Eleven months is a considerable length of time to anticipate the birth of a foal. A great deal of hope, excitement, dreams, and financial investment can accompany the arrival of a newborn. Because of the long wait, most owners want to monitor the birth of the foal, to make sure nothing goes wrong--and 90% of the time, the birth goes as Nature intended. However, there are times when human intervention is necessary, and being there makes the difference between a healthy newborn foal and one which does not survive. That is why interest in predicting foaling has become so great.

Most mares like to foal when it is quiet and they are undisturbed. This is a natural instinct, in order to protect their foals from predators. Therefore, having a mare foal when it is convenient for you is unlikely. Most mares foal either late at night or in the early hours of the morning. Therefore, close monitoring of the late-term mare for sometimes weeks at a time has been the only way to ensure that the birth was attended. This can make monitoring the mare for the birth of the foal costly. The costs can come in the form of using a closed circuit television, hiring someone to monitor the foaling, or having the mare foal at a special care facility.

Monitoring The Late-Term Mare

Using a closed-circuit television is a very convenient method to monitor the mare, as you do not have to travel to the barn or stall-side to watch what is going on. You can watch the mare from your house or from a separate room in the barn so that she will remain undisturbed. The disadvantage of this monitoring system is that the mare might place herself in a position that is not easily seen by the television camera. Most importantly, someone still has to watch the television screen during the night, and you might not notice her until she already is in labor. Many breeding farms and veterinary clinics use a closed-circuit television to monitor late-term mares since the mares can be monitored without disturbing them, and those facilities already are staffed 24 hours.

Another method of monitoring the mare for foaling is a system to alert you that your mare is in labor. The Foalert system is composed of a transmitter that is attached to the vulva of the mare. When the vulvar lips are separated as occurs during labor, the transmitter is activated. A receiver alerts the attendant or yourself by sounding an alarm. This is a good system, but you must be close by since it alerts you when the mare is in labor. So, if you are 30 minutes away, it could be too late by the time you arrive.

A similar system is the Breeder Protech 2000. This is based on a similar principle as the Foalert system. A transmitter is encased in a sponge that is placed in the vagina of the mare. When the mare is in labor, the sponge and transmitter are expelled from the vagina and the change in ambient temperature activates the transmitter. Again, it notifies the attendant of labor in progress.

Why Predict Foaling?

Even though close monitoring of late-term mares is still very important, predicting foaling is studied not only to predict when a mare is going to foal naturally, but to determine when the mare is ready to foal. Or more accurately, when the foal is ready to adapt to life outside of the uterus.

Remember, the mare begins to show external signs of impending birth as the foal develops and matures inside the uterus. Unlike humans, pregnancy length in mares is not related to fetal maturation; meaning that in humans, it can be safe to induce labor if a woman is in the last two weeks or so of her pregnancy and the baby will be mature. In horses, the length of pregnancy is so variable that you cannot rely on the length of pregnancy to determine if the foal is mature.

This is extremely important for mares which need to have the birth process induced so that they can be attended, such as mares with pre-pubic tendon ruptures (this is a tearing of the ligament that supports the abdomen, and loss of this structure makes it impossible for the mare to contract her abdominal muscles and deliver the foal normally). Veterinarians need to know when the foal is ready to be born; otherwise, if the mare is induced when the foal is not ready to handle life outside the uterus, the foal could need serious intensive care to survive and might die regardless of treatment.

What Is Normal?

Before we talk about predicting foaling, let's talk about normal gestation. Because each mare is different, there is no definitive gestation length. Normal gestation (pregnancy) in a mare is anywhere from 320 to 350 days. However, normal healthy foals have been delivered anywhere from 305 to 360 days. Foals born before day 300 usually are considered non-viable. Foals born between day 300 and 320 usually are weak and have a low birth weight and although usually considered premature, have a reasonable chance of survival with intensive care.

Some mares might even carry their foals for a ‘normal’ gestation and have incomplete development of the foal (premature) and the resulting foal is termed dysmature. These foals often show the physical characteristics of a premature foal--silky coat, pliant ears, and low birth weight. Mares might have an extended pregnancy and deliver a normal foal. If a mare has eaten fescue grass infected with the fungus Acremonium coenophialum, she might carry a foal
for a prolonged period. When pregnancy is prolonged due to a mare's ingestion of fescue infected with this fungus, then dystocia (difficult birth) and other problems associated with milk production and the placenta are more common. (For more information about the dangers of fescue, see ‘Hidden Dangers’ in the March 1997 issue of The Horse.)

So, how do you know when your mare is going to foal? There are physical changes that occur in the mare that indicate readiness to give birth, but is there anything more specific? Read on.

