A horse with classic sabino belly spots, white above its knees and hocks, a white chin and wide white facial markings.A sabino horse with extensive roaning
Sabino describes a distinct pattern of white spotting in horses. In general, Sabino patterning is visually recognized by roaning or irregular edges of white markings, belly spots, white extending past the eyes or onto the chin, white above the knees or hocks, and "splash" or "lacy" marks anywhere on the body. Some sabinos have patches of roan patterning on part of the body, especially the barrel and flanks. Some sabinos may have a dark leg or two, but many have four white legs. Sabino patterns may range from slightly bold face or leg white markings—as little as white on the chin or lower lip—to horses that are fully white.
The known causes of the sabino patterns are the SB-1 allele and several other dominant white (W) alleles on the KIT gene. The genetics behind some types of sabino, such as that found in Clydesdales, have not yet been identified. Some genes, such as Sabino-1, are incomplete dominants, producing irregular spotting when heterozygous, but when homozygous, can produce a horse that is almost completely white. Some forms of sabino are thought to be a reason for solid-colored horses with bold white markings on the face and high white leg markings.
Prior to the development and widespread use of DNA testing to determine equine coat color, the term broadly encompassed pinto patterns that did not clearly appear to be tobiano or frame overo. Some breed registries still use the term to describe spotting phenotypes that include roaning or irregular spotting, regardless of the precise genetics involved.
Description
Horses described as Sabino can have varying amounts of white, from bold white face and leg markings all the way up to fully white coats. Sabino patterns often have speckling and roaning. The different white spotting patterns usually have some consistency in which areas of the horse are white and which are pigmented. At the minimal end, there will typically be white on the legs and face, and the horse may also be lightly roaned. In horses with a bit more white, it usually extends above the knees and hocks onto the belly. At the other end of the spectrum, nearly white sabino horses may still have scattered flecks of color, though it is also fairly common to have color on the ears, lower neck and chest, flanks, tailhead, and back.[1]
Unlike white markings on non-sabino horses, the white leg markings of the sabino pattern often have a strip of white extending up the front or the back of the legs toward the belly. Some people call these "lightning strikes".[1]
Terminology
The term “sabino” was in use prior to the mapping of the horse genome to describe a wide range of pinto spotting patterns that are characterized by irregular edges, and is used by some breed registries. For example, the American Paint Horse Association still groups sabino patterns in its “overo” family of color patterns, even though sabino, splashed white, and frame overo are produced by different genetic mechanisms and are visually distinct.[2] Since the APHA classification system was created prior to modern genetic studies, it was based on physical description and not genetics.[3]
In Welsh ponies and some other UK breeds, sabino patterns are sometimes called “blagdon.”[1] To confuse matters further, in Spanish-speaking countries, the term "overo" refers to horses with what are called "sabino" patterns in English; meanwhile, in these countries the term "sabino", which literally translated from Spanish means "speckled" or sometimes "roan", refers to a flea-bitten gray.[4]
Breed standards that recognize the sabino pattern include the Mustang, American Paint, Miniature horse, Morgan, Hackney (and Hackney pony), Tennessee Walking Horse, and the pinto color breed registries. Horse breeds that are generally solid-colored and do not allow most pinto coloring in their breed registries, but who may have representatives with sabino-style patterns (such as the Arabian, Thoroughbred, and Clydesdale) have at times classified sabino horses as roan or even gray.[5]
Genetics
Most spotting patterns described as sabino are thought to be created by various mutations, most on the KIT gene, grouped broadly as dominant white (W), which now includes the SB-1 allele. DNA testing is often required to verify the specific genes influencing a pattern. There are over 30 alleles of dominant white identified to date, though only some produce sabino-like spotting. Confusing matters further, some horses may carry more than one allele that produces spotting patterns, thus visual verification of any specific genetic mechanism may be challenging. For example, some blue-eyed horses described as sabino may have a pattern created by the splashed white (SW) gene family.
Variants affecting the KIT gene are also responsible for tobiano and classic roan. KIT is also the gene associated with unpigmented patches of skin and hair on the extremities and midline of humans, mice, and pigs. KIT plays an important role in the migration of early pigment cells (melanocytes) from the neural crest to their ultimate location in the skin. Mutations on KIT appear to limit the migration of melanocytes, leaving the extremities and midline devoid of pigment cells. Other factors, including stochastic events and other genes, affect the amount of unpigmented skin and hair in the fully developed animal.
