Farming Magazine - August, 2012


Working Horses: Curious About Callosities

By Vicki Schmidt

Fifty million years ago, there lived a horse named eohippus. Actually, eohippus is the name given to the early ancestors of our modern horses. One curious characteristic of eohippus was that it had multiple toes, with the center toe evolving into what we now call the hoof.

Many believe two of the toes from this ancestral horse have lost all of their original function and evolved into vestigial areas: the callosity areas we call chestnuts and ergots. While some mystery exists, one remnant characteristic of chestnuts and ergots is that they, along with the modern hoof, continue to grow.

Other schools of thought note there is no evidence that chestnuts and ergots are leftovers from former toes. Theories exist that these areas harbor scent glands, as they do carry a strong trademark aroma of the horse. You will also often see horses scratching their face and eyes on the chestnut areas. Whether the reason is convenience, the fact that the surface is somewhat rougher than hair, or scent distribution, is open for discussion.

Chestnuts are normal, healthy growths found on the upper inner front knee and usually on the inner hocks of most horses. One curiosity of the chestnut is that its size, shape and pattern are unique for every horse. Chestnuts near the front knees are typically larger than those found on the back legs, and a horse may have large chestnuts on the front legs with none or nearly nonexistent chestnuts on the hind legs.

Ergots are smaller callosity areas found on the underside of the fetlock. Some horses have ergots on all four feet, while others have none. In addition, some horses have very small, almost undetectable ergots, while the feathered breeds, namely Clydesdales and Shires, often have very large ergots, sometimes up to 1.5 inches in diameter.

The ergot is also far from a useless little bump. It may serve to keep the frog healthier, as the shape of the ergot allows water that is shed down the leg to drip away from the pastern and hoof area. In addition, the ergot is the anchoring point for the ergot ligament, which is the ligament closest to the surface on the leg of a horse. In this regard, does the ergot help to balance and further protect the ligament from hostile ground surface impact?

Overgrown or protruding chestnuts, especially on a working draft, should be trimmed close to the skin.
Photo by Vicki Schmidt.

Both chestnuts and ergots grow over time and at about the same rate as your horse's hoof. The formations originate from the epidermal layer of the skin and protrude from the surface of the leg. Show horses will often have these callosity areas trimmed and groomed close to the skin, allowing for a neater appearance.

For working draft horses, it is recommended to keep the chestnuts trimmed and as flush to the leg as possible. Harness straps, branches and even tall, coarse grass can get trapped by the rough edges and tear the chestnuts from the skin, often with enough force to leave a deep, bleeding wound.

Ergots, especially in feathered draft breeds, can grow excessive enough to split and allow mud and moisture to get trapped close to the skin. Keeping the ergots trimmed to within an inch of the leg prevents debris entrapment, while also allowing the ergot to direct water away from the area under the pastern.

Other tidbits about chestnuts and ergots:

Photos of a horse's chestnuts are still used by the Universal Horse Identification System, especially with thoroughbred racing, to prevent ringers. This assures that the racehorse the public is betting on is in fact the same horse running in the race.

Native American folklore tells how the chestnuts are a horse's "night eyes" and were once believed to allow horses to see in the dark.

The Jockey Club often requires a set of chestnut photos to secure the identification of horses that have no white or other unique markings, and for further identifying gray/roans.

In medieval Europe it was said that the ground-up powder of the chestnut from inside a docile horse's leg, when blown into the nostrils of a wild horse, would tame it instantly.

Modern horsemen are known to carry the shed chestnut from a dominant horse with the goal of being instinctively accepted into a horse's herd family.

Chestnuts will peel naturally in most domesticated instances, but if you wish to remove the harder outer surfaces, first soften them with baby oil, petroleum jelly or other moisturizer. Then remove them gently with a sharp knife or nippers.

Vicki Schmidt is owner and manager of Troika Drafts in Hebron, Maine. Visit the farm online at