Eager anticipation has been building over the last few weeks as you anxiously wait for the newborn, but the mare seems to be set on keeping the time of arrival a secret. She looks at you as if absolutely nothing is happening, then shifts uncomfortably before wading once around the stall, only to return to the hay manger. With one last look, you head for the house feeling confident there will be time for a leisurely dinner before another all night vigil.

     The mare isn’t going to make it easy for you to predict exactly when she’s going to unwrap her package, but with accurate records and an educated eye you’ll avoid some of the anxiety created by many sleepless nights.

     Determining the ETA (Estimated Time of Arrival) starts with good record keeping. Miscalculated foaling dates can lead to serious problems. Under-estimating the foaling date may cause you considerable distress, as you watch and wait day and night, for a foal that isn’t actually due to arrive for another couple of weeks, but even more serious complications can be created for the mare. Feeding the mare for fetal development is only necessary during the last trimester (last 90 days). Ninety percent of a foal’s growth occurs at this time. Surplus feed before hand leads to over weight mares which tend to have more problems during the last stages of gestation and parturition. On the other hand, over-estimating the time of arrival can be just as tragic. The loss of newborns due to mares foaling unattended at pasture during inclement weather are often the result of such a miscalculation.

     To prevent such mathematical errors, it is a good idea to keep a Broodmare record of Produce file on every mare in the brood band.  The dates of each stallion cover should be recorded as well as the foaling date, length of gestation, sex of the foal, and any complications that may have occurred. Signs of nearing parturition and any peculiarities should also be noted for future reference. The information entered in your file will assist in discovering the mare’s individual signs of preparation and calculating subsequent foaling dates.

     The mare’s average length of gestation is 340 days, but mares are known for their vast individuality so you may be looking at anywhere from 320 to 365 days of anticipation. Several factors can play a part in altering the length of gestation. The time of year the mare conceived will dictate the length to some extent. Mares bred earlier in the year tend to carry longer while the long daylight hours and warm climatic conditions of late spring foals shorten the pregnancy.

     The mare’s environment will also have a significant effect on the duration of pregnancy. Under nourishment, illness and stress can prolong the gestation by as much as 10 or more days, while a well nourished mare in excellent health usually foals a few days early.

     It has been reported that the sex of the foal has some influence on the length of gestation. Colts on average are carried 2-7 days longer than fillies. This isn’t much help since the sex of the foal is just a guess until the moment of birth, unless sophisticated and expensive laboratory tests are used. Gestation characteristics are also influenced by the individual traits of the mare as well as the stallion’s genetic make-up. Much of the fetus’s growth rate is determined by the genes he inherited from both his dam and sire.

     In addition to mathematical calculations in determining the projected foaling date, the mare will display signs of her present situation. There are no hard and fast "rules" of the foaling mare. Each mare is an individual and her normal routine must be learned from experience. With an educated eye, the changes in your mare’s body will give you a clue to when parturition is approaching.

     Some of the signs of nearing parturition are subtle, some are more obvious. During the last few months the abdomen will grow increasingly larger and pendulous. At about one week prior to the birthing, the belly may appear to shrink as the foal begins to move into the birth canal.

     As the mare enters the preparatory stage her body will begin to reveal some subtle signs. Relaxation of the entire posterior reproductive tract begins to occur about 6 weeks prior to foaling and continues up to the last moments. The sacral ligament begins to relax under the influence of Relaxin, a hormone which increases its affect as the mare nears her time, allowing for the expansion of the birth passage. By observing the mare closely you’ll begin to notice a hollowing and softening of the muscles on either side of the tail head. In a period of three to ten days prior to parturition, the consistency of these muscles will become so soft and loose they will resemble jello.

     The vulva undergoes relaxation at approximately the same time frame as the sacral ligaments. As the mare’s time approaches the vulva will slacken, becoming wider and longer than normal. Occasionally this sign of preparation is missed due to "shy" mares who tend to contract their vulvar muscles when their tails are lifted for observation, though if you examine the vulva closely you’ll notice that the vulva will appear to be considerably wrinkled in their attempt to reduce the evidence. This loosening will become much more noticeable within 24 to 48 hours of the blessed event, when the vulva may reach such relaxation that it will be level with the point of the buttocks. Shortly before parturition the cervix will also relax, and a small discharge of lubricating secretions may be noticed.

     One of the more obvious signs encountered is the "making of the bag". The udder will began to change from the cool, soft, flabby mass to a warm, firm, shiny mound as it prepares nourishment for the foal’s arrival. Normally the onset of this filling begins between the fourth and sixth week of the countdown. This is often seen earlier in maiden mares than the seasoned broodmare. Stabled mares may also seem to "make bag" earlier than pastured mares, due to inactivity. The udder will swell up at night, but shrink during the day while turned out. When the udder remains tight after a day of free exercise, the wait typically won’t be too much longer.

     Some mares, more frequently in mares having their first foal, may carry most of their bag concealed within the body cavity and show little evidence of enlargement right up to the time of delivery. Though the bag may seem quite small, it will still feel firm and warm to the touch.

     As pressure builds within the udder, the teats will enlarge and deflect out from the bag about four to six days before parturition. In some mares, the pressure of the filled udder may become so intense that the milk veins will show over the length of her belly. Soon the dry plugs will be expelled from the teat openings by the pressure allowing secretions to form on the ends of the teats. These sticky, yellowish-brown secretions, referred to as wax, are very small amounts of drying colostrum. Seventy-five percent of all mares will wax sometime before foaling. It has been reported that 90% of those mares that do wax, will wax just 6-48 hours prior to the birth.

     A more precise way to predict the time of foaling is to test the calcium level of the milk. A small sample of the mare’s milk is collected and tested daily with a commercial kit, beginning ten to fourteen days in advance of the expected foaling date. When the calcium values exceed 200 ppm (parts per million), there is a 51% chance that the mare will foal in the next 24 hours or 84% chance within 48 hours. The majority of mares will foal within a short period of time when a value of 300-500 ppm is obtained. This test is not 100% accurate with all mares, as some mares may deliver with their milk still thin and clear, while others will not let down their milk until after foaling.

     Just prior to foaling, mares often become restless. She may pace the stall or contained area with a patchy sweat dampening the hair behind the elbow, on the sides of her neck and on her flanks. Sometimes she will appear colicky, lying down and getting up repeatedly, but if she eats, drinks, defecates and urinates it is a good indication that the first stages of labor are in progress. Even then a mare may trick you. Some mares will put on a good performance of a mare in the first stages of labor only to quit. These mares are generally experiencing early or false labor pains. Don’t let your guard down. The minute you give up and walk up to the house for a cup of coffee, she may launch into the real thing.

     Weighing and deciphering all the information the mare gives you to predict her foaling date is an art built on experience. Some mares will try to fool you, no matter how diligently you observe them, but experience coupled with precise record keeping will stand you a better chance of witnessing the big event.