Mare Gestation Calculator

For horse breeders and owners, the anticipation of a new foal is a highlight of the year. Accurate prediction of the foaling date is crucial for ensuring the mare receives the proper care, for preparing a safe foaling environment, and for being present for the birth. Our Mare Gestation Calculator provides a helpful estimate to guide your preparations.

Understanding Equine Gestation

A mare's pregnancy is a long journey, significantly longer than many other domestic animals. The calculator uses the last known breeding date to forecast the most likely foaling date.

• Average Gestation Period: The average length of a mare's pregnancy is approximately 340 days, or about 11 months.
• Normal Range: It's important to know that this is just an average. A normal, healthy pregnancy can range widely, typically from 320 to 365 days. It is not uncommon for a mare to go nearly a full year!
• Factors Influencing Length: The time of year the mare was bred (mares bred in the spring often have slightly shorter gestations), the sex of the foal (colts may be carried a few days longer than fillies), and individual mare tendencies can all affect the exact length.

The calculator uses the 340-day average to give you a target date, but you should be prepared for the foal to arrive in the entire window of 320-365 days.

Confirming the Pregnancy

A veterinarian is your best partner in managing a pregnant mare. They can confirm the pregnancy and monitor its progress.

• Ultrasound: An ultrasound is the most common method. It can detect a pregnancy as early as 14-16 days after ovulation. It can also be used to check for twins, which is a high-risk situation in horses.
• Blood/Urine Tests: Hormonal tests can detect pregnancy-related hormones, usually done between 45 and 120 days of gestation.
• Palpation: An experienced veterinarian can manually feel for signs of pregnancy by rectal palpation, typically after 45 days.

Signs of Impending Foaling

As the estimated due date approaches, watch your mare closely for these signs that foaling is near:

• Udder Development ("Bagging Up"): The mare's udder will begin to fill with milk, usually 2 to 6 weeks before foaling.
• "Waxing": In the final days or hours, small, waxy beads of colostrum may appear on the ends of her teats. This is a very reliable sign that foaling is imminent (usually within 24-48 hours).
• Relaxation of Muscles: The muscles around her tailhead and vulva will become soft and relaxed.
• Behavioral Changes: The mare may become restless, pace, sweat, or show signs similar to colic. She may frequently look at her flank. Most mares prefer to foal at night in a quiet environment.

Frequently Asked Questions (FAQ)

Is it really just an estimate? Why can't the date be exact?

Unlike humans, mares have a highly variable gestation length. The 320-365 day window is considered normal. It's best to use the calculated date as a guideline to start preparing and monitoring, not as a fixed appointment.

What is the "1-2-3 Rule" of foaling?

This is a guideline for a normal birth. The foal should be standing within 1 hour of birth, nursing within 2 hours, and the mare should have passed the placenta within 3 hours. If any of these milestones are significantly delayed, it's important to contact your veterinarian.

What should I have ready for foaling?

Prepare a "foaling kit" with essential supplies: clean towels, a bucket for water, iodine or chlorhexidine solution for the foal's navel stump, a tail wrap for the mare, a flashlight, and your vet's emergency phone number. The foaling stall should be large, clean, and deeply bedded with straw.