FOAL? WILL SHE

BY HEATHER SMITH THOMAS

Gestation in mares is estimated at about 340 days (roughly 11 months) but that number is just an average, since mares can easily foal as much as 3 weeks earlier or later than this expected date. Normal gestation is considered to be 340 to 345 days, plus or minus 12 days. Gestation length is also affected by genetics and season of the year. Mares foaling in winter or early spring tend to go 10 to 15 days longer than mares foaling in late spring or summer.

Since mares can be so unpredictable in gestation length (which may be anywhere between 320 to 360 days and still be considered normal), breeders often try to find ways to more closely pinpoint when a certain mare might foal. Dr. Ahmed Tibary, Professor of Theriogenology, Department of Veterinary Clinical Sciences, Washington State University, says it is important to examine the mare periodically to see how she is changing and preparing for parturition. “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. These signs can be quite subtle in some mares, and difficult to discern. They tell you that the mare is getting ready, but they don’t narrow down the time of foaling to an actual day,” he says.

“We talk about relaxation of the pelvic ligaments (and a softening of the muscles next to the tail head and vulva), elongation of the vulva, mammary gland development, etc. Relaxation and enlargement of the vulva usually occurs within a few hours of foaling.” These are all things you should look at, to make sure the mare is progressing normally in her preparation for foaling.

All the signs of impending foaling are variable. “A mare may start some changes as much as three or four weeks before foaling and then become obviously more intense during the last two weeks. Changes in the mammary gland may take place closer to parturition in some mares than others. The sign most people look for is waxing (a bit of dry colostrum that accumulates on the end of the teat), since this usually doesn’t occur until the last two to three days,” says Tibary. The mare might have a large udder for two or three weeks but generally doesn’t wax until about 24 to 48 hours before she foals.

“It is important to realize that we are talking about probability, rather a definite time frame, when we see a mare waxing. 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. One year we had a mare here at the hospital that waxed for nearly a week. That might be due to being in the hospital, however, where there is a lot more going on—and if the mare doesn’t find a quiet time she may delay foaling,” he explains.

“All of these signs (relaxation of pelvic ligaments, elongation of the vulva, larger udder, and waxing) are good indications that the mare is progressing normally in her pregnancy, as long as she seems fine and remains healthy. For monitoring, and for the purpose of making sure that 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 a little more precise. This is where most of the research has been focused over the past 40 years--trying to find more precise ways of predicting when a mare will foal.”

MONITORING METHODS – Some monitoring technique are electronic and others involve chemical methods such as checking mammary secretions. “Most of the 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 out to the barn,” says Tibary.

These signaling devices can be useful, however, and include products like Foal-Alert, Birth Alert, Foal Alarm, etc. These are attached in various places (such as on the halter, or stitched into the mare’s vulva) and send a signal when the mare lies down flat or when the vulva lips are spread apart. These devices are designed to notify the owner, farm manager, or foaling attendant that the mare is in second stage labor. Some systems can notify multiple people. A signal is transmitted from the device to a receiver that sounds an alarm, notifies a pager, or calls a telephone number.

“One device sends a signal based on the position of the mare— such as if she lies flat for a long time. Another type of device sends a signal when the vulva stretches and pulls the sensors apart. This one is only activated when something is passing through the vulva opening (water bag, or the amnion sac and front feet of the foal). These devices can be helpful, but can’t fully replace visual observation,” he says.

Other electronic methods for monitoring include closed-circuit TV or webcam, which can be useful because you can watch the mare from your house or smart phone. You can see her preparing to foal (signs of early labor) before the other types of monitoring would kick in. The methods that allow continuous monitoring enable us to see behavioral changes in the mare, and clues that tell when she is about to foal.

“Here at our hospital we constantly watch (on webcam) all the mares that are being monitored for foaling, particularly those that have had a difficult pregnancy. The webcam presents an advantage because you are watching the mare from a distance, without disturbing her.” The presence of someone nearby may cause a mare to become worried and put off foaling.

The other category for monitoring includes several biochemical tests. “Recent advances have been made in this area. Re- search has made a lot of progress with these tests since they were first used in the early 1980’s. These tests continue to be refined and improved,” says Tibary.

The traditional test is based on changes in electrolytes in secretions of the mammary gland. “If we want to do a full monitoring (which can be done at a hospital lab) we can look at the calcium, sodium and potassium levels. The real trigger in knowing when the mare is going to foal, however, is when we see the level of sodium and the level of potassium invert. At first the sodium would be very high, then as the mare gets close to foaling the sodium level would be lower than the potassium. That point of inversion, when sodium becomes lower concentration than potassium, tells us the mare is within about 24 hours of foaling,” he explains. At this point you could intensify visual monitoring.

“There are other tests that focus primarily on the calcium, which is also a good indicator of imminent foaling. Calcium in the mammary secretions progressively increases in concentration as the mare gets closer to foaling. There are many types of test strips commercially available. Those use the same principle as measuring water hardness, to identify the concentration of calcium,” he says.

“The initial studies looked at probability of a mare to give birth within a certain number of hours, based on calcium concentration. These studies showed that when the calcium content of mammary gland secretions reaches 200 parts per million the mare has about 50% chance of going into labor within 24 hours, about 85% chance of going into labor within 48 hours, and about 95% chance of going into labor within 72 hours. This principal is used with the commercial strip tests,” says Tibary.

“You collect a small amount of mammary gland secretion, add a reagent, and dip a strip into the mixture. That strip contains a reagent that reacts with the other one by showing a change of color. The strip has about five squares and you look to see how many of those squares change from green to red. The more squares that change, the more likely the mare will foal within a certain time frame. If all five squares have changed, the mare has high likelihood of foaling within the next 12 to 24 hours,” he explains.

“Another method we are using in combination with the calcium strip test looks at the pH of the secretions. Research in recent years has shown that the pH of the mammary gland secretions is highly correlated with the 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. However, not all mares will drop their pH in the same way; some can drop quickly while others drop more slowly. Some may even foal while the pH is still more alkaline,” he says.

“In our hospital, we use all monitoring methods. We use the camera for continual monitoring, and the calcium test—sometimes with the full panoply of electrolytes. Since we already have the secretions for that test, we may also take a quick pH measurement which can be done with the typical pH paper (as for a litmus test). This gives us a very good monitoring system,” he says.

Not all mares follow the book, however. “We’ve had mares that remained very high in calcium on the calcium test for up to five days before foaling. Probably one reason they may go longer is that you’ve changed the routine of the mare. She may put off foaling, since mares can delay labor for 24 hours or more,” says Tibary.

“These tests are very predictable at home, in the mare’s familiar environment. All these changes in mammary gland secretions are not as useful, however, if the pregnancy is not normal or if mammary gland development is not normal. When we have a high risk pregnancy, we can’t rely on this test. For example, mares that have had a problem and have gone too long, or don’t have normal development of the mammary gland, or have a lot of edema, etc. won’t have a reliable test. In mares with fescue toxicosis, for instance (and lack of udder development), these tests will not work.”

Some maiden mares, or a mare that doesn’t come to her milk until after she foals, or mares that have leaked milk prior to foaling may also throw the test off. “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. Then we must fall back on watching them closely and using electronic devices,” he says. TFH

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