Chestnut is a
hair coat colorHorses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them. Color is one of the first things that is noticed about a horse...
of
horseThe horse is a hoofed mammal, a subspecies of one of seven extant species of the 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
maneThe 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
blackBlack 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.
Chestnut is a
hair coat colorHorses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them. Color is one of the first things that is noticed about a horse...
of
horseThe horse is a hoofed mammal, a subspecies of one of seven extant species of the 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
maneThe 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
blackBlack 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
palominoPalomino 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
blackBlack 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 hair. 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 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...
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
recessiveIn genetics, dominance describes a relationship between different forms of a gene at a particular physical location on a chromosome. Typical plants and animals have two sets of chromosomes, one set inherited from each parent, and are described as diploid. They therefore have two alleles at each...
gene. Unlike many coat colors, chestnut can be true-breeding; that is, the mating between two chestnuts will produce chestnut offspring every time. If any color other than chestnut occurs, one of the parents was not chestnut. Some breeds, such as the
BudyonnyThe 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 PunchThe 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
HaflingerThe Haflinger, also known as the Avelignese, is a breed of horse developed in Austria and northern Italy during the late 1800s. There are several theories as to this breed's origin, but its current conformation and appearance are the result of infusions of Arabian and various European breeds' blood...
are exclusively chestnut. Other breeds, such as the
BelgianThe Belgian horse, Belgian Heavy Horse, Brabançon, or Brabant is a draft horse breed which comes from the West-Brabantian region of Belgium...
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
blackBlack 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 ponyThe Ariegeois pony, also known as the Merens, is a breed of mountain pony that is noted for being cold hardy and sturdy. It is native to the Pyrenees and Ariegeois mountains of Spain and southern France, where the Ariège River flows...
is another example.
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 is a term used by American stock horse
A Stock horse is a horse that has a phenotype suitable 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 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
Liver is a term used to describe certain types of dark brown color in dogs and horses.In dogs, It is a dark brown grayish chocolate 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...
chestnuts are a very dark-reddish brown. Liver chestnuts are included in the term "dark chestnut." The darkest chestnuts, particularly common in the Morgan 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 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 DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
or pedigree testing. Recently, it has been suggested that the trait or traits that produce darker shades of chestnut and bay follow a recessiveIn genetics, dominance describes a relationship between different forms of a gene at a particular physical location on a chromosome. Typical plants and animals have two sets of chromosomes, one set inherited from each parent, and are described as diploid. They therefore have two alleles at each...
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. Haflingers
The Haflinger, also known as the Avelignese, is a breed of horse developed in Austria and northern Italy during the late 1800s. There are several theories as to this breed's origin, but its current conformation and appearance are the result of infusions of Arabian and various European breeds' blood...
are exclusively of this shade. It is considered desirable in other breeds, though seldom true-breeding. Some flaxen chestnuts can be mistaken for palominoPalomino 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, and produces distinct characteristics common to wild equids
Equidae 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. HaflingersThe Haflinger, also known as the Avelignese, is a breed of horse developed in Austria and northern Italy during the late 1800s. There are several theories as to this breed's origin, but its current conformation and appearance are the result of infusions of Arabian and various European breeds' blood...
and BelgiansThe Belgian horse, Belgian Heavy Horse, Brabançon, or Brabant is a draft horse breed which comes from the West-Brabantian region of Belgium...
are examples of mealy chestnuts. The flaxen characteristic is sometimes associated with pangare, but not always.
- Light chestnut is a lighter body shade of chestnut without the influence of pangare. The mechanism for producing a light chestnut, whether genetic, nutritional, or otherwise, is not understood.
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 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...
, means that a horse is not chestnut.
- Seal brown
Seal brown is a hair coat color of horses characterized by a near-black body color, with a black mane, tail and legs, and 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. 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
The 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 knowledgable 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.
- Palominos are genetically distinct from chestnuts, having their coats modified 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 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. Furthermore, unless they have blue eyes linked to white markings, the eyes of chestnuts are usually dark brown, while those of a palomino are sometimes slightly lighter. Some color 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.
- Red duns
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...
are a pale, dusty tan shade that resembles the light undercoat color of a body-clipped chestnut. Red duns can be distinguished from light chestnuts by the presence of a bold, dark dorsal stripe in dark red, a red mane, tail and legs, plus the presence of other primitive markings.
Related coat colors
Chestnut is considered a "base color" in the discussion of equine coat color genetics. Many more unusual colors are described in terms of their relationship to chestnut:
- 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 are chestnuts heterozygous (one copy) for the cream 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...
- Cremellos are chestnuts 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 are homozygous. Similarly, horses with a bay...
.
- Red duns are chestnuts 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 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).
- Gold champagnes are chestnuts 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 at birth, respectively...
(one or two copies).
- Red or strawberry roans are chestnuts with the classic roan
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).
Combinations such as chestnut with multiple
dilution genesDilution 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:...
do not always have consistent names. Dunalinos are chestnuts with both the
dun 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...
and heterozygous for the
cream 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...
.
Inheritance and expression
Red color is determined by the equine
melanocortin-1-receptorThe 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)
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
. It is positioned on
chromosomeA chromosome is an organized structure of DNA and protein that is 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...
3 (ECA3) at the Extension
locusIn the fields of genetics and evolutionary 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 functional protein, which is encoded by the
wild typeWild 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...
,
dominantIn genetics, dominance describes a relationship between different forms of a gene at a particular physical location on a chromosome. Typical plants and animals have two sets of chromosomes, one set inherited from each parent, and are described as diploid. They therefore have two alleles at each...
E alleleAn allele is one of a series of different forms of a gene. The word is a short form of allelomorph , which was used in the early days of genetics to describe variant forms of a gene detected as different phenotypes...
, is part of the pathway that allows melanocytes to produce black pigment. The MC1R protein lies within the
cell membraneThe cell membrane is the biological membrane separating the interior of a cell from the outside environment....
, and is signalled by
melanocyte-stimulating hormoneThe melanocyte-stimulating hormones are a class of peptide hormones that in nature are produced by cells in the intermediate lobe of the pituitary gland. They were first isolated by the Yale professor Aaron B. Lerner...
(MSH) released by the pituitary gland. Normally, MC1R is briefly or locally
antagonizedA 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
agouti signalling peptideAgouti signalling peptide, also referred to as Agouti, is a peptide consisting of 131 amino acids. Its discovery was published in 1994 in the scientific magazine Nature where its functional properties were described...
, permitting red pigment to be formed. This results in alternating bands or localized regions of black-rich or red-rich pigmentation, as seen in bay horses.
A
missense mutationIn 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 results in a protein that cannot bind to MSH. This mutation is called the
e allele. So long as one functional gene copy is present, the protein is formed normally and black pigment is produced normally. However, when only mutant copies of the gene are available, only non-functional MC1R proteins are produced. As a result, no black pigment is deposited into the hair and the entire coat is red, yielding a chestnut or red-based coat color.
The recessive nature of the red-coated trait in horses is caused by the ability of a single copy of the functional
E allele to compensate for the non-functional
e allele; bay and
blackBlack 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 "carry" this silent
e.
External links