Technology plus clinical signs equal success in the horse-breeding business.
By Dr. Patrick McCue in The American Quarter Horse Journal | January 1, 0001
Clinical signs of impending foaling begin subtly a month or so prior to the due date. Changes become more dramatic and occur more rapidly as the day of foaling approaches. The first noticeable change is in the mare's mammary gland, which begins to enlarge two to six weeks prior to term. Some mares can develop a large amount of edema around the udder before the gland itself becomes enlarged. Mammary gland development will be much more pronounced in mares that have previously had foals than in maiden mares. The teats or nipples will remain relatively flat until the last few days prior to foaling, at which time they will engorge or fill with milk. The mammary gland secretion changes from a clear straw-colored fluid to a more turbid milk-like substance as the due date draws near. The secretion
becomes thick and honey-like as colostrum develops in the last few days prior to foaling. A thick, waxy material of dried colostrum can accumulate at the ends of the teats 24 to 48 hours prior to foaling. This “waxing” is a classic sign that foaling is imminent. The extent of waxing can range from tiny droplets to elongated candlewax-like formations that project an inch or more from the teat ends. As a general rule, most mares that wax will foal within 24 to 72 hours. However, not all mares wax up, and the time from waxing to foaling can vary.
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In the last two to three weeks of pregnancy, the abdominal muscles relax, causing a pronounced dropping of the abdomen, especially noticeable in older mares. During the last week prior to foaling, the ligaments, muscles and other structures surrounding the mare’s pelvis and perineum soften in preparation for birth. The vulva becomes relaxed in the hours prior to foaling. The mare’s behavior often changes during the last few days or hours preceding foaling. Mares near term tend to isolate themselves from other mares, go off feed and pass small amounts of manure or urine frequently.
There are several tests to predict the onset of labor in addition to close observations. Calcium concentrations in mammary secretions have been used successfully for many years to predict impending labor. Calcium concentration in milk increases sharply as the mare approaches the time of foaling. It is recommended that testing be initiated several days prior to the expected due date. Testing in mares with an unknown breeding date should begin when significant udder development is noted and a small amount of secretion can be obtained. One commercial kit uses a test strip that is dipped into a specific dilution of milk and distilled water and observed for color change in any of five test squares. The chance of foaling within 24 hours increases as the number of squares changing color increases.
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A second test kit is based on a chemical reaction, measuring calcium carbonate. Again, high calcium levels suggest a high probability of foaling, while low calcium levels suggest that the mare is less likely to foal in the next 12 to 24 hours. More recently, changes in the acidity or pH of a mare’s milk have been used to indicate that foaling is near. Mare milk pH is usually around 7.0 to 7.4 in late gestation. A dramatic drop in milk pH to approximately 6.4 or lower occurs the day prior to foaling. Commercial pH test strips, calibrated in the range of 5.5 to 8.0, can be used as an on-farm indicator of impending labor. The last few days prior to foaling can be especially tedious for the owner, farm manager or foaling staff. Late-term pregnant mares should be monitored closely to optimize services of farm or veterinary personnel, maximize use of foaling space and to assist with the safe delivery of the foal if needed.