Dun Colour Test
Sorts out the three versions of the TBX3 gene behind the Dun colour and the old wild markings: D (Dun),...
€49.20 Incl. VAT
About
This test shows whether your horse is dun, and whether it carries a version that gives the old wild markings without the dun colour.
It is useful for horses of many breeds, including Warmbloods, and for any horse used for breeding.
Why test?
Explaining faint markings. Owners often ask why a horse has leg bars but no dun colour. This test answers it.
Telling one copy from two. Only the DNA test shows whether a dun parent gives dun foals half the time or every time.
Registration and breed standards. Where Dun is part of the breed standard, the genotype is the objective record.
Clinical signs
Dun lightens the body coat and adds the old markings. One Dun copy is enough, so one and two copies look alike.
Dun: the body is lightened and the markings are there: usually a stripe down the back and bars on the legs, often a stripe across the shoulder and darker ear tips too.
- A bay base gives bay dun
- A chestnut base gives red dun
- A black base gives grulla, also called grullo or blue dun
Not dun, with markings: the body is not lightened, but a dorsal stripe and faint leg bars can be there.
Not dun, unmarked: no lightening and no markings.
What fools the eye:
- A marked horse that is not dun read as a Dun. This is the mistake the discovery paper warns about.
- Shading along the back, which imitates a dorsal stripe
- A buckskin read as a bay dun. A horse can also be both at once.
- A palomino read as a red dun
- A grulla read as a blue roan or a faded black
- Grey, which slowly strips any of these colours away
Health. No disease is linked to any of the three versions.
Transmission
There is a pecking order: D beats nd1, and nd1 beats nd2. Every horse carries two of the three, and the stronger one shows. The gene is not on a sex chromosome, so colts and fillies are the same.
Dun or not dun:
- D/D x anything gives 100% dun
- D/nd x D/nd gives 75% dun, 25% non-dun
- D/nd x non-dun gives 50% dun, 50% non-dun
- non-dun x non-dun gives 100% non-dun
Markings in a non-dun foal:
- nd1/nd1 x nd1/nd1 gives 100% nd1/nd1
- nd1/nd2 x nd1/nd2 gives 25% nd1/nd1, 50% nd1/nd2, 25% nd2/nd2
- nd1/nd2 x nd2/nd2 gives 50% nd1/nd2, 50% nd2/nd2
- nd2/nd2 x nd2/nd2 gives 100% nd2/nd2
Prevention
The result lets you plan for dun foals and for the markings.
To guarantee a dun foal. Use a parent with two Dun copies.
To keep dun out. Use two partners that are not dun. Because one Dun copy always shows, a horse that is not dun does not carry it.
To plan around the markings. If a registry or a buyer objects to a dorsal stripe on a horse that is not dun, the version to avoid is the marked non-dun version, not Dun. Two parents that tested unmarked give foals with no markings.
Results
D/D: dun, two copies. Passes Dun to every foal.
D/nd1 and D/nd2: dun, one copy. Passes Dun to about half of its foals.
nd1/nd1 and nd1/nd2: not dun, may carry the markings. Cannot produce a dun foal. An nd1/nd2 horse passes nd1 to about half of its foals.
nd2/nd2: not dun, unmarked. Cannot produce a dun foal or pass on markings.
Naming the exact colour (bay dun, red dun or grulla) needs the Extension and Agouti results as well.
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.
There is no need to sample the dorsal stripe or any particular part of the coat. The DNA is the same everywhere in the body.
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.
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 test Cream, Pearl, Champagne, Silver, Grey, Mushroom, the base colour or any white pattern. It says nothing about health, performance or temperament.
At what age can a horse be tested?
Any age. The genotype is fixed at conception and never changes. Foal coats show the old markings unreliably, so the DNA test tells you more than looking at a young foal.
For Professionals
Genetic and clinical detail for veterinarians, geneticists and laboratories.
- Gene / locus: TBX3 (T-box transcription factor 3), Dun (D) locus, ECA8; regulatory variants outside the coding sequence, which do not alter the protein.
