How Long Are Horses Pregnant? Your Guide to Horse Gestation

A mare’s gestation period can vary depending on factors such as breed, age, health, and previous pregnancies. Understanding these factors can help owners better prepare for the birth and ensure the mare receives proper prenatal care.

On average, a mare carries her foal for 340 days (11 months). However, each pregnancy is unique, and some broodmares may give birth slightly earlier or later.

“Gestational length in the mare is highly variable, and a normal pregnancy can range from 320 days to 365 days,” says Alana King, DVM, DACT, a theriogenologist at Millbrook Equine in Millbrook, New York. “Shorter gestational lengths are usually due to a problem, commonly placentitis or twins. These foals may show signs of prematurity, such as underdeveloped lungs and joints.”  

Veterinarians often use the concept of a “safe date,” which is the earliest point at which a foal can be born and still be considered viable, likely to survive. Generally, a foal born before 320 days of gestation is considered premature and may require intensive veterinary care, just like a human preemie.

Like a human pregnancy, a horse’s gestational period is divided into three distinct trimesters, each marked by significant developmental milestones for the foal and physiological changes in the mare.

“Pregnancy is confirmed via ultrasound at 14–16 days, when the veterinarian should also check the mare’s uterus for twins,” says Courtnee Morton, DVM, CVA, CVC, a veterinarian at Chewy and the owner of Southern Comfort Equine, based in Hico, Texas.

“The heartbeat and viability of the embryo are then confirmed around 25–30 days of gestation,” Dr. Morton adds.

Because most early embryonic losses occur within the first 60 days, veterinarians may want to recheck the mare around that time, Dr. Morton says. This timestamp is also the beginning of the limited window for potential foal sexing (determining the embryo’s sex) via ultrasound.

Throughout the first trimester, mares may not have much of a belly or show significant outward signs of pregnancy. Regular veterinary checkups and careful monitoring are essential to ensure a healthy start and early development.

During this period, the fetus grows rapidly and the mare’s body begins to change in response.

The foal’s body takes shape, with distinguishable features such as a mane and tail beginning to form. The fetus also experiences a significant growth spurt and moves frequently in the womb.

The mare may also begin to show slight physical changes, such as weight gain and a thickening of the abdomen.

“The uterus drops lower in the abdomen as the foal grows, and typically changes position to have the head pointing backward towards the mare’s cervix,” Dr. Morton explains.

During this second trimester, the mare’s nutritional requirements increase. Broodmare owners should consult a veterinarian about appropriate diet changes to support the foal’s development. Your mare may need a specific grain made for pregnant horses, such as Nutrena SafeChoice Mare & Foal Pellet Horse Feed.

It’s also important to maintain the mare’s overall health and meeting her pregnant body’s ever-growing needs. This includes maintaining appropriate hoof care as the body carries extra weight, and making sure you’re giving your expecting mare high-quality hay.

The third trimester is the final stage of pregnancy, spanning from day 226 to the foal’s birth (day 320–360). This is a crucial time for both the mare and the foal as final preparations for birth take place. The mare’s belly can enlarge significantly as the foal reaches their birth weight, gaining about a pound per day.

• Waxing teats: In the final days of pregnancy, the mare’s teats wax as her udder begins filling with colostrum, the nutrient-rich first milk that provides essential antibodies to the newborn foal. “Once the mare is within two to four weeks of foaling, udder development (“bagging up”) may be visible, indicating very late gestation and impending foaling,” Dr. King says.
• Relaxed rear end muscles: “You will also notice ‘softening’ or relaxation of the muscles around the tail head and rear end (perineum) in preparation for labor,” Dr. Morton adds.
• General discomfort: When labor is imminent, the mare will almost certainly display signs of discomfort, like pacing and sweating. “She may lay down often, trying to get the fetus in a more comfortable position prior to labor. She may also isolate more from her herdmates,” Dr. Morton says.

Mares should be monitored closely during this time to maximize the chances of a smooth and safe delivery. Preparing a foaling kit, including towels, antiseptics, and emergency veterinary contact information, is essential for a stress-free birth and proper newborn foal care.

Dr. Morton emphasizes the need for in-utero foal care, long before birth.

“Be sure to follow all vaccination and deworming protocols throughout pregnancy, as advised by your veterinarian,” she says. “This usually involves a rhinopneumonitis (EHV) vaccine at five, seven, and nine months of gestation and yearly boosters four to six weeks before parturition.”

If you know when your mare was bred, use her breeding date and add 340 days to estimate her due date. While not an exact science, this is a good predictor of when the foal will most likely arrive.

If you acquire a pregnant mare without much background information, it’s not as easy to determine how far along she is.

“Gestational age can be very difficult to determine in a mare with an unknown breeding date,” Dr. King says. “In earlier stages of pregnancy (up to 60 days), the embryo’s development follows a very predictable course and ultrasound can easily and accurately determine age. The size of the pregnancy on palpation (feeling for the foal/embryo via a rectal exam) can also be determined up to approximately 90 days of gestation.”

Beyond that, gestational age can only be estimated within a 30-day accuracy window.

Whether you breed horses professionally or are looking forward to the birth of your own beloved mare’s first foal, try to keep up with the equine gestation timeline and phases. In either case, your veterinarian will be closely involved from conception to birth to ensure the health and well-being of both mare and foal.

This content was medically reviewed by Kaela Schraer, DVM.