Gestation Period for Horses: How Long are Horses Pregnant for?

Who doesn’t love the spidery legs, the fuzzy mane and tail, the silky baby fur and velvety muzzle of a foal? The idyllic images of a mare and her baby running through the grass make the rest of the world disappear as the beauty of motherly love takes the viewer’s breath away. Interestingly enough, the period of horse pregnancy is nearly as fascinating and beautiful as the first year of a foal’s life.

Horses are pregnant for an average of 330 days, or roughly eleven months. That said, a horse pregnancy can also last up to 362 days and as little as 300 days (though neither of those extremes is ideal). Mares go into heat every three weeks starting around one year old, and continue to go into heat for the rest of their lives. Unlike humans, they do not experience menopause. Depending on how severe the climate is, many mares do not go into heat during the wintertime. The best case scenario is for the foal to be conceived in summertime and born in the following spring. This way their mothers can get the maximum nutrients from the spring grass, passing these nutrients to the foals in their milk. The foals have the maximum time throughout the spring, summer, and fall to grow up before winter sets in. That said, horses can be born anytime throughout the spring and summer. 

Most of a horse fetus’ growth takes place in the last three months of the pregnancy. This means that during most of the time that a mare is pregnant, she can still be exercised normally. In fact, this is all the better for the growing fetus – it will have a stronger mother who has better circulation, more developed muscle tone, and can overall manage her pregnancy better. After about the eighth month of pregnancy, however, the foal will have grown big enough that it is exacting greater pressure on her diaphragm. This inhibits the mare’s ability to breathe deeply during exercise, and her workload should be adjusted accordingly.

You can tell when a mare is pregnant after about a month. Pregnancy can be confirmed by ultrasound or by palpation around day 12. For palpation, the veterinarian can feel the uterus and fallopian tubes through the rectum, and their size and shape can confirm whether the mare is pregnant or not. The size of the mare’s belly is not a guarantee of pregnancy! The basic bodily structures of the foal are generally formed by day 23, and the heartbeat can be detected by day 24.

Around the fourth month of pregnancy, the foal is about the size of a kitten, with fine hairs forming what will become whiskers on their muzzle, lips, chin, and eyelashes. Around this time, certain weeks your mare’s behavior may change – she may be very cuddly some days, or more standoffish other days. Her foal has less room to move around, so she feels its kicks and movements more acutely. She may even begin to react to these, stomping her legs and swishing her tail in response.

 In the eighth month of pregnancy, the beginnings of a mane, tail, and forelock are visible on the foal. The mare’s belly is extending to the sides and down, and if she is standing still, the foal’s kicks can be seen and felt on her flanks. The kicking is often more visible when she is grazing, and carbohydrates cause the blood sugar of both her and her baby to rise. Beginning in the ninth month, the foal gains about a pound a day, reaching the size of a dalmatian at the end of the ninth month and a jersey calf at the end of the tenth month. In the last month of pregnancy, it is important to check for signs of blood or discharge around the vulva, and to monitor the mare for signs of labor and colic.

The first week or so after your mare is bred, she should stay relaxed for about a week to maximize her chances for a successful conception. After this time, care of the pregnant mare is similar to care for any other horse up until month eight. That is, the mare can continue on her regular vaccination schedule. Confirm with your veterinarian about deworming based on fecal egg counts, and what deworming medications are safe for your mare and her baby.  Throughout the pregnancy, your mare should have access to high quality forage, and a well-rounded supplement for pregnant mares. After the eighth month, the foal starts to grow at a much faster rate, and the mare’s workload can be reduced and her feed increased. She should not be overfed at any point in her pregnancy, so don’t let her body condition get above a 6. Be sure that her feeding regimen does not include fescue!

As the pregnancy nears its end, watch your mare for tell-tale signs of foaling: the belly drops, leaving a dip in the back between the ribs and the hipbones; the muscles around the tailhead relax and get spongy; the mare’s udder begins to fill with milk. As the birth approaches, the mare may begin to drip milk from her teats, and the milk will get a pH of 7.4 in the days around foaling, dropping to 6.4 in the 12 hours before foaling. You can test this with regular pH test strips.  Prepare for the birth by having a first aid kit with betadine and a  thermometer on hand, and wrapping the mare’s tail in a bandage. I hate to mention this, but in case of tragedy, it is also a good idea to order colostrum replacement and have rubber nipples handy, in case you need to bottle-feed the foal when it is born. Nipples designed for lambs or goat kids are ideal for foals.

The 11 months of pregnancy represent the most accelerated rate of growth your horse does in its whole life. Enjoy the chance to bond with your mare, and take good care of her as she grows a new equine life to bring into our world! 

What part of equine pregnancy is the most interesting to you?