Foaling predictor tests measure certain electroyte levels (calcium, sodium and potassium), and pH in the mare’s mammary secretions (milk or colostrum) as she gets closer to foaling.
In normal mares, these levels change as foaling nears, and the pH drops right before foaling. Monitoring the levels of these electrolytes and pH gives additional information about when a mare might foal.
These tests should not be relied upon entirely for the prediction of a foaling time. Rather they should be thought of as one more piece of information to consider when guessing when a mare will foal.
There are multiple commercial tests available, most measuring calcium levels in the milk sample. Commercial water hardness tests (measuring calcium carbonate) are frequently used and are cheaper and may be more reliable than those marketed as foaling predictors. They are widely available online.
In my experience, foaling predictor tests are only marginally more useful than my clinical examination and visual examination of milk color change, which correlates with the change in calcium level. In most mares, the initial secretion one can express from the teats is a honey colored, sticky, thin and mostly clear fluid that has low levels of calcium and a high pH. Within 24-48 hours of the time most mares deliver their foals, the secretion turns into something that looks more like milk. It is cloudy, white to yellow in color and is increased in volume. These visible changes usually correlate pretty closely to the electrolyte changes, but in some cases, they do not.
Shortly before a mare foals, the calcium and potassium content of udder secretions should increase sharply, and the sodium content should decrease. Depending upon the specific test: If the calcium> 250 then the likelihood is high that the mare will foal within 24 hours. The pH should also sharply decrease within 24 hours of foaling.
HOW TO USE THE TESTS
Dedicated foaling prediction kits have specific instructions for sampling and testing. For water hardness tests a small sample of milk – usually 1cc (1ml) is milked into a clean glass vial.
Depending upon the specific test being used, it is diluted in distilled water 1:6 usually. The test strip is immersed in the mixture. The test squares change color based on the level of calcium within the sample. The pH strips work similarly, with color coded squares on the strip correlating to a particular pH.
Talk to your vet about the validity and usefulness of these tests, when to start testing and how often to test. Overzealous use of these tests can be a waste of precious colostrum (first milk).
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