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What to Expect:
Facts About Equine Pregnancy


As My Special Girl approaches the birth of her foal, here are some pregnancy facts that can help clarify what she's going through. 

 When Will My Special Girl Foal?

By Regina Turner, VMD, PhD, Associate Professor of Large-Animal Reproduction at Penn Vet New Bolton Center

One of the most common questions that we are receiving is, “When will My Special Girl have her foal?” The most honest answer that we can give you is: “We don’t really know.” The average length of an equine pregnancy is about 340 days – a little over 11 months. Based on this average, we have listed her “due date” as March 14.

However, although the average length of an equine pregnancy is 340 days, some normal mares foal as early as day 320, while other normal mares carry for a year or more.  Since My Special Girl has not had a foal before (that we know of), we have no idea what “normal” is for her.  She could foal tonight, or she might not foal for another month!

Given this wide range of possible foaling dates, we watch My Special Girl very carefully, many times each day, to see if she is showing physical signs that her delivery day is getting close.

My Special Girl's udder has started to form.

Probably the best external indicator is the development of her udder (mammary gland). Most mares develop a prominent udder, filled with ‘first milk’ (colostrum) before they foal. The udder usually develops gradually.  It starts out small and empty, then, days or weeks before foaling, the back half of the udder will start to fill with milk. As foaling gets closer, the front half also will become full. Finally, when foaling is very close (usually within a day or two), the mare’s teats will fill with milk. The day before she foals, many mares will develop ‘wax’ on the tips of their teats.  Wax is really just dried colostrum that sticks to the end of each teat. When the mare enters the earliest stage of labor, she may even stream milk from her teats.  

We also look for other, more subtle signs including relaxation and elongation of her vulva, and relaxation of the ligaments around her back end. If you are watching the Foal Cam regularly, you have probably seen our veterinarians peeking under her belly to see her udder, lifting her tail to examine her vulva, and feeling the ligaments around her tail head to assess the degree of relaxation.

Dr. Tamara Dobbie feels My Special Girl's ligaments to see if they are relaxing.

So, how does My Special Girl look? Is her body showing signs that she will foal on or around her March 14th due date? As of today, the answer is, “no.” All of the clinical signs suggest that she is going to carry this foal beyond (and possibly well beyond) her predicted due date. 

Could she foal tonight? Absolutely. Although it is unusual for a mare to foal without any external signs, it certainly can happen. Will she hold on for another week or two?  That is the more likely scenario.  Could she hold on for another month?  Yes, she could. The bottom line is that she will foal when she is good and ready.

Some may ask whey we don’t induce labor. This is apparently a common practice in women (although we do not claim to specialize in human labor and delivery!) When women are induced on or near their formal due date, you can usually count on the baby being healthy and ready for birth. But mares are not women and they do things very differently.

In horses, critical developmental changes occur in the in utero foal as late as within a few days before birth. For example, if My Special Girl’s normal gestation length would be 355 days if we left her alone, but we become impatient and induce her to foal on day 340, we could very easily deliver a compromised, premature foal that does not have fully developed lungs, kidneys, and other vital organs. Because of this, we very, very rarely induce labor in mares.

Since all of our monitoring suggests that My Special Girl’s pregnancy is perfectly normal, there would be no reason to induce labor. So we will continue to sit, wait and monitor her until she decides that the time has come. We will keep you updated as much as possible through our Penn Vet New Bolton Center Facebook page, and this webpage. We are as eager as you are for this baby to be born, but we know that the best thing for My Special Girl and her foal is to wait...and watch…and wait some more.

Why Is My Special Girl...

...receiving oral medications?

  • We fully expect that My Special Girl will deliver a happy and healthy foal. 
  • But we have been watching her closely and have noticed that, on her last three abdominal ultrasound examinations, a small part of her placenta is thicker than it should be.   This is most likely nothing to worry about. 
  • The location of the thickening is not in an area that is commonly affected by infection (placentitis). 
  • Additionally, she is not showing any other signs that there is a problem with her pregnancy. 
  • Her udder remains small and is growing only slowly; all the baby’s vital signs are consistently normal; and My Special Girl herself is not ill in any way.
  • However, on the outside chance that she has a low-grade, atypical placentitis brewing, we have decided to start her on a course of antimicrobials and progesterone, just to be sure that we cover all bases.
  • If we didn’t treat her, would she and her foal be fine? Probably. But on the chance that there really is something wrong, we are concerned that if we didn’t treat her the problem could spread and the foal could develop problems. So we decided to be better safe than sorry. 
  • As a result, you may see her receiving oral antimicrobials twice daily and an oral progestin once daily.  

... acting so cranky?

  • My Special Girl is typically an amazingly sweet and tolerant mare.  Her recent behavior might suggest otherwise.
  • You may have noticed her pinning her ears when people approach or pet her and even making some attempts to kick or threatening to bite when she is being examined. This is not her usual behavior.
  • But remember that she is very, very pregnant and behavior changes like these are common in late- gestation mares. You might even know a human mom who acted similarly when they were close to delivering their baby. 
  • My Special Girl is no different. And really, you can’t blame her!  She is carrying around a couple of hundred pounds of extra weight and the foal is moving around all the time with those little hooves.
  • So it’s really no surprise that she is a bit on the cranky side these days.


About the Fetal Heart Rate

By Jonathan Palmer, VMD, Chief of Penn Vet New Bolton Center's Neonatal Intensive Care Unit

We monitor the heart rates of My Special Girl and her foal throughout the night, from about 6 p.m. to 6 a.m.

A telemetry unit is attached to the connections on her back and sides, which we put on with special adhesive. The unit transmits the signal to a receiver in the nursing station. The heart rates of both the mare and foal are recorded, and checked about every two hours throughout the night.

The telemetry unit is attached to My Special Girl.

We look at the fetal heart rate patterns to make sure they don’t indicate fetal distress. The heart rate is quite variable and it may change as the mare gets close to giving birth, although the heart rates can’t predict when she is going to foal.

We expect to see a baseline, or average heart rate, as well as acceleration when there is fetal activity, and a decrease associated with contractions of the uterus. My Special Girl is already having “practice” contractions.

What we are looking for is a variety of heart rates, with the foal at rest, but also galloping around the uterus. What we don’t want to see is consistently high or low heart rates, which could indicate fetal distress.

Dr. Jonathan Palmer measures the foal's heart rate from the monitor printout.

The range for My Special Girl’s foal in recent days has gone as high of 136 beats per minute, and as low as 68 beats per minute, with a baseline of about 83. My Special Girl’s heart rate ranges from about 45 to 65 beats per minute. These indicators are both considered in the normal range.