- Variant: three alleles. nd2 carries a deletion of about 1.6 kb and is the allele represented in the EquCab3.0 reference, so D and nd1 are written as insertions relative to it. HGVS (EquCab3.0): D, NC_009151.3:g.[20665796_20665797insCCTTCTGGC;20665807_20665808ins[1609]]; nd1, NC_009151.3:g.[20665796_20665797insCCTTCTGGC;20665807_20665808ins[1610]]; nd2, reference sequence.
- Alternative designations: D = Dun (wild type); nd1 = non-dun 1 (primitive markings without dilution); nd2 = non-dun 2 (no dilution, no markings) (Imsland et al., 2016).
- Variant identifiers: no rs/EVA identifiers listed in OMIA; OMIA variants 1701 (D), 1028 (nd1), 1029 (nd2).
- Variant classification: not currently evaluated (ISAG/AVCG, per OMIA), all three alleles.
- Mechanism: in Dun horses TBX3 is expressed asymmetrically around the hair follicle, restricting melanocytes to one side of the growing hair; pigment fills about a quarter to a half of the hair diameter. nd1 and nd2 reduce TBX3 expression, giving fully pigmented hairs; nd1 has a weaker effect than nd2 at the phenotypic and histological level (Imsland et al., 2016).
- Inheritance: autosomal dominant (OMIA code D), dominance series D > nd1 > nd2.
- Evolution: Dun is the ancestral state, shared with Przewalski's horse and other wild equids. Ancient DNA: a horse dated 42,700 years ago was D/nd1 and one from 4,400 years ago was nd1/nd1, so nd1 predates domestication while nd2 is more recent (Imsland et al., 2016).
- Penetrance / expressivity: genotype matched phenotype in all 1,814 horses of known colour from more than 45 breeds, including Przewalski horses; none of 529 Dun horses was nd2/nd2 (Imsland et al., 2016). About two in three non-dun horses carry nd2; the rest carry nd1.
- Breeds with documented carriers or cases: D documented in American Trotter, Arab, Curly Horse, Faeroes Pony, Fjord, Gotland Pony, Icelandic Horse, Mongolian, Polish Konik, Quarter Horse, Shetland Pony, Swedish Warmblood and Vyatka. Avila et al. (2022; 28 breeds): D in 19 breeds, not detected in Arabian, Dutch Warmblood, Gypsy Vanner, Hanoverian, Knabstrupper, Oldenburg, Percheron, Standardbred or Thoroughbred; nd1 absent only in Gypsy Vanner and Norwegian Fjord; nd2 absent only in Norwegian Fjord. Absence in a sample does not prove absence in the breed.
- Allele / carrier frequencies: allele frequencies (Avila et al., 2022; 11,281 horses tested, 6,878 after removing close relatives; per-breed n given only where stated in our sources): D 100% in Norwegian Fjord (n=90), down to 0.6% in Tennessee Walking Horse; nd1 79% Pura Raza Espanola, 78% Andalusian, 68% Arabian, 57% Lusitano, down to 1.7% Gypsy Cob; nd2 100% Gypsy Vanner down to 20% Pura Raza Espanola, and the commonest allele in most modern breeds. The authors note ascertainment bias, as samples were submitted for colour testing, so figures for less-sampled breeds may be overestimated.
- Clinical / diagnostic notes for veterinarians: coding variants in human TBX3 cause a syndrome affecting the upper limbs and breast; the equine alleles are regulatory and no comparable condition has been reported in horses.
Key references:
- Imsland F, McGowan K, Rubin CJ, et al. (2016). Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses. Nat Genet 48:152-158. doi:10.1038/ng.3475. PMID 26691985.
- Adalsteinsson S (1978). Matings in Icelandic horses showing that a dominant dilution gene, D, turns bay into yellow dun with a dark mane and tail, chestnut into yellow dun with a dun mane and tail, and black into blue dun (mouse or grullo).
- 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.
- Melvin K, Ivey J, Johnston L. Equine Genetics: Basic Coat Color Inheritance. University of Tennessee Institute of Agriculture, UT Extension publication W891.