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Black

Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and it is not uncommon to mistake dark chestnuts or bays for black.

True black horses have dark brown eyes, black skin, and wholly black hair coats without any areas of permanently reddish or brownish hair. They may have pink skin beneath any white markings under the areas of white hair, and if such white markings include one or both eyes, the eyes may be blue. Many black horses "sun bleach" with exposure to the elements and sweat, and therefore their coats may lose some of their rich black character and may even resemble bay or seal brown, though examination of the color of hair around the eyes, muzzle and genitals often will determine color. Black horses that do not sun bleach are called "non-fading" or "sheer" blacks.

Some breeds of horses, such as the Friesian horse, Murgese and Ariegeois(or Merens) are almost exclusively black. Black is also common in the Fell pony, Dales pony, Ostfriesen and Alt-Oldenburger, Kladruber, and Groningen.

Visual identification

When identifying the base color of a horse, it is important to disregard all pink-skinned white markings. White markings and patterns such as pinto and leopard have no bearing on the underlying base coat color of the animal.

Black foals are typically born a mousy gray but can be darker shades. As many foals have primitive markings at birth, some black foals are mistaken for grullo or even bay dun; the primitive markings on a black foal will, however, disappear as the black hair coat grows in. Black foals have dark skin and eyes at birth. An adult-like black foal coat often indicates that the foal will gray, if the foal has at least one gray parent. Graying can be confirmed by the presence of white hairs around the eyes and muzzle. Gray Lipizzaner horses are frequently born black.

Black adult horses are easier to identify, as the coat must be entirely black, even if superficially sun bleached. A sun bleached black may be confused with a dark bay, but a trained eye can distinguish between them, particularly by examining the fine hairs around the eyes and muzzle. When a black horse is sun-bleached, the mane and tail often sun bleach most prominently, and the rest of the coat may have a rusty tinge. A sun-bleached black may also be mistaken for the less common smoky black, but can be distinguished by pedigree analysis or DNA testing.

Black mimics

  • Dark bay or seal brown: The darkest shades of bay are commonly confused with black, even by experienced horse persons. However, a dark bay will always show some rich red character in its coat. Horses with a very dark coat that may appear black, but have tan or reddish hairs around the eyes, muzzle, armpits, and stifle are sometimes called "seal brown", "mahogany bay", or "black bay." Both colors are genetically distinct from black and can be confirmed with a DNA test.
  • Liver chestnut: Some red horses are so dark that they appear black, and are often called "black chestnuts" as a consequence. However, even the darkest liver chestnuts will show some red character in their coats, usually in the hair around the pastern or in the mane or tail. Even dark liver chestnuts do not have any true black pigment in their coats. This can be verified with DNA testing. Liver chestnut is very common in the Morgan horse.
  • Smoky black: The action of the cream gene in the heterozygous condition has a minimal effect on black pigment, so heterozygous creams with a black base coat (smoky blacks) differ little from true blacks. A smoky black will have at least one cream parent, is often born a pewter shade with blue eyes, and usually retains reddish hair inside the ear through adulthood.

Genetic identification

In the study and discussion of equine coat colour genetics, black is considered a "base" color, as is red. This designation makes the effects of other coat colour genes easier to understand. Coat colors that are designated "black-based" include grullo (also called blue dun), smoky black, smoky cream, silver black, classic champagne, and blue roan. Sometimes this designation includes the bay family: bay, seal brown, buckskin, bay dun, silver bay, perlino, amber champagne, and bay roan. Horses with a black-based coat may also have added spotting patterns including leopard patterns seen on Appaloosas and the pinto coloring known as piebald.

The genetics behind the black horse are relatively simple. The color black is primarily controlled by two genes: Extension and Agouti. The functional, dominant allele of the extension gene (labeled "E") enables the horse to produce black pigment in the hair. Without this gene (homozygous recessive condition "ee"), the coat is devoid of black pigment and the horse is some shade of red. The functional, dominant allele (or alleles) of the agouti gene (labeled "A") enable the horse to restrict black pigment to certain parts of the coat, notably the legs, mane and tail, allowing the underlying red to show through, resulting in bay coloring. Without this gene (homozygous recessive condition "aa"), any black pigment present is unrestricted, resulting in a uniformly black coat.

Thus a black horse has at least one copy of the functional, dominant "E" allele and two copies of the non-functional, recessive "a" allele. A mature true black horse can be safely said to possess at least one dominant extension gene (EE or Ee); and has no other dominant genes (such as agouti, gray, or any of the dilution factors) that further modify colour.

