Gray (horse)
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 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 color 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 color is most commonly seen in breeds descended from Arabian
Arabian horse
The Arabian or Arab horse is a breed of horse that originated on the Arabian Peninsula. With a distinctive head shape and high tail carriage, the Arabian is one of the most easily recognizable horse breeds in the world. It is also one of the oldest breeds, with archaeological evidence of horses...
ancestors. Some breeds that have large numbers of gray-colored horses include the Thoroughbred
Thoroughbred
The Thoroughbred is a horse breed best known for its use in horse racing. Although the word thoroughbred is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed...
, the Arabian
Arabian horse
The Arabian or Arab horse is a breed of horse that originated on the Arabian Peninsula. With a distinctive head shape and high tail carriage, the Arabian is one of the most easily recognizable horse breeds in the world. It is also one of the oldest breeds, with archaeological evidence of horses...
, the American Quarter Horse
American Quarter Horse
The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph...
, the Percheron
Percheron
The Percheron is a breed of draft horse that originated in the Perche valley in northern France. Percherons are usually gray or black in color. They are well-muscled, and known for their intelligence and willingness to work. Although their exact origins are unknown, the ancestors of the breed were...
, the Andalusian
Andalusian horse
The Andalusian, also known as the Pure Spanish Horse or PRE , is a horse breed developed in the Iberian Peninsula. Its ancestors have been present on the Iberian Peninsula for thousands of years. The Andalusian has been recognized as an individual breed since the 15th century, and its conformation...
, the Welsh pony
Welsh Pony
The Welsh Pony and Cob are closely related horse breeds including both pony and cob types, which originated in Wales in the United Kingdom...
, 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
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...
that were white at birth) and dark eyes. This is how to discern a gray horse from a white horse. White
White (horse)
White horses are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white genes, are rare...
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
Roan (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...
. Some horses that carry 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 may also be confused with white or gray.
While gray is commonly called a coat color by breed registries
Breed registry
A breed registry, also known as a stud book or register, in animal husbandry and the hobby of animal fancy, is an official list of animals within a specific breed whose parents are known. Animals are usually registered by their breeders when they are still young...
, genetically it may be more correct to call it a depigmentation pattern. It is a dominant gene
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 thus a horse needs only one copy of the gray 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...
, that is, heterozygous, to be gray in color. 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 horseAndalusian horse
The Andalusian, also known as the Pure Spanish Horse or PRE , is a horse breed developed in the Iberian Peninsula. Its ancestors have been present on the Iberian Peninsula for thousands of years. The Andalusian has been recognized as an individual breed since the 15th century, and its conformation...
s. Many breeds of French draft horse such as the Percheron
Percheron
The Percheron is a breed of draft horse that originated in the Perche valley in northern France. Percherons are usually gray or black in color. They are well-muscled, and known for their intelligence and willingness to work. Although their exact origins are unknown, the ancestors of the breed were...
and Boulonnais are often gray as well. Gray is also found among Welsh Ponies
Welsh Pony
The Welsh Pony and Cob are closely related horse breeds including both pony and cob types, which originated in Wales in the United Kingdom...
, Thoroughbred
Thoroughbred
The Thoroughbred is a horse breed best known for its use in horse racing. Although the word thoroughbred is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed...
s, and American Quarter Horse
American Quarter Horse
The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph...
s. All of these breeds have common ancestry in the Arabian horse
Arabian horse
The Arabian or Arab horse is a breed of horse that originated on the Arabian Peninsula. With a distinctive head shape and high tail carriage, the Arabian is one of the most easily recognizable horse breeds in the world. It is also one of the oldest breeds, with archaeological evidence of horses...
. In particular, all gray Thoroughbreds descend from a horse named Alcock's Arabian, a gray born in 1700. The gray coat color makes up about 3% of Thoroughbreds.
