White (horse) - AbsoluteAstronomy.com

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

Dominant white

Dominant white is a group of genetically related coat color conditions in the horse, best known for producing an all-white coat, but also for producing some forms of white spotting and white markings. Dominant white horses are born with unpigmented pink skin and white hair with dark eyes, although...

(W) genes, are rare. Most horses that are commonly referred to as "white" are actually "gray" horses

Gray (horse)

Gray or grey is a coat color 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 color Their adult hair coat is white, dappled, or white intermingled...

whose hair coats are completely white.

True white horses

White horses have unpigmented skin and a white hair coat. They are born white and remain this way throughout life. Many white horses have dark eyes, though some have blue eyes. Some white horses are born with partial pigmentation in their skin and hair, which may or may not be retained as they mature. White coloring, whether 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...

, white 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 dominant white

Dominant white

is collectively known as depigmentation phenotypes, and all are caused by areas of skin that lack pigment cells (melanocyte

Melanocyte

-External links: - "Eye: fovea, RPE" - "Integument: pigmented skin"...

s). Depigmentation phenotypes have various genetic causes, and those that have been studied usually map to the EDNRB and KIT
CD117
Mast/stem cell growth factor receptor also known as proto-oncogene c-Kit or tyrosine-protein kinase Kit or CD117 is a protein that in humans is encoded by the KIT gene...

genes. However, much of the genetics behind various all-white depigmentation phenotypes is still unknown.

Dominant white

Dominant white is best known for producing pink-skinned all-white horses with brown eyes, though some dominant white horses have residual pigment along the topline. Dominant white is, as the name implies, a genetically dominant

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...

color. At least one parent must be dominant white and it does not "skip" generations because it is not recessive

Recessive

In genetics, the term "recessive gene" refers to an allele that causes a phenotype that is only seen in a homozygous genotype and never in a heterozygous genotype. Every person has two copies of every gene on autosomal chromosomes, one from mother and one from father...

. Nonetheless, new variations or mutation

Mutation

In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

s producing dominant white do occur spontaneously from time to time. Dominant white is rare, but has occurred in many breeds. It has been studied in 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, 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...

s, the American White horse

American creme and white horse registry

The American White & American Creme Horse Registry was originally named the American Albino Horse Club and first established by Caleb Thompson and his wife, Ruth....

and the Camarillo White horse

Camarillo White Horse

The Camarillo White Horse is a rare horse breed less than 100 years old known for its pure white color. It dates back to 1921, when Adolfo Camarillo, one of the last Californios, purchased a 9-year-old stallion named Sultan at the California State Fair in Sacramento...

. There are 11 identified variants of dominant white, each corresponding to a spontaneously-white foundation animal and a mutation

Mutation

on the KIT
CD117
Mast/stem cell growth factor receptor also known as proto-oncogene c-Kit or tyrosine-protein kinase Kit or CD117 is a protein that in humans is encoded by the KIT gene...

gene. No horse has been identified as homozygous dominant white, and researchers have suggested that at least some forms of dominant white results in nonviable embryos in the homozygous state. While homologous mutations in mice are often linked to anemia

Anemia

Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...

and sterility

Infertility

Infertility primarily refers to the biological inability of a person to contribute to conception. Infertility may also refer to the state of a woman who is unable to carry a pregnancy to full term...

, no such effects have been observed in dominant white horses. Dominant white horses typically have white noses that can be subject to sunburn

Sunburn

A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...

Sabino-white

Sabino-white horses are pink-skinned with all-white or nearly-white coats and dark eyes. They are homozygous for the dominant SB1 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...

at the Sabino 1 locus

Locus (genetics)

In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...

, which has been mapped to KIT
CD117
Mast/stem cell growth factor receptor also known as proto-oncogene c-Kit or tyrosine-protein kinase Kit or CD117 is a protein that in humans is encoded by the KIT gene...

. Without a DNA test, Sabino-white horses are indistinguishable from dominant white horses. The Sabino1 allele, and the associated spotting pattern, is found in Miniature horse

Miniature horse

Miniature horses are found in many nations, particularly in Europe and the Americas. The designation of miniature horse is determined by the height of the animal, which, depending on the particular breed registry involved, is usually less than as measured at the last hairs of the mane, which are...

s, 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, American Paint Horse

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 Horse and Thoroughbred bloodlines, the American Paint Horse...

s, Tennessee Walker

Tennessee Walker

The Tennessee Walker or Tennessee Walking Horse is a breed of riding horse. The breed was originally bred in the Southern United States to carry the owners of plantations around their lands...

s, Missouri Fox Trotter

Missouri Fox Trotter

The Missouri Fox Trotter is an American breed of horse with a unique four beat gait. It was bred in the Ozark Mountain foothills, and used by settlers who valued its smoothness.-Breed characteristics:...

s, Mustangs

Mustang (horse)

A Mustang is a free-roaming horse of the North American west that first descended from horses brought to the Americas by the Spanish. Mustangs are often referred to as wild horses, but there is intense debate over terminology...

