Horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...
s 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. Most
white markings are present at birth, and the underlying skin color of a healthy horse does not change. Some Equine coat colors are also related to the breed of horse, like the Friesian breed for instance.
The basic outline of
equine coat color genetics
Equine coat color genetics determine a horse's coat color. Many colors are possible, but all variations are produced by changes in only a few genes. The "base" colors of the horse are determined by the Extension locus, which in recessive form (e ...
has largely been resolved, and
DNA tests to determine the likelihood that a horse will have offspring of a given color have been developed for some colors. Discussion, research, and even controversy continues about some of the details, particularly those surrounding spotting patterns, color sub-shades such as "
sooty
Sooty is a British children's television media franchise created by Harry Corbett incorporating primarily television and stage shows. The franchise originated with his fictional glove puppet character introduced to television in 1955, with the ...
" or "
flaxen", and
markings.
Basic coat colors
The two basic pigment colors of horse hairs are
pheomelanin
Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the a ...
("red") which produces a reddish brown color, and
eumelanin, which produces black. These two hair pigment genes create two base colors:
chestnut, which is fully red, and
black
Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white ...
, which is fully black.
All other coat colors are created by additional genes that modify these two base colors. The most common modifier creates
point coloration
Point coloration refers to animal coat coloration with a pale body and relatively darker extremities, i.e. the face, ears, feet, tail, and (in males) scrotum. It is most recognized as the coloration of Siamese and related breeds of cat, but can ...
of both red and black hairs, known as
bay, which is classified as a base color as well. The vast range of all other coat colors are created by additional genes' action upon one of these three base colors.
*
Chestnut/
Sorrel
Sorrel (''Rumex acetosa''), also called common sorrel or garden sorrel, is a perennial herbaceous plant in the family Polygonaceae. Other names for sorrel include spinach dock and narrow-leaved dock ('dock' being a common name for the genus '' ...
: A red coat with no black. The mane and tail are the same shade of chestnut or lighter chestnut than the body coat. The main color variations are:
**
Liver
The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
Chestnut: very dark red chestnut coat. Sometimes a liver chestnut is also simply called "brown".
** Light Chestnut: seldom-used term for a pale chestnut coat, mane, and tail
** Flaxen Chestnut: Any shade of chestnut, with a significantly lighter mane and tail
*
Black
Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white ...
: Black is relatively uncommon, though it is not "rare". There may be two types of black, fading black and non-fading black. Many, though not all black horses will fade to a brownish color if the horse is exposed to sunlight regularly. This may be due to nutrition or genetics. Some horses appear to have a non-fading black coat that does not fade in the sun. Most black foals are usually born a mousy grey color resembling
grullo
Grulla or grullo, also called blue dun, gray dun or mouse dun, 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 t ...
. As their foal coat begins to shed out, their black color will show through. For a horse to be considered black, it must be completely black except for white markings. A sun-bleached black horse is still called a black horse, even though it may appear to be a dark bay or brown. A visible difference between a black and a dark chestnut or bay is seen in the fine hairs around the eyes and muzzle. On a black these hairs are black, even if the horse is sun-bleached; on other colors, they will be lighter. The hairs around the coronet band of the hoof will be black on a black horse, but on a chestnut (no matter the shade) they will always be red.
*
Bay: Body color ranges from a light reddish-brown to rich chocolate brown with
black points: the mane, tail, lower legs, and tips of the ears The terminology for various color variations are:
** Dark Bay: a dark brown or dark reddish-brown coat with black points, difficult to distinguish from
seal brown. Sometimes also called "black bay" or "mahogany bay."
** Blood Bay/Red Bay: a bright red chestnut coat with black points
** Brown: The word "brown" is used by some
breed registries to describe dark bays. Informally, "brown" is applied to many distinct coat colors. Most often, horses described by casual observers as "brown" are actually bay or chestnut.
In the absence of DNA testing, chestnut and bay can be distinguished from each other by looking at the mane, tail and legs for the presence of black points. There is a proposed
allele
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution.