There are differences in terminology amongst genetics researchers and certain organizations that promote sabino patterns. Because several dominant white alleles produce sabino-style patterns rather than completely white horses, some propose the W gene be called the “white spotting” gene. In some cases, a horse that is homozygous for the SB-1 gene is often called “sabino-white,” some researchers prefer the term "maximum sabino" rather than "sabino-white" to describe horses more than 90% white.[6] Groups promoting sabino color have a more generous definition; the Sabino Arabian Horse Registry considers a "Maximum" Sabino to be a horse that is over 50% white.[7]
Horses who are heterozygous for Sabino-1 (SB1/sb1) generally have a distinctive white spotting pattern of irregular, rough-edged white patches that usually include two or more white feet or legs, a blaze, spots or roaning on the belly or flanks, and jagged margins to white markings.[10][11] Horses homozygous for the Sabino 1 allele (SB1/SB1) are “sabino-white,” typically at least 90% white-coated at birth with unpigmented skin under white hair. Horses in both cases have dark eyes.[12]
The Sabino 1 locus is at the KIT gene. The mutation responsible for Sabino 1 is a single nucleotide polymorphism designated KI16+1037A.[13] The Sabino 1 mutation results in the skipping of exon 17.[8] The gene in the equine wildtype is recessive (sb1) and the SB1 mutation is dominant, though an sb1/sb1 horse may have white markings due to other factors. Modest Sabino 1 markings can be difficult to tell apart from other white markings; the phenotypes overlap. Sabino 1 and the other KIT alleles in horses are not known to cause blue eyes. Blue eyes are linked to splashed white genes, and green-blue eyes are seen in horses with two dilution genes.
Researchers named the allele "Sabino 1" with the expectation that later alleles would be named "Sabino 2", "Sabino 3", and so on.[14] However, based on mouse nomenclature, it would have been more consistent to label the SB-1 gene as a W allele as it was part of the dominant white allelic series. The decision to name it “sabino” was to match the existing nomenclature used by horse breeders and to avoid confusion with various controversial known-lethal white genes in horses. However, confusion occurred anyway as more alleles at the same locus were discovered and the subsequent mutations labeled W to match the symbol used in mouse research.[15]
Neither Sabino 1 or any other alleles of W are linked to lethal white syndrome (LWS). LWS occurs when a foal is homozygous for frame overo, which is a mutation on a different gene, EDNRB.[16] Some of the genes in the W allelic series are embryonic lethal when homozygous and only one copy was needed for a horse to be fully white, while others, including SB-1, produced sabino patterns when heterozygous and appear to be viable when homozygous.[15]
"Sabino" but not Sabino 1
A Thoroughbred horse that carries the W5 allele and has sabino patterning
The term "sabino" is also used for horses who do not carry SB-1, but have white leg markings above the knees and hocks with jagged margins, wide blazes, and belly spots or roaning. In some cases, the term is defined even more broadly, to include white spots on the lower lip or chin, distal white patches on the legs, or "pointy" leg markings.[17] The “dominant white” alleles W5, W8, W10, W15, and W19 are particularly noted for producing sabino-type markings.[18][19]
Prior to the mapping of the horse genome and the widespread use DNA testing to verify parentage, assorted rules were created by to distinguish "spotted" from "non-spotted" horses; some breeds selected for bold white patterns, others disqualified horses with “too much white” from registration. The rules were not based on modern genetic studies, as such information was not yet available. In many cases, horses with sabino patterns fell into the middle—what was “excessive” white for one registry might be allowable in another. When early parentage testing using blood typing developed, revealing the variability of white patterns and markings, rules were modified to allow “cropouts” with extra white to be registered when previously excluded, and likewise, various color breed registries began to allow visually solid-colored foals to be registered.
Today, most breed registries allow DNA-verified offspring of registered animals to be registered regardless of color pattern, though some are slow to catch up to modern understanding of genetics. Yet others have refined their breeding goals to include or exclude horses based upon DNA color testing.
