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Chestnut is a hair coat color of
horse The horse (''Equus ferus caballus'') is a Domestication, domesticated, odd-toed ungulate, one-toed, ungulate, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two Extant taxon, extant subspecies of wild horse, ''Equus fer ...
s consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat. Chestnut is characterized by the absolute absence of true
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white have of ...
hairs. It is one of the most common
horse coat color Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them. While most horses remain the same color throughout life, a few, over the course of several years, will develop a diff ...
s, seen in almost every breed of horse. Chestnut is a very common coat color but the wide range of shades can cause confusion. The lightest chestnuts may be mistaken for
palomino Palomino is a genetic color in horses, consisting of a gold coat and white mane and tail; the degree of whiteness can vary from bright white to yellow. Genetically, the palomino color is created by a single allele of a dilution gene called th ...
s, while the darkest shades can be so dark they appear
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white have of ...
. Chestnuts have dark brown eyes and black skin, and typically are some shade of red or reddish brown. The mane, tail, and legs may be lighter or darker than the body coat, but unlike the
bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a na ...
they are never truly black. Like any other color of horse, chestnuts may have pink skin with white hair where there are
white markings Markings on horses are usually distinctive white areas on an otherwise dark base coat color. Most horses have some markings, and they help to identify the horse as a unique individual. Markings are present at birth and do not change over the co ...
, and if such white markings include one or both eyes, the eyes may be blue. Chestnut foals may be born with pinkish skin, which darkens shortly afterwards. Chestnut is produced by a
recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
gene. Unlike many coat colors, chestnut can be true-breeding; that is, assuming they carry no recessive modifiers like
pearl A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle) of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pearl is composed of calcium carb ...
or
mushroom A mushroom or toadstool is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground, on soil, or on its food source. ''Toadstool'' generally denotes one poisonous to humans. The standard for the name "mushroom" is t ...
, the mating between two chestnuts will produce chestnut offspring every time. This can be seen in breeds such as the
Suffolk Punch The Suffolk Horse, also historically known as the Suffolk Punch or Suffolk Sorrel,Dohner, ''Encyclopedia of Historic and Endangered Livestock and Poultry Breeds'' pp. 349–352 is an English breed of draught horse. The first part of the na ...
and
Haflinger The Haflinger, also known as the Avelignese, is a breed of horse developed in Austria and northern Italy (namely Hafling in South Tyrol region) during the late 19th century. Haflinger horses are relatively small, are always chestnut with flaxe ...
, which are exclusively chestnut. Other breeds including the
American Belgian Draft The American Belgian Draft is an American list of horse breeds, breed of heavy draft horse. It derives from the draft horses of Belgium but, as a result of isolation and different selective breeding, became genetically distinct from them in the e ...
and
Budyonny Semyon Mikhailovich Budyonnyy ( rus, Семён Миха́йлович Будённый, Semyon Mikháylovich Budyonnyy, p=sʲɪˈmʲɵn mʲɪˈxajləvʲɪdʑ bʊˈdʲɵnːɨj, a=ru-Simeon Budyonniy.ogg; – 26 October 1973) was a Russian c ...
are predominantly chestnut. However, a chestnut horse need not have two chestnut parents. This is especially apparent in breeds like the
Friesian horse The Friesian (also Frizian) is a horse breed originating in Friesland, in the Netherlands. Although the conformation of the breed resembles that of a light draught horse, Friesians are graceful and nimble for their size. It is believed tha ...
and Ariegeois pony which have been selected for many years to be uniformly
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white have of ...
, but on rare occasions still produce chestnut foals.