::"The chro ...
that darkens a bay coat to
seal brown, and the
sooty gene
A horse coat color that has the sooty trait is characterized by black or darker hairs mixed into a horse's coat, typically concentrated along the topline of the horse and less prevalent on the underparts. Sootiness is presumed to be an inherited ...
is linked to other forms of dark bay.
Genetically
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar working i ...
, a chestnut horse is a horse without the ability to produce black pigment, while a black horse does not have dominant agouti to restrict their black pigment to points. The MC1R (extension) either binds alpha-MSH and signals for black and red pigment to be produced ('E' at extension), or it only signals for red ('e' at extension). ASIP (agouti) either blocks MC1R from binding to alpha-MSH and signalling for black ('A' at agouti), or it does not ('a' at agouti). The
extension gene determines whether the cells can decide to produce black and red, and can be either ''E'' (able to produce black and red) or ''e'' (only able to produce red, as in chestnut). To be chestnut a horse must have two copies of ''e'', so the
genotype is ''e''/''e''. A horse with a genotype of ''E''/''E'' or ''E''/''e'' can still make black and red pigments and will be bay or black. Meanwhile, the
agouti gene
Agouti-signaling protein is a protein that in humans is encoded by the ASIP gene. It is responsible for the distribution of melanin pigment in mammals. Agouti interacts with the melanocortin 1 receptor to determine whether the melanocyte (pigment ...
determines whether the cells can stop producing black. The ''A'' version of ''agouti'' means that it can, so as long as has ''E'' at ''extension'' the base color will be bay. The ''a'' version of ''agouti'' means the cells cannot stop producing black, so a horse with two copies of ''a'' (genotype ''a''/''a'') and ''E'' at ''extension'' will be black rather than bay.
Gray
A
gray horse
A gray horse (or grey horse) has a coat color characterized by progressive depigmentation of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike some equine dilution genes and some other genes that lead to depig ...
can be born any color, but as it gets older some hairs turn white. Most will eventually develop a complete white or a "fleabitten" coat, which retains speckles of the horse's original color. Grays are sometimes confused with certain roan, dun, or white coat colors. In particular, most "white" horses are actually grays with a fully white hair coat. A gray horse is usually distinguishable from a
dominant white
Dominant white (W) is a group of genetically related coat color alleles on the KIT gene of the horse, best known for producing an all-white coat, but also able to produce various forms of white spotting, as well as bold white markings. Prior ...
or a
cremello
The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino if they are heterozygous, having one copy of the cream gene, or cremello, ...
horse by dark skin, particularly noticeable around the eyes, muzzle, flanks, and other areas of thin or no hair. A roan has intermixed light and dark hairs similar to a young gray horse, but unlike a gray does not lighten to white. Dun horses have a solid-colored hair coat that also does not lighten with age. Gray horses are prone to
equine melanoma
An equine melanoma is a tumor that results from the abnormal growth of melanocytes in horses. Unlike in humans, melanomas in horses are not thought to be caused by exposure to ultraviolet light. Melanomas are the third most common type of skin ...
.
Variations of gray that a horse may exhibit over its lifetime include:
* Steel Grey/Iron Grey: A grey horse with intermingled black and white hairs. This color occurs in a horse born black, or in some cases, dark bay, and slowly lightens as the horse ages.
* Rose Grey: A grey horse with a reddish or pinkish tinge to its coat. This color occurs in a horse born bay or chestnut and slowly lightens as the horse ages.
* Dapple Grey: Grey coat with lighter rings of grey hairs, called dapples, scattered throughout. Will eventually fade to a pure white or fleabitten coat.
* Fleabitten Grey: an otherwise fully white-haired horse with red or dark grey dots flecked throughout the coat, sometimes extensively.
Diluted colors
Several different genetic allelic families produce colors are lighter versions of the base colors, caused by
dilution genes.
Cream family
Cream dilution is an
incomplete dominant gene that produces a lightened or "partial dilute" coat color when one copy of the
allele
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution.
