Quick Summary

The gray gene causes progressive depigmentation of the hair, often resulting in a color that is almost completely white by 6-8 years of age.
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Gray Horse Example
Andalusian with the gray gene showing progressive depigmentation

Phenotype: The gray gene causes a progressive depigmentation of the hair, often resulting in a color that is almost completely white by 6-8 years of age, and can act on any base coat color.

Mode of Inheritance: Autosomal dominant

Alleles: N = Normal or non-gray, G = Gray

Breeds appropriate for testing: Many breeds

Explanation of Results:

  • Horses with N/N genotype will not be gray and cannot transmit this gray variant to their offspring.
  • Horses with N/G genotype will be gray and will show a progressive graying of the coat. They may transmit this gray variant to 50% of their offspring. Matings with N/N genotype will result in a 50% chance of producing a gray foal.
  • Horses with G/G genotype will be gray and will show a progressive graying of the coat. They will transmit this gray variant to all of their offspring.

$25 one test per animal

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Additional Details

Gray Horse Example #2
Andalusian with the gray gene showing depigmentation progressing toward an almost completely white coat

The gray gene causes progressive depigmentation of the hair, often resulting in a coat color that is almost completely white by the age of 6-8 years. Horses that inherit progressive gray can be born any color, then begin gradually to show white hairs mixed with the colored throughout the body. Usually the first signs of gray hair can be found on the head, particularly around the eyes.

Gray is dominant, therefore a single copy of the gray allele will cause a horse to turn gray. If a horse has two copies of gray, all offspring of this horse will be gray. Research indicates that horses with one copy of gray often retain some of the original pigment while horses with two copies of gray tend to progress to almost completely white.

Gray is found in many breeds and is the predominant color of the Lipizzan breed. Researchers at Uppsala University in Sweden discovered that a 4.6 kilobases duplication in intron 6 of gene syntaxin 17 (STX17) produces progressive graying in horses. Their research hypothesized that the mutation in STX17 affects the production of melanocytes and thus predisposes gray horses to melanoma as well as causes the graying of the coat.

Gray Horse Example 3
Arabian with the gray gene showing depigmentation resulting in an almost completely white coat color

Gray horses have a high incidence of dermal melanomas that are commonly seen around the tail and head. Over 70% of gray horses older than 15 years will develop melanoma. Gray homozygotes are more likely to develop melanoma than heterozygotes. Gray horses that are also homozygous for black (a/a genotype at the Agouti locus) have a higher risk for melanoma. Many gray horses show depigmentation of the skin around the eyes, mouth, and anus, but there are no known additional health risks associated with this condition.

Testing for this gray variant can help owners identify homozygous horses (animals with two copies of the variant) which will always produce gray offspring, and can assist in determining a foal's coat color, as gray is a progressive pigmentation pattern.

Turnaround Time
10-15 business days
Type of Sample



Crossbred Unknown Akhal Teke American Sport Horse American Sport Pony American Warmblood Andadura Andalusian Appalachian Singlefoot Appaloosa Appendix Arabian Arriador Australian Stock Horse Azteca Baden-Wurttemberg Barockpinto Baroque Pinto Bashkir Curly Bavarian Belgian Belgian Sport Horse Belgian Warmblood Brandenburg British Sport Horse Bucking Horse Burchell's Zebra Caballo Deportivo la Silla Camarillo White Canadian Horse Canadian Warmblood Caspian Horse Chapman's Zebra Chilean Horse Cleveland Bay Clydesdale Connemara Pony Continental Warmblood Costa Rican Paso Horse Cream Draft Criollo Curly Dales Pony Danish Warmblood Deutsches Reitpony Deutsches Sportpferd Draft Cross Dutch Harness Horse Dutch Warmblood Exmoor Pony Falabella Faux Friesian Fell Pony Finnhorse Fire Friesian Frederiksborg French Warmblood "Selle Francais" Friesian Friesian Cross Friesian Sporthorse Georgian Grande German Riding Pony Gotland Pony Grevy's Zebra Gypsian Gypsy Cob Gypsy Vanner Hackney Horse Hackney Pony Haflinger Half Andalusian Half Arabian Half-Marchador Hanoverian Hartmann's Zebra Heck Tarpan Hessen Hibrido Holsteiner Iberian Warmblood Iceland Pony Icelandic Horse Imperial Heritage Horse Sporthorse International Sport Pony Irish Draught Irish Hunter Kallblodstravare Kentucky Mountain Horse Kerry Bog Pony Kiang Kiger Mustang Knabstrupper Kulan Latvian Warmblood Lipizzaner Lusitano Mangalarga Mangalarga Marchador Mexican Sport Horse Miniature Horse Missouri Fox Trotter Mongolian Domestic Horse Morab Morgan Horse Moriesian Moroccan Barb Mountain Pleasure Horse Mule Mustang National Show Horse Newfoundland Pony Nokota North American Trakehner Norwegian Fjord Horse Oldenburg Onager Other Paint Horse Paso Fino Percheron Performance Horse Int'l Peruvian Paso Pinto Polish Warmblood Pony of the Americas Przewalski Pura Raza Española Quarter Horse Racking Horse Rheinland Rheinland Pfaltz-Saar Rocky Mountain Horse Russian Orloff Russian Warmblood Saddlebred Scottish Highland Pony Shetland Pony Shire Shire Crossbred Sillo Argentino Single-Footing Horse Spanish Barb Spanish Heritage Horse Spanish Mustang Spotted Saddle Horse Standardbred Suffolk Punch Swedish Warmblood Tarpan Tennessee Walking Horse Thailand Pony Thoroughbred Trakehner Trocha Trocha y Galope Trote y Galope Turbo Friesian Uruguayan Criollo Virginia Warmblood Warlander Welsh Pony Welsh Pony Weser Ems Ponies Westfalen Wild Horse Zangersheide British Spotted Pony Noriker Ardennes Norwegian Nordland Breton Comtois New Forest Pony Cob Normand Rhenish German Coldblood South German Coldblood Saxon-Thuringian Coldblood
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Type of Test

Results Reported As
Test Result Gray
N/N No copies of the gray gene. Horse will not turn gray.
N/G 1 copy of the gray gene. Horse will turn gray and approximately 50% of offspring will be gray.
G/G 2 copies of the gray gene. Horse will turn gray and all offspring will be gray.

Pielberg, G. R., Golovko, A., Sundström, E., Curik, I., Lennartsson, J., Seltenhammer, M. H., Druml, T., Binns, M., Fitzsimmons, C., Lindgren, G., Sandberg, K., Baumung, R., Vetterlein, M., Strömberg, S., Grabherr, M., Wade, C., Lindblad-Toh, K., Pontén, F., Heldin, C.H., Sölkner, J., & Andersson, L. (2008). A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse. Nature Genetics, 40(8), 1004-1009. doi: 10.1038/ng.185