Mare Gestation Calculator

Equine Gestation Milestones

Key gestation milestones for mares are important markers that indicate the progress of the pregnancy and the development of the fetus. Here's a timeline outlining these milestones:

1. Days 14-16 (27 Dec 2024) - Post-Ovulation: First opportunity to confirm pregnancy through ultrasound. Vets look for the presence of an embryonic vesicle.
2. Day 25-30 (7 Jan 2025) - Heartbeat Detection: A critical milestone where the fetus's heartbeat can be detected via ultrasound. This is also a time when twins can be identified and managed if necessary.
3. Day 40-45 (22 Jan 2025) - End of Embryonic Period: The transition from the embryonic to the fetal period. The risk of embryonic loss decreases significantly after this point.
4. Day 60-65 (11 Feb 2025) - Sex Determination: It's possible to determine the sex of the foal via ultrasound.
5. Day 150 (12 May 2025) - Fetus Resembles a Tiny Horse: By this time, the fetus has developed most of the adult features and begins to look like a miniature horse.
6. Day 180 (11 Jun 2025) - Fetal Movement: The mare owner might start to observe fetal movements.
7. Day 210 (11 Jul 2025) - Rapid Fetal Growth: The fetus enters a period of rapid growth which continues until birth.
8. Day 270 (9 Sep 2025) - Colostrum Formation: The mare's body begins to prepare for foaling by starting colostrum production.
9. Day 300 (9 Oct 2025) - Preparation for Birth: It's a good time to start preparing for the foaling, ensuring that all necessary supplies and facilities are ready.
10. Day 320-345 (29 Oct 2025) - Final Stages: This is the typical range when most mares will foal, although some may go as long as 365 days. Owners should monitor for signs of impending birth, such as the mare's udder filling and the relaxation of the pelvic ligaments.
11. Foaling (18 Nov 2025): The culmination of the gestation period. Most mares will foal quickly and without human intervention, but it's important to be prepared to assist or call a veterinarian if complications arise.

How Do You Calculate a Mare's Foaling Date?

Calculating a mare's foaling date involves a few straightforward steps. Here's a list to guide you through the process:

1. Determine the Date of Conception: This is the day when the mare was successfully bred. If the exact date is unknown, use the last date of the breeding period.
2. Understand the Average Gestation Length: The average gestation period for a mare is approximately 340 days, but it can range from 320 to 365 days.
3. Adjust for Breed Variations: If you know the breed of the mare, adjust the average gestation period based on typical lengths for that breed (if available).
4. Consider Seasonal Variations: Mares foaling in colder months might have a slightly longer gestation period, while those in warmer months might have a slightly shorter one.
5. Account for Mare's History: If the mare has had previous foals, consider her past gestation lengths as they can be a good indicator of her usual gestation period.
6. Regular Veterinary Check-ups: Regular check-ups can help estimate the foaling date more accurately, especially as the mare approaches the end of her pregnancy.
7. Watch for Physical Signs: As the expected foaling date approaches, observe the mare for physical signs of impending birth, such as udder development and relaxation of the pelvic ligaments.
8. Adjust Expectations: Be prepared for a range of possible foaling dates, as predicting the exact day is often challenging.
9. Use a Gestation Calculator: To simplify the process, you can use our equine gestation calculator. You enter the date of conception, and it automatically calculates the estimated foaling date.

Keep detailed records of breeding, gestation, and foaling for future reference, as this data can be invaluable for managing subsequent pregnancies.

Gestation Periods For Different Mare Breeds

Below is a table showing the gestation periods for various breeds of mares. While there are average gestation lengths for different breeds, individual mares may deviate from these averages due to various factors like age, health, environment, and genetics.

Mare Gestation Reference Table

Below is a reference table showing the foaling date for all days of the year.