A DNA test, which uses hair with the root intact, has been developed to test for the Extension and Agouti genotypes. However, the terminology can be manipulated. Unfortunately, the extension test is often mislabeled as the "black test", leading to confusion. Neither the extension test nor the agouti test alone can identify a black horse. Together, they can determine that a horse that appears visually black is not actually a dark bay or liver chestnut.

Horses described as "homozygous black" are simply homozygous for the dominant extension gene (EE); they are homozygous "not-red". Such horses are only "guaranteed" to never produce a red foal. The actual horse may carry additional genetic modifiers that could make it bay, buckskin, gray, bay roan, perlino, silver bay, and so on. A visually black horse that is tested "homozygous black" is EE and has no other color modifiers.

However, it has become popular for individuals owning a horse that is homozygous for the extension gene (EE) to claim that the horse will "throw black." But, generally speaking, one horse cannot be guaranteed to "throw black" with all mates. The mate of a true black horse may contribute the a dominant Agouti allele, which will suppress the black coloring and result in a bay foal. If a black is bred to a gray, the ensuing foal may also be gray. Other modifiers present in the mate may produce additional dilution colors or spotting patterns. Nonetheless certain individual pairings with appropriate DNA testing can, in some cases, be guaranteed to produce black.

Chestnut

Chestnut is a hair coat colour of horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in colour than the coat. Genetically and visually, chestnut is characterized by the absolute absence of true black hairs. It is one of the most common horse coat colours, 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 palominos, while the darkest shades can be so dark as to resemble a 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 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 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, Suffolk Punch, and Haflinger are exclusively chestnut. Other breeds, such as the Belgian 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, but on rare occasions chestnuts are born. The Ariegeois pony 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 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.

The lower legs of this liver chestnut horse are distinctly red, even underneath the white markings.

  • 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, may be indistinguishable from true 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 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 mode of inheritance.[2]
  • 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 palominos 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 equids: pale hairs around the eyes and muzzle and a pale underside. Haflingers and Belgians are examples of mealy chestnuts. The flaxen characteristic is sometimes associated with pangare, but not always.

Chestnut family colours

Chestnut is considered a "base colour" in the discussion of equine coat color genetics. Additional coat colors based on chestnut are often described in terms of their relationship to chestnut:

  • Palominos have a chestnut base coat colour that is genetically modified to a golden shade by a single copy of the incomplete dominant cream gene. 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 colour breed 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. 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 (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).
  • skewbald, "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.

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, means that a horse is not chestnut.
  • Seal brown or dark bay horses are not chestnut but may be confused with a liver chestnut. Those unfamiliar with horse coat colour 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

The chestnut colour, called "red" by geneticists, is created by an allele that is a mutationfrom the wildtype and is genetically the most recessive coat colour 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. The wild type version of the gene encoding MC1R is the E allele (colloquially, though imprecisely, called the "Extension gene"), and is part of the genetic pathway that allows melanocytesto produce eumelanin, or black pigment. When the "E" allele is not present, no eumelanin is produced, but the "e" allele still allows melanin to be produced in the form of pheomelanin, or red pigment, creating a chestnut or red-based coat colour. In general, alleles that create fully functional MC1R proteins are inherited dominantly and result in a black-based coat colour ("E"), while mutated alleles that create "dysfunctional" MC1R are recessive and result in a lighter coat colour ("e").

Red hair color in horses ("e") is created by a missense mutation in the code for MC1R, which results in a protein that cannot bind to the Melanocyte-stimulating hormone(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. 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 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. Thus, unlike many coat colours, chestnut can be true-breeding; if any colour 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 (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.

Grey

Gray or grey is a coat colour of horses characterized by progressive silvering of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike many depigmentation genes, gray does not affect skin or eye colour. Their adult hair coat is white, dappled, or white intermingled with hairs of other colors. Gray horses may be born any base color, depending on other color genes present. White hairs begin to appear at or shortly after birth and become progressively lighter as the horse ages. Graying can occur at different rates—very quickly on one horse and very slowly on another.

Gray horses appear in many breeds, though the colour is most commonly seen in breeds descended from Arabian ancestors. Some breeds that have large numbers of gray-colored horses include the Thoroughbred, the Arabian, the American Quarter Horse, the Percheron, the Andalusian, the Welsh pony, and the most famous of all gray horse breeds, the Lipizzaner.

People who are unfamiliar with horses may refer to gray horses as "white." However, a gray horse whose hair coat is completely "white" will still have black skin (except under markings that were white at birth) and dark eyes. This is how to discern a gray horse from a white horse. White horses usually have pink skin and sometimes even have blue eyes. Young horses with hair coats consisting of a mixture of colored and gray or white hairs are sometimes confused with roan. Some horses that carry dilution genesmay also be confused with white or gray.

