Foaling Date Nearing?
David W. Freeman
OSU Extension Equine Specialist

Most mares are bred naturally by scheduled breedings with the stallion (hand mating) or through artificial insemination. Knowing the last breeding date and approximating the expected gestation length should get you in the ballpark of the expected foaling date. The normal gestation length of mares averages 338 to 345 days. Simply moving ahead 11 months from the last breeding should get you on the early side of expected foaling date. However, gestation length will be variable between mares and even the same mare from year to year. There are several conformational and behavioral changes in the mare that suggest the foaling day is approaching. They should better pinpoint the day of foaling. Some of the more consistent changes in mares that suggest approaching delivery date are provided below. The changes in the mineral concentration of the milk immediately prior to foaling can be monitored with commercially available kits (FoalWatch), and similarly with water hardness check strips found at several commercial outlets such as plumbing supply and home improvement stores.

Changes in Mares Suggesting Approaching Foaling Day

- Udder Fills 2 to 4 weeks prior: maiden mares may not exhibit; may have filling and regression periodically through last trimester.

- Change in tailhead conformation 1 week to 1 month prior; musculature relaxes; abdominal area drops down.

- Teats fill with milk 2 days to 1 week prior: variable response.

- Dripping of milk 1 day to 1 week prior: variable response.

- Waxing 1 to 4 days prior: secretions form wax-like beads on end of teats.

- Changes in milk mineral content 1 1/2 to 1 day prior: calcium concentration increases.

- External genitalia relaxes 1/2 to 1 day prior: musculature under tailhead relaxes, becomes soft and loose.

Not all signs are seen in all mares and signs will differ in intensity and occurrence from maiden pregnancy to those following previous births.