Visual identification

Chestnuts can vary widely in shade and different terms are sometimes used to describe these shades, even though they are genetically indistinguishable. Collectively, these coat colors are usually called "red" by geneticists. *A basic chestnut or "red" horse has a solid copper-reddish coat, with a mane and tail that is close to the same shade as the body coat. *
Sorrel Sorrel (''Rumex acetosa''), also called common sorrel or garden sorrel, is a perennial herbaceous plant in the family Polygonaceae. Other names for sorrel include spinach dock and narrow-leaved dock ('dock' being a common name for the genus '' ...
is a term used by American
stock horse A stock horse is a horse of a type that is well suited for working with livestock, particularly cattle. The related cow pony or cow horse is a historic phrase, still used colloquially today, referring to a particularly small agile cattle-herdin ...
registries to describe red horses with manes and tails the same shade or lighter than the body coat color. In these registries, chestnut describes the darker shades of red-based coats. Colloquially, in the American west, almost all copper-red chestnuts are called "sorrel." In other parts of the English-speaking world, some consider a "sorrel" to be a light chestnut with a flaxen mane and tail. * Liver chestnut or dark chestnut are not a separate genetic color, but a descriptive term. The genetic controls for the depth of shade are not presently understood. Liver chestnuts are a very dark-reddish brown. Liver chestnuts are included in the term "dark chestnut." The darkest chestnuts, particularly common in the
Morgan horse The Morgan horse is one of the earliest horse breeds developed in the United States. Tracing back to the foundation sire Figure, later named Justin Morgan after his best-known owner, Morgans served many roles in 19th-century American hist ...
, may be indistinguishable from true
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white have of ...
without very careful inspection. Often confusingly called "black chestnuts," they may be identified by small amounts of reddish hair on the lower legs, mane and tail, or by DNA or pedigree testing. Recently, it has been suggested that the trait or traits that produce certain darker shades of chestnut and
bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a na ...
, referred to as "sooty" coloration follow a
recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
mode of inheritance. * Flaxen chestnut and blond chestnut are terms that describe manes and/or tails that are flaxen, or significantly lighter than the body color. Sometimes this difference is only a shade or two, but other flaxen chestnuts have near-white or silverish manes and tails. Haflingers are exclusively of this shade. It is considered desirable in other breeds, though the genetic mechanism is not fully understood. Some flaxen chestnuts can be mistaken for
palomino Palomino is a genetic color in horses, consisting of a gold coat and white mane and tail; the degree of whiteness can vary from bright white to yellow. Genetically, the palomino color is created by a single allele of a dilution gene called th ...
s and have been registered in palomino color registries. *
Pangaré Pangaré is a coat trait found in some horses that features pale hair around the eyes and muzzle and underside of the body. These pale areas can extend up to the flanks, throat and chest, behind the elbows, in front of the stifle, and up the b ...
or mealy is thought to be controlled by a single gene, unrelated to chestnut color, and produces distinct characteristics common to wild equids: pale hairs around the eyes and muzzle and a pale underside. Haflingers and
Belgians Belgians ( nl, Belgen; french: Belges; german: Belgier) are people identified with the Kingdom of Belgium, a federal state in Western Europe. As Belgium is a multinational state, this connection may be residential, legal, historical, or cultur ...
are examples of mealy chestnuts. The flaxen characteristic is sometimes associated with ''pangaré''.


