FAQ Horse Care

Lumps & Baffling Bumps: What’s a Horse Chestnut?

Horse legs walking chestnut visible
Written by Holly N.

Chestnuts, But We Don’t Mean The Color

A chestnut is more than just a beautiful horse coat color. The word “chestnut” also refers to the hardened patch of rough, scaly tissue on the inside of a horse’s legs. While they may look strange, they’re nothing to be concerned about—they’re a perfectly normal part of an equine’s body.

Chestnuts are hard, callous-like growths on the inside of your horse’s legs above the knee and below the hock. They’re totally harmless—possibly the remnant of a toe that horses used to have. Chestnuts can range from tiny and flat to large and bumpy. If they bother you (they don’t affect your horse), you can ask your farrier to trim them down. Similar to the chestnut is the ergot, a pea-sized callous on the back of the fetlock (another harmless bump that evolution left behind).

variations of the word chestnut color nut and leg bump

Source: Canva

What’s With That Weird Bump?

No horse owner likes to see a mysterious bump on their horse, but chestnuts should be the exception. They’re not a result of injury, nor are they painful. In fact, they are something your horse is born with.

Chestnut Appearance

Chestnuts can vary in their appearance and size. Some lay close to the skin, others protrude around an inch. Chestnuts can be small or large. They’re almost always scratchy or flaky (similar to the hardness of your horse’s hooves). While they’re basically masses of dead, hardened skin, the base of the chestnut is alive, so be careful when grooming around the chestnut as some horses are more sensitive there than others.

Chestnut locations on front and rear legs

Source: Horse Rookie

Chestnut Location

Chestnuts can be found in two locations. On the front legs, they are on the inside just above the knee. On the back legs, they are on the inside just below the hock.

Chestnut Function

Truth be told, no one is quite sure why horses have chestnuts. The best theory is that it’s a remnant of an extra toe horses used to have (kind of like how humans have a tailbone, but no tails).

While chestnuts no longer serve a purpose, they’re harmless. Your horse probably doesn’t even know it has them.

The Evolution of the Chestnut

Chestnuts are a sure sign that horses have evolved over the years. While many believe the chestnut is the remnant of an extra toe, others liken it to the wrist pad on a dog. Another theory is that chestnuts are a type of vestigial scent gland, like what’s found in deer.

Fun Fact: Some equines, including zebras and Icelandic horses, don’t have chestnuts.

Chestnut Care

Chestnuts are made from small keratin deposits. They continually grow, but the growth is slow. If you plan to trim or sand a chestnut (trimming is a purely aesthetic choice, it’s not required), make sure to soften the area with petroleum jelly or baby oil for several days first.

Sometimes, you can gently pick at them. It’s better to ask your farrier for help, however, if you’d like a chestnut trimmed (they can use the same tools they use on your horse’s hooves).

gray horse in leg wraps with chestnuts visible

Source: Canva

Fun Facts About a Horse Chestnut

  • Chestnuts are sometimes called night eyes. This nickname comes from an erroneous belief that chestnuts could help horses see at night.
  • Chestnuts have living tissue at the base which is why they can’t be pulled or twisted off. Definitely don’t try to remove them! It will cause bleeding and pain.
  • Chestnuts are also the horse equivalent of a fingerprint and are even recognized by the FEI (International Equestrian Federation) as an identifying marker.

Other Evolutionary Equine Bumps

The chestnut isn’t the only bump that evolution left behind on horses.

The Ergot…erwhat?

An ergot is similar to a chestnut in that it’s a harmless, hard bump found on your horse’s legs. Ergots are typically much smaller than chestnuts and are located on the back of the fetlock. Not all horses have them, however. They are most common in breeds with feathers or long hair around the fetlocks.

ergot on horse's fetlock

Source: Canva

Ergot Care and Maintenance

If you trim or shave the hair around your horse’s fetlocks, make sure to check for an ergot first, and be careful when trimming around them (like chestnuts, they can become painful if improperly trimmed or pulled at). Ergots don’t require any special care.

Frequently Asked Questions

Q: What’s that weird growth on my horse’s leg?

Chances are good that growth is a chestnut or an ergot. These growths are hard, scaly bumps found on the inside of a horse’s leg around the knee and hock. Both are normal and aren’t dangerous.

Q: How do you get rid of chestnuts on a horse’s legs?

You can’t remove a chestnut completely, but you can trim it down. Your farrier can also sand them.

Q: What is the hard callus on a horse’s leg?

The hard callus on the inside of your horse’s front leg just above the knee is called a chestnut. Chestnuts can also be found on the inside of the hind legs, just below the hocks.

Q: What are the bumps on a horse’s leg?

The bump could be a chestnut if it’s hard and above the knee on the front legs. It could also be an ergot if it’s a hard bump on the back of the fetlock.

If the bump is soft, however, it’s probably a hematoma or a seroma.

Q: What is a hunter bump on a horse?

A hunter’s bump, most commonly found in jumpers and hunters, is when the tuber sacrale (near the croup) is pushed up and forward, usually as a result of an injury. Stall rest, anti-inflammatories, and muscle relaxants are used to treat this.

Q: What do protein bumps look like on horses?

Protein bumps, most commonly found along the neck, withers, and back, are lumps or bumps that start soft and get firmer. They don’t cause pain. They’re typically the result of collagen deposits from an allergic reaction to insect bites.

chestnut on horse's rear leg

Source: Canva

Parting Thoughts

Not all horses will like their chestnuts being picked at or trimmed, so it’s something you may have to learn to live with. Aside from their unpleasant appearance, chestnuts and ergots are harmless—and perhaps the only bumps on your horse you don’t have to worry about!

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About the author


Holly N.

Holly started riding as a six years old in the UK and competed regularly in local events, including showjumping, cross country, showing, working hunter, and gymkhana. She now lives and rides in South Africa, working as a trail guide with Wild Coast Horseback Adventures. Her interests are primarily in the areas of DIY horse ownership, trail riding, barefoot horses, endurance, competitive trail riding, and South African breeds.