Chestnut (coat)
Encyclopedia
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 different coat color from that with which they were born...
of horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s consisting of a reddish-to-brown coat with a mane
Mane (horse)
The mane is the hair that grows from the top of the neck of a horse or other equine, reaching from the poll to the withers, and includes the forelock or foretop. It is thicker and coarser than the rest of the horse's coat, and naturally grows to roughly cover the neck...
and tail the same or lighter in color than the coat. Genetically and visually, chestnut is characterized by the absolute absence of true black
Black (horse)
Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and novices frequently mistake dark chestnuts or bays for black. However, some breeds of horses, such as the Friesian horse, Murgese and Ariegeois are almost exclusively black...
hairs. It is one of the most common horse coat colors, 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
Palomino is a coat color in horses, consisting of a gold coat and white mane and tail. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a "red" base coat...
s, while the darkest shades can be so dark as to resemble a black
Black (horse)
Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and novices frequently mistake dark chestnuts or bays for black. However, some breeds of horses, such as the Friesian horse, Murgese and Ariegeois are almost exclusively black...
coat. Chestnuts have dark brown eyes, black skin, and a coat that is entirely devoid of true black hairs. Typical chestnuts are some shade of red or reddish brown. The mane, tail, and legs may be lighter or darker than the body coat, but are never truly black. They may have pink skin beneath any white markings
Horse markings
Markings on horses usually are 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 course of the horse's life...
under the areas of white hair, and if such white markings include one or both eyes, the eyes may be blue.
Chestnut is produced by a recessive
Dominance relationship
Dominance in genetics is a relationship between two variant forms of a single gene, in which one allele masks the effect of the other in influencing some trait. In the simplest case, if a gene exists in two allelic forms , three combinations of alleles are possible: AA, AB, and BB...
gene. Unlike many coat colors, chestnut can be true-breeding; that is, the mating between two chestnuts will produce chestnut offspring every time. Some breeds, such as the Budyonny
Budyonny (horse)
The Budyonny is a breed of horse from Russia. They were developed for use as a military horse following the Russian Revolution and are currently used as an all-purpose competition horse and for driving.-Conformation:...
, Suffolk Punch
Suffolk Punch
The Suffolk Punch, also historically known as the Suffolk Horse or Suffolk Sorrel, is an English breed of draught horse. The breed takes the first part of its name from the county of Suffolk in East Anglia, and the name "Punch" from its solid appearance and strength...
, and Haflinger
Haflinger (horse)
The Haflinger, also known as the Avelignese, is a breed of horse developed in Austria and northern Italy during the late 19th century. Haflinger horses are relatively small, are always chestnut in color, have distinctive gaits described as energetic but smooth, and are well-muscled yet elegant...
are exclusively chestnut. Other breeds, such as the Belgian
Belgian (horse)
The Belgian Draft horse or Belgian, also known as Belgian Heavy Horse, Brabançon, or Brabant, is a draft horse breed from the Brabant region of modern Belgium, where it is called the or Flemish: . It is one of the strongest of the heavy breeds...
are predominantly chestnut. However, a chestnut horse need not have two chestnut parents. For example, Friesian horses have been selected for many years to be uniformly black
Black (horse)
Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and novices frequently mistake dark chestnuts or bays for black. However, some breeds of horses, such as the Friesian horse, Murgese and Ariegeois are almost exclusively black...
, but on rare occasions chestnuts are born. The Ariegeois pony is another example.
Visual identification
- 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.
- SorrelSorrel (horse)Sorrel is an alternative word for one of the most common equine coat colors in horses. While the term is usually used to refer to a copper-red shade of chestnut, in some places it is used generically in place of "chestnut" to refer to any reddish horse with a same-color or lighter mane and tail,...
is a term used by American stock horseStock horseA Stock horse is a horse of a type that is well suited for working with livestock, particularly cattle. Such horses are riding horsescharacterized by agility, quickness, and powerful hindquarters...
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 chestnutLiver (color)Liver is a term used to describe certain types of dark brown color in dogs and horses.In dogs, it is a dark brown shade.In horses, "liver chestnut" is a term used to describe a chocolate-colored chestnut horse. A liver chestnut is the same genetically as a regular chestnut, but the shade is a dark...
