PREDICTION OF FOALING
Patrick M. McCue, DVM, PhD, Diplomate ACT
Equine Reproduction Laboratory
Colorado State University
Fort Collins, CO 80521
The last few days prior to foaling can be especially tedious for an owner, farm manager or the 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 as needed.
Physical Parameters
Clinical signs of impending foaling begin subtly a month or so prior to the expected due date (Table 1). Changes become more dramatic and occur more rapidly as day of foaling approaches.
Table 1. Clinical signs of impending foaling.
Article
The first noticeable change is in the mammary gland, which begins to enlarge 2 to 6 weeks prior to term. Some mares may 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 fill with milk. The secretion by the mammary gland changes from a clear straw-colored fluid to a more turbid milk-like substance as the due date draws near. The mammary secretion becomes thick and honey-like as colostrum develops within the last day or two prior to foaling.
A thick dried exudate is often observed to accumulate at the ends of the teats 24 to 48 hours prior to foaling. This ‘waxing’ of the teat ends is due to colostrum that has slowly emanated from the udder and dried upon contact with air and is a classic sign that foaling is imminent. The extent of waxing can range from tiny droplets to elongated candle wax-like formations that project up to an inch from the teat ends. However, not all mares will wax up and the duration from onset of waxing to foaling can be quite variable. In addition, some mares will transiently develop wax at the teat ends 1-2 weeks prior to foaling.
Clinical Comment
Waxing is the most commonly observed clinical sign that a mare is close to foaling. Approximately 70 % of mares ‘wax up’ prior to foaling. Of those mares that produce ‘wax’, approximately 70 % will foal within 24 to 48 hours.
In the last 2 to 3 weeks of pregnancy the abdominal muscles relax causing a pronounced ‘dropping’ of the abdomen, which is 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, elongated and edematous in the hours immediately prior to foaling. The behavior of the mare often changes during the last few days or hours preceding foaling. Mares near term may tend to isolate themselves, go off feed and pass small amounts of manure or urine frequently.
Monitoring Milk Calcium Levels
Prediction of foaling based on changes in calcium concentrations in mammary secretions has been used successfully for many years. Calcium concentration in milk increases sharply as the mare approaches the time of foaling. Calcium levels above 200 ppm indicate that the mare has a high probability of foaling within the next 48 hours. Conversely, mares with a milk calcium level of less than 200 ppm are unlikely to foal in the next 24 hours. 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.
Two tests are available commercially. Predict-a-FoalTM (Animal Reproduction Systems, Inc., Ontario, CA) uses a test strip that measures both calcium and magnesium. The strip is dipped into a specific dilution of milk and distilled water and observed for color change in any of the 5 test squares. The chance of a mare giving birth that night increases as the number of squares that change color increases.
FoalWatchTM (CHEMetrics, Inc., Calverton, VA) is based on a quantitative chemical reaction measuring calcium carbonate. A milk sample is obtained and mixed with distilled water. An indicator dye is added and small amounts of the test sample are aspirated into a calibrated titration chamber until the color in the chamber turns from orange-pink to blue. Level of calcium carbonate is determined using a scale provided on the glass chamber. 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.
Mammary Fluid pH
Mammary fluid pH can be used in conjunction with clinical signs and other laboratory tests to predict foaling. A decrease in pH has been reported in the milk of mares prior to giving birth. A pH value of 6.4 has been suggested as a standard value for assessment of impending parturition in mares. Unfortunately, the positive predictive value to estimate the likelihood of an individual mare foaling within 24 hours when her milk pH first decreases to = 6.4 is only 54.2 %. Perhaps the best clinical use of the milk pH test is to predict when a mare is not ready to foal. The negative predictive value of an individual mare not foaling within 24 hours if the pH is ? 6.4 is 99.4 %.
Measurement of pH with a meter is more accurate than estimation with pH paper. The type of pH paper may be critical as some cannot detect a small change in pH. It is recommended that pH paper that detects pH in a range of 5.5 to 8.0 in increments of 0.2 be used to evaluate mare mammary fluid.
Clinical Comment
Measurement of milk pH is less sensitive and less accurate in predicting impending foaling than measurement of milk calcium.
Labor Alert Devices
Labor alert devices are intended to signal an owner or foaling attendant that the mare is in the process of giving birth. The design and physical location of the various devices vary between units. Some units contain a radio transmitter attached to either a girth strap or a halter. The transmitter sends a signal to the receiver when the mare lies in a lateral or foaling position. Another system (Foalert®) utilizes a transmitter sutured to the vulva of the mare. Separation of the vulva lips at foaling pulls a magnet out of the transmitter, which then sends a signal to receiver. The receiver can be attached to an auto-dialing device which can be programmed to activate a pager or send a message to one or more phones pre-programmed into the unit.
None of the labor alert devices are without inherent problems associated with false alarms or failure of the system to be activated during labor. They are beneficial in that mares can be monitored continuously without constant or periodic observations.
Clinical Comment
Labor alert devices may be most effective in allowing farm personnel to go about their routine chores or business during the daytime when one does not necessarily expect a mare to foal.
Video Monitoring Systems
Video systems are becoming common on broodmare farms to monitor late-term mares. These systems allow for close supervision of mares without the necessity of the foaling attendant to wait by the stall or to make repeated visits to the stall every 15 to 30 minutes throughout the night. An added benefit is that the systems minimize disturbances to nervous mare by decreasing stall visits. However, in the end someone still needs to monitor the mare and the position of the mare relative to the camera may limit visibility.
Two general types of video monitoring systems can be implemented. Closed-circuit television systems utilize a small video camera to evaluate activity in the foaling stall. The video feed is transmitted to a television monitor at a site distant to the stall (i.e. a house, barn office, etc.) by either hardwiring or by wireless technology. Hardwiring may be preferred in many instances because the wireless system 1) may not be able to transmit the signal if a long distance is involved, 2) may not be able to transmit through steel or block buildings adequately, and 3) may not transmit the signal adequately during severe weather. It may be preferable to install a black-and-white camera system rather than a color camera system because of the enhanced sensitivity of black-and-white cameras in low light settings. This may change as camera technologies improve in the future.
A second video system utilizes a digital video camera connected to the internet. An owner or foaling attendant can monitor the video image from any computer or smart phone with internet access. The traditional camera systems may be advantageous over web camera systems in the image is often better in low light, there is no lag time in the image transmitted as can occur with some computer-based systems, and hard-wired systems will continue to function in the event that internet access is limited or unavailable.
| Sign |
Time frame relative to foaling |
| Mammary gland development |
Begins 2-6 weeks prior to foaling |
| Perineal relaxation |
1-3 weeks prior to foaling |
| Engorgement of teat ends with colostrum |
7-10 days prior to foaling |
| Waxing of teat ends |
48-72 hours prior to foaling |
| Elongation and swelling of the vulva |
0-24 hours prior to foaling |
| Dripping milk from udder |
12-24 hours prior to foaling |
Clinical Comment
Evaluation of calcium levels in mammary gland secretions is useful in prediction of when mares are likely to foal and are equally useful in predicting that a given mare is unlikely to foal in the next few days. Calcium testing may not be necessary on farms if trained foal-watch personnel are available. However, the tests may be quite valuable on smaller operations with limited staff.
Animal Reproduction Systems
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