If you have a pregnant mare, one thing you would like to know is when she going to foal. Even if you have a breeding date, there is still a lot of variability and this causes a lot of sleepless nights. In the past, milk from the mare has been tested for calcium and electrolytes to get a range of foaling period and these tests are fairly successful if you have experience with them. There is a technique in Japan that was reported in the AVMA journal using simple pH strips to check the mare's milk and determine foaling time. Dr. Rob Franklin, a board certified internal medicine specialist, reports the pH testing of milk seems to be as accurate at predicting foaling time as the standard calcium tests strips. The pH strips are also less expensive and require less time to run the test.
The pH milk test is performed by milking a very small amount of milk out of the teat, applying it to the test strip, and reading it immediately. Unlike the calcium test strips, this requires no mixing. If the pH is less than or equal to 6.4, the mare has a 97.7% likelihood of foaling within the next 72 hours. In the study, pH values greater than 6.4 corresponded to a 99.4% chance the mare would not foal within the next 24 hours. The bottom line is if the pH of the mare's milk is greater than 6.4, you can feel fairly sure she will not foal that night. Once it gets less than 6.4, she will foal within the next three days. You will need a pH paper with a narrow range of measurement from 5.5 to 8 and with a scale broken down into tenths of a pH to accurately perform this test. These are strips are available online.