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 horseMorgan horseThe Morgan is one of the earliest horse breeds developed in the United States. Tracing back to the stallion Figure, later named Justin Morgan after his best-known owner, the breed excels in many disciplines, and is known for its versatility....
, may be indistinguishable from true blackBlack (horse)Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and novices frequently mistake dark chestnuts or bays for black. However, some breeds of horses, such as the Friesian horse, Murgese and Ariegeois are almost exclusively black...
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 DNADNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
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 recessiveDominance relationshipDominance in genetics is a relationship between two variant forms of a single gene, in which one allele masks the effect of the other in influencing some trait. In the simplest case, if a gene exists in two allelic forms , three combinations of alleles are possible: AA, AB, and BB...
mode of inheritance.
- Flaxen chestnut and blond chestnut are terms that describe manes and/or tails 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. HaflingersHaflinger (horse)The Haflinger, also known as the Avelignese, is a breed of horse developed in Austria and northern Italy during the late 19th century. Haflinger horses are relatively small, are always chestnut in color, have distinctive gaits described as energetic but smooth, and are well-muscled yet elegant...
are exclusively of this shade. It is considered desirable in other breeds, though seldom true-breeding. Some flaxen chestnuts can be mistaken for palominoPalominoPalomino is a coat color in horses, consisting of a gold coat and white mane and tail. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a "red" base coat...
s and have been registered in palomino color registries.
- Pangare or mealy is thought to be controlled by a single gene, unrelated to chestnut color, and produces distinct characteristics common to wild equidsEquidaeEquidae is the taxonomic family of horses and related animals, including the extant horses, donkeys, and zebras, and many other species known only from fossils. All extant species are in the genus Equus...
: pale hairs around the eyes and muzzle and a pale underside. HaflingersHaflinger (horse)The Haflinger, also known as the Avelignese, is a breed of horse developed in Austria and northern Italy during the late 19th century. Haflinger horses are relatively small, are always chestnut in color, have distinctive gaits described as energetic but smooth, and are well-muscled yet elegant...
and BelgiansBelgian (horse)The Belgian Draft horse or Belgian, also known as Belgian Heavy Horse, Brabançon, or Brabant, is a draft horse breed from the Brabant region of modern Belgium, where it is called the or Flemish: . It is one of the strongest of the heavy breeds...
are examples of mealy chestnuts. The flaxen characteristic is sometimes associated with pangare, but not always.
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:- PalominoPalominoPalomino is a coat color in horses, consisting of a gold coat and white mane and tail. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a "red" base coat...
s have a chestnut base coat color that is genetically modified to a golden shade by a single copy of the incomplete dominant cream geneCream geneThe 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 are homozygous. Similarly, horses with a bay...
. 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 breedColor breedA color breed is a term that refers to horses that are registered based primarily on their coat color, regardless of the horse's actual breed or breed type....
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 geneCream geneThe 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 are homozygous. Similarly, horses with a bay...
. They have a cream-colored coat, blue eyes and lightly pigmented pink skin.
- Red duns have a chestnut base coat with the dun geneDun geneThe dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene has the ability to affect the appearance of all black, bay, or chestnut -based horses to some degree by lightening the base body coat and suppressing the underlying base color to the...
(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 markingsPrimitive markingsPrimitive markings among domestic horses are a group of hair coat markings and qualities associated with primitive breeds, and the dun coat color family in particular. All dun horses possess at least the dorsal stripe but the presence of the other primitive markings varies...
, which distinguish a red dun from a light or body-clipped chestnut. - Gold champagnes have a chestnut base coat with the champagne geneChampagne geneThe 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 at birth, respectively...
(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 roanRoan (horse)Roan is a horse coat color pattern characterized by an even mixture of colored and white hairs on the body, while the head and "points"—lower legs, mane and tail—are more solid-colored. The roan pattern is dominantly-inherited, and is found in many horse breeds...
gene (one or two copies). - A skewbaldSkewbaldSkewbald is a color 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 color besides black coat. Skewbald horses which are bay and white are sometimes called tricoloured...
, "chestnut pinto" or "sorrel PaintAmerican Paint HorseThe American Paint Horse is a breed of horse that combines both the conformational characteristics of a western stock horse with a pinto spotting pattern of white and dark coat colors. Developed from a base of spotted horses with Quarter Horse and Thoroughbred bloodlines, the American Paint Horse...
" is a pinto horsePinto horseA 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 throughout history appear to have selectively bred for pinto...
with chestnut and white patches.
Combinations of multiple dilution gene
Dilution gene
Dilution gene is a popular term for any one of a number of genes that act to create a lighter coat color in living creatures. There are many examples of such genes:-General:...
s do not always have consistent names. For example, "dunalinos" are chestnuts with both the dun gene
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 has the ability to affect the appearance of all black, bay, or chestnut -based horses to some degree by lightening the base body coat and suppressing the underlying base color to the...
and one copy of the cream gene
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 are homozygous. Similarly, horses with a bay...
.
Chestnut mimics
- Bay horses also have reddish coats, but they have a black mane, tail, legs and other "points". The presence of true black points, even if obscured by white markingsHorse markingsMarkings on horses usually are 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 course of the horse's life...
, means that a horse is not chestnut.
- Seal brownSeal brown (horse)Seal brown is a hair coat color of horses characterized by a near-black body color; with black points, the mane, tail and legs; but also reddish or tan areas around the eyes, muzzle, behind the elbow and in front of the stifle...
and/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 baySilver dapple geneThe silver dapple gene is a dilution gene that affects the black base coat color. It will typically dilute a black mane and tail to flaxen, and a black body to a shade of brown or chocolate. It is responsible for a group of coat colors in horses called "silver dapple" in the west, or "taffy" in...
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 alleleAllele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
that is a mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
from the wildtype and is genetically the most recessive
Dominance relationship
Dominance in genetics is a relationship between two variant forms of a single gene, in which one allele masks the effect of the other in influencing some trait. In the simplest case, if a gene exists in two allelic forms , three combinations of alleles are possible: AA, AB, and BB...
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
Melanocortin 1 receptor
The melanocortin 1 receptor , also known as melanocyte-stimulating hormone receptor , melanin-activating peptide receptor, or melanotropin receptor, is a G protein-coupled receptor which binds to a class of pituitary peptide hormones known as the melanocortins, of which include adrenocorticotropic...
(MC1R), a protein positioned on chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
3 (ECA3) at the Extension locus
Locus (genetics)
In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
. The wild type
Wild type
Wild type refers to 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, "mutant" allele...
version of the gene encoding MC1R is the E allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
(colloquially, though imprecisely, called the "Extension gene"), and is part of the genetic pathway that allows melanocytes to produce eumelanin, or black pigment. When the "E" allele is not present, no eumelanin is produced, but the "e" allele still allows melanin
Melanin
Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...
to be produced in the form of pheomelanin, or red pigment, creating a chestnut or red-based coat color. In general, alleles that create fully functional MC1R proteins are inherited dominantly
Dominance relationship
Dominance in genetics is a relationship between two variant forms of a single gene, in which one allele masks the effect of the other in influencing some trait. In the simplest case, if a gene exists in two allelic forms , three combinations of alleles are possible: AA, AB, and BB...
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
Missense mutation
In genetics, a missense mutation is a point mutation in which a single nucleotide is changed, resulting in a codon that codes for a different amino acid . This can render the resulting protein nonfunctional...
in the code for MC1R, which results in a protein that cannot bind to the Melanocyte-stimulating hormone
Melanocyte-stimulating hormone
The melanocyte-stimulating hormones are a class of peptide hormones that are produced by cells in the intermediate lobe of the pituitary gland...
(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
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 at birth, respectively...
. It is a genetic mechanism not fully understood, but may be related to the pheomelanistic characteristics of "e".
The recessive nature 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 (horse)
Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and novices frequently mistake dark chestnuts or bays for black. However, some breeds of horses, such as the Friesian horse, Murgese and Ariegeois are almost exclusively black...
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
Foal
A foal is an equine, particularly a horse, that is one year old or younger. More specific terms are colt for a male foal and filly for a female foal, but these terms are used until the horse is age three or four. When the foal is nursing from its dam , it may also be called a suckling...
. 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
Receptor antagonist
A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...
by the agouti signalling peptide
Agouti signalling peptide
Agouti signalling peptide, a product of the Agouti gene, is a peptide consisting of 131 amino acids. Its discovery was published in 1994 in the scientific journal Nature where its functional properties were described...
(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.