, Shetland Ponies

Shetland pony

The Shetland pony is a breed of pony originating in the Shetland Isles. Shetlands range in size from a minimum height of approximately 28 inches to an official maximum height of 42 inches at the withers. Shetland ponies have heavy coats, short legs and are considered quite intelligent...

, and Aztecas

Azteca (horse)

The Azteca is a horse breed from Mexico, with a subtype, called the "American Azteca", found in the United States. They are well-muscled horses that may be of any solid color, and the American Azteca may also carry pinto colors. Aztecas are known to compete in many western riding and some English...

. Sabino 1 has not been found in the Arabian horse

Arabian horse

, Clydesdale

Clydesdale

Clydesdale was formerly one of nineteen local government districts in the Strathclyde region of Scotland.The district was formed by the Local Government Act 1973 from part of the former county of Lanarkshire: namely the burghs of Biggar and Lanark and the First, Second and Third Districts...

, Thoroughbred

Thoroughbred

, Standardbred horse

Standardbred horse

Standardbreds are a breed of horse best known for their ability to race in harness at a trot or pace instead of under saddle at a gallop. Developed in North America, the breed is now recognized worldwide for its harness racing ability...

, or Shire horse

Shire horse

The Shire horse is a breed of draught horse or draft horse . The breed comes in many colours, including black, bay and grey. They are a tall breed, with mares standing and over and stallions standing and over. The breed has an enormous capacity for weight pulling, and Shires have held the world...

. The Sabino 1 allele is not linked to any health defects, though sabino-whites may need some protection from sunburn

Sunburn

. Horses with only one copy of the Sabino1 gene usually have dramatic spotting, including two or more white legs, often with white running up the front of the leg, extensive white on the face, spotting on the midsection, and jagged or roaned margins to the pattern.

White born leopards

The leopard complex, related to the Leopard (LP) gene, characterizes the 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...

and Knabstrupper breeds with their spotted coats. Leopard is genetically quite distinct from all other white and white-spotting patterns. The fewspot leopard pattern, however, can resemble white. Two factors influence the eventual appearance of a leopard complex coat: whether one copy (heterozygous LP/lp) or two copies (homozygous LP/LP) Leopard allele

Allele

s are present, and the degree of dense white patterning present at birth. If a foal is homozygous for the LP allele and has extensive dense white patterning, they will appear nearly white at birth, and may continue to lighten with age. In other parts of the world, these horses are called "white born." "White born" foals are less common among Appaloosa horses than Knabstruppers or Norikers, as the extensive dense white patterning is favored for producing dramatic full leopards. Homozygous leopards have the LP/LP genotype, and may be 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...

, fewspot leopard, or snowcap patterned. Homozygous leopards are substantially more prone to congenital stationary night blindness. Congenital Stationary Night Blindness is present at birth and is characterized by impaired vision in dark conditions.

Lethal white syndrome

Lethal white syndrome is a genetic disorder linked to the Frame overo

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...

(O) gene and most closely studied in the American Paint Horse

American Paint Horse

. Affected foal

Foal

A foal is an equine, particularly a horse, that is one year old or younger. More specific terms are colt for a male foal and filly for a female foal, but these terms are used until the horse is age three or four. When the foal is nursing from its dam , it may also be called a suckling...

s are carried to term and at birth appear normal, though they have pink-skinned all-white or nearly-white coats and blue eyes. However, the colon

Colon (anatomy)

The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...

of these foals cannot function due to the absence of nerve cells, and the condition cannot be treated. Foals with Lethal White Syndrome invariably die of colic

Colic

Colic is a form of pain which starts and stops abruptly. Types include:*Baby colic, a condition, usually in infants, characterized by incessant crying*Renal colic, a pain in the flank, characteristic of kidney stones...

within 72 hours, and are usually humanely euthanized. Carriers of the gene, who are healthy and normal, can be identified by a DNA test. While carriers often exhibit the "frame overo" pattern, this is not a dispositive trait and testing is necessary, as the pattern can appear in a minimal form as normal white markings

Horse markings

or be masked by other white spotting genes.

