Managing Pregnant Mares

Three hundred and forty-five days, give or take about 25. That’s approximately how long your mare will be pregnant. Mares are somewhat unique in the fact that even though their gestation period lasts the better part of a year, it’s only in the final three months of pregnancy that owners must treat them as “pregnant mares”.

The foal really starts major growth in the last trimester, the last three months or so. Up to eight months she’s mostly just another horse. However, every rule has an exception – mares with particular health problems, older mares, or those with complicated gestational histories such as repeat abortions. But, here’s what you should be doing for typical healthy mares.

Riding Pregnant Mares and Other Exercise

Many horse owners think that riding a mare during pregnancy will harm her or even cause her to abort. However, there’s no reason to fear. If her pregnancy isn’t considered high-risk (a mare with a history of abortion or pregnancy loss) and she’s generally healthy to start with, feel free to saddle her up and enjoy a ride! And there’s no need to stick to a gentle walk/trot session. You can continue a normal workout and even jump and compete up to about eight months of pregnancy. Some Thoroughbred mares continue racing until very late term.

However, during the first month of pregnancy, your pregnant mares should be on particularly light work as a special precaution. That first month is really critical. So, until the pregnancy is more well-established your mare shouldn’t be doing any high-level exercise, especially in the hot summertime.

Regular riding, in most cases, should cause no problems past that first month. As the pregnancy advances and the foal grows, there is a slight possibility of the fetus damaging or rupturing the abdominal wall during too much exercise. This happens very rarely, but in case it does the mare will need assistance with delivery as she will lose her ability to push the foal out. Mares with ruptured abdominal walls can no longer be used as sport horses or broodmares. Luckily, abdominal wall ruptures are very rare and far between. So this should not discourage owners from riding their pregnant mares.

However, when pregnancy reaches the eighth month it’s time to start reconsidering the workouts. The growing fetus starts taking a toll mostly on the mare’s lungs but also on the whole body. They may have trouble getting enough air as the diaphragm is displaced in late pregnant mares. Plus,even though this is unlikely to cause abortion, horses have fairly inefficient placentas that don’t favor oxygen transfer to the foal and if there’s any impairment, this can make both the foal and mare suffer.

So in the last trimester, stick to simple walk-trot hacking in the countryside. In the final two or three weeks the mare might become so heavy that riding is uncomfortable for her. However, exercise continues to be important. Mares in late pregnancy tend to stand still a lot in the paddock. This can cause developing significant edema (fluid swelling) in the legs. About 10 minutes of hand-walking twice a day will be enough to keep her spirits up and that fetlock edema down.

Housing and Social Life

You could fall into temptation to pamper your pregnant mares by keeping them in a warm, clean stall with fresh, soft bedding at all times. But don’t forget that horses don’t exactly see stall life as a luxury. What your mare, even when pregnant, will need is to spend time grazing with compatible pasturemates, move around, and get out in the fresh air. Open field with a shelter would be ideal. However, don’t forget to check for tall fescue growing in the pasture. It usually contains a fungus that can cause low milk supply, difficult birth, and prolonged gestation. Remove mares from fescue fields at around nine months of gestation.

It’s natural for pregnant mares to separate out naturally from other horses in the last few weeks of pregnancy. They don’t want to fight or play; they keep behind the herd. They’re afraid of getting kicked. So put your mare in a separate paddock with a friendly companion or another pregnant mare. This will keep her stress levels. Once the foal is about a week old, she can join a larger group again.

As horses are very cold-resistant, there’s really no need to worry too much about cold temperatures during pregnancy. Your mare most likely won’t need a blanket if she’s not clipped. As a matter of fact, blankets can be troublesome and get in the way during nursing and foaling. Just keep her out of the wind and dry.

However, as newborn foals can suffer and in somecases die from getting too cold (hypothermia), you’ll want to make sure the mare doesn’t foal outside during winter. It’s wise to stall your mare at night near the end of her pregnancy.

Gestation-Friendly Food and Water

When the pregnancy reaches the final eight to 10 weeks, a mare’s nutritional requirements and energy needs increase significantly. At a minimum, that means you’ll have to purchase high-quality feed designed especially for pregnant mares and following the directions on the package. Even better, ask your equine nutritionist or veterinarian to help you customize a diet for your particular mare.

Each horse is different and will have different needs. A Thoroughbred mare might need several pounds of grain three times a day, while a Quarter Horse mare might need a handful a day. We need to make sure we don’t overfeed our mares while making sure they have enough flesh on their bones to support their growing babies and themselves. Allowing your pregnant mares to become overweight can have serious consequences, and too many owners do allow it.

