Dun is a coat color in horses produced by the dominant D-locus dilution gene, which lightens the body while leaving the mane, tail, lower legs, and primitive markings at full pigment intensity. Every dun horse carries at least one copy of the D allele; two copies are visually identical to one. The gene does not affect black pigment (eumelanin) and red pigment (phaeomelanin) equally, which produces three distinct base expressions: bay dun (classic dun), black dun (grullo or grulla), and red dun.
The defining mark of a true dun is the dorsal stripe — a dark line of full-intensity pigment running from the poll or withers to the tail. Most duns also show leg barring (horizontal stripes on the lower legs), and some display a transverse shoulder stripe or cobwebbing on the forehead. Dun leg barring is distinct from brindle striping, which differs from dun leg barring in being irregular, distributed across the trunk, and caused by chimerism rather than a dilution gene. These markings are called primitive markings because they appear in wild equids, including the Przewalski’s horse and the onager, and are thought to represent the ancestral equine coat pattern. The full guide to coat colors covers how the D gene interacts with base coat genetics.
Dun is often confused with buckskin. Buckskin is produced by the cream gene acting on a bay base, producing a gold body with a black mane and tail but no primitive markings. A dun horse has primitive markings; a buckskin does not. A horse carrying both the D allele and the cream allele on a bay base is a dunalino, showing both dilutions simultaneously.
Dun coloring appears across many breeds and is particularly common in breeds with ancient roots: the Sorraia, the Norwegian Fjord, and the Konik. The color does not affect gait or soundness and carries no health linkage. Among the recognized base dilutions, dun is genetically distinct from cream, champagne, and silver.
Among breeds with ancient dun genetics — Sorraia, Konik, Norwegian Fjord — another rare modifier pattern occasionally appears alongside dun markings: rabicano, a white-ticking pattern concentrated at the flanks and base of the tail. Rabicano is not a dilution gene; it is a separate allele whose visual expression can overlap with light-roaned dun horses and cause misidentification. The distinction between rabicano and roan, and how both differ from brindle, is detailed at brindle vs. rabicano.
Further Reading
Further reading on the D-locus gene and how dun interacts with other dilutes: