teats  – I am on foal watch. I once had a mare foal with such rich colostrum that it did not even look like milk but it was like honey it was so sticky.

If you want to test the milk with some little strips (I use pool strips to test for Ph) or the commercial kit; start once you have some real milk-skim milk or whiter.

Again here,  the rate of change is the most telling.

I had a mare go from amber clear liquid in the morning to sticky white skim milk at evening feed and she foaled that night (yes I was there ;-).

Others will go a week or more with clear-ish skim milk very slowly getting cloudier and more opaque and after two or three days of pure milk testing at a Ph of  7 to 7.2 will drop to 6.8 or lower and foal within 24 hours-48 hours.

Other secretions worth mentioning:

As the udder preps for milk production, the milk ducts will get distended from within. This leads to little plugs of crusty to sticky material coming out. Don’t confuse that with wax and start your foal watch! Is the udder full and warm, are the teats full? Probably not. I find that those little plugs come out as the udder is just reaching fleshy to pouch stage so weeks before foaling.

Also sometimes the teat will produce some little beads from their pores on the surface (not their tip!): it can look like a bit of sugary coating all around the lower base of the teat- again nothing to get excited about, just the increasing heat of the skin distending and opening the pores on the skin surface of the teats.

Picture of wax from the article linked below in the references.

Wax is produced once the mare’s udder has reached the milk and/or colostrum production stage. It’s basically thick sticky milk dripping out. It can be amber to pale white. Some mares will drip candles while others will give you just a few beads of it. If you see those amber, extremely sticky beats on full teats and the milk has been progressing toward white: you are on foal watch or at the very least on very close observation for any progression.

Potential trouble: leaking milk.

Some mare’s udder will have trouble holding on to milk once the udder is full and will start to drip or spray milk. If you see the sign of dripping milk on the back legs it’s a sign that you need to be on foal watch. A few mares will drip for days. Some will drip milk but still have colostrum for the foal, others will literally leak out all their good colostrum. It can be frustrating and not that common but it does happen. Try not to panic too much if your mare leaks some milk. By then she should be kept quiet and in a comfortable spot and so with not too much activity, you can keep the amount of leakage to a minimum. I would not try to collect the milk. It’s hard to do without milking the mare and that simply stimulates the udder to release more milk so not ideal either.

Dripping milk (not streaming!) for up to two days is not uncommon and will coat the back leg of your mares copiously. The moment I see some drips I like to coat the front of the back leg (the cannon bone down to the hoof area) with some brand of coat shiner (I use Absorbine show shine)  to make them easier to clean later on. You can also put petroleum jelly but everything will stick to it-although one good wipe and it will all come off.

Not as popular and less useful: rectal temperature.

You need to have a solid baseline (meaning you need to keep track of your mare’s temperature pretty systematically) but between 6 and 4 hours before the onset of labour the temperature will often drop. When you are that close to foaling you are probably on foal watch anyway so… Maybe if you are debating going and getting a shower or getting a short nap maybe then it could be useful… I have not used this myself but it is physiologically relevant so I thought it was worth noting.

Other signs

There are other signs that your mare is approaching delivery but they are not that precise: you will find the shape of the mare’s belly can change. Some speak of the belly dropping and taking on a V shape, or of becoming “slab-sided” after months of looking like a beach ball- that has to do with the foal positioning itself for delivery.

It can happen hours or weeks sometime before delivery.

Others will see a loosening of the muscles and ligament in the rear end of the mare: from the tail to the back legs you will see some change, sometimes and maybe: those changes can be absolutely obvious while some mares show no clear changes. I have seen mares go slightly lame in the back a day or two before delivery.

The shape of the vulva is often mentioned. There is mention of elongating and again that will depend on the mare. The colour inside the vulva will go from pink to red as blood flow increase in preparation for the delivery and I have seen that. The shape of the vulva is something you have to look at regularly to see any change really, it will look less wrinkled and look loose for sure but to the untrained eye, I am not sure it’s that obvious. Besides, I have seen a relaxed mare with a very loose looking perineal area weeks away from foaling. But if other signs are starting to appear I will check under the tail and slightly part the lips of the vulva to check for the colour. Sometimes that is the last thing I check before putting the mare in her foaling area so she gets some quiet time before the start of labour.