Horses that appear white, but are not

True white horses have unpigmented pink skin and unpigmented white hair, though eye color varies. The lack of pigment in the skin and hair is caused by the absence of pigment-producing cells called melanocyte

Melanocyte

-External links: - "Eye: fovea, RPE" - "Integument: pigmented skin"...

s. Some coat colors are characterized by light or white-like coats and even pinkish skin, however these white-like coats are not lacking melanocytes. Instead, white-like coat colors result from various changes in the ways melanocytes produce pigment

Melanin

Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

Gray

Gray (horse)

horses have the most common "white-like" coat color. However, the most noticeable difference between a gray horse whose hair coat is completely white and a white horse is skin color: most gray horses have black skin and dark eyes, white horses have light, unpigmented skin. 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 true white horses. The skin and eyes may be other colors if influenced by other factors such as white markings

Horse markings

, certain white spotting patterns

Pinto horse

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. Gray foals may be born any color, but the colored hairs of their coat become progressively silvered as they age, eventually giving mature gray horses a white or nearly-white hair coat. Gray is controlled by a single dominant allele

Allele

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. Gray horses are at an increased risk for melanoma; 70-80% of gray horses over the age of 15 have a melanoma tumor.

Diluted coat colors

True white hair is rooted in unpigmented skin that lacks melanocytes. In contrast, diluted coat colors have melanocytes, but vary due to the concentration or chemical structure of the pigments made by these pigment-producing cells, not the absence of the cells themselves. There are at least five known types of pigment dilution in horses, three which, as described below, can act to produce off-white phenotypes. Horses with strongly diluted coat colors usually have pale blue eyes, cream-colored coats, and rosy-pink skin. White markings

Horse markings

are usually visible upon closer inspection.

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...

produces two types of diluted color. Cremellos, perlinos, and smoky creams have rosy-pink skin, pale blue eyes, and cream-colored coats that can appear almost white. These coat colors, collectively called "double dilutes" or "blue-eyed creams", result when a horse is homozygous for 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...

. When heterozygous, the cream gene is also responsible for palomino
Palomino
Palomino is a coat color in horses, consisting of a gold coat and white mane and tail. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a "red" base coat...

and buckskin. A few Palominos have a very light hair coat is occasionally mistaken for either cremello or white. White markings and patterns are visible against the slightly-pigmented coat and skin. The cream gene is not known to be associated with any health problems.

Pearl-Cream pseudo-double dilute occurs when a horse has one cream gene and one 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...

. These two distinct dilution factors interact to produce a cremello-like coat. Pearl-creams have pale but pigmented skin and blue-green eyes, and are distinctly pale cream-colored. To date, the Pearl gene has been found in 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, Paint horses, and some Iberian horse
Iberian horse
The Iberian horse is a title given to a number of horse breeds native to the Iberian peninsula. At present, 17 horse breeds are recognized by FAO as characteristic of the Iberian Peninsula....

s. Pearl is not known to be associated with any health problems.

Champagne-Cream pseudo-double dilute occurs when a horse has one cream gene and one 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...

. Champagne and cream are another pair of unrelated dilution factors that interact to produce a cremello-like coat. Champagne-creams have freckled, pinkish skin, pale eyes, and pale coats. These colors were formerly referred to as "ivory champagnes." Champagne is found in North American breeds such as the American Cream Draft
American Cream Draft
The American Cream Draft is a rare draft horse breed, the only such breed developed in the United States that is still in existence. It is known for its cream color and amber eyes, produced by the champagne gene. The only other color found in the breed is chestnut, and the cream color produced by...

, Tennessee Walking Horse, American Saddlebred
American Saddlebred
The American Saddlebred, formerly known as the American Saddle Horse, is a breed of horse that was developed in Kentucky by plantation owners. Today, in the horse show world, they are most commonly seen under saddle in Saddle seat style riding, and in various types of driving, including pleasure...

, 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 Miniature horse
Miniature horse
Miniature horses are found in many nations, particularly in Europe and the Americas. The designation of miniature horse is determined by the height of the animal, which, depending on the particular breed registry involved, is usually less than as measured at the last hairs of the mane, which are...

. It is not known to be associated with any health problems.

Albinism

There is no reported case of a true "albino

Albinism

Albinism 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...

