Extension Red Factor Test
Tells you whether your horse can make black pigment at all, by reading the MC1R variant c.248C>T, the e version...
€43.05 Incl. VAT
About
This test shows whether your horse can make black pigment or only red pigment. A horse that makes only red pigment is chestnut.
The chestnut variant occurs in horses of many breeds, including Warmbloods. The test helps any breeder who wants to plan foal colour.
Why test?
Breeding. Knowing what both parents carry lets you work out the odds of a chestnut foal instead of guessing.
Studbooks and buyers. Where a studbook or a buyer wants chestnut, or wants it kept out, the DNA result is the reliable tool.
Hidden carriers. Only the DNA test shows whether a bay or black horse carries chestnut.
A colour that is hard to read. When the coat is hard to judge by eye, the DNA gives a clear answer.
Clinical signs
This gene sets coat colour. It is not linked to any illness.
Horses that can make black pigment. Carriers and non-carriers look the same. Agouti then decides where the black goes: onto the legs, mane and tail only for a bay or brown, or all over for a black.
Chestnut horses. The coat has only red pigment. The shade runs from a pale sorrel to a very dark liver chestnut, and the mane and tail may be darker, the same shade or flaxen. Sorrel, chestnut and liver chestnut are names for the same result. Agouti has no black pigment to work on, so it does not change a chestnut.
What fools the eye:
- A very dark liver chestnut against a true black, especially in winter coat
- A sun-bleached black, which can read as dark brown or dark chestnut
- A flaxen chestnut against a palomino: both have a light mane and tail on a golden body
- A dilution on top of the base colour: Cream, Pearl, Champagne, Dun or Silver
- Grey, which slowly strips the base colour away and in the end hides it completely
Transmission
Chestnut is recessive. A horse needs one chestnut copy from the sire and one from the dam to be chestnut. The gene is not on a sex chromosome, so colts and fillies are the same.
What each mating can produce:
- E/E x E/E gives 100% E/E: no chestnut foals and no carriers
- E/E x E/e gives 50% E/E, 50% E/e: no chestnut foals
- E/E x e/e gives 100% E/e: no chestnut foals, every foal a carrier
- E/e x E/e gives 25% E/E, 50% E/e, 25% e/e: one foal in four chestnut
- E/e x e/e gives 50% E/e, 50% e/e: one foal in two chestnut
- e/e x e/e gives 100% e/e: every foal chestnut
Prevention
The result lets you plan whether a mating can give chestnut foals.
To get chestnut foals. Both parents must carry the chestnut variant. The crosses under Transmission give the odds.
To keep chestnut out. At least one parent must have no copy of the chestnut variant.
Breeding for black. Test both parents at Agouti too. Both must be able to pass on black.
Chestnuts and Silver. Silver only lightens black pigment, so a chestnut can carry Silver without showing it and pass it on unseen. In breeds where Silver occurs, keep this in mind: Silver is linked to an eye condition, Multiple Congenital Ocular Anomalies.
Colour should not be the only thing that decides a mating.
Results
E/E: no chestnut copy. The horse can make black pigment. It cannot have a chestnut foal, whatever the partner, and passes E to every foal.
E/e: chestnut carrier. One chestnut copy, hidden in the coat. Passes e to about half of its foals.
e/e: two chestnut copies. The horse makes only red pigment and passes e to every foal.
Sample
Hair roots: 20 to 40 hairs pulled (not cut) from the mane or tail, with the roots attached. Tape them inside the marked area of the printable sample submission form. Hairs without roots cannot be analysed.
Blood: 5 mL of whole blood in a K3-EDTA tube, collected by a veterinarian. Label the tube with the horse's name and send it with the submission form.
Keep samples dry and at room temperature, and do not freeze them. Do not send hair that is wet, mouldy or soiled with bedding or faeces.
Coat colour does not affect the analysis. A white or grey horse gives DNA as good as a dark one, as long as the roots are there.
Send your sample by regular mail or express delivery to:
Equigerminal Lab HIESE
Rua da Quinta do Sobreiro Nº25
3230-343 Penela, Portugal
Turnaround
Standard processing: results within 5 to 10 working days of the sample arriving at the laboratory. Shipping is arranged and paid for by the client, and transit time is not included in the 5 to 10 working days.
Samples that fail DNA extraction or amplification are repeated at no extra cost, which may add a few working days. We contact you if a new sample is required.
How it works
🛒 Purchase the test: select and buy the test online.
📧 Receive instructions: after payment confirmation you receive sample collection instructions by e-mail.
✨ Collect the sample yourself: pull 20 to 40 hair roots with the bulb attached, or ask your veterinarian to collect blood in a K3-EDTA tube.
📄 Complete the form: print and complete the submission form with the animal identification.
📮 Send it to the laboratory: Equigerminal, S.A., HIESE, Rua da Quinta do Sobreiro, 25, Quinta Vale do Espinhal, 3230-343 Penela, PORTUGAL.
