In foal is the standard equine term for a pregnant mare. The phrase appears in sales listings, breeding records, and veterinary documentation as confirmation that a mare is carrying a developing foal. A mare is confirmed in foal by a veterinary examination that may include rectal palpation, transrectal ultrasound (the most common modern method), or blood/urine hormone testing. Ultrasound confirmation is typically possible by day 14 to 16 after ovulation; a heartbeat is visible by day 25 to 28.
Gestation Length
The average equine gestation period is 340 days (approximately 11 months), with a normal range of 320 to 360 days. Individual mares tend toward consistent gestations. Foals born before day 300 are premature and have significantly reduced survival rates without intensive veterinary care. Foals born between days 300 and 320 are premature to early-term and may require additional support. The foaling season in the Northern Hemisphere is typically February through June, as horses are seasonally polyestrous and naturally cycle in spring.
In Foal in Sales Listings
A mare listed for sale as in foal to [stallion name] is being sold with a confirmed pregnancy. This is a significant value factor: the buyer receives both the mare and a foal due in the next breeding season, plus the stud fee (already paid) is effectively included in the purchase price. The listing should specify: the stallion name, breeding date or confirmed pregnancy date, the method of confirmation (ultrasound is standard), the number of days of gestation at time of sale, and whether a live foal guarantee applies. Buyers should verify the pregnancy independently via veterinary examination before completing the purchase.
Care of the In-Foal Mare
Nutritional needs increase significantly in the final trimester (months 9-11), when 80% of fetal growth occurs. Mares in late pregnancy require increased digestible energy, protein (especially lysine), calcium, phosphorus, and vitamin E. Vaccination and deworming protocols for in-foal mares follow specific timing restrictions; consult a veterinarian before administering any product to a pregnant mare. Exercise continues to be beneficial through late pregnancy unless complications arise.
See also: dam; foal; at stud; selective breeding.