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Foaling Predictor Tests



The concept behind foaling predictor tests relates to the monitoring of 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 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, not.

I currently do not use these tests when I am foaling out mares in our veterinary practice. I do use a foaling monitor – the Foalert System, which I have found vital.


Shortly before a mare foals, the calcium and potassium content of udder secretions should increase sharply, and the sodium content should decrease. The pH should also sharply decrease within 24 hours of foaling.

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.


These tests should only be used in addition to other means of determining foaling time. Do not rely on them entirely. Talk to your vet about the reliability of these tests.


These tests provide one more valuable piece of information that can help foaling supervisors more accurately predict when foaling will occur. They are inexpensive and non-invasive.


These tests are not always more reliable than a clinical examination performed by your vet or experienced breeder.

In some cases, mares do not "read the book". In my experience, the most common problem is that calcium levels rise, and can stay high, for days prior to foaling.

Placental or fetal abnormalities can influence the reliability of these tests.

Overzealous use of these kits may be a waste of precious colostrum.

Helpful Outside ResourcesCredible Equine Health Information on the Internet

Helpful Terms & Topics in HSVGWritten, Reviewed or Shared by Experts in Equine Health


  • How reliable are foaling prediction tests?
  • Do you use these tests when monitoring foaling mares?
  • What specific test is best?
  • How often should the mare be tested, and when should testing start?
  • What other signs should be monitored to accurately predict foaling?
  • How do you ensure that mares under your care are observed foaling?
  • Foalalert, Inc.
    Birth Monitoring System
    Foalert is the foremost birth monitoring system available to breeders large and small. Originally developed for the equine industry, the foalert system is applicable to a wide variety of breeds and species. Whether you are breeding mares, cows, sheep or llamas, foalert offers the equipment that allows you to be there to welcome your new foal, calf, lamb, or cria into the world. If you have questions, or would like to purchase a foalert system, please click on the "Learn More" button.
    * Would you like to showcase your equine product or service in
    Horse Side Vet Guide? Contact us to start the conversation.
    Author: Doug Thal DVM Dipl. ABVP


    Madigan JE, Manual of Equine Neonatal Medicine 4th edition. on IVIS IF, Ball BA, Troedsson MH, Elisa SM. Decreasing pH of Mammary Gland Secretions Predict Foaling and Are Correlated With
    Electrolyte Concentrations in Prefoaling Mares. In AAEP Proceedings 2014.


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