Expected birth date is an age-old question for horse breeders tending four-legged mothers-to-be as much as any proud parent. Most mares are bred naturally by scheduled breeding with the stallion or through artificial insemination.

Dave Freeman, PhD, Oklahoma State University Cooperative Extension equine specialist, said knowing the last breeding date and approximating the expected gestation length should get a horse manager in the ballpark of the expected foaling date.

"The normal gestation length of broodmares averages 338 to 345 days," he said. "Simply moving ahead 11 months from the last breeding should get you on the early side of expected foaling date."

One point of caution, however: gestation length will be variable between mares and even the same mare from year to year