While gray is commonly called a coat colour by breed registries, genetically it may be more correct to call it a depigmentation pattern. It is a dominant allele, and thus a horse needs only one copy of the gray allele, that is, heterozygous, to be gray in colour. A homozygous gray horse, one carrying two gray alleles, will always produce gray foals.

Prevalence

Gray is common in many breeds. Today, about one horse in 10 carries the mutation for graying with age. The vast majority of Lipizzaners are gray, as are the majority of Andalusian horses. Many breeds of French draft horse such as the Percheron and Boulonnais are often gray as well. Gray is also found among Welsh Ponies, Thoroughbreds, and American Quarter Horses. All of these breeds have common ancestry in the Arabian horse. In particular, all gray Thoroughbreds descend from a horse named Alcock's Arabian, a gray born in 1700. The gray coat colour makes up about 3% of Thoroughbreds.

Gray also occurs in spotted horses such as pintos or Appaloosas, but its effects wash out the contrast of the markings of these patterns. For this reason, some colour breed registries refuse or cancel registration of gray horses.

Changes in the colour of gray horses

A gray foal may be born any color. However, bay, chestnut, or black base colours are most often seen. As the horse matures, white hairs begin to replace the base or birth colour. Usually white hairs are first seen by the muzzle, eyes and flanks, occasionally at birth, and usually by the age of one year. Over time, white hairs replace the birth colour and the horse changes slowly to either a rose graysalt and pepper (or iron gray), or dapple gray. As the horse ages, the coat continues to lighten to a pure white or fleabitten gray hair coat. Thus, the many variations of gray colouring in horses are intermediate steps that a young horse takes while graying out from a birth color to a hair coat that is completely "white."

Different breeds, and individuals within each breed, take differing amounts of time to gray out. Thus, graying cannot be used to approximate the age of a horse except in the broadest of terms: a very young horse will never have a white coat (unless it is a true white horse), while a horse in its teens usually is completely grayed out. One must also be careful not to confuse the small amount of gray hairs that may appear on some older horses in their late teens or twenties, which do not reflect the gray gene and never cause a complete graying of the horse.

This change in hair color can be confusing. Many new horse owners, not understanding the workings of the gray gene, are disappointed to discover that their dapple gray horse turns completely white a few years later. Other times, people traveling with gray horses who have a pure white hair coat have encountered problems with non-horse-oriented officials such as police officers or border guards who are unclear about a horse who has papers saying it is "gray" when the horse in front of them appears white.

To further complicate matters, the skin and eyes may be other colours if influenced by other factors such as white markings, certain white spotting patterns or dilution genes.

Young gray horses

An intermediate stage in young horses that are in the early stages of turning gray is sometimes called "salt and pepper," "iron gray," or "steel gray." This colouring occurs when white and black hairs are intermingled on the body, usually seen in horses that are born black or dark bay. This is the most common intermediate form of gray, which can give a silvery look to the coat. "Rose gray" is a term used to describe this intermediate stage for a horse born a chestnut or lighter bay color. While these colors are "graying out," both red and white hairs are often mixed on the body. Thus rose gray horses have a slight pinkish tinge to their graying coat. These horses are sometimes confused with roans, but a gray continues to lighten with age, while a roan does not. Roaning also causes fewer white hairs on the legs and head, giving the horse the appearance of dark points, which is usually not true of gray.

Dapple gray

"Dapple gray" is an intermediate stage not seen on all grays, but often considered highly attractive. It consists of a dark hair coat with "dapples," which are dark rings with lighter hairs on the inside of the ring, scattered over the entire body of the animal. It is another possible intermediate step in the graying process of the horse. Dappled grays should not be confused with the slight dappling "bloom" seen on horses that are very healthy or slightly overweight, as "bloom" dapples disappear should the horse lose condition.

The "flea-bitten" gray

A horse that has completely changed its base coat will either be pure white or "flea-bitten" gray. Flea-bitten gray is a color consisting of a white hair coat with small speckles or "freckles" of red-colored hair throughout. Most horses who become flea-bitten grays still go through a brief period when they are pure white.

The flea-bitten pattern, like freckles on a human, can also vary: Some horses may appear almost pure white, with only a few speckles observed on close examination. Others may have so many speckles that they are occasionally mistaken for a roan or even a type of sabino. One unique form of flea-bitten gray is the "bloody shouldered" horse. This is an animal that is so heavily flea-bitten on certain parts of the body, usually the shoulder area, that it almost appears as if blood had been spilled on the horse, hence the name. Arabian horse breeders hold the view that traditions of the desert Bedouin people considered the "bloody shoulder" to be a prized trait in a war mare and much desired.