Gray also occurs in spotted horses such as pinto
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 throughout history appear to have selectively bred for pinto...
s or Appaloosa
Appaloosa
The Appaloosa is a horse breed best known for its colorful leopard-spotted coat pattern. There is a wide range of body types within the breed, stemming from the influence of multiple breeds of horses throughout its history. Each horse's color pattern is genetically the result of various spotting...
s, but its effects wash out the contrast of the markings of these patterns. For this reason, some color breed
Color breed
A 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 refuse or cancel registration of gray horses.
Changes in the color of gray horses
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...
may be born any color. However, bay
Bay (color)
Bay is a hair coat color of horses, characterized by a reddish brown body color with a black mane, tail, ear edges, and lower legs. Bay is one of the most common coat colors in many horse breeds....
, chestnut
Chestnut (coat)
Chestnut is a hair coat color of horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat. Genetically and visually, chestnut is characterized by the absolute absence of true black hairs...
, or 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...
base colors are most often seen. As the horse matures, white hairs begin to replace the base or birth color. 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 color and the horse changes slowly to either a rose gray, salt 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 coloring 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
White (horse)
White horses are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white genes, are rare...
), 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 colors if influenced by other factors such as 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...
, certain white spotting patterns
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 throughout history appear to have selectively bred for pinto...
or 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.
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 coloring occurs when white and black hairs are intermingled together 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 together on the body. Thus rose gray horses have a slight pinkish tinge to their graying coat. These horses are sometimes confused with 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...
, but a gray continues to lighten with age, while a roan does not.
Dapple gray
The "flea-bitten" gray
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
Sabino horse
Sabino is a group of white spotting patterns in horses that affect the skin and hair. A wide variety of irregular color patterns are accepted as sabino. In the strictest sense, "sabino" refers to the white patterns produced by the Sabino 1 gene, for which there is a DNA test...
. 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. In the traditions of the desert Bedouin
Bedouin
The Bedouin are a part of a predominantly desert-dwelling Arab ethnic group traditionally divided into tribes or clans, known in Arabic as ..-Etymology:...
people who bred the Arabian horse
Arabian horse
The Arabian or Arab horse is a breed of horse that originated on the Arabian Peninsula. With a distinctive head shape and high tail carriage, the Arabian is one of the most easily recognizable horse breeds in the world. It is also one of the oldest breeds, with archaeological evidence of horses...
, the "bloody shoulder" was a prized trait in a war mare and much desired. In some cases, a "bloody shoulder" might in theory also be caused the sabino or rabicano
Rabicano
Rabicano, also called white ticking, is a horse coat color characterized by limited roaning in a specific pattern: interspersed white hairs most dense and originating from the flank and the tailhead...
gene acting in addition to a gray coat.
The flea-bitten pattern comes about because of somatic loss of the duplication that causes Greying with age, enabling normal pigmentation to be reestablished. Generally only occurs in heterozygous Greys.
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 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...
, even if it has a gene for another coloring, will always become gray. If a gray horse is homozygous (GG), meaning that it has a gray 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...
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 color 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 color, so grays typically have dark skin and eyes, as opposed to the unpigmented pink skin of white horses
White (horse)
White horses are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white genes, are rare...
.
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
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...
of a gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
that regulates specific kinds of stem cell
Stem cell
This article is about the cell type. For the medical therapy, see Stem Cell TreatmentsStem cells are biological cells found in all multicellular organisms, that can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells...
s.
The identification of the gray mutation is also of great interest in of medical research since this mutation also enhances the risk for melanoma
Melanoma
Melanoma is a malignant tumor of melanocytes. Melanocytes are cells that produce the dark pigment, melanin, which is responsible for the color of skin. They predominantly occur in skin, but are also found in other parts of the body, including the bowel and the eye...
in horses; About 75% of grey 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.