The genetics behind white patterns and markings in horses are complex. Two full siblings with the same genotype for a particular white spotting pattern may phenotypically be considered "solid" or "spotted", depending on the amount of patterning that is visible. Furthermore, the amount of white that a foal ends up with does not solely depend on known white spotting genes. For example, research suggests that chestnuts express more white than non-chestnuts.[20]
Research indicates that there are many genes, and different alleles on those genes, that produce so-called "normal" white markings.[21] Complicating matters further, when multiple, different alleles for white patterns are present, they have an additive effect, producing more white together than any single allele would do alone.[21] A similar effect is observed in pinto horses with both the tobiano and frame overo pattern; these "toveros" often have more white than either tobiano or frame overo-patterned horses. Similarly, two apparently solid-colored horses with separate factors for white markings may produce a foal expressing both, with more white than either parent.
In Arabians
Sabino patterns have long existed in Arabians
It was long known that sabino-type white patterns existed in purebred Arabians, but neither the tobiano nor frame overo genes existed in the breed. Thus, prior to the use of parentage testing as a registration requirement, white spotting in Arabians was controversial and viewed as evidence of crossbreeding or "impure" breeding, with such horses discouraged from registry and penalized in competition. Once DNA testing began to verify parentage, a significant number of Arabians met the definition of having minimal to moderately expressed sabino characteristics, though the genetic mechanisms involved were not understood. Thus term sabino came into vogue to describe any type of bold markings or body spotting, with “minimum” sabino describing horses with slightly bold markings, and "maximum sabino" describing spotted Arabians that were close to 50% white.[7]
In 2007, a white horse born from solid-colored parents, originally identified as "bay sabino" was determined to carry an original mutation of a previously undiscovered form of dominant white, labeled W3, and has passed this trait on to his descendants.[22] Further research identified alleles that created “sabino” patterns in Arabians, each alleles of W, labeled W15 and W19. Studies at the University of California, Davis indicated that the none of the alleles involved in Arabians were SB1.[23][24]
The Clydesdale and Shire are closely related draft horses originally bred in the United Kingdom. Apart from massive build and copious feathering, both breeds are known for consistent white markings. The most popular and acceptable form of white markings on both breeds includes a bold blaze and four even socks.[25] These markings are often described as sabino. In particular, white facial markings often extend to the chin or lip, and may wrap around the head with irregular, feathery borders. When white markings on the forelegs extend above the knees, they may trail up the shoulder or up the back of the leg to the elbow with irregular, feathered, or roaned borders. White markings above the hocks on the hindlegs are common, and typically trail up the front of the leg to the stifle joint and flank. Extensive white leg markings are often accompanied by body spotting, typically on the belly. These markings are also often accompanied by interspersed white hairs that give the horse a roan-like pattern. Such horses are called "roan" by the Shire and Clydesdale breed registries.[25][26][27]
The high white markings characteristic of these two breeds follow a pattern similar to that found in Sabino 1, which led researchers to include these horses in the original study that discovered SB1. However, none of the draft-type sabinos possessed the SB1 allele.[8] Later, the W20 allele was identified in Clydesdales, but there has been very little research done on draft breeds.[28]
Breed standards for Clydesdale horses no longer state that "excessive white" is a fault.[26] Conversely, even in modern times, the Shire horse breed standard counts excessive white, body spotting, or roaning as a fault, especially in stallions.[27]
This pattern, informally labeled “draft-type sabino,” appears to be dominantly inherited, but it does not result in a sabino-white phenotype when homozygous.[29] As the gene pool for these two breeds is limited, most registered animals most likely possess the gene responsible for their white spotting pattern. Thus, if the draft-type sabino gene produced sabino-whites, near-white coats would be expected in nearly a quarter of foals, but they do not occur. Though occasional near-white Shires and Clydesdales can be found, they are quite uncommon.[30]
In Thoroughbreds, American Quarter Horses and Paints
Historically, Thoroughbreds with irregular spotting patterns have been documented, some in photographs. Examples include The Tetrarch, Birdcatcher, and others. In modern times, multiple alleles of W have been identified in Thoroughbreds. While some alleles produce mostly white or near-white horses, those that produce sabino-style spotting include W5, W20, W22, and W27.[18] While white coats and spotting was not considered “fashionable” in Thoroughbreds and generally selected against by breeders, nor were the colors recognized by the Jockey Club, spotted horses were sometimes recorded as “roan or gray,” including Puchilingui, founding sire of the W5 line. [5][31][32]
White patterning was originally considered undesirable by American Quarter Horse breeders, who also selected for horses that were solid-colored and minimally-marked. However, the Quarter Horse arose from multiple sources, including Thoroughbreds and other breeds now known to carry spotting genes. Among Quarter Horse breeders, foals with large amounts of white born to parents eligible for registration were referred to as cropouts," and, until 2004, “white” horses, or horses that had areas of white hair rooted in pink skin above the gaskin on the hindleg, above the halfway point between the knee and elbow in the foreleg, or beyond the eye could not be registered.[33] However, spotting patterns were clearly in the genepool, and because of the large number of horses that had these patterns (as well as a significant number of double dilute creams also caught up by this rule), the American Paint Horse Association (APHA) formed, allowing horses of verifiable Quarter Horse or Thoroughbred ancestry to be registered as "Paints". The APHA recognizes sabino in their "overo" family of color patterns.
