Hay Belly vs Pregnant Mare: What’s The Difference? (Important Facts)

By Zunnun Ahmed •  Updated: 10/28/22 •  7 min read

Does your horse look pregnant and you are torn between hay belly vs. pregnant mare? How can you tell the difference? Well, if your horse has gained body weight and looks skinny too with a sagging belly, this is a sign of a hay belly.

Hay belly is not only common in female horses but also in male horses. A non-pregnant horse appears pregnant with the belly extending outwards and looks slimmer in other parts of the body.

Horses suffering from this condition have accumulated gas in the gut that results from feeding them low-quality grass hay. Luckily, horse owners can treat this condition by feeding their horses high-quality alfalfa hay to meet their nutritional requirements.

Let’s dig deeper into the causes of hay belly, how it looks, how to prevent the condition, and how to determine horse pregnancy.

What does a hay belly look like?

Did you notice a change in your mare belly? What did this mean for you? OK, I know what you’re thinking: You are probably expecting a newborn foal.

But wait, let me tell you something!

Your “pregnant mare” might be suffering from a hay belly. So, what does a hay belly look like, and how does it differ from pregnancy? Horses with hay belly condition have a distended abdomen and gas accumulation in the gut because the forage takes a longer time to digest.

When looking at your mare or stallion from the front, the horse appears pregnant and the belly distends outwards. However, other parts of the body look slimmer. Your horse might have protruding ribs, and no padding on various muscles around the withers, haunches, and neck.

Here are other symptoms of hay belly:

horse hay belly

What are the causes of a hay belly?

Hay belly is not a condition that appears at once. The belly enlarges gradually because of poor diet and lack of exercise hence giving horses this body condition. A horse owner should avoid this condition because it makes horses poor performers and they look unwell.

Basically, the main cause of hay belly is feeding your horse a low-quality horse diet, overly mature hay, or hay that doesn’t contain enough protein. Horses that lack grain supplements in their diet also develop distended abdomen.

In other situations, a horse can have a sagging belly because of overeating to pay off the nutrients they lack in its diet. If your horse does not exercise sufficiently to promote healthy digestion and tone muscles, they are likely to suffer from this condition.

Lastly, giving your horse too much fiber and low protein affects the fermentation process in their gut and this leads to excessive production of gas, hence the distended abdomen.

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How can you prevent a hay belly in your horse?

In case you might be asking yourself: How can I prevent hay belly in horses?

Let me show you how!

Balanced diet

Maintaining proper nutrition is the first step to preventing hay belly. Consider giving your horse high-quality alfalfa hay. Hay that contains more stems compared to green leaves has more fiber, and this makes it hard for young growing horses or senior horses to digest.

According to the American Association of Equine Practitioners, horse owners should feed their horses legume hay harvested during the early bloom stage. For owners that feed their horses grass hay, get hay harvested before the formation of head seed.

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Grain supplements

Grain supplements come in handy when the horse has protein deficiency from the food it takes. The grain supplements contain concentrates that give your horse proteins and energy that lack in their forages. You can consult your equine practitioner for advice on high-quality grain supplements for horses.

Regular exercise

Engaging your horse in regular exercise reduces the chances of a sagging stomach. A physically fit mare or stallion has well-toned muscles on the belly and other body parts. Doing this for older horses and broodmares to support their stomach muscles promotes healthy digestion.

Difference between hay belly vs pregnant mare

At first, it can be tricky for horse owners to differentiate between pregnant mares and hay belly. While the most common sign of a pregnant horse is a swollen abdomen, not all pregnant mares have an enlarged belly because they have a gestation period of close to a year.

Therefore, pregnant mares can maintain their normal shape throughout the mare’s pregnancy. You can easily tell your horse is not pregnant but suffering from a hay belly by checking its physical appearance.

Horses with hay belly are slimmer in other body parts and have extended stomachs. However, a pregnant horse has a proportional body weight in comparison to its belly.

pregnant mare

Why has my horse got a big belly?

The main reason why your horse has a big belly is because of feeding high-fiber forage like hay and grass which ferments in the hindguts for some days. This makes the belly expand.

It is good for horse owners to check the quality of forage they give their horses to prevent a big belly. Change to high-quality forage gradually and engage your horse in exercises like walking, jumping, transitions, and working over poles to reduce expanded belly.

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How do you tell if a mare is pregnant or just fat?

If you brought your mare a stallion, you probably want to know whether the growing belly is a result of an unborn foal or just hay. Determining equine pregnancy can be difficult because pregnant mares have a gestation of 11 months.

You can hardly notice any sign of pregnancy within the first three months. The best thing you can do is an ultrasound to determine if your horse is pregnant or not. Mares start to show signs of pregnancy within 6 months when the belly begins to get bigger. Below are other ways you can tell if a mare is pregnant.

Avoiding regular heats

Mares experience heat cycles several times a year, especially during warm months. If the mare is pregnant, she will hardly show any signs of heat.

Weight gain

It is normal for horses to gain weight because of inactivity or taking a diet high in calories. If you notice your mare is gaining weight without a change in diet, it could be because of pregnancy.

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Abdominal movement

If you see any movement in your mare’s abdomen, there is an unborn foal waiting for birth. These sudden movements are common when the horse is at the end of the pregnancy period which shows a healthy foal is inside.

Bigger mares under

Two weeks before the horse gives birth, the under becomes bigger because of milk or colostrum production. You might also notice some milk leaking some days before foaling.

Loose vulva

A pregnant mare nearing birth will have a relaxed and loose mares vulva. This is to prepare for stretching that will take place when giving birth. Horses that are not pregnant have a normal and tight vulva.


Hay belly is a common problem for horses that feed on low-quality diets. Horse owners should provide quality forage to alleviate this condition in performance horses. If you were wondering about the cause of a big belly in your horse, by now, you can tell the difference between a hay belly and a pregnant horse. 

Zunnun Ahmed

We are a group of horse enthusiasts. We want to provide information and tips to help others learn more about horses, how to care for them, and how to enjoy them.

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