Sabino horse

Sabino is a color spotting pattern in horses that is usually recognized as a form of pinto horse color. A sabino horse has a dark base coat with a unique overlying spotting pattern. It is one of the most confusing colors to explain because a wide range of patterns are considered acceptable. Further, the polygenic combination of genes that produce this color pattern is not yet fully understood and is hotly debated by both researchers and horse breeders.

One of the many possible genes that creates the Sabino pattern, the Sabino1 (SB1) gene, now can be detected by a DNA test. [ [http://www.pacificpintos.com/articles/genetic_testing_color.html The Sabino Pinto test] ]

Sabino Markings

Sabino coloring is usually characterized by roaning at the edges of white markings, belly spots, irregular face markings, especially white extending past the eyes or onto the chin, white above the knees or hocks, and "splash" or "lacy" marks anywhere on the body, but particularly on the belly. Many sabinos have patches of roan coloring on part of the body, especially the barrel and flanks. Some sabinos may have a dark foot or two, but most have four white feet. Both blue and brown eyes are seen. A wide variety of irregular color patterns are accepted as Sabino. Sabino genetics are also thought to be the most common cause of solid-colored horses with "chrome," a term referring to horses that have lots of facial white and high leg white, with the occasional belly spot or roan patch.

White stockings that extend past the knee or hock, sometimes combined with a bald face (white extending to or past the eyes) are considered evidence of at least minimal expression of the sabino gene-complex. The most extreme manifestation of sabino is called "sabino white," produced when a horse is homozygous for the SB-1 gene, and is a totally white-colored horse (see section "below").

Genetics

There are multiple theories about Sabino coloring. Most likely, the pattern is polygenic, that is, it could be produced by multiple genes. [ [http://www.apha.com/breed/geneticeq4.html APHA Genetic Equation, "Sabino Spotting"] ] There is another theory that at least some forms of sabino are recessive. [ [http://equine-qanda.stablemade.com/kb/glossary.php?l=S Information on recessive Sabino] ]

There is one gene that is linked to Sabino coloring, "Sabino1" or "SB1," which is a dominant gene, and now can be detected with a DNA test. [http://www.vgl.ucdavis.edu/services/coatcolorhorse.php "Horse Coat Color Tests" "Veterinary Genetics Laboratory," University of California, Davis.] web page accessed August 21, 2008] SB-1 has been mapped to the equine KIT gene, in the same general region as the tobiano gene, though sabino is also not created by the same genetic mechanism as tobiano. [http://genetics.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pgen.0030195&ct=1/ Haase B, Brooks SA, Schlumbaum A, Azor PJ, Bailey E, et al. (2007) "Allelic Heterogeneity at the Equine KIT Locus in Dominant White (W) Horses." "PLoS Genet" 3(11): e195 doi:10.1371/journal.pgen.0030195] ]

However, many sabino marked horses do not carry SB1. [ [http://www.horse-genetics.com/sabino-horses-genetics.html "the genetics of sabino horses"] ] [ [http://www.equinecolor.com/sabino.html Equine Color Genetics Information: Sabino] ] [ [http://www.apha.com/breed/geneticeq4.html APHA site: "Genetic Equation: Sabino"] ] For example, there are a some Arabian horses that are sabino, but Arabians never have any other type of pinto coloring and to date no Arabians have been found to carry SB-1.

Combination patterns

Because horses with spotted color patterns are often crossbred to one another, it is possible for a horse to carry more than one gene for a spotting pattern, often creating a horse with a coat color that has characteristics of both. This can, at times, make identification and registration of spotted horses a challenge.

Overo and Sabino

Sabino is included in the Overo family of spotting patterns by the American Paint Horse Association (APHA), though it is created by a different genetic process than is overo patterning. This classification was created by the APHA prior to modern genetic studies and has not yet been amended by the association. However, other breeds which do not recognize Overo spotting patterns in their horses, such as the Arabian horse and the Clydesdale horse, do not consider Sabino to be an overo pattern.

To confuse matters further, in Spanish-speaking countries, the term "Overo" itself actually refers to horses with what is called Sabino in the USA, and in South America, the term "Sabino," which literally translated from Spanish means "speckled" or sometimes "roan," refers to a flea-bitten gray. [ [http://www.equinecolor.com/sabino.html Equinecolor.com sabino page] ]

Genetic sabinos without any overo genetics, even those with maximum white, also do not appear to carry the recessive gene for lethal white syndrome, which has been linked to the "frame overo" pattern, though it can be carried by horses that do not exhibit overo coloring; to date, all LWS foals do have overo ancestors.

Tobiano and Sabino

Some horses may simultaneously carry genes for both the tobiano spotting pattern and for sabino. This is generally noticed when a tobiano horse has spots with roaning around the edges, or other sabino traits such as belly white, white on the chin, or "high white" markings. Tobiano is a dominant gene, is not related to sabino, but because pinto horses with different spotting patterns are often crossed on one another, it is easily possible for a horse to carry multiple spotting pattern genes.

Roan and Rabicano versus Sabino

Sabino color may at times resemble a roan, or a Rabicano, but it is quite different genetically. Sabino, rabicano, and roan patterns have even been confused by some breed associations, including the Arabian, Thoroughbred, Tennessee Walker, Clydesdale and Shire registries, some of which still use the term "roan" to describe both sabinos and rabicanos.