::"The chro ...
is present and a fully dilute (or "double dilute") with two copies. The double cream dilute phenotypes overlap regardless of base coat color and often cannot be distinguished visually. Sometimes the creme allele is combined with an unrelated dilution gene from another family, which creates a cremello-like coat. Such coloration is called a "pseudo-double dilute." These distinctions usually require DNA testing to verify which alleles are present.
*
Cremello
The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino if they are heterozygous, having one copy of the cream gene, or cremello, ...
: A horse with a chestnut base coat and two
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 ...
s that wash out almost all color until the horse is a pale cream or light tan color. Often called "white", they are not truly
white
White is the lightest color and is achromatic (having no hue). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully reflect and scatter all the visible wavelengths of light. White o ...
horses, and they do not carry the white (W) gene. A cremello usually has blue eyes.
*
Buckskin: A bay horse with one copy of the
cream gene
The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino if they are heterozygous, having one copy of the cream gene, or cremello, if ...
, a
dilution gene that "dilutes" or fades the coat color to a yellow, cream, or gold while keeping the black points (mane, tail, legs).
*
Palomino: chestnut horse that has one cream dilution gene that turns the horse to a golden, yellow, or tan shade with a flaxen or white mane and tail. Often cited as being a color "of twenty-two carat gold", palominos range in shades from extremely light, almost cremello, to deep chocolate, but always with a white or flaxen mane and tail.
*
Perlino
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, ...
: similar to a cremello, but is genetically a bay base coat with two dilute genes. Eyes are usually blue. Mane, tail and points are not black, but can sometimes be darker than the body coat, generally a reddish or rust color, though not to be confused with a red dun.
*
Smoky black: A horse which visually appears to be only black, but actually has a black base coat and one copy of the
cream gene
The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino if they are heterozygous, having one copy of the cream gene, or cremello, if ...
.
*
Smoky Cream
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, ...
: Virtually indistinguishable from a cremello or perlino without DNA testing, a horse with a black base coat and two copies of the cream gene.
Dun
*
Dun
A dun is an ancient or medieval fort. In Ireland and Britain it is mainly a kind of hillfort and also a kind of Atlantic roundhouse.
Etymology
The term comes from Irish ''dún'' or Scottish Gaelic ''dùn'' (meaning "fort"), and is cognat ...
is Yellowish or tan coat with
primitive markings
Primitive markings are a group of hair coat markings and qualities seen in several equine species, including horses, donkeys, and asses. In horses, they are associated with primitive breeds, though not limited to such breeds. The markings are ...
, sometimes called "dun factors": a darker-colored mane and tail, a dorsal stripe along the back and occasionally faint horizontal zebralike stripings on the upper legs and a possible transverse stripe across the withers. There are several variations:
** Grulla, or Blue Dun: A horse with a black base color and the dun gene. Coat is a solid "mouse-colored" gray or silver (can also be almost brownish-gray) with black or dark gray primitive markings.
** Red Dun: A chestnut base coat with dun factors. Coat is usually pale yellow or tan with chestnut (red) primitive markings.
** "Bay Dun" or "Zebra dun" are terms sometimes used to describe the classic dun color of yellow or tan with black primitive markings, used when necessary to distinguish it from red duns or grullos.
** "Buckskin dun" or "Dunskin" describes a bay dun that also carries 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 ...
dilution and has a coat of pale gold with a black mane, tail, legs and primitive markings.
Mixtures of dliution genes produce colors such as "dunalino" — a red dun that also carries a single cream gene and thus has a pale gold coat, white mane and tail, and very faint primitive markings.
Other dilution genes
*
Champagne
Champagne (, ) is a sparkling wine originated and produced in the Champagne wine region of France under the rules of the appellation, that demand specific vineyard practices, sourcing of grapes exclusively from designated places within it, ...
: Produced by a different
dilution gene than 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 ...
. It lightens both skin and hair, but creates a metallic gold coat color with mottled skin and light-colored eyes. Champagne horses are often confused with palomino, cremello, dun, or buckskins.
