How Long is a Mare Pregnant? (The 340-Day Equine Rule Explained Simply)
On average, a horse carries her foal for 340 days (approximately 11 months). However, healthy foals can arrive anywhere between Day 330 and Day 350 from breeding day.
Why such a wide foaling window? Mares bred in early spring (January or February) frequently carry their foals 5 to 10 days longer than mares bred in late spring when warm weather and long days naturally stimulate birth hormones.
Use simple water-hardness or milk-calcium test strips starting on Day 325. When calcium in the mare's milk rises above 200 ppm, over 98% of mares foal within 24 to 48 hours!
Does My Horse's Breed Change Her Foaling Date?
While 340 days is the standard average, different equine breeds naturally vary by a few days:
🏇 Thoroughbred (Natural Live Cover)
Strict RegistryThe Jockey Club requires natural live breeding. Foaling close to January 1 is prized for racing age registry, making exact breeding day tracking essential.
🚜 Draft Horses (Clydesdale, Percheron)
Longer CarryLarge draft mares frequently carry foals up to 345–350 days. Due to their size, make sure your foaling box stall is at least 16x16 feet for safe delivery.
🤠 American Quarter Horse
Average 338 DaysAthletic stock horse mares often deliver 2 to 3 days ahead of the standard average. Keep a night camera active in the stall from Day 330.
🐴 Miniature Horse & Ponies
Watch FoalingPonies and mini horses have a slightly shorter gestation (335 days). Miniature mares have a higher incidence of difficult delivery, so have your vet on standby.
Month-by-Month Care: Critical Rhino Vaccine Milestones
Your vet checks for a healthy single embryo. Twin pregnancies in horses are dangerous and require veterinary reduction.
Administer killed Equine Herpesvirus-1 (EHV-1) vaccines at Month 5, Month 7, and Month 9 to protect against virus-induced abortion.
Boosters for Tetanus, West Nile, and Sleeping Sickness ensure her rich first milk (colostrum) protects the newborn foal with antibodies.
Waxy yellow colostrum appears at teat tips ("waxing up"). Active foal delivery takes only 15 to 25 minutes!
🚨 Emergency Signs: When to Call the Equine Vet Immediately
- Active pushing (Stage 2) lasts for more than 30 minutes without the foal arriving.
- A dark red velvet bag appears ("Red Bag" delivery) — rupture it immediately to prevent suffocation!
- The 1-2-3 Rule: Foal must stand in 1 hour, nurse in 2 hours, and mare must pass the placenta in 3 hours.
- If the placenta is retained past 3 hours, call your vet immediately (causes toxic founder/laminitis).
Quick Comparison: Pregnancy Length Across Animals
Frequently Asked Questions About Horse Pregnancy
Can a pregnant mare stay out on pasture? ▼
Yes, mares benefit from gentle turnout during the first 7 to 8 months. However, beware of endophyte-infected tall fescue pasture, which causes no milk and thickened placenta. Remove mares from fescue pastures 60 to 90 days before foaling.
What is a "Red Bag" delivery during foaling? ▼
A red bag delivery occurs when the placenta detaches early. The velvety red membrane appears before the water bag. The foal cannot breathe! You must immediately snip the red bag and pull the foal out to save its life.
Why should you use straw instead of wood shavings in a foaling stall? ▼
Newborn foals are wet. Wood shavings and sawdust stick to their nostrils, eyes, and wet umbilical cord stump, causing breathing issues and infections. Clean wheat straw provides soft, clean, non-stick bedding.
How do I save or print my mare's foaling schedule? ▼
Simply click the blue "Print / Save Due Date Schedule (PDF)" button in Step 3 above. It generates an official 1-page certificate with all your dates and emergency supplies ready to pin on the stall door or save as a PDF!