Since the relaxation of the “white rule,” at least one registered Quarter Horse has tested homozygous for the SB1 allele.[29] In addition, several other alleles that produce sabino-type patterns have been found in Quarter horses, including all six SW alleles,[34] and the W spotting alleles W10, W13, W20, and W31. W32 has separately been identified in Paints.[18]
Combination patterns and mimics
Not all white horses are sabino-white or even dominant white. Combinations of other white spotting patterns, such as tobiano with heterozygous frame overo, can produce a horse that is 90% white or more. Cremello horses are superficially similar to sabino-whites, however, cremellos have blue eyes, rosy-pink skin, and a cream-colored rather than a white coat. “Fewspot” Appaloosas are nearly all white, but carry the Lp gene. Gray horses have a white hair coat at maturity but unless they also happen to carry dilution or white spotting genes, they do not have pink skin and are not white at birth.
In some cases, horses with high white stockings and bold face markings often labeled sabino carry a splashed white allele, notably SW-1, SW-2 and SW-3.[35]
Pinto combinations
The horse on the left most likely carries multiple spotting alleles. The horizontallyxoriented white patches on the body of the horse are indicative of the frame pattern. The wrap-around blaze suggest splash white genetics are present. The irregular stockings and roaned edges of the white patches indicate sabino patterning.Some splashed white horses may closely resemble sabino, but tend to have more white on the head and belly, with sharper-edged white markings
Sabino patterns are produced by many different alleles, plus may bear some resemblance to other spotting patterns. Because breeders who desire pintos often crossbreed horses various color patterns, it is possible for a horse to carry genes for more than one pattern. The presence of multiple white spotting alleles often produces more white, or such horses may show characteristics of both patterns.[8] This can, at times, make identification and registration of spotted horses a challenge. Conversely, even if a spotting gene is present, white body markings may be so minimal in some individuals that they are registered as solid-colored. However, they may produce strongly colored offspring.
The frame pattern, one of the first spotting patterns to have a DNA test developed, is produced by the Ile118Lys mutation on the equine Endothelin receptor type B gene and when homozygous produces lethal white syndrome.[3][36] Frame is characterized by jagged but sharply defined, horizontally oriented white patches. By itself, the frame pattern does not produce white markings that cross the back, or affect the legs or tail.[3] The expression of the frame pattern varies from minor white markings to the distinctive framed pattern.[37]
Horses carrying both frame and sabino genes can be expected to show characteristics of both patterns. While frame alone is seldom responsible for white leg markings, a frame-sabino blend might have frame body markings and white markings on the legs. Similarly, while frame alone usually produces markings with jagged but sharply defined white patches, the addition of sabino can add roaned edges and roaning on the body. [37]
Splash, or splashed white, is characterized by blue eyes and crisp, smooth markings. The legs, tail, underside and head are typically white; the white head is distinct in that most of the head is white.[38] The most minimal splashes may have only a bottom-heavy, off-center snip and low hind socks.[39]
Blue eyes are not considered a sabino characteristic, but splashed white-sabino blends may have a lot of facial white and even blue eyes. Splash-sabino blends may have characteristics of both patterns, such as jagged patches, roaning, blue eyes and blocky white markings. Splash in conjunction with sabino may also produce the "medicine hat" pattern, where only the ears and poll and sometimes the topline or chest have pigment.[37]
This tobiano has an irregular, wrap-around blaze and chin white, the tobiano markings have ragged edges, extend high on the legs, and some roaning is visible. Thus, this horse may carry sabino or splash genetics as well as tobiano.