Chestnut family colors

Chestnut is considered a "base color" in the discussion of equine coat color genetics. Additional coat colors based on chestnut are often described in terms of their relationship to chestnut: *
Palomino Palomino is a genetic color in horses, consisting of a gold coat and white mane and tail; the degree of whiteness can vary from bright white to yellow. Genetically, the palomino color is created by a single allele of a dilution gene called th ...
s have a chestnut base coat color that is genetically modified to a golden shade by a single copy of the incomplete dominant
cream gene The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino if they are heterozygous, having one copy of the cream gene, or cremello, if ...
. Palominos can be distinguished from chestnuts by the lack of true red tones in the coat; even the palest chestnuts have slight red tints to their hair rather than gold. The eyes of chestnuts are usually dark brown, while those of a palomino are sometimes a slightly lighter amber. Some
color breed A color breed refers to groupings of horses whose registration is based primarily on their coat color, regardless of the horse's actual breed or breed type. Some color breeds only register horses with a desired coat color if they also meet speci ...
registries that promote palomino coloring have accepted flaxen chestnuts because registration is based on a physical description rather than a genetic identity. * Cremellos have a chestnut base coat and homozygous (two copies) for the
cream gene The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino if they are heterozygous, having one copy of the cream gene, or cremello, if ...
. They have a cream-colored coat, blue eyes and lightly pigmented pink skin. * Red duns have a chestnut base coat with the dun gene (one or two copies). Their body color is pale, dusty tan shade that resembles the light undercoat color of a body-clipped chestnut but with a bold, dark dorsal stripe in dark red, a red mane, tail and legs. They may have additional primitive markings, which distinguish a red dun from a light or body-clipped chestnut. * Gold champagnes have a chestnut base coat with the
champagne gene The champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink ...
(one or two copies). They resemble a palomino, or they may be an all-over apricot shade, but can be distinguished from other colors by amber or green eyes and lightened skin color with freckling. * Red or "strawberry" roans have a chestnut base coat with the classic roan gene (one or two copies). * A
skewbald Skewbald is a colour pattern of horses. A skewbald horse has a coat made up of white patches on a non-black base coat, such as chestnut, bay, or any colour besides black coat. Skewbald horses which are bay and white (bay is a reddish-brown colo ...
, "chestnut pinto" or "sorrel Paint" is a pinto horse with chestnut and white patches. Combinations of multiple dilution genes do not always have consistent names. For example, "dunalinos" are chestnuts with both the dun gene and one copy of the
cream gene The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino if they are heterozygous, having one copy of the cream gene, or cremello, if ...
.


Chestnut mimics

*
Bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a na ...
horses also have reddish coats, but they have a black mane, tail, legs and other
point coloration Point coloration refers to animal coat coloration with a pale body and relatively darker extremities, i.e. the face, ears, feet, tail, and (in males) scrotum. It is most recognized as the coloration of Siamese and related breeds of cat, but can ...
. The presence of true black points, even if obscured by
white markings Markings on horses are usually distinctive white areas on an otherwise dark base coat color. Most horses have some markings, and they help to identify the horse as a unique individual. Markings are present at birth and do not change over the co ...
, means that a horse is not chestnut. *
Seal brown Seal brown is a rich dark brown color, resembling the color of the dyed fur from the fur seal. Usage The specifications for the U.S. Army Air Corps Type A-2 jacket (regulation summer flying jacket), adopted in 1931 and the most familiar among ...
or dark
bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a na ...
horses are not chestnut but may be confused with a liver chestnut. Those unfamiliar with horse coat color terminology often call most horses "brown". including chestnuts. Brown, which may be difficult to distinguish visually from dark
bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a na ...
, is always accompanied by black points. Liver chestnuts, in particular, are mistakenly called brown or "seal brown". * Silver bay horses typically have chocolate- to red-brown bodies with silvered mane, tail, and legs. The flat reddish-brown color and lack of easily identified black points can confuse even knowledgeable horse persons. Silver dapple horses usually hint at black or dark gray pigment at the roots of the mane and tail, and where their silver points end on the legs. Silvers look a bit "off"-chestnut. To further confuse matters, some flaxen chestnuts have silverish streaks in their manes and tails. However, genetic testing can clarify matters.


Inheritance and expression

The chestnut color, called "red" by geneticists, is created by an
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
that is a mutation from the
wildtype The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, "m ...
and is genetically the most
recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
coat color that exists in modern horses. The gene for "red" color is designated as "e". This is because the presence or absence of red color in horses is determined by the equine melanocortin 1 receptor (MC1R), a protein positioned on chromosome 3 (ECA3) at the Extension
locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * ''Locus'' (magazine), science fiction and fantasy magazine ** ''Locus Award' ...
. The wild type version of the gene encoding MC1R is the ''E''
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
(colloquially, though imprecisely, called the "Extension gene"), and is part of the genetic pathway that allows
melanocytes Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea), the inner ear, vaginal epithelium, meninges, bones, and heart. Mel ...
to produce
eumelanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amin ...
, or black pigment.Online Mendelian Inheritance in Man, OMIM (TM). Johns Hopkins University, Baltimore, MD. MIM Number: 155555: 15 Feb. 2008