*
Mushroom
A mushroom or toadstool is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground, on soil, or on its food source. ''Toadstool'' generally denotes one poisonous to humans.
The standard for the name "mushroom" is ...
dilutes red-based horses to a pale tan colour, so far found only in Shetland ponies or ponies with Shetland influence.
*
Pearl
A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle) of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pearl is composed of calcium carb ...
: Also called the "barlink factor", A
dilution gene that when
homozygous
Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.
Mo ...
, lightens red coats to a uniform apricot color, often also resulting in horses with blue eyes. When combined with cream dilution, it may produce horses that appear to be cremello or perlino.
*
Silver or silver dapple: Caused by a dilution gene that only acts upon black hair pigment, it lightens black body hair to a chocolate brown and the mane and tail to silver in most cases. The gene may be carried but will not be visible on horses with a red base coat. Silver horses have informally been called Chocolate, Flaxen, or Taffy.
White spotting patterns
These patterns all have white hairs and often pink skin, varying from a fully
white
White is the lightest color and is achromatic (having no hue). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully reflect and scatter all the visible wavelengths of light. White o ...
horse through the
pinto
Pinto is a Portuguese language, Portuguese, Spanish language, Spanish, Sephardi Jews, Jewish (Sephardic), and Italian language, Italian surname. It is a high-frequency surname in all List of countries and territories where Portuguese is an officia ...
patterns and smaller
white markings to
roan which only adds a few white hairs spread throughout the coat. These patterns can occur on top of any other color. The base color determines the color of the colored hairs, while the white patterns determine where and how many white hairs are present. Biologically the white comes from a lack of
pigment cells
Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea),
the inner ear,
vaginal epithelium, meninges,
bones,
and heart.
M ...
. There are many different genetic alleles that create these patterns.
Leopard complex
There are a group of coat patterns caused by the leopard gene complex. Not every horse with leopard genetics will exhibit hair coat spotting. However, even solid individuals will exhibit secondary characteristics such as vertically striped hooves and mottled skin around the eyes, lips, and genitalia, plus a white
sclera of the eye.
Several breeds of horse can boast leopard-spotted (a term used collectively for all patterns) individuals including the
Knabstrupper
The Knabstrupper or Knabstrup is a Danish breed of warmblood horse. It is principally a riding horse, but is also used as a harness horse and as a circus animal.
It is broadly similar to the Frederiksborger, but often has a spotted coat. In ...
,
Noriker, and the
Appaloosa
The Appaloosa is an American horse breed best known for its colorful 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 colo ...
. There are several distinct leopard patterns:
* blanket: white over the hip that may extend from the tail to the base of the neck. The spots inside the blanket (if present) are the same color as the horse's base coat.
*
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 w ...
: a mix of body and white hairs that extends over the entire body—no relation to genetic roan.
* snowflake: white spots on a dark body. Typically the white spots increase in number and size as the horse ages.
* leopard: dark spots of varying sizes over a white body.
* few spot leopard: a nearly white horse from birth that retains color just above the hooves, the knees, "armpits", mane and tail, wind pipe, and face.
* frost: similar to varnish but the white hairs are limited to the back, loins, and neck.
Pinto
A pinto has large patches of white over any other underlying coat color. Sometimes called "Paint" in the western United States, a word that which technically refers to the
American Paint Horse
The 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 Hors ...
, a specific breed of mostly pinto horses with known Quarter Horse and/or Thoroughbred bloodlines. Other regional terms for certain pinto spotting patterns include "blagdon" in the UK. Pinto spotting is produced by a large number of genetic mechanisms, with dozens now mapped and identifiable through DNA testing.
Variations of pinto based on the observable color include:
*
Piebald
A piebald or pied animal is one that has a pattern of unpigmented spots (white) on a pigmented background of hair, feathers or scales. Thus a piebald black and white dog is a black dog with white spots. The animal's skin under the white backgro ...
: a black-and-white (term more commonly used in the UK than the US). This is pinto spotting on top of black.