The tobiano pattern is easily recognizable, genetically distinct, and tobiano horses are categorized separately from other patterns in breeding associations for pinto-spotted horses. The simple dominant allele responsible for the tobiano pattern (TO) is a large inversion approximately 100kb downstream of KIT and is expected to impact KIT protein function.[40] The tobiano pattern is characterized by smooth, crisp-edged white markings arranged in a vertical orientation that often cross the back. The head is usually dark with some markings, but the legs are often white, and the tail is often white or partly white. A tobiano-sabino blend might then have more than the expected amount of facial white markings, blotchy or roaned edges to tobiano markings, or white on the stifle and flanks.
This true or "classic" roan has the characteristic darker head and legs.
A true roan is neither sabino nor gray, but instead refers to a pattern of evenly-interspersed white hairs on the body with minimal white hairs on the head and legs and few, if any white markings. In contrast, primary characteristics of sabino include bold white markings on the head and legs, often with roaning at the edges. When both roan and sabino are present in the same horse, it can be difficult to tell whether the roaning is due to sabino or true roan, especially if the white markings entirely cover up the telltale dark head and legs.
In some breed registries, the term "roan" is used to record sabinos, particularly with Thoroughbreds and Arabians. Sabinos have also been described as "roan" by Clydesdale, Shire, and Tennessee Walking Horse registries.
The extensive roaning or ticking of this horse's barrel is typical of the rabicano pattern, which is sometimes confused with sabino. High white markings and patches are not controlled by rabicano.
Rabicano is another type of "roaning" or ticking characterized by scattered white hairs centered on the flanks, barrel and white hairs at the base of the tail. It is unknown if the roaning characteristic of some sabino-type patterns is due to the additional presence of rabicano or a separate mechanism. Rabicanos are also often identified as roans, even among breeds that do not have true roans, such as Thoroughbreds and Arabians.
Gray and sabino
Gray horses undergo progressive silvering that begins at or shortly following birth. Young gray horses often exhibit a mixture of whitish and colored hairs which can be mistaken for roaning. Grays develop more and more white hairs over the course of several years, most eventually losing all or almost all of their original colored hair. Sabino markings are permanent, and while some changes are not out of the ordinary, drastic color changes are not characteristic of sabino-type patterns. If a horse carries both genes, it will show spotting patterns while young, but they will fade over time as the overall coat lightens to white. Once the horse has fully grayed, the pink skin beneath the original white markings will still exist, but may not be obvious unless the horse has a body-clipped hair coat or is wet.
See also
Wikimedia Commons has media related to Sabino horses .
Roan is a coat color found in many animals, including horses, cattle, antelope, cat and dogs. It is defined generally as an even mixture of white and pigmented hairs that do not "gray out" or fade as the animal ages. There are a variety of genetic conditions which produce the colors described as "roan" in various species.
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 Association (APHA) breed registry is now one of the largest in North America. The registry allows some non-spotted animals to be registered as "Solid Paint Bred" and considers the American Paint Horse to be a horse breed with distinct characteristics, not merely a color breed.
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 born after the full 11-month gestation and externally appear normal, though they have all-white or nearly all-white coats and blue eyes. However, internally, these foals have a nonfunctioning colon. Within a few hours, signs of colic appear; affected foals die within a few days. Because the death is often painful, such foals are often humanely euthanized once identified. The disease is particularly devastating because foals are born seemingly healthy after being carried to full term.
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 background is not pigmented.
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 are sometimes called tricoloured. These horses usually have pink skin under white markings and dark skin under non-white areas. Other than colour, it is similar in appearance to the piebald pattern. Some animals also exhibit colouration of the irises of the eye that match the surrounding skin. The underlying genetic cause is related to a condition known as leucism. The term is also used to describe spotting patterns in various other animals, such as goats.