" horse, despite references to white horses that are called "albino". There are also references in literature calling white horses "albino." All so-called "albino" horses have pigmented eyes, usually brown or blue, and thus are not true albinos. In contrast, many albino mammals, such as mice or rabbits, typically have a white hair coat, unpigmented skin and reddish eyes.

Dominant white in horses is caused by the absence of pigment cells (melanocyte

Melanocyte

-External links: - "Eye: fovea, RPE" - "Integument: pigmented skin"...

s), whereas albino animals have a normal distribution of melanocytes. In other animals, patches of unpigmented skin, hair, or eyes due to the lack of pigment cells (melanocyte

Melanocyte

-External links: - "Eye: fovea, RPE" - "Integument: pigmented skin"...

s) are called piebaldism

Piebaldism

Piebaldism is a rare autosomal dominant disorder of melanocyte development. Common characteristics include a congenital white forelock, scattered normal pigmented and hypopigmented macules and a triangular shaped depigmented patch on the forehead....

, not albinism nor partial albinism.

The definition of "albinism

Albinism

Albinism 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...

" varies depending on whether humans, other mammals, or other vertebrates are being discussed.

Despite this, some 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...

still refer to "albino" horses. For example, the Paso Fino Horse Association

Paso Fino

The Paso Fino is a naturally gaited light horse breed dating back to horses imported to the Caribbean from Spain. Pasos are prized for their smooth, natural, four beat, lateral ambling gait and are used in many disciplines, but are especially popular for trail riding...

registers cremellos

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...

and other cream colors as "albino." Until 1999, the American Quarter Horse Association

American Quarter Horse

(AQHA) described cremellos as "albino" in rule 227(j). The AQHA later replaced the word "albino" with "cremello or perlino," and in 2002 the rule was removed entirely. Among Connemara pony

Connemara pony

The Connemara pony is a pony breed originating in Ireland. They are known for their athleticism, versatility and good disposition. The breed makes excellent show ponies.-History:...

breeders, homozygous creams are called "blue-eyed creams" or sometimes "pseudo-albino" and remain barred from the stud book.

Types of albinism in humans and other animals

The best-known type of albinism is OCA1A, which impairs tyrosinase

Tyrosinase

Tyrosinase also known as monophenol monooxygenase is an enzyme that catalyses the oxidation of phenols and is widespread in plants and animals...

production. In other mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s, the diagnosis of albinism is based on the impairment of tyrosinase

Tyrosinase

Tyrosinase also known as monophenol monooxygenase is an enzyme that catalyses the oxidation of phenols and is widespread in plants and animals...

production through defects in the Color (C) gene

Gene

. Mice and other mammals without tyrosinase have unpigmented pink skin, unpigmented white hair, unpigmented reddish eyes, and some form of vision impairment. No mutation

Mutation

s of the tyrosinase or C gene are known in horses.

Humans exhibit a wide range of pigmentation levels as a species. However, the diagnosis of albinism in humans is based on visual impairment

Visual impairment

Visual impairment is vision loss to such a degree as to qualify as an additional support need through a significant limitation of visual capability resulting from either disease, trauma, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive...

, which has not been described in white horses. Vision problems are not associated with gray, dilute, or white coat colors in horses, and blue eyes in horses do not indicate poor vision. Eyes are pigmented at the front of the iris called the stroma

Stroma of iris

The stroma of the iris consists of fibers and cells.The former are made up of delicate bundles of fibrous tissue; a few fibers at the circumference of the iris have a circular direction; but the majority radiate toward the pupil, forming by their interlacement delicate meshes in which the vessels...

, and in a thin layer at the back of the iris in tissue called the iris pigment epithelium

Iris pigment epithelium

The iris pigment epithelium is a two-cell thick layer of cuboidal cells lying behind the iris. Both layers are jet black due to the numerous large melanosomes which pack the cytoplasm of each cell. Towards the central axis, the IPE terminates at the pupillary margin...

. The iris pigment epithelium prevents damaging light scattering within the eye. Blue-eyed humans and mammals have little or no pigment in the stroma, but retain pigment in the iris pigment epithelium. If pigment is missing from both the stroma and the iris pigment epithelium, the only pigment in the eye is the hemoglobin in blood vessels. This accounts for the reddish appearance of eyes in some types of albinism.

In research mammals, such as mice, albinism is more strictly defined. Albino mice occur due to a recessive mutation of the C gene. No such mutation exists in horses. Albino mice lack pigment, but "...the inability of albino animals to produce pigment stems not from an absence of melanocytes...but from a deficiency and/or alteration of the structure of tyrosinase in melanocytes which are otherwise normal." This definition of albinism in mice - the inability to make tyrosinase - is extended to other mammals.

