Horse chestnuts are rough patches of tissue found on the inner surfaces of a horse’s legs. These growths, which resemble small, horn-like calluses, are a normal part of equine anatomy. They are typically located just above the knee on the forelegs and below the hock on the hind legs. Often appearing as irregular, oval-shaped formations, chestnuts are a distinctive feature of horses.
What Are Chestnuts
Chestnuts are firm, keratinized growths on a horse’s legs, varying in size, shape, and texture among individual animals. They can be smooth or jagged, and their color often ranges from light tan to dark brown. These structures are comprised of keratin, the same fibrous protein that forms hooves and human fingernails, making them tough and insensitive on their outer surface.
Chestnuts are present on all four legs of domestic horses, though some breeds may lack them on their hind legs. They are located on the inner side of the leg, above the carpal joint (knee) on the front legs and below the tarsal joint (hock) on the rear legs. While unique to equids, other members of the equine family like donkeys and zebras have chestnuts only on their front legs. Chestnuts are non-functional growths that serve no active purpose in modern horses.
The Evolutionary Story of Chestnuts
Scientific understanding suggests that chestnuts are vestigial remnants, anatomical features that have lost their original function over evolutionary time. The prevailing theory proposes that chestnuts correspond to the carpal and tarsal pads of ancient, multi-toed ancestors of the horse. These pads were tough, fibrous cushions similar to those found on the feet of modern dogs or cats, which helped support the animal’s weight and provided traction.
Over millions of years, as horses evolved from small, multi-toed creatures like Eohippus to the single-hoofed animals seen today, these foot pads became obsolete. The reduction in the number of toes, adapting horses for speed on open plains, led to the diminished size and function of these pads. Consequently, the carpal and tarsal pads gradually reduced to the small, non-functional growths now recognized as chestnuts. While some alternative theories suggest chestnuts might be vestigial scent glands, similar to those found in deer, their main interpretation relates to the evolution of the horse’s foot.
Chestnut Care and Common Misconceptions
Horse chestnuts do not require extensive care, as they are harmless and do not cause discomfort. They continuously grow throughout a horse’s life, much like human fingernails, and the outer layers may naturally flake or peel off. While some horse owners choose to trim or peel chestnuts for aesthetic reasons or to prevent them from snagging, this is not medically necessary. The outer layers of chestnuts lack nerve endings, so trimming them does not cause pain, but care should be taken not to cut too deeply into the sensitive layers closer to the leg.
There are several common misconceptions surrounding chestnuts. They are not indicators of a horse’s age, nor are they related to warts or tumors. While chestnuts are unique in shape and texture to each individual horse, similar to human fingerprints, their appearance can change over time due to growth and grooming, which limits their use as sole identifiers for registration purposes. The old belief that chestnuts, sometimes called “night eyes,” helped horses see in the dark is also a misconception.