Dun coats
Grullo (black dun)
A grullo horse has mouse-gray or slate-colored hair on its trunk and neck, with a black mane and tail. Its dorsal stripe is dark and its legs may be barred. The grayish body hairs are still pigmented hairs.
Grullo (black dun): how the color works and is inherited
Grullo is Dun on a black base. Dun, associated with TBX3, distributes black pigment unevenly within the hair. The trunk looks lighter while the mane, tail and some markings remain black.
A grullo foal inherits the variants producing a black base and at least one Dun copy. It does not need a Gray parent: Gray and grullo have different causes.
Grullo (black dun): origins and the role of breeding
Dun is an ancient way of distributing pigment within a horse’s hair. DNA research shows that Dun and one non-dun variant existed long before domestication. Breeders did not invent the Dun markings. Fjord and Icelandic horses are among the modern breeds that carry this dilution.
Grullo combines two old traits: a black base and Dun. Selective breeding can make the combination more common, but did not originate the Dun mechanism.
Grullo (black dun): photographs of horses
A grullo Icelandic mare in her winter coat.
A close-up of the dark dorsal stripe on a grullo Konik.
Agawate, a grullo Lac La Croix Indian Pony mare.
A grullo Icelandic horse with black mane and slate-colored hair.
Dark leg markings on a grullo Konik.
A grullo Hucul’s head, with mane darker than the hair.
Photograph credits
Photographs have been resized. Photographs within scientific figures have been separated by cropping. Colors are preserved.
- A grullo Icelandic mare in her winter coat. — Paula Jantunen · Public domain
- A close-up of the dark dorsal stripe on a grullo Konik. — Tsaag Valren · CC BY-SA 4.0
- Agawate, a grullo Lac La Croix Indian Pony mare. — Llcips09 · CC BY-SA 4.0
- A grullo Icelandic horse with black mane and slate-colored hair. — Just chaos · CC BY 2.0
- Dark leg markings on a grullo Konik. — Tsaag Valren · CC BY-SA 4.0
- A grullo Hucul’s head, with mane darker than the hair. — Überraschungsbilder · CC BY-SA 3.0
Grullo (black dun): telling similar coats apart
A Gray horse gradually becomes whiter as white hairs replace colored ones. A grullo horse gets its shade from colored hairs lightened by Dun rather than from progressive whitening.