In summary, I do not let one sign send me into sleep deprivation foal watch: I need to see that a few signs are converging.


With the help of technology

Cameras and baby monitors

Those are getting so affordable these days that there is no reason not to have one, unless your mare is foaling in a large area outside (mine foal in a roomy paddock out on grass most of the time so the camera often cannot see the whole area). Find one that has infrared capability as mares often go into labour at night and you want to see what is going on without needing to leave the lights on all the time. Some have cables, some are connected via wi-fi. Find something that works for you there are lot of factors to consider but it’s not the point of this blog.

Another option is a baby monitor or something that carries sound very well. Mares going into labour will be more active, shuffling around a lot, and breathe harder and yes if you hear the grunts of a mare in labour there is no mistaking it. Also, you might hear the splash of water breaking. I find the sounds a signal for me to look at the camera, and confirm that the mare is in labour and I can get to her side at that point.

Foaling alert

Two different kinds of foaling alerts:

The one attached to the halter of your mare. It will send a signal when the mare is flat out and likely pushing out her foal. Lots of false alarms (pregnant mares do sleep flat out sometimes, as uncomfortable as that looks) and some mares will do most of the delivery standing up and walking around.

A variation on that one is a surcingle that is worn by the mare and that also signals when the mare is lying down. Same disadvantages as the one above and it’s bulkier and more expensive generally.

The ones sown into the vulva. That one requires a vet to come and install it and while it might sound terrible: the mares usually don’t mind it. The vet will numb the area and install two small metal pieces that when separated by the parting of the vulva for delivery will send off an alarm. Less false alarm and it will work when the mare is up, walking or lying down.

Best not to put it in too early because mares can rub their back ends and rip them out.


Nighttime or daytime?

Mares generally foal during the quietest time of the day and yes most often that is nighttime. But mine often foal early in the morning as that is the time during the rest of the year when they usually come back to the paddocks to snooze and that seems to be the most comfortable time for them.

I have observed mares that I put in a foaling pen or stall as they were very close, cross their legs and did not deliver until I put them back in a more well-known area. It can be useful in a way but the best practice is to have the mare used to the foaling area a week or two (or however long your mares takes to generally settle in a new routine) before your best estimate of her foaling time.

If things are progressing relatively normally (aka slowly) when the mare’s udder starts to get some definite enlargement and I know this is for real I will start to put her into her new routine.

Sometimes I hear people say that their mares showed absolutely no sign and simply delivered their foal with no warning. From my experience I find that a bit difficult to believe to be honest but I guess it can happen. I am with my mares a few times a day, every day. I check udders and under the tails and their general demeanour every time I am out there so I guess I am a bit more  on hands than some.  I had mare delivered sooner than I expected for sure and a few fooled me over the years yes, but they all showed signs I just misjudged them a bit and that is on me. Sometimes I was literally away for 10 minutes and they went into labour. Yes, that certainly happens but I never had one show absolutely no sign.

Hope this was useful. Drop me a question if you have one, or a comment if you want.

Expecting a Foal?

If you are expecting a bundle of legs and joy,  take a look at this handy foal book I put together.

A way to keep track of your foal’s key milestones. It has room for journal entries, putting down markings and identification, some photographs, and a place to graph its growth and keep track of its deworming, vaccination and registration. It’s on Amazon and if you have Amazon Prime it’s free shipping so: yay! From this year on, my foals will all go home with a filled-out foal book


Foal Book on Amazon :



This blog is unlike the others mostly based on my own experience over the year (45+ foals and counting) with a variety of mares, maidens and experienced broodies.

But if you want the words of a vet to confirm some things:

Article by Dr. David Ley DVM


Owner and worrier in chief at Formosus Sporthorses in Alberta she's been breeding horses for over 18 years. Warmblood, warmblood crosses, and a few saddlebreds. She loves handling mare and foals and is passionate about giving foals the best start possible.

Leave a Reply

%d bloggers like this: