Learn the signs of impending parturition and what prognostic tools are at your disposal

Your mare was bred on June 1 of last year. Equine gestation is about 340 days (roughly 11 months), so her expected due date is coming up in a few months, around May 6. That 340-day figure is just an average, however, meaning it’s perfectly normal for a mare to foal as many as three weeks earlier or later than expected.

You’d like to be present at the birth in case there’s a problem, but that’s quite a window and you’ve got a lot going on this spring. Hovering over the expectant dam in the barn 24/7 is impractical and, quite frankly, could make her nervous and delay the process. Like many breeders, you’d like to be able to predict when exactly she might foal.

Good news: There are signs and tools to help. Here two reproduction-focused vets offer their expertise and suggest ways to take away some of the mystery, so you can be there for the big event.

Physical Changes

In late gestation (from Day 250 onward) mares experience several observable physical changes. Ahmed Tibary, DVM, PhD, Dipl. ACT, professor of theriogenology in Washington State University’s Department of Veterinary Clinical Sciences, in Pullman, advises breeders to examine the mare periodically to monitor how her body is changing to be ready for parturition (birth).

“Mares are quite variable in their signs of preparation for foaling, depending on whether they are older broodmares that have had several foals or maiden mares,” he says. “Premonitory signs based primarily on morphological (structural) changes can be quite subtle in some mares, difficult to discern, and are not precise. They tell you that the mare is getting ready, but they don’t narrow down the time of foaling to an actual day.”

There are, however, things you can monitor to make sure the mare is progressing normally in preparation for foaling.

“The classic physical change is mammary development, or a significant increase in udder size,” says Robyn Ellerbrock, DVM, Dipl. ACT, a PhD candidate at the University of Illinois Urbana-Champaign’s College of Veterinary Medicine. This can begin two to three weeks before foaling—further out than this can signal problems such as placentitis (inflammation of the placenta). As the mare gets closer to parturition (usually in the last two to three days of pregnancy) she’ll begin accumulating dried secretions on the tips of her teats, a process known as waxing.

“It is important to realize that we are talking about probability, rather than a definite time frame, when we see a mare waxing,” says Tibary. “About 90% of mares will foal within 24 to 48 hours, but some mares wax longer. A mare might wax very briefly or for several days. Last year we had a mare at the hospital that waxed for about a week. That might be due to being in the hospital where there is a lot more going on; if the mare doesn’t find a quiet time she may delay foaling.”

Other signs include relaxation and elongation of the vulva, as well as softening of the pelvic ligaments around the tailhead. “Sometimes you can also see an actual change in the shape of her abdomen as the foal is repositioning and preparing to enter the birth canal,” Ellerbrock says.

“All of these are good indications that the mare is progressing normally in pregnancy, as long as she seems fine and remains healthy,” says Tibary. “For the purpose of making sure someone is there in case there is trouble, however—particularly for maiden mares or mares that have had problems in the past—we need something more precise. Most of the research over the past 40 years has been focused on finding more precise ways of predicting when the mare will foal.”

Check on late-gestation mares several times daily (at feeding time, for instance). As physical signs of parturition progress, you can institute round-the-clock monitoring using cameras and other devices we’ll describe in a moment.

Behavioral Changes

If you know your mare’s normal behavior and habits, you can pick up on the subtler changes that indicate impending labor. Mares usually begin showing behavioral signs of early labor (Stage 1) one to four hours before going into active labor (Stage 2), although some mares show signs of early labor for more than a day. These include:

• Acting restless and alert;
• Lying down or getting up and down more frequently than normal;
• Pawing, tail-swishing;
• Lifting the tail and turning around to look at or bite the flanks;
• Pacing around the pen or stall;
• Sweating;
• Curling the upper lip in the flehmen position;
• Making unusual mouth movements and yawning;
• Urinating and defecating small amounts frequently;
• Going off feed or eating less than normal; and
• Dripping or streaming milk.

For some owners it can be challenging to differentiate between signs of early labor and signs of colic, because both cause discomfort. Most mares show subtle colicky signs during first-stage labor when experiencing initial uterine contractions and repositioning of the fetus. Many mares circle or look like they are preparing to lie down. “As more contractions occur, they usually start sweating— particularly on the neck, shoulders, and flanks,” Tibary says.

For this reason it’s important to monitor the mare’s water intake and manure production. If both are normal she’s probably foaling, not colicking, says Ellerbrock.

Tibary says the best-qualified person to observe the mare is someone who knows her and how she behaves daily in the stall or pasture. “That person can pick up on subtle behavioral changes, when she is acting a little different—more alert or worried,” he says. “Mares have a typical routine through the day. If a mare starts behaving a bit different from her normal routine, this is a sign that something is changing.”

Indeed, the mare feels internal changes and becomes more preoccupied with these sensations than her regular routine.

“A lot depends on whether you are observing a mare on pasture, out with other horses, or in a stall,” Tibary says. “Each case is different. Perhaps she is too quiet today or spending more time with her head down and is just not herself. Then the signs progress to more increased alertness, circling, etc.”

If the mare is with other horses, she might go off by herself or stay behind the group. If she is confined she might become frustrated and start pacing her pen or stall.

“We tell mare owners to be looking for any of these subtle signs during pregnancy and not just before she is supposed to foal, because those are also signs you might see if she’s about to lose the fetus or foal prematurely,” Tibary says.

He points out that these behavioral signs are quite variable from one mare to another. “We’ve seen mares that just continue to do what they’ve been doing; they munch on hay and go on about business as usual and then suddenly go into second-stage labor,” he says. Others might appear to have mild discomfort for several days before labor begins.

Picking up on these signs becomes more difficult at a veterinary clinic, where the observer isn’t familiar with the mare. “We don’t know her normal routine,” says Tibary. “We changed it, and she may be more nervous anyway or may not want to show any signs. This is when the biochemical tests (more on these in a minute), particularly the strip tests for calcium and pH, become very helpful for monitoring.”

Monitoring Devices

A number of signaling devices (e.g., Foal-Alert, Birth Alert, Foal Alarm, etc.) are available to notify the owner, farm manager, or foaling attendant that a mare is or could be in labor. Some attach to the mare’s halter, while others are stitched to her vulva. When she lies flat or her vulva lips begin to spread apart, respectively, each device transmits a signal to a receiver that sounds an alarm or calls your phone.

“These devices can be helpful, but can’t fully replace visual observation,” says Tibary. “Most electronic techniques are triggered by the second stage of labor, and in some instances these alarms might be a little too late, since mares foal so quickly. The mare could foal before you are able to get to the barn.”

Also, in the case of a dystocia (difficult birth), the sensor sutured to the vulva might not work because the foal can’t reach the vulva to trigger an alert, says Ellerbrock.

“There is also a company working on devices on the halter that monitor the mare’s heart rate as well as when she is getting up and down—looking at the horse’s vital parameters,” says Ellerbrock. “This would signal that the mare is either foaling or colicking.”

Other monitoring methods include closed-circuit TV or webcam, which allow you to watch the mare from your house or smartphone. You can observe signs of early labor before the other types of monitoring kick in.

“Here at our hospital we constantly watch (on webcam) all the mares being monitored for foaling, particularly those that have had a difficult pregnancy,” says Tibary, adding that this allows you to watch the mare from a distance, without disturbing her.

Ellerbrock describes the convenience of apps that connect to the webcams: “You could be out for dinner and pull up the mare on your phone to watch what she is doing,” as long as the barn has Wi-Fi access.

“Night-vision cameras are the best option because you don’t have to leave a light on in the barn all night, which could interfere with the mare’s natural circadian rhythm and when she decides to foal,” she adds.

Mammary Secretion Tests

Owners and veterinarians can use a variety of biochemical tests to determine when a mare is near foaling. The traditional one is based on electrolyte changes in mammary secretions.

“To do a full monitoring (which must be done at a lab) we can look at calcium, sodium, and potassium levels,” says Tibary. “The real trigger in knowing when the mare is going to foal is when we see the level of sodium and level of potassium invert. At first the sodium would be very high, then as the mare gets close to foaling the sodium will be lower than potassium. That point of inversion … tells us the mare is within about 24 hours of foaling.”

At this point you can intensify your visual monitoring.

“Other tests focus primarily on calcium, which is also a good indicator of imminent foaling,” he says. “Calcium in mammary secretions progressively increases in concentration as the mare gets closer to foaling. There are many types of test strips (e.g., Predict-A-Foal, FoalWatch) that are commercially available.”

When these tests show the secretions’ calcium content reaches 200 parts per million, the mare has about a 50% chance of going into labor within 24 hours; about an 85% chance within 48 hours; and about a 95% chance within 72 hours.

“Another method we are starting to use in combination with the calcium strip test looks at pH of the secretions,” says Tibary, which decrease progressively leading up to foaling. “Research over the last five years has shown that pH of mammary gland secretions is highly correlated with electrolyte changes. When the pH reaches 6.5 or lower, there’s high likelihood the mare will foal within the next 24 hours. These two tests combined add a little more precision for the mare owner or for the veterinary clinic. However, not all mares drop their pH in the same way.”

For instance, maiden mares’ milk pH levels tend to decrease very rapidly in the 24 hours before foaling, while those of older mares that have had foals previously tend to decrease more slowly (you can find these pH ranges in Ellerbrock’s research at TheHorse.com/39054).

“When using pH strip tests, it is important to use commercial strips providing readings in 0.1- or 0.2-unit increments,” she says. “Test strips measuring pH in 0.5-unit increments won’t be useful for identifying subtle changes that predict imminent foaling.”

Despite these tests, not all mares go by the book. “We’ve had mares that remained very high in calcium … for up to five days before foaling,” says Tibary, noting that a likely reason was that their routines had changed; mares can delay labor for 24 hours or more. For that reason, these tests are probably more predictable at home, in the mare’s familiar environment, he says.

Other things that affect these tests include high-risk pregnancies and abnormal mammary gland development. Some maiden mares or mares that have leaked milk prior to foaling might also throw off test results.

“Mares that have been treated for placentitis or mares that have undergone surgery for colic during pregnancy or have had other stresses or disturbances of the normal hormonal changes will not have a reliable test,” says Tibary. “Then we must fall back on watching them closely and using electronic devices.”

While monitoring calcium, electrolytes, and milk pH levels in healthy mares is typically a more accurate predictor of foaling than evaluating physical changes alone, it does add an expense.

Calcium tests and full panel electrolytes are going to cost more than ommercially available pH strip tests, adds Ellerbrock.

Take-Home Message

Gestation length varies so widely in mares that it pays to monitor them closely in late gestation, to watch for the changes that signal readiness for foaling. Careful observation, monitoring devices, and milk test kits are all useful tools for helping predict impending parturition.