Tri-coloured refers to a horse with three different coat colours in a pinto spotting pattern of large white and dark patches, usually bay and white. This colouring is also commonly called skewbald. In modern usage in British English, skewbald and piebald horses are collectively referred to as coloured, while in North American English, the term pinto is used to describe the colour pattern.
Bay is a hair coat color of horses, characterized by a reddish-brown or brown body color with a black point coloration on the mane, tail, ear edges, and lower legs. Bay is one of the most common coat colors in many horse breeds.
A gray 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 depigmentation, gray does not affect skin or eye color. 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 more prevalent as the horse ages as white hairs become intermingled with hairs of other colors. Graying can occur at different rates—very quickly on one horse and very slowly on another. As adults, most gray horses eventually become completely white, though some retain intermixed light and dark hairs.
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. Bay is the most common color of horse, followed by black and chestnut. A change at the agouti locus is capable of turning bay to black, while a mutation at the extension locus can turn bay or black to chestnut.
A pinto horse has a coat color that consists of large patches of white and any other color. Pinto coloration is also called paint, particolored, or in nations that use British English, simply coloured. Pinto horses have been around since shortly after the domestication of the horse.
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 change throughout the horse's lifetime, unless the horse also carries the gray gene. It is a dominant gene, so any tobiano horse must have at least one parent who carries the tobiano gene.
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 a Spanish word, originally meaning "like an egg". The most common usage refers to frame overo, but splashed white and sabino are also considered "overo". A horse with both tobiano and overo patterns is called tovero.
Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them.
A white horse is born predominantly white and stays white throughout its life. A white horse has mostly pink skin under its hair coat, and may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white (W) genes, are rare. Most horses that are commonly referred to as "white" are actually "gray" horses whose hair coats are completely white. Gray horses may be born of any color and their hairs gradually turn white as time goes by and take on a white appearance. Nearly all gray horses have dark skin, except under any white markings present at birth. Skin color is the most common method for an observer to distinguish between mature white and gray horses.
Markings on horses are usually 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. Most markings have pink skin underneath most of the white hairs, though a few faint markings may occasionally have white hair with no underlying pink skin. Markings may appear to change slightly when a horse grows or sheds its winter coat, however this difference is simply a factor of hair coat length; the underlying pattern does not change.
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 interspersed white hairs seen first at the flank, then other parts of the body radiating out from the flank, where the white hairs will be most pronounced. Rabicano is distinct from true roan, which causes evenly interspersed white hairs throughout the body, except for solid-colored head and legs.
A cropout, crop-out or crop out is a horse with body spots, including pinto or leopard complex spotting, or "high white" horse markings, with a sire and dam who both appeared to have been solid-colored. There are several variations in the definition, depending on the breed registry involved. There are multiple genetic reasons that may cause a horse to be a cropout. Sometimes solid-colored horses throw cropouts because some spotting patterns are recessive genes that are not necessarily expressed unless the relevant allele is inherited from both parents. Other times a gene may be a dominant or incomplete dominant but so minimally expressed that the horse looks solid but can pass flashy color on to its offspring.
Splashed white or splash is a horse coat color pattern in the "overo" group of spotting patterns that produces pink-skinned, white markings. Many splashed whites have very modest markings, while others have the distinctive "dipped in white paint" pattern. Blue eyes are a hallmark of the pattern, and splash may account for otherwise "solid" blue-eyed horses. Splashed white occurs in a variety of geographically divergent breeds, from Morgans in North America to Kathiawari horses in India. The splashed white pattern is also associated with congenital deafness, though most splashed whites have normal hearing. Splashed white can be caused by multiple variants across two different genes, for which genetic testing is available.
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 to the discovery of the W allelic series, many of these patterns were described by the term sabino, which is still used by some breed registries.
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 mostly solid-colored. Horses with roan coats have white hairs evenly intermingled throughout any other color. The head, legs, mane, and tail have fewer scattered white hairs or none at all. The roan pattern is dominantly inherited, and is found in many horse breeds. While the specific mutation responsible for roan has not been exactly identified, a DNA test can determine zygosity for roan in several breeds. True roan is always present at birth, though it may be hard to see until after the foal coat sheds out. The coat may lighten or darken from winter to summer, but unlike the gray coat color, which also begins with intermixed white and colored hairs, roans do not become progressively lighter in color as they age. The silvering effect of mixed white and colored hairs can create coats that look bluish or pinkish.