*
Skewbald
Skewbald is a colour pattern of horses. A skewbald horse has a coat made up of white patches on a non-black base coat, such as chestnut, bay, or any colour besides black coat. Skewbald horses which are bay and white (bay is a reddish-brown colou ...
: a spotting pattern of white over chestnut or any other color other than black (term more commonly used in the UK than the US).
*
Tricoloured: A variation of Skewbald, specifically referring to pinto spotting over a bay base coat or other coat color that features black points.
Terminology variations based on the observable shape of the white patterns include:
*
Overo
Overo refers to several genetically unrelated pinto coloration patterns of white-over-dark body markings in horses, and is a term used by the American Paint Horse Association to classify a set of pinto patterns that are not tobiano. ''Overo'' is ...
: Describes a group of spotting patterns genetically distinct from one another, characterized by sharp, irregular markings with a horizontal orientation, usually more dark than white. In some cases, the face is usually white, often with blue eyes. The white rarely crosses the back, and the lower legs are normally dark. Variations include "
frame overo" and "
splashed white".
*
Sabino: Describes a range of spotting patterns characterized by high white on legs, belly spots, white markings on the face extending past the eyes and/or patches of roaning patterns standing alone, or on the edges of white markings. Usually produced by certain
dominant white
Dominant white (W) is a group of genetically related coat color alleles on the KIT gene of the horse, best known for producing an all-white coat, but also able to produce various forms of white spotting, as well as bold white markings. Prior ...
or "white spotting" alleles, though not all sabino patterns have been genetically mapped. Sometimes grouped with the overo color pattern group by breed registries that record spotting patterns even thoug created by different genetics from frame or splash.
*
Tobiano
Tobiano is a spotted color pattern commonly seen in pinto horses, produced by a dominant gene. The tobiano gene produces white-haired, pink-skinned patches on a base coat color. The coloration is almost always present from birth and does not c ...
: Spotting pattern characterized by rounded markings with white legs and white across the back between the withers and the dock of the tail, usually arranged in a roughly vertical pattern and more white than dark, with the head usually dark and with markings like that of a normal horse. i.e. star, snip, strip, or blaze. Produced by the Tobiano (TO) gene.
*
Tovero
The Tovero (also known as Tobero)PHAA
Retrieved on 13 January 2009 c ...
: spotting pattern that is a mix of tobiano and overo coloration, such as blue eyes on a dark head, usually results from the presence of more than one spotting pattern gene.
Roaning
Roaning adds white hairs to any of the other colors and, unlike gray, the color does not steadily lighten over the horse's lifetime, though there may be some minor color variation from year to year or especially between summer and winter coats.
*
![Koning Albert KWPN Stallion](https://upload.wikimedia.org/wikipedia/commons/e/e0/Koning_Albert_KWPN_Stallion.jpg)
* Classic
Roan: a color pattern that causes white hairs to be evenly intermixed within the horse's body color. Roans are distinguishable from greys because roans typically do not change color in their lifetimes, unlike gray that gradually gets lighter as a horse ages. Roans also have heads that are either solid-colored or much darker than their body hair, and do not lighten. Variations of roan include:
** Red Roan: A chestnut base coat with a roaning pattern with the mane and tail being the same red as the body. Red roan is sometimes called Strawberry Roan, and the term Red Roan is occasionally used to describe a Bay Roan.
** Bay Roan: A Bay base coat with a roaning pattern (the mane and tail of the Bay Roan will be Black). Bay roans are sometimes also called Red Roans.
** Blue Roan: A black with a roaning pattern, not to be confused with a gray or a blue dun/grullo. A roan tends to have a darker head, while grays not only lighten with age, but their heads tend to lighten before the rest of their bodies. A blue roan has mixed-color hairs, a blue dun will usually be a solid color and have dun striping.
Rabicano
Rabicano, sometimes called white ticking, is a horse coat color characterized by limited roaning in a specific pattern: its most minimal form is expressed by white hairs at the top of a horse's tail, often is expressed by additional intersperse ...
