Red Factor

Quick Summary

The extension gene, or red factor, determines whether a horse will have a chestnut base coat color or a black or bay base coat color.

Example of a chestnut coat color. Image credit: Nicole Kingsley

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Phenotype: Red factor is responsible for determining whether a horse will have a chestnut base coat color or a black or bay base coat color.

Mode of Inheritance: Autosomal recessive

Alleles: E = Dominant red factor allele, e = recessive red factor allele, ea = alternate recessive red factor allele

Breeds appropriate for testing: All breeds

Explanation of Results:

  • Horses with E/E genoytpe will be capable of producing black pigment and cannot transmit the recessive red factor allele to their offspring.
  • Horses with E/e or E/ea genotype will be capable of producing black pigment. They may transmit the dominant red factor allele (E) to 50% of their offspring, and may transmit the recessive red factor allele (e or ea, depending on genotype) to 50% of their offspring.
  • Horses with e/e, e/ea, or ea/ea genotype will not produce black pigment in their coat. They will transmit a recessive red factor allele to all of their offspring.


$40 one test per animal
+ $15 each additional coat color/type test on the same animal

Panels Available
Turnaround Time
At least 15 business days; may be delayed beyond 15 business days if sample requires additional testing, or a new sample is requested.
Additional Details

Arabian Horse with chestnut coat
Arabian with chestnut coat color

The extension gene, also known as melanocortin 1 receptor (MC1R) or red factor, has three alternative states (alleles). The two recessive alleles (e and ea ) produce only red pigment (phaeomelanin), hence the name red factor. The ea allele is rare and known to occur in Black Forest,  Knabstrupper, and Canadian horse breeds. Red horses (chestnuts, sorrels, palominos, and red duns, to name a few) have two copies of recessive red allele/s (e/e, e/ea, or ea/ea).

Horses capable of producing black pigment (black, bay, brown, buckskin, and grullo, to name a few) have at least one copy of the dominant E allele. They can be homozygous E/E or heterozygous E/e or E/ea. A horse that is homozygous E/E will not produce red offspring, regardless of the color of the mate. Red factor works epistatically in that the genotype for red factor determines whether or not a horse will produce any black/brown pigment regardless of the genotype at the agouti gene.

This DNA diagnostic test for the extension gene helps to determine the base color of horses and can be used to identify those black-pigmented horses for which neither pedigree nor breeding records is informative for identifying carriers of the recessive red factor. Since red is inherited as a recessive trait, it is relatively easy to start up a breeding program that will produce only red horses. Results from the DNA test help breeders to determine the genetic make-up of the Extension gene in breeding stock to choose appropriate mating pairs to establish a breeding program to produce only black-pigmented horses.

Type of Sample



Akhal Teke American Sport Horse American Sport Pony American Warmblood Andadura Andalusian Appalachian Singlefoot Appaloosa Appendix Arabian Ardennes Arriador Australian Stock Horse Azteca Baden-Wurttemberg Barockpinto Baroque Pinto Bashkir Curly Bavarian Belgian Belgian Sport Horse Belgian Warmblood Brandenburg Breton British Sport Horse British Spotted Pony 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 Cob Normand Coldblooded Trotter Colorado Ranger Comtois Connemara Pony Continental Warmblood Costa Rican Paso Horse Cream Draft Criollo Crossbred 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 Highland Pony Holsteiner Iberian Warmblood Iceland Pony Icelandic Horse Imperial Heritage Horse 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 New Forest Pony Newfoundland Pony Nokota Noriker North American Trakehner Norwegian Fjord Horse Norwegian Nordland Oldenburg Onager Other Paint Horse Paso Fino Percheron Performance Horse Int'l Peruvian Horse Pinto Polish Warmblood Pony of the Americas Przewalski Pura Raza Española Quarter Horse Racking Horse Rheinland Rheinland Pfaltz-Saar Rhenish German Coldblood Rocky Mountain Horse Russian Orloff Russian Warmblood Saddlebred Saxon-Thuringian Coldblood Scottish Highland Pony Selle Français Shetland Pony Shire Shire Crossbred Silesian Horse Sillo Argentino Single-Footing Horse South German Coldblood Spanish Barb Spanish Heritage Horse Spanish Mustang Sporthorse 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 Unknown Uruguayan Criollo Virginia Warmblood Warlander Welsh Pony Weser Ems Ponies Westfalen Wild Horse Zangersheide
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Type of Test
Coat Color and/or Type
Results Reported As
Test Result Red Factor
e/e Only red factor detected. Basic color is red in the absence of modifying genes.

Only red factor detected. Basic color is red in the absence of modifying genes.


Only red factor detected. Basic color is red in the absence of modifying genes.

E/e Both black and red factors detected.
E/ea Both black and red factors detected.
E/E No red factor detected. Offspring cannot be chestnut/sorrel.

Marklund, L., Moller, M. J., Sandberg, K., & Andersson, L. (1996). A missense mutation in the gene for melanocyte-stimulating hormone receptor (MCIR) is associated with the chestnut coat color in horses. Mammalian Genome, 7(12), 895-899. doi: 10.1007/s003359900264

Wagner, H-J., & Reissmann, M. (2000). New polymorphism detected in the horse MC1R gene. Animal Genetics, 31, 280-291. doi: 10.1046/j.1365-2052.2000.00655.x