Horse Color Genetics: Dun

Review: E=black, A=bay, G=gray, C=cream.

The next color is dun. What is dun? A dun horse is a horse that receives special markings through its genetic code. Dun horses always posses a very clear dorsal stripe, or a black stripe that runs across their spine. Dun horses commonly have faint stripes on their legs, and sometimes a faint dark shading across their shoulder blade. Duns always have a darker mane and tail than their base coat; whether the mane and tail is black depends on whether they also have an E gene. The only exception to this rule is a palomino dun, whose mane and tail will still be white, or cremello dun. In the second picture, the horse has a dark bar along his shoulder; some duns may or may not have this. There are lots of duns with dorsal stripes below!

The dun gene, or D, is a simple dominant, meaning that whether the horse is homozygous dominant or heterozygous, it will effect the horse in the same way. When I say almost, I mean that depending on the base coat, it will vary. It does not necessarily effect different colors in the same way; the original color without the D gene will still show through.

The D gene has a lightening effect on any coat. Usually combined with a chestnut horse (ee, aa), black horse (E?, aa), or a bay horse (E?, A?), the base coat will show through, but if it is a bay horse (E?, A?), the rules of how it goes can be confusing. The dun gene pushes any existing black to the edges, similar to to the A gene; however, it usually leaves the face and legs darker.

There are several different technical terms within dun, depending on what the underlying coat is. The most common color is 'classic dun', or sometimes 'bay dun' or just 'dun'. Bay dun (E?, A?, D?), when the D gene is added, dilutes the dun to a very light color. This color is usually the same or nearly the same as a buckskin, although there is a clear difference; buckskin by itself usually doesn't have the dorsal stripe. The horse below looks an awful lot like a buckskin, right? But he is actually a bay dun. He is so cute!

To make matters more confusing, there is such thing as a buckskin dun. This horse's code will look something like this: E?, A?, Cc, D?. This means that it was a bay, then diluted to buckskin, then diluted further to a dun. Buckskin bay, or dunskin, is more of a bright golden, while a bay dun may be slightly duller, more brown.  If you aren't sure, you may need to have your horse genetically tested. If there is ever any question as to which, if you know about the parents that could help. Remember: buckskin is the result of a bay with a cream gene. If there is no cream gene in either of the parents, then you know it is a bay dun. See how much more golden he is? Much less brown.

Chestnut dun, or red dun, turns the horse's chestnut coat to a lighter, more rosy shade. Remember, chestnut horses are recessive black, so the mane and tail are not black. They will turn a darker shade than main coat though. A clear dorsal stripe still shows, but it will probably be dark red instead of black.

Black dun horses are called grullo (or grulla (pronounced Grew-yo, or Grew-ya) depending on who you talk to). Grullo horses are black horses with the dun dilute; they turn almost a blue roan color, or sort of grayish with a dark head and dun characteristics. 

Dun can also effect horses with other color genes, including pinto, roan, palomino, among others. I won't post pictures of them all; basically dun will always lighten a color, and add a dorsal stripe. The horse below is a tobiano dun.

There is something else called 'countershading' that can sometimes be confused with the D gene. Countershading looks like a dorsal stripe, but it won't be very clear, or might go halfway up the back, or may be a thicker line. A dorsal stripe should be very clear and straight, like someone took a juicy dark marker and ran it up their back. If the stripe is kind of thick with not clear edges, then it is countershading. The horse below is so close! But....it isn't complete. He is not a dun. The stripe isn't clear, and it doesn't go up the back all the way.