: A roan-style effect that is caused by a yet-to-be-mapped genetic modifier that creates a mealy, splotchy, or roaning pattern on only part of the body, usually limited to the underside, flanks, legs, tail and head areas. Unlike a true roan, much of the body will not have white hairs intermingled with solid ones, nor are the legs or head significantly darker than the rest of the horse.
White
One of the rarest colors, a true genetic
white horse has white hair and fully or largely unpigmented (pink) skin. These horses are born white or mostly white and remain white for life. The vast majority of so-called "white" horses are actually
grays with a fully white hair coat. A truly white horse occurs one of two ways: either by inheriting one copy of a
dominant white
Dominant white (W) is a group of genetically related coat color alleles on the KIT gene of the horse, best known for producing an all-white coat, but also able to produce various forms of white spotting, as well as bold white markings. Prior ...
("W") allele that produces white when
heterozygous
Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.
Mo ...
but may be a
genetic lethal if homozygous, or by inheriting two copies of a non-lethal dominant white ("W") allele that produces a white coat when
homozygous
Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.
Mo ...
. There are also some genetic lethal genes unrelated to the W allelic series: a foal homozygous for the frame overo gene will have a condition known as
lethal white syndrome
Lethal white syndrome (LWS), also called overo lethal white syndrome (OLWS), lethal white overo (LWO), and overo lethal white foal syndrome (OLWFS), is an autosomal genetic disorder most prevalent in the American Paint Horse. Affected foals are bo ...
dies shortly after birth.
There are no "
albinos
Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and pink or blue eyes. Individuals with the condition are referred to as albino.
Varied use and interpretation of the term ...
" in the horse world. Albino, defined as animals with a white coat with pink skin and reddish eyes, is created by genetic mechanisms that do not exist in horses.
In some cases, homozygous dominant white (W) is thought to be an embryonic lethal, though this does not occur with all W alleles.
White markings
White markings are present at birth and unique to each horse, making them useful in identifying individual animals. Markings usually have pink skin underneath them, though some faint markings may not, and white hairs may extend past the area of underlying pink skin. Though markings that overlie dark skin may appear to change, the underlying skin color and hair growing from pink skin will not. The distinction when white markings confined to the face and legs or a few small body spots become extensive enough to constitute a white spotting pattern is usually determined by breed standards set by registries. White markings generally are now hypothesized to be a minimal expression of certain genes in the dominant white (W) allelic series.
Other colors and modifiers
*
Brindle
Brindle is a coat coloring pattern in animals, particularly dogs, cattle, guinea pigs, cats, and, rarely, horses. It is sometimes described as "tiger-striped", although the brindle pattern is more subtle than that of a tiger's coat.
Brindle ty ...
: One of the rarest colors in horses, characteristics are any base coat color with "zebralike" stripes, but the most common is a brown horse with faint yellowish markings. Usually linked to
chimerism
A genetic chimerism or chimera ( ) is a single organism composed of cells with more than one distinct genotype. In animals, this means an individual derived from two or more zygotes, which can include possessing blood cells of different blood ...
,
but one heritable brindle pattern that affects coat texture and color in a family of
American Quarter Horses has been named Brindle1 was announced in 2016.
*
Sooty
Sooty is a British children's television media franchise created by Harry Corbett incorporating primarily television and stage shows. The franchise originated with his fictional glove puppet character introduced to television in 1955, with the ...
is a proposed genetic modifier not yet mapped that causes dark hairs to be dispersed within the coat, darkening the whole coat with age.
*
Pangaré
Pangaré is a coat trait found in some horses that features pale hair around the eyes and muzzle and underside of the body. These pale areas can extend up to the flanks, throat and chest, behind the elbows, in front of the stifle, and up the b ...
is a modifier that is the opposite of sooty, it causes individual hairs to lighten, causing lightened areas on the muzzle, flank and belly of a horse.
* "
Flaxen" is used only to describe the lightened mane and tail of a chestnut, and has been proposed as a genetic modifier, particularly when it appears to be a trait of certain breeds. However, the genetic mechanism of this process has yet to be identified.