/ref> When the "E" allele is not present, no eumelanin is produced, but the "e" allele still allows
melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
to be produced in the form of
pheomelanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the am ...
, or red pigment, creating a chestnut or red-based coat color. In general, alleles that create fully functional MC1R proteins are inherited dominantly and result in a black-based coat color ("E"), while mutated alleles that create "dysfunctional" MC1R are recessive and result in a lighter coat color ("e"). Red hair color in horses ("e") is created by a
missense mutation In genetics, a missense mutation is a point mutation in which a single nucleotide change results in a codon that codes for a different amino acid. It is a type of nonsynonymous substitution. Substitution of protein from DNA mutations Missense m ...
in the code for MC1R, which results in a protein that cannot bind to the
Melanocyte-stimulating hormone The melanocyte-stimulating hormones, known collectively as MSH, also known as melanotropins or intermedins, are a family of peptide hormones and neuropeptides consisting of α-melanocyte-stimulating hormone (α-MSH), β-melanocyte-stimulating ho ...
(MSH), which is released by the pituitary gland, and stimulates the production and release of melanin in skin and hair. So long as one functional copy ("E") is present, the protein is formed normally and black pigment is produced. However, when only mutant copies ("e) of the gene are available, non-functional MC1R proteins are produced. As a result, no black pigment is deposited into the hair and the entire coat is red-based. However, the skin of chestnut horses is still generally black, unless affected by other genes. Some chestnut foals are also born with lighter eyes and lightened skin, which darken not long after birth. This is not the same as the blue eyes and pink skin seen at birth in foals carrying the
champagne gene The champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink ...
. It is a genetic mechanism not fully understood, but may be related to the pheomelanistic characteristics of "e". The recessive nature of the chestnut or "red" coat in horses occurs because a single copy of the ''E'' allele is dominant over the ''e'' allele. Therefore, for example,
bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a na ...
and
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white have of ...
horses may be heterozygous for ''e'' and if so, could produce a chestnut foal when bred to another horse with at least one copy of "e". However, all chestnut horses are homozygous for the "e" allele and thus breeding a chestnut to another chestnut will always produce a chestnut
foal A foal is an equine up to one year old; this term is used mainly for horses, but can be used for donkeys. More specific terms are colt for a male foal and filly for a female foal, and are used until the horse is three or four. When the foal i ...
. Thus, unlike many coat colors, chestnut can be true-breeding; if any color other than chestnut occurs, then one of the parents was not chestnut. Red can occur in horses that carry "E" when other genes influence its expression. In some cases, MC1R exists but is locally antagonized by the
agouti signalling peptide Agouti-signaling protein is a protein that in humans is encoded by the ASIP gene. It is responsible for the distribution of melanin pigment in mammals. Agouti interacts with the melanocortin 1 receptor to determine whether the melanocyte (pigment ...
(ASIP), or "agouti gene", which "suppresses" black color and allows some red pigment to be formed. This results in localized regions of black-rich or red-rich pigmentation, as seen in
bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a na ...
horses.


See also

*
Equine coat color Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them. While most horses remain the same color throughout life, a few, over the course of several years, will develop a diff ...
* Equine coat color genetics


References


"Horse coat color tests"
from the
UC Davis The University of California, Davis (UC Davis, UCD, or Davis) is a public land-grant research university near Davis, California. Named a Public Ivy, it is the northernmost of the ten campuses of the University of California system. The institu ...
Veterinary Genetics Lab
"Introduction to Coat Color Genetics"
''from'' Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008


External links



{{Equine coat colors Horse coat colors