While mammals derive their pigments only from melanins, fish, reptiles and birds rely on a number of pigments

Biological pigment

Biological pigments, also known simply as pigments or biochromes are substances produced by living organisms that have a color resulting from selective color absorption. Biological pigments include plant pigments and flower pigments...

apart from melanins: carotenoids, porphyrins, psittacofulvins, pterins, etc. Most commonly, reptiles with a condition homologous to human OCA1A retain their reddish and orangish hues. As a result, birds and reptiles without the ability to manufacture tyrosinase are more accurately described as "amelanistic." Horses do not have non-melanin pigments and so if they were albino, would have no pigmentation. The retained pigment of dilute horses, like cremellos, is not comparable to the retained pigment of amelanistic "albino" birds and reptiles.

Why cream is not albino

The cream gene, which is responsible for palomino, buckskin, and cremello coat colors, was mapped to the MATP
SLC45A2
Membrane-associated transporter protein also known as solute carrier family 45 member 2 or melanoma antigen AIM1 is a protein that in humans is encoded by the SLC45A2 gene.-Function:...

gene in 2003. This gene is sometimes called the OCA4 gene, because one mutation

Mutation

on MATP is associated with oculocutaneous albinism type 4

Oculocutaneous albinism

Oculocutaneous albinism is a form of albinism involving the eyes , skin , and in rare instances, the hair as well.Four types of oculocutaneous albinism have been described, all caused by a disruption of melanin synthesis and all autosomal recessive disorders.Common Albinism requires genes from both...

. However, other benign mutations on MATP are responsible for normal variations in skin, hair, and eye color in humans. MATP is not the "albino gene"; one of many mutations of the human MATP is responsible for a form of albinism.

Famous White Horses

Many famous horses, past and present, were alleged to be "white" by observers, but were actually grays

Gray (horse)

with hair coats turned fully white. Likewise, most white horses used in movies are actually grays

Gray (horse)

, in part because they are easier to find.

However, there are a few truly white horses who were used in film. One of the best-known examples was "Silver," ridden by the Lone Ranger, a role actually played by two different white horses. At least one horse who played "Topper," ridden by Hopalong Cassidy

Hopalong Cassidy

Hopalong Cassidy is a fictional cowboy hero created in 1904 by the author Clarence E. Mulford, who wrote a series of popular short stories and twenty-eight novels based on the character....

, was also white. Another famous white horse is Yukichan, a Japanese Thoroughbred

Thoroughbred

racehorse who won the Kanto Oaks at Kawasaki Racecourse

Kawasaki Racecourse

is located in Kawasaki, Kanagawa, Japan.-Physical attributes:Kawasaki Racecourse has a dirt course.The dirt course measures 1200 meters .900m, 1400m, 1500m, 1600m, 2000m and 2100m races run on the oval.- Notable races :...

Mythology

Throughout history, white horses have been mythologized

White horse (mythology)

White horses have a special significance in the mythologies of cultures around the world. They are often associated with the sun chariot, with warrior-heroes, with fertility , or with an end-of-time saviour, but other interpretations exist as well...

in many cultures. For example, Herodotus

Herodotus

Herodotus was an ancient Greek historian who was born in Halicarnassus, Caria and lived in the 5th century BC . He has been called the "Father of History", and was the first historian known to collect his materials systematically, test their accuracy to a certain extent and arrange them in a...

reported that white horses were held as sacred animals in the Achaemenid court of Xerxes the Great (ruled 486-465 BC), In more than one tradition, a white horse carries patron saints or the world saviour in the end times, including Hinduism

Hindu eschatology

Contemporary Hindu eschatology is linked in the Vaishnavite tradition to the figure of Kalki, or the tenth and last Avatar of Vishnu before the age draws to a close, and Shiva dissolves and Brahma regenerates the universe....

, Christianity

Christian eschatology

Christian eschatology is a major branch of study within Christian theology. Eschatology, from two Greek words meaning last and study , is the study of the end of things, whether the end of an individual life, the end of the age, or the end of the world...

, and Islam

Islamic eschatology

Islamic eschatology is concerned with the al-Qiyāmah . Like the other Abrahamic religions, Islam teaches the bodily resurrection of the dead, the fulfillment of a divine plan for creation, and the judgement of the soul; the righteous are rewarded with the pleasures of Jannah while the unrighteous...

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