* Primitive marking variants sometimes called "bider markings" have been seen in
Przewalski's horse
Przewalski's horse (, , (Пржевальский ), ) (''Equus ferus przewalskii'' or ''Equus przewalskii''), also called the takhi, Mongolian wild horse or Dzungarian horse, is a rare and endangered horse originally native to the steppes of ...
s and
Mongolian horse
The Mongol horse ( Mongolian Адуу, ''aduu'': "horse" or ''mori''; or as a herd, ''ado'') is the native horse breed of Mongolia. The breed is purported to be largely unchanged since the time of Genghis Khan. Nomads living in the traditio ...
s.
Eye and hoof color
Most horses have brown eyes with minor shade variations. Blue eyes are linked to the
splashed white spotting allele, and cream dilution may produce a bluish-green eye color. The champagne and pearl genes also produce lightened eye colors in the blue or green shades. The leopard complex produces a white
scelara around an otherwise dark eye.
The yellow or amber
Tiger eye
Tiger eye or goat eye is a gene causing diluted eye color in horses. There are two variants, Tiger-eye 1 (TE1) and Tiger-eye 2 (TE2), which are both recessive. Horses displaying tiger eye typically have a yellow, orange, or amber iris. Tiger ey ...
gene has been found only in the Puerto Rican Paso Fino and has two variants, Tiger-eye 1 (TE1) and Tiger-eye 2 (TE2), which are both
recessive
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
.
There is no obvious link between eye shade and coat color, making this the first studied gene in horses to affect eye color but not coat color.
Exterior hoof wall color is usually linked to coat color. Most horses have a dark grayish hoof wall unless they have white leg markings, in which case they will have pale-colored hooves. The leopard complex gene will create a light and dark striped hoof, and many chestnut horses have brownish hooves that are somewhat lighter than the usual dark gray.
Color breeds
Registries have opened that accept horses (and sometimes ponies and mules) of almost any breed or type, with color either the only requirement for registration or the primary criterion. These are called "
color breed
A color breed refers to groupings of horses whose registration is based primarily on their coat color, regardless of the horse's actual breed or breed type.
Some color breeds only register horses with a desired coat color if they also meet speci ...
s". Unlike "true" horse breeds, there are few if any unique physical characteristics required, nor is the
stud book
A breed registry, also known as a herdbook, studbook 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 ...
limited to only certain breeds or offspring of previously registered horses. As a general rule, offspring without the stated color are usually not eligible for recording with the color breed registry, although there are exceptions. The best-known color breed registries are for
buckskins
Buckskins are clothing, usually consisting of a jacket and leggings, made from buckskin, a soft sueded leather from the hide of deer. Buckskins are often trimmed with a fringe – originally a functional detail, to allow the garment to s ...
,
palominos, and
pintos.
Some
horse breeds may have a desired coat color that usually breeds on as a characteristic that is part of the breed standard, in addition to distinctive physical characteristics and a limited
stud book
A breed registry, also known as a herdbook, studbook 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 ...
. They are not color breeds, and include the
Friesian horse
The Friesian (also Frizian) is a horse breed originating in Friesland, in the Netherlands. Although the conformation of the breed resembles that of a light draught horse, Friesians are graceful and nimble for their size. It is believed tha ...
(must be uniformly black for mainstream registration), the
Appaloosa
The Appaloosa is an American horse breed best known for its colorful 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 colo ...
(with
Leopard complex
The leopard complex is a group of genetically related Equine coat color, coat patterns in horses. These patterns range from progressive increases in interspersed white hair similar to Gray (horse), graying or Roan (horse), roan to distinctive, Da ...
patterns) and the
American Paint Horse
The 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 Hors ...
. In some of these breeds, though not all, offspring of animals registered in these stud books may be registered even if they do not have the desired color, sometimes with restrictions.
References
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* Performs new gray gene testing for horses.
External links
{{short description, Horse coat colors and markings
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equine coat