White Horses
Many people who are unfamiliar with horses refer to a gray horse as "white." However, most WhiteWhite (horse)
White horses are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white genes, are rare...
horses have pink skin and frequently have blue eyes. A horse with dark skin and dark eyes under a white hair coat is gray. In theory, a gray horse with an underlying cremello base color may be born and mature to have pink skin and 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 blue 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...
, strawberry roan or red roan. Some heavily fleabitten grays may also be confused with a red roan. 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. 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
Varnish roan
Varnish roan describes a horse with coloration similar to roan, but with some changes in color over the years, though not to the extreme of a gray. This type of roaning only occurs in conjunction with the Leopard complex. Varnish roans are born with a dark base coat color, usually with some spotting...
is another unusual coloration, sometimes seen in Appaloosa
Appaloosa
The Appaloosa is a horse breed best known for its colorful leopard-spotted coat pattern. There is a wide range of body types within the breed, stemming from the influence of multiple breeds of horses throughout its history. Each horse's color pattern is genetically the result of various spotting...
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 thought to be linked to the leopard complex
Leopard complex
The leopard complex is a group of genetically-related coat patterns in horses. These patterns range from progressive increases in interspersed white hair similar to graying or roan to distinctive, Dalmatian-like leopard spots on a white coat. Secondary characteristics associated with the leopard...
within the Appaloosa breed and are seldom seen elsewhere.
Diluted colors
The dilution geneDilution 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 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
Grullo
Grullo is a color of horses in the dun family, characterized by tan-gray or mouse-colored hairs on the body, often with shoulder and dorsal stripes and black barring on the lower legs. In this coloration each individual hair is mouse-colored, unlike a roan which is composed of a mixture of dark and...
, or grulla, appear to be a solid gray. However, this color is caused by 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...
acting 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. This particular color is most commonly seen in the American Quarter Horse
American Quarter Horse
The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph...
, and because Quarter Horses can also be born gray or roan, there is sometimes a bit of confusion amongst aficionados of the breed.
Horses who are a light cream color are also not grays. These are usually cremello or perlino horses, colors produced by action 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...
. However, if a gray parent passes on the gene, the gray gene will be dominant over cremello. Another cream-colored dilition, the pearl gene
Pearl gene
The Pearl gene, also known as the "Barlink factor," is a dilution gene that somewhat resembles the cream gene and the champagne gene, but is neither. It is a somewhat rare dilution gene found in the American Quarter Horse, American Paint Horse, and Peruvian Paso. The same mutation appears in...
or "barlink factor," may also create very light-coated horses.
In spite of its name, the silver dapple gene
Silver dapple gene
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...
has nothing to do with graying. It is a dilution gene that acts only on 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, 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 with the color and it will not lighten. However, again, if one parent passes on the gray gene, the gray gene will again be dominant. Similarly, 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...
can lighten coat color, often producing dappling or light colors that can be confused with gray.
Mythology
Throughout history, both gray and whiteWhite (horse)
White horses are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white genes, are rare...
horses have been mythologized. As part of its legendary dimension, the gray horse in myth has been depicted with seven heads Uchaishravas
Uchaishravas
In Hindu mythology, Uchchaihshravas or is a seven-headed flying horse, that was obtained during the churning of the milk ocean. It is considered the best of horses, prototype and king of horses. Uchchaihshravas is often described as a vahana of Indra - the god-king of heaven, but is also...
or eight feet Sleipnir
Sleipnir
In Norse mythology, Sleipnir is an eight-legged horse. Sleipnir is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson...
, sometimes in groups or singly. There are also mythological tales of gray horses which are divinatory, who prophesy or warn of danger.
See also
- AlbinismAlbinismAlbinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin...
- Equine coat colorEquine coat colorHorses 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...
- Equine coat color geneticsEquine coat color geneticsEquine coat color genetics determine a horse's coat color. There are many different coat colors possible, but all colors are produced by the action of only a few different genes. The simplest genetic default color of all domesticated horses can be described as either "red" or "non-red", depending...
- White (horse)White (horse)White horses are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white genes, are rare...