The flea-bitten pattern comes about because of somatic loss of the duplication that causes graying with age, enabling normal pigmentation to be reestablished. Generally only occurs in heterozygous Grays.

The genetics of gray

The gray gene (G) is an autosomal dominant gene. In simple terms, a horse which has even one copy of the gray allele, even if it has a gene for another colouring, will always become gray. If a gray horse is homozygous (GG), meaning that it has a gray allele from both parents, it will always produce gray offspring. However, if a gray horse is heterozygous (Gg), meaning it inherits one copy of the recessive gene (g), that animal may produce offspring who are not gray (depending on what colour gene an offspring inherits from its other parent). Conversely, a gray horse must have at least one gray parent. Genetic testing is now possible to determine whether a horse is homozygous or heterozygous for gray, or if it does not carry the gene at all. The gray gene does not affect skin or eye colour, so grays typically have dark skin and eyes, as opposed to the unpigmented pink skin of white horses.

In 2008, researchers at Uppsala University in Sweden identified the genetic mutation that governs the graying process. The study also revealed that gray horses carry an identical mutation that can be traced back to a common ancestor that lived thousands of years ago. The discovery that gray can be linked to a single animal provides an example of how humans have "cherry-picked" attractive mutations in domestic animals.

Gray is controlled by a single dominant allele of a gene that regulates specific kinds of stem cells.

The identification of the gray mutation is also of great interest in of medical research since this mutation also enhances the risk for melanoma in horses; About 75% of gray horses over 15 years of age have a benign form of melanoma that in some cases develops into a malignant melanoma. The study of gray genetics has pointed to a molecular pathway that may lead to tumour development. Both STX17 and the neighboring NR4A3 gene are overexpressed in melanomas from gray horses, and those carrying a loss-of-function mutation in ASIP (agouti signaling protein) had a higher incidence of melanoma, implying that increased melanocortin-1 receptor signaling promotes melanoma development in Gray horses.

Horse coat colours sometimes confused with gray

White horses

Many people who are unfamiliar with horses refer to a gray horse as "white". However, most white horses have pink skin and some have blue eyes. A horse with dark skin and dark eyes under a white hair coat is gray. However, a gray horse with an underlying homozygous cream base coat colour may be born with rosy-pink skin, blue eyes and near-white hair. In such cases, DNA testing may clarify the genetics of the horse.

Roan

Some grays in intermediate stages of graying may be confused with a roan or a rabicano. Some heavily fleabitten grays may also be confused with roans. However, roans are easily distinguishable from grays: roan consists of individual white hairs on a dark base coat, usually with the head and legs of the horse darker than the rest of the body. Rabicanos also have intermixed white hairs primarily on the body with a dark head. With gray horses, the head is often the first area to lighten, especially around the eyes and muzzle. Also, roans do not lighten with age, while grays always do.

The varnish roan is another unusual coloration, sometimes seen in Appaloosa horses, that, like gray, can change with age, but unlike gray, the horse does not become progressively lighter until it is pure white. Varnish roans are created by the action of leopard complex within breeds such as the Appaloosa and are seldom seen elsewhere.

Diluted colours

The dilution genes that create dun, cream, pearl, silver dapple and champagne coloring may occasionally result in confusion with gray.

Some horses with a particular type of dun hair coat known as a "blue dun", grullo, or "mouse" dun appear to be a solid gray. However, this color is caused by the dun geneacting on a black base coat, and horses who are dun have all hairs the same color; there is no intermingling of white and dark hairs. Also, dun horses do not get lighter as they age. Horses who are a light cream color are also not grays. These are usually cremello, perlino or smoky cream horses, all colors produced by the action of the cream gene. However, if a gray parent passes on the gene, the gray gene will be dominant over cremello. Another cream-colored dilition, the pearl gene or "barlink factor", may also create very light-coated horses. Similarly, the champagne gene can lighten coat colour, often producing dappling or light colors that can be confused with gray.

In spite of its name, the silver dapple gene has nothing to do with graying. It is a dilution gene that acts only on a black coat, diluting the coat to a dark brown and the mane to a flaxen shade. Horses that express the silver dapple gene (and do not have the gray gene) are born that colour and it will not lighten. However, again, if one parent passes on the gray gene, the gray gene will again be dominant.

Mythology

Throughout history, both gray and white horses have been mythologized. As part of its legendary dimension, the gray horse in myth has been depicted with seven heads (Uchaishravas) or eight feet (Sleipnir), sometimes in groups or singly. There are also mythological tales of divinatory gray horses who prophesy or warn of danger.

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