Detection of Impending Parturition

An individual horse's gestation length can be extremely variable. The rate of in utero maturation of the fetus influences a particular gestation length [1]. Determination of the expected time of foaling allows appropriate observation of the foaling for detection of problems. The vast majority of mares foal at night.

I. Maternal Physical Factors

1. Gestation length > 320 days.
2. Relaxation of the pelvic ligaments and elongation of the vulva and relaxation of the cervix.
3. Waxing of teats - Small droplets of milk on the ends of nipples.
4. Colostrum in mammary gland: Editor's Comment - Must measure immunoglobulin in milk to determine if it is colostrum. Use specific gravity or glutaraldehyde test. None of these signs indicate that foaling will occur within a certain time period.

II. Mammary Secretion Changes

1. Changes in electrolyte composition of mammary secretions during late pregnancy have been used to determine fetal readiness for birth [2,3].
2. Immediate prefoaling changes are an increase in calcium to (≥40 mg/dl), potassium (≥35 mEq/L), and a decrease in sodium (≤30 mEq/L).
3. Three field tests [4-6] using a form of water hardness test strips for calcium content have indicated some practical applications.

1. Predict A Foal™️ - Mare foaling predictor kit [a]

1. 1 cc mammary section taken every evening and 5 zones on the test strip are examined.
   According to one study [5]:

1 zone or less <1% chance of foaling within 12 hrs
4 zone 80% chance of foaling within 12 hrs
5 zone 95% chance of foaling within 12 hrs

2. This test is not 100% accurate but provides additional information on the time of foaling which may minimize sitting up with the mare.
3. Another comparison study found a 53% probability that the mare would spontaneously foal within 24 hours after reaching a 4 color bar change, 20% chance of not foaling within 24 hours after 4 bar color change, and a 27% chance of foaling without reaching this cutoff level. Placental or fetal abnormalities may influence the reliability of any of these tests [3].

2. Softcheck™️ Water Hardness Test Strip [b] (Determines Ca and Mg)

1. Mammary secretions checked once daily until total hardness exceeded 120 ppm. Then mares were checked twice daily [6].
2. 250 ppm water hardness used as decision point (for maximal observations) along with other physical findings [6].
3. 72% probability of foaling within 24 hours when 250 ppm water hardness first detected in prefoaling mammary secretions [6].
4. 22% chance mare would not foal in 24 hours when ≤ 250 ppm water hardness detected [6].
5. 6% chance mare would foal prior to reaching the 250 ppm water hardness [6].

3. Titrets™️ Calcium Hardness Test Kits (Determines Ca in milk only)

1. > 250 ppm calcium carbonate content used as cut off point for ready-to-foal in one study [6].
2. 59% probability of foaling within 24 hours and 23% chance mare would not foal within 24 hours if > 250 ppm test result. 18% chance of foaling within 24 hr of ≤ 250 ppm test.
3. Authors of study suggest using 200 ppm with this test would improve chance of foaling within 24 hours to 88%.
4. This method considered most reliable

Editor's Comment - To use these methods, collect 1-5 ml of mammary secretion in clean plastic vial. Dilute 1:6 with double distilled water.

III. Foal Alert System [d]

This system has a transducer which is sutured to the mares' vulva and when the foal enters the birth canal, it is activated and sets off an alarm or auto dialer. When used according to manufacturer's directions, a very reliable unit.

1. Animal Health Care Products, 1-800-689-7601, https://www.arssales.com/epfo-predictafoal.html
2. Environmental Test Systems, Elkhart, IN 46514, https://www.etsstrips.com
3. CHEMetrics, Inc. Calverton, VA 22016 1-800-356-3072, https://www.chemetrics.com
4. Foal Alert - 1-800-237-8861 - https://foalert.com