Sabino horse
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
Prior to the development and widespread use of
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
In Welsh ponies and some other UK breeds, sabino patterns are sometimes called “blagdon.”
Breed standards that recognize the sabino pattern include the
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
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
Sabino 1 allele
Sabino 1 was identified in 2005 by researchers at the
trait; homozygous individuals have significantly more white than horses that are heterozygous.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
The Sabino 1
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
"Sabino" but not Sabino 1
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
Research indicates that there are many genes, and different alleles on those genes, that produce so-called "normal" white markings.
In Arabians
It was long known that sabino-type white patterns existed in purebred
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]
In draft horses
The
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
White patterning was originally considered undesirable by
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
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
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]
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.
Roan and rabicano
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.
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
See also
- Equine coat color
- Equine coat color genetics
- White (horse)
- Dominant white
References
- ^ a b c Sponenberg, D. Phillip; Bellone, Rebecca (2017). Equine Color Genetics (4 ed.). Wiley Blackwell. pp. 171–172, 185–197.
- ^ "Coat Patterns APHA". American Paint Horse Association. Retrieved 18 October 2021.
- ^ S2CID 19536624.
- ^ "Equinecolor.com sabino page". Archived from the original on 2008-01-17.
- ^ a b Hunter, Avalyn (July 26, 2013). "Mahubah's Corner: White Thoroughbreds". www.bloodhorse.com. Retrieved 18 October 2021.
- ^ "Why Color Your Horse?"
- ^ a b "Sabino Arabian Horse Registry; "Rules and Regulations," accessed April 1, 2007". Archived from the original on June 9, 2007. Retrieved April 2, 2007.
- ^ S2CID 32782072.
Chapter 3
- ^ 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)."
- ^ a b Stamatelakys, Irene (January 2016). "The Color Inside" (PDF). Paint Horse Journal. APHA. Archived from the original (PDF) on Feb 1, 2022.
- ^ "Horse coat color tests" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008
- ^ "Markings". Sabino Horse Registry. Retrieved 2009-06-16.
- ^ a b c "W variants with associated breeds". etalondx.com.
- ISBN 9781780643298.
- PMID 18296388.
- ^ PMID 2273238.
...[T]he results support the model that additively acting genes (polygenes) influence the presence and extent of common white markings...
- PMID 17997609.
- ^ UC Davis. "Horse Coat Color Tests". Veterinary Genetics Laboratory. University of California - Davis. Retrieved 2008-01-11.
- ^ "Animal Genetics, Incorporated. "Sabino 1"". Archived from the original on 2009-10-10. Retrieved 2007-04-02.
- ^ a b "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.
- ^ a b "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.
- ^ a b "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.
- PMID 23659293. Retrieved 18 October 2021.
- ^ a b Stamatelakys, Irene (August 2007). "The science of sabino" (PDF). Paint Horse Journal. 41 (8). American Paint Horse Association. 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."
- ^ Hunter, Avalyn (March 13, 2009). "A Horse of a Different Color". www.bloodhorse.com. Retrieved 18 October 2021.
- ^ "White Spotting (formerly Dominant White) Thoroughbreds". www.whitehorseproductions.com. Retrieved 18 October 2021.
- ^ "2004 Registration Changes" (PDF). American Quarter Horse Association. Archived from the original (PDF) on 2008-05-11. Retrieved 2009-06-18.
- ^ "Splashed White Mutations – SW1, SW2, SW3, SW4, SW5, and SW6 |". Veterinary Genetics Laboratory. UC Davis. Retrieved 18 October 2021.
- PMID 22511888.
- ^ "Genetic Equation". American Paint Horse Association. Archived from the original on 2008-09-07. Retrieved 2008-09-04.
- ^ a b c Vrotsos, PD; Santschi EM; Mickelson JR (2001). "The Impact of the Mutation Causing Overo Lethal White Syndrome on White Patterning in Horses" (PDF). Proceedings of the Annual Convention of the AAEP 2001. 47. American Association of Equine Practitioners: 381–91. Retrieved 2008-09-05.
- ^ American Paint Horse Association. "Splashed White". Genetic Equation. Archived from the original on 2009-04-02.
- ^ Laura Behning. "Splashed White". Morgan Colors.
- S2CID 22835035.
External links
- Sabino Horse Registry
- Horse genetic testing for color and patterns
- American Paint Horse Association – Sabino Spotting
- Animal Genetics Inc.