A true roan is differentiated from a Sabino by the absence of splashy white markings and a head and legs that are darker than the body. Most roans have very little white, in fact. However, again, the sabino gene does sometimes occur in conjunction with a roan-colored coat, producing a horse with both roan and sabino traits. A rabicano is even more distinct, having roan patches confined only to limited parts of the body, with large solid areas.

"Maximum White" Sabino

A "Maximum Sabino" or "Sabino-White" horse is all white--essentially is either one big white spot, or is so covered with white spots that no darker color shows through. Such a horse will have pink skin and may have blue or brown eyes, or speckled skin spots under the white hair. A maximum sabino must not be confused with a genetically white horse, which is caused by a different gene and is much rarer. There also are differences in terminology between genetics researchers and certain organizations that promote sabino color, particularly in Arabians. Researchers at the University of California, Davis use the term "Sabino-White" to describe horses that are at least 90% white. [http://www.vgl.ucdavis.edu/services/coatcolorhorse.php "Horse coat color tests"] "from" Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008] Other researchers, such as Dr. Phillip Sponenberg, use the term "maximum Sabino" to describe the same pattern. [ [http://www.mfthba.com/ColorPanel/CPArticle7.htm "Why Color Your Horse?"] ] To further complicate matters, 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.

A sabino-white horse is produced if the foal is homozygous for the autosomal dominant gene sabino1 (SB1). However, a sabino-white is not a "lethal white," there is no known connection between sabino genes and lethal white syndrome (LWS), though a sabino horse may inherit an LWS allele (designated as "O" by some laboratories ) from another source. So, if a foal is ill within the first few days of life, testing for SB1 can help to determine if a white foal is a maximum sabino (with, presumably, an unrelated treatable illness) or if it carries the lethal white gene (and thus will need to be euthanized).

SB1 is not the only gene that creates sabino color, as it is not present in all sabino-patterned horses. It is most commonly found in Tennessee Walking Horses. Other breeds in which the SB1 mutation has been found include: Miniature horses, American Paint Horses, Aztecas, Missouri Foxtrotters, Shetland Ponies, Spanish Mustangs and Pony of the Americas. On the other hand, breeds of horses have sabino patterns, such as Clydesdales and Arabians, have so far tested negative for SB1, and neither breed produces white horses

Breeds that recognize sabino patterning

Breeds that recognize the sabino pattern include the Mustang, American Paint Horse, Miniature horse, Morgan, Hackney, Hackney Pony, Tennessee Walker and the Pinto horse color breed. Horse breeds that are generally solid-colored and do not allow most Pinto coloring in their breed registries, but who may have representatives with the Sabino gene pattern expressed by high white, belly spots, lacy or roaning patches and white extending past the eyes include the Clydesdale horse, Arabian horse, Thoroughbred and Shire.

The most controversial expression of the Sabino gene-complex was in the American Quarter Horse, which for years did not register horses with "cropout" color or blue eyes, i.e. typical Sabino patterns as well as cremello and perlino horses. This exclusion of cropout foals, even from two solid-colored parents, led in part to the formation of the American Paint Horse registry. However, since the advent of DNA testing to confirm parentage, the AQHA has repealed this controversial "white rule," allowing light-colored horses and those with body spots to be registered.

abino in Arabians

It is known that the sabino does exist in purebred Arabians, though it was at one time controversial and body spotting was viewed as a sign of "impure" breeding, with such horses excluded from the registry. Today, with DNA testing to verify parentage, a large number of Arabians meet the definition of having minimal to moderately expressed sabino characteristics. [http://www.sahr.homestead.com/rulesregs.html Sabino Arabian Horse Registry; "Rules and Regulations," accessed April 1, 2007] ]

Heavily sabino Arabians are particularly controversial, as for decades such horses were refused registration. Studies at the University of California, Davis indicate that the gene (or genes) which produces sabino in Arabians does not appear to be SB1.

While minimal sabino traits are not rare in Arabians, "sabino-white" is exceedingly uncommon, possibly exhibited by as few as eleven horses worldwide, [ [http://www.esplendour.com/sabino.html sabino ] ] and there is no evidence to date that these horses carry the SB1 gene. [ [http://www.mapleridgefarm.homestead.com/rkhasper.html A maximum sabino Arabian] ] A dominant color usually will appear more often. [ [http://www.animalgenetics.us/Sabino1.htm Animal Genetics, Incorporated. "Sabino 1"] ]

ee also

*Equine coat color genetics
*Equine coat color
*Pinto horse
*Overo
*Arabian horse
*Clydesdale horse

References

External links

* [http://www.sabinohorseregistry.com/ Sabino Horse Registry]
* [http://www.mustangs4us.com/Horse%20Colors/sabino.htm Sabino color from Mustangs 4 Us page, includes photos of sabino horses]
* [http://www.pacificpintos.com/articles/genetic_testing_color.html Horse genetic testing for color and patterns]
* [http://www.apha.com/breed/geneticeq4.html American Paint Horse Association -- Sabino Spotting]
* [http://www.Animalgenetics.us Animal Genetics Inc.]