The chestnut, also known as a night eye, is a

callosity A callosity is a type of callus, a piece of skin that has become thickened as a result of repeated contact and friction. Primates All Old World monkeys, gibbons, and some chimpanzees have pads on their rears known as ''ischium, ischial callos ...

on the body of a

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 mi ...

or other

equine Equinae is a subfamily of the family Equidae, known from the Hemingfordian stage of the Early Miocene (16 million years ago) onwards. They originated in North America, before dispersing to every continent except Australia and Antarctica. They are ...

, found on the inner side of the leg above the knee on the foreleg and, if present, below the

hock Hock may refer to: * Hock (wine), a type of wine * Hock (anatomy), part of an animal's leg * To leave an item with a pawnbroker * Hock (surname) * Richard "Hock" Walsh (1948-1999), Canadian blues singer * A type of wine bottle A wine bottl ...

on the hind leg. It is believed to be a

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

toe, and along with the

ergot Ergot ( ) or ergot fungi refers to a group of fungi of the genus ''Claviceps''. The most prominent member of this group is '' Claviceps purpurea'' ("rye ergot fungus"). This fungus grows on rye and related plants, and produces alkaloids that c ...

form the three toes of some other extinct

Equidae Equidae (commonly known as the horse family) is the Taxonomy (biology), taxonomic Family (biology), family of Wild horse, horses and related animals, including Asinus, asses, zebra, zebras, and many extinct species known only from fossils. The fa ...

Darren Naish Darren William Naish (born 26 September 1975) is a British vertebrate palaeontologist, author and science communicator. As a researcher, he is best known for his work describing and reevaluating dinosaurs and other Mesozoic reptiles, including ...

dissents from this belief, noting that the chestnut is "not associated with the metacarpus or metatarsus, the only places where digits occur." Chestnuts vary in size and shape and are sometimes compared to the fingerprints in humans. For purposes of identification some

breed registries A breed registry, also known as a herdbook, studbook or register, in animal husbandry, the hobby of animal fancy, is an official list of animals within a specific breed whose parents are known. Animals are usually registered by their breeders w ...

require photographs of them among other individual characteristics. However, because chestnuts grow over time and horse groomers often peel or trim off the outer layers for neatness, their appearance is subject to change.

Distribution among equines

The

evolution of the horse The evolution of the horse, a mammal of the family Equidae, occurred over a geologic time scale of 50 million years, transforming the small, dog-sized, forest-dwelling '' Eohippus'' into the modern horse. Paleozoologists have been able to piece ...

involved a reduction in the number of toes to one, along with other changes to the ancestral

equid Equidae (commonly known as the horse family) is the Taxonomy (biology), taxonomic Family (biology), family of Wild horse, horses and related animals, including Asinus, asses, zebra, zebras, and many extinct species known only from fossils. The fa ...

foot, and the chestnut is thought to correspond to the ''wrist pad'' of dogs and cats. Alternatively, it may be a

scent gland similar to those found in some deer and other animals. chapter 2 The domestic horse is almost alone among

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

equines in having chestnuts on the hind legs. Chestnuts are absent from the hind legs of

ass Ass most commonly refers to: * Buttocks (in informal American English) * Donkey or ass, ''Equus africanus asinus'' **any other member of the subgenus ''Asinus'' Ass or ASS may also refer to: Art and entertainment * Ass (album), ''Ass'' (albu ...

es and

zebra Zebras (, ) (subgenus ''Hippotigris'') are African equines with distinctive black-and-white striped coats. There are three living species: Grévy's zebra (''Equus grevyi''), the plains zebra (''E. quagga''), and the mountain zebra (''E. ...

s. The majority of

domestic horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million ...

s have chestnuts on all four legs, as does the

Przewalski's horse Przewalski's horse (''Equus ferus przewalskii'' or ''Equus przewalskii''), also called the takhi, Mongolian wild horse or Dzungarian horse, is a rare and endangered wild horse originally native to the steppes of Central Asia. It is named after t ...

, but a few

horse breed A horse breed is a selectively bred population of domesticated horses, often with pedigrees recorded in a breed registry. However, the term is sometimes used in a broader sense to define landrace animals of a common phenotype located within a ...

s are reported to lack chestnuts on the hind legs. These include: *

Banker horse The Banker horse is a horse breed, breed of feral horse (''Equus ferus caballus'') living on barrier islands in North Carolina's Outer Banks. It is small, hardy, and has a docile temperament. Descended from domesticated Iberian horse, Spanish h ...

(most individuals) *

Caspian pony The Caspian is an Iranian breed of pony or small horse of Oriental type. The breed was rediscovered in 1965 by an Iranian aristocrat in Tehran, Narcy Firouz, and his American-born wife, Louise Laylin from a base stock of a small number of sma ...

(some individuals) *

Icelandic horse The Icelandic horse ( ), or Icelandic, is a Horse breed, breed of horse developed in Iceland. Although the horses are smaller (at times pony-sized) than other breeds, most Breed registry, registries for the Icelandic refer to it as a horse. Th ...

(most individuals)

Grooming

Chestnuts grow over time, protruding from the surface of the leg. Grooming for horse showing may include peeling or trimming the outer layers to give a neater appearance to the leg; they may peel more easily if softened first with

baby oil Baby oil is an inert oil used to keep Human skin, skin soft and supple, named for its use on babies and also often used on adults for skincare and massage. The skin of an infant, especially a Preterm birth, premature one, is sensitive, thin, a ...

or moisturizer. Also, if the horse is exercised so that it has sweated, the chestnut is temporarily softened by the body moisture and can be peeled easily. If left alone, eventually the chestnut peels naturally.

References

External links

Chestnuts And Ergots In Horses
* {{Commons-inline, Chestnut (Horse Anatomy) Horse anatomy

Distribution among equines

Grooming

See also

References

External links