Physical Changes

First, let's talk about the more obvious signs a mare will have as she nears foaling. These signs will let you know she is getting ready, so you should prepare, too. A mare will physically prepare to give birth as her foal matures inside of the uterus. As a mare nears the date of parturition, not only will her abdomen continue to increase in size, but she will begin to develop an udder. This might start as early as one month prior to the date of birth. The udder gradually will fill with milk, then as parturition nears, the mare will begin to drip milk. At first, the ‘milk’ will be more of a clear fluid, then it will turn the more familiar white. The milk will, within a few days to hours before the birth of the foal, turn from white to a sticky yellow, which is the colostrum, or first milk.

Other changes that you can monitor are relaxation of the perineal area--the mare's vulva will begin to get longer as she prepares to give birth. The mare also will develop a sinking on either side of the tailhead as the ligaments of her pelvis relax in order to accommodate the foal through the birth canal. All of these signs are telling you that the mare is getting ready; however, they are not very accurate and staying up every night for a week gets tiring.

What About The Milk?

Researchers, in an attempt to find a more accurate method to determine when a mare is going to foal, have been studying the electrolytes (calcium, potassium, and sodium) produced in the pre-foaling milk. Changes and concentration of the electrolytes within the milk have been shown to be associated with the foal's readiness to be born, or maturation. In response to these studies, several methods have been utilized to predict when a mare is going to foal. The most popular electrolyte to monitor in mare's milk, for predicting foaling, is calcium. It is logical to think that the calcium concentration of a mare's milk will increase as the mare draws closer to foaling.

Researchers from one study found that when calcium concentrations in the pre-foaling milk are low, there is only a small chance that a mare will foal within the next 24 hours. However, when calcium concentrations are greater than 200 parts per million (ppm), then there is a 51% chance that the mare will foal in 24 hours, 84% chance that she will foal in 48 hours, and 97% chance that she will foal in 72 hours. This is the basis for the commercial FoalWatch Kit. This kit uses the mare's milk, which is sampled once daily in the morning. The milk is diluted with distilled water. An indicator dye is used to show the amount of calcium carbonate in ppm in the diluted sample. When the ppm of calcium carbonate reach 200--it indicates the mare's readiness to give birth.

Calcium also can be measured by automated chemistry tests. The level of calcium in the milk, which indicates readiness to give birth, has been shown to be greater than 40 mg/dl in these tests. Of course, as with any test, 100% accuracy is not always possible. Often times, mares produce maximum calcium before the day of parturition. However, these tests can be very helpful in indicating when not to attend a mare at night.

There are several types of test kits to measure the calcium or calcium and magnesium of the mare's milk. One such kit is the Predict-a-Foal Test, which measures calcium and magnesium levels in the milk. With this test, there is an indicator strip with five square indicators that correlate to different levels of calcium and magnesium in the milk. If only one or none of the squares change color, then the mare has a 1% chance of foaling in the next 12 hours. When four to five of the squares change color, then there is an 80% chance of foaling within the next 12 hours.

Sodium And Potassium

Another method for detecting readiness to give birth is measuring the electrolytes sodium and potassium of pre-foaling milk. During the last week of pregnancy for the mare, her milk will undergo marked changes in these electrolytes, along with the increase in calcium concentration. The sodium levels will decrease as the potassium levels increase (inversion). These electrolytes can be charted on a graph to follow their respective increases or decreases. Eventually, the two lines intersect, and when the potassium levels become greater than the sodium levels in the milk, it is a strong indicator of readiness for birth.

The potassium concentration in pre-foaling milk usually is higher than the sodium concentration within 24 hours of parturition (birth). The graph shows a mare's concentration of electrolytes and the changes that occurred in them as she neared her foaling date. The milk samples were taken once daily in the morning and were measured using automated chemistry techniques.

All of the electrolytes can be measured and used to evaluate when a mare is ready to give birth. Veterinarians can use calcium, sodium, and potassium values along with the physical examination findings to determine very accurately when a foal will be mature enough to induce labor in a mare. Milk should be evaluated daily from 10 days before the due date or whenever the mare begins to produce milk. This will help more accurately determine when the foal is ready to be delivered into its new world.

If you have a mare that is due to foal this spring, and you want to measure her pre-foaling electrolytes in her milk, make sure you discuss with your veterinarian which test(s) you should perform. Furthermore, make sure your mare is ready for the delivery by making sure she is up to date on her vaccinations.

About the Author

Christina S. Cable, DVM, Dipl. ACVS

Christina S. Cable, DVM, Dipl. ACVS, owns Early Winter Equine in Lansing, New York. The practice focuses on primary care of mares and foals and performance horse problems.

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