📄 Receive your report: your certified report is issued as soon as the analysis is validated.
FAQs
What does this test not detect?
It does not read a second, much rarer chestnut variant called e-a. It does not test Agouti. It does not test Cream, Pearl, Champagne, Silver, Dun, Grey, Roan, Tobiano, Overo, Splashed White, Sabino, Dominant White or the Appaloosa patterns. It says nothing about health, performance or temperament.
My horse is chestnut. Do I still need the test?
Usually not, since a chestnut horse already has two chestnut copies. It still makes sense when the colour is hard to read.
At what age can a horse be tested?
Any age. The result never changes, so a newborn foal gives the same answer as an adult.
For Professionals
Genetic and clinical detail for veterinarians, geneticists and laboratories.
- Gene / locus: MC1R (melanocortin 1 receptor), Extension (E) locus, ECA3.
- Variant: e allele, c.248C>T, missense, loss of receptor function: the receptor no longer takes the hormone signal that switches the pigment cell to black pigment. HGVS (EquCab3.0): NC_009146.3:g.36979560C>T; NM_001114534.1:c.248C>T; NP_001108006.1:p.(Ser83Phe). Marklund et al. (1996) showed that chestnut in 12 breeds comes from this change.
- Alternative designations: chestnut, red factor. A second chestnut allele, e^a (NM_001114534.1:c.250G>A; NP_001108006.1:p.(Asp84Asn); NC_009146.3:g.36979562G>A; rs3443929753), was described in the Belgian Draft (Wagner and Reissmann, 2000) and is also reported in the Black Forest horse. Avila et al. (2022) concluded that detecting e^a matters when breeding to a colour.
- Variant identifiers: e: rs68458866 (EVA); OMIA variant 154. e^a: OMIA variant 155.
- Variant classification: not currently evaluated (ISAG/AVCG, per OMIA).
- Inheritance: autosomal recessive for the chestnut phenotype (e/e); E is dominant. OMIA code: A (autosomal). Recessive inheritance was first argued by Hurst (1906), disputed by Weldon the same year, and settled from studbook records in Hurst's favour.
- Breeds with documented carriers or cases: widespread. Avila et al. (2022) found e in all 28 breeds studied: Andalusian, Appaloosa, Arabian, Connemara Pony, Dutch Warmblood, Gypsy Cob, Gypsy Vanner, Hanoverian, Icelandic Horse, Knabstrupper, Lusitano, Miniature Horse, Missouri Fox Trotter, Morgan Horse, Mustang, Norwegian Fjord Horse, Oldenburg, Paint Horse, Percheron, Pony of the Americas, Pura Raza Espanola, Quarter Horse, Rocky Mountain Horse, Shetland Pony, Standardbred, Tennessee Walking Horse, Thoroughbred and Welsh Pony. e^a carriers: Knabstrupper 6/91, Paint Horse 1/2,076, Percheron 1/52, Quarter Horse 2/110 (Avila et al., 2022).
- Allele / carrier frequencies: allele frequency of e from 76% (Pony of the Americas) to 12% (Percheron) across 28 breeds (Avila et al., 2022; 11,281 horses tested, 6,878 after removal of close relatives). The authors note ascertainment bias, since samples were submitted for colour testing, so figures for less-sampled breeds may be overestimated.
- Clinical / diagnostic notes for veterinarians: the report gives the c.248C>T genotype only. An E/E or E/e horse from Belgian Draft, Knabstrupper, Paint, Percheron or Quarter Horse lines may still carry e^a; an e/e-like phenotype with an E/e result should prompt e^a testing. Source for the Silver note under Prevention: Brunberg et al. (2006). Mura et al. (2024) documented mismatch between genetic and recorded visual colour in the Sarcidano horse. Reported links between MC1R and behaviour (Jacobs et al., 2016; Finn et al., 2016) are early exploratory work and no basis for decisions.
Key references:
- Marklund L, Moller MJ, Sandberg K, Andersson L (1996). A missense mutation in the gene for melanocyte-stimulating hormone receptor (MC1R) is associated with the chestnut coat color in horses. Mamm Genome 7:895-899. PMID 8995760.
- Wagner HJ, Reissmann M (2000). New polymorphism detected in the horse MC1R gene. Anim Genet 31:289-290. doi:10.1046/j.1365-2052.2000.00655.x. PMID 11086549.
- Rieder S, Taourit S, Mariat D, Langlois B, Guerin G (2001). Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses. Mamm Genome 12:450-455. doi:10.1007/s003350020017. PMID 11353392.
- Avila F, Hughes SS, Magdesian KG, Penedo MCT, Bellone RR (2022). Breed distribution and allele frequencies of base coat color, dilution, and white patterning variants across 28 horse breeds. Genes 13:1641.