References
1 2 3 Sponenberg, D. Phillip; Bellone, Rebecca (2017). Equine Color Genetics (4ed.). Wiley Blackwell. pp.171–172, 185–197.
1 2 3 Metallinos, DL; Bowling AT; Rine J (June 1998). "A missense mutation in the endothelin-B receptor gene is associated with Lethal White Foal Syndrome: an equine version of Hirschsprung Disease". Mammalian Genome. 9 (6). New York: Springer New York: 426–31. doi:10.1007/s003359900790. ISSN0938-8990. PMID9585428. S2CID19536624.
↑ Brooks, Samantha (2005). "The SNP was found among American Miniature Horses, American Paint Horses, Azteca, Missouri Fox Trotters, Shetland Ponies, and Spanish Mustangs."
↑ Brooks, Samantha, et al (2005). "[W]hite patches often extend to include the belly and midsection, either as distinct areas of white hair, or as a diffuse scattering of white hairs resembling roan."
↑ Brooks, Samantha et al (2005). "Horses characterized as having a Sabino 1 white spotting pattern possessed 3 out of 4 of the following characteristics: 1) two or more white feet or legs, 2) blaze (white patch extending the length of the face), 3) jagged margins around white areas, and 4) spots or roaning in the midsection."
↑ Brooks, Samantha, et al. (2005). "[H]omozygosity for the Sabino 1 gene may result in a phenotype exhibiting extensive white coat color, hereafter referred to as sabino-white in order to distinguish it from White (W)."
↑ Brooks, Samantha et al (2005). "...base substitution for T with A in intron 16, 1037 bases following exon 16."
↑ Brooks, Samantha, et al. (2005), "Consequently, we anticipate future discoveries of other genes encoding different sabino phenotypes (possibly designated SB2, SB3, etc)."
1 2 Stamatelakys, Irene (January 2016). "The Color Inside"(PDF). Paint Horse Journal. APHA. Archived from the original(PDF) on February 1, 2022. Retrieved September 5, 2020.
↑ "Horse coat color tests"from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008
1 2 Woolf, CM (Jul–Aug 1990). "Multifactorial inheritance of common white markings in the Arabian horse". Journal of Heredity. 81 (4): 250–6. doi:10.1093/oxfordjournals.jhered.a110987. PMID2273238. ...[T]he results support the model that additively acting genes (polygenes) influence the presence and extent of common white markings...
1 2 "History of the Breed". Clydesdale Breeders of the USA. Archived from the original on 2009-05-01. Retrieved 2009-06-18. Popular markings for today's big hitches are four white socks to the knees and hocks, and a well-defined blaze or bald face, however, the show ring does not discriminate on color, with light roans and dark legs being considered equally with solid colored horses with traditional markings.
1 2 "The Modern Clydesdale". The Clydesdale Horse. The Clydesdale Horse Society. Archived from the original on 2010-11-07. Retrieved 2010-12-16. After the 1900s, breeders used Shire blood to increase white markings...the white hair occasionally strayed onto the Clydesdales' body, giving an animal of a roan colour. The purists frowned upon these animals, believing that only a good solid colour was correct. However, most people today believe that a good horse cannot be a bad colour, so roan horses and horses with white areas on the body are acceptable.
1 2 "Standard of Points for Shires". The Shire Horse Society. Archived from the original on 2011-10-07. Retrieved 2011-11-21. No good stallion should be splashed with large white patches over the body. He must not be roan or chestnut.
1 2 Stamatelakys, Irene (August 2007). "The science of sabino"(PDF). Paint Horse Journal. 41 (8). American Paint Horse Association. Archived from the original(PDF) on 2008-08-07. Retrieved 2009-06-18. "The draft-type sabino, for example, is present in heavy horses, Shires, Clydesdales, etc. This population, until the recent popularity of draftcrosses and spotted drafts, was not intermingled much with the light horses. And, though it seems to be dominantly inherited, it does not produce a white phenotype." [Samantha Brooks]
↑ Brooks, Samantha, et al (2005). "[W]hite Clydesdale horses are uncommon despite the high frequency of a gene for a sabino-type pattern among horses of that breed."
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