Managing Pregnant Mares

A lot of horse owners think now the horse is eating for two, and as soon as they know for sure their mare is pregnant they start overfeeding. But the increased weight of the foal plus the extra weight she’ll have to carry can lead to a potentially life-threatening hoof disease (laminitis). It can also cause fat deposits in the pelvis. This can narrow the birth canal, which makes foaling difficult.

Because in horses, the fetus takes what it needs and the rest goes to the mare, overfeeding probably won’t result in a fat foal. If you have access to a scale weigh your mare regularly, or use a weight tape to make sure she’s in line with the recommendations from your veterinarian for weight increase. Remember, a weight tape might be slightly inaccurate for pregnant mare bellies. Learn to judge your mare’s body condition. It’s important to make sure she stays at a five or six (on a scale of one to nine) throughout her pregnancy.

Pregnant mares should have clean fresh water—preferably from the tap or a running stream. They should also have unlimited access quality hay. Drinking stagnant water can cause horses to contract the abortion-inducing bacterial disease leptospirosis.

A few supplements can even harm fetuses, and they are almost never necessary. For instance, devil’s claw is a common ingredient in many joint supplements. However, it can cause uterine contractions. On the other hand, most supplements have not been scientifically tested on pregnant mares. As we don’t know much about these herbal supplements, it is better to avoid them, rather than use them and realize too late that they are unsafe.

Last-Minute Critical Details

It’s important to pay particular attention to certain details in the last two or three weeks of gestation to avoid dystocia (difficult birth) or preterm birth. Avoid transportation of pregnant mares during this time, as the stress hormone (cortisol) spikes from transportation stress can induce labor. This can occur even in a mare that travels easily. When you have to transport the late pregnant mare, give her plenty of space in the trailer to get comfortable and move around.

It’salso important to keep a close eye on the mare’s udder. Any kind of leaking or premature development is a bad sign. It’s not normal, and almost alwaysit’s a sign that something might be wrong. Until just a few hours before parturition she shouldn’t lose any milk. If she does, call your veterinarian to come check the placenta. Early udder development generally needs to be treated with antibiotics, in case of infection.

Check your pregnant mare’s vulva before term, too. Many horse owners don’t remember that their mares have had their vulva sewn shut in a Caslick’s procedure. In order toprevent damaging and very painful perineal lacerations that can be detrimental to the mare’s future breeding career, your vet must remove the stitches before foaling.

Lastly, make sure to monitor your pregnant mare really continuously when she’s close to term. Checking them at 10 p.m. and then again at 8 a.m. isn’t enough. You need to do it every hour. The No. 1 sign to look for: lying down. Start your timer when the labor begins. She has 20 minutes to deliver. You need to call the vet if it goes any longer than that.

Preventive Care & Your Veterinarian

Generally, when compared to other horses, pregnant mares suffer more serious consequences from disease. It’s because some infections can be more difficult to treat because of medications that endanger the fetus, and many infections can lead to abortion. So it’s best to keep your pregnant mares separated from horses such as competition animals and young stock. They’re more likely to pick up and carry illnesses.

Also designate separate grooming tools, stall-cleaning equipment, and barn supplies for your pregnant mares. Just be careful to wash and disinfect them between horses or don’t use them with the rest of your herd.

Maintain your mare’s regular core vaccination program, as vaccines won’t harm the fetus and are important for both mare and foal immunity. To help protect the foal repeat most vaccines at about five weeks before foaling. To reduce the risk of abortion from that respiratory disease add rhinopneumonitis immunization at five, seven, and nine months of pregnancy. (American Association of Equine Practitioners’ vaccination guidelines can be found at

It’s essential for your pregnant mare’s welfare and health to kep her parasite-free, so consult with your vet to design a suitable deworming protocol. In the last four weeks of pregnancy you should avoid deworming as this can cause abortion.

Just because you’re not riding and tending to your mare’s feet as frequently you shouldn’t neglect them. Pregnant mares still need regular trims on a normal schedule, even though they don’t usually have special hoof needs.

Lastly, building and maintaining a good relationship with your vet is important. Your vet will be an excellent resource, as each mare may have different needs. Plus, you’ll already have the relationship established just in case you run into problems during the pregnancy or foaling.


Your pregnant mare is a double treasure as she’s about to bring an exciting new life into your barn. Even though she might not need specialized prenatal care during most pregnancy, the quality of the last trimester of gestation are critical to both her foal’s and her health. It’s your responsibility to manage her in a way that will provide them the best possible welfare and health.

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