Chestnut is a
hair coat color of
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 y ...
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 o ...
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 t ...
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 o ...
. 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 they are never truly black. Like any other color of horse, chestnuts may have pink skin with white hair where there are
white markings, 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 nam ...
and
Haflinger
The Haflinger, also known as the Avelignese, is a horse breed, 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 chestnu ...
, which are exclusively chestnut. Other breeds including the
American Belgian Draft
The American Belgian Draft is an American 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 early part of the twen ...
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 ca ...
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 that ...
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 o ...
, 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 histo ...
, 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 o ...
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, 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 t ...
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 t ...
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.
*
Cremello
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 ...
s 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
The dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene lightens most of the body while leaving the mane, tail, legs, and primitive markings the shade of the undiluted base coat color. ...
(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
Primitive markings are a group of hair coat markings and qualities seen in several equine species, including horses, donkeys, and asses. In horses, they are associated with primitive breeds, though not limited to such breeds. The markings are ...
, 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
Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture. Paint can be made in many ...
" is a
pinto horse
A pinto horse has a coat color that consists of large patches of white and any other color. The distinction between "pinto" and "solid" can be tenuous, as so-called "solid" horses frequently have areas of white hair. Various cultures through ...
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
The dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene lightens most of the body while leaving the mane, tail, legs, and primitive markings the shade of the undiluted base coat color. ...
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 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, 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 a ...
or dark
bay 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, 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
![Feromoni Kuu](https://upload.wikimedia.org/wikipedia/commons/b/b3/Feromoni_Kuu.jpg)
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
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mi ...
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
The melanocortin 1 receptor (MC1R), also known as melanocyte-stimulating hormone receptor (MSHR), melanin-activating peptide receptor, or melanotropin receptor, is a G protein–coupled receptor that binds to a class of pituitary peptide hormones ...
(MC1R), a protein positioned on
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
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
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 ...
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.
...
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 amino ...
, 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 h ...
(MSH), which is released by the pituitary
In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypop ...
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 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 o ...
horses may be heterozygous
Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.
Mo ...
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
Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.
Mo ...
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 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
Equine coat color genetics determine a horse's coat color. Many colors are possible, but all variations are produced by changes in only a few genes. The "base" colors of the horse are determined by the Extension locus, which in recessive form (e ...
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 institut ...
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