When the average horse person thinks of dun horses, they are typically picturing a bay dun or a buckskin dun. This dilution gene, though, can affect horses of every coat color.
In fact, depending on the other genes the horse may carry, the horse’s color may not appear dun at all.
In order to understand the dun gene in horses, we should first look at how it is represented genetically, and then how it affects the three common coat colors of chestnut, black, and bay.
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Dun Horse Color Gene
The dun gene in horses is dominant. That means that if a horse has even one copy, the gene will be expressed. This gene can, however, be camouflaged by other genes.
So how do you know if a horse carries the dun gene?
On the large majority of horses, you can tell if they carry the dun gene by looking for the telltale dorsal stripe running down the back of the horse.
There may be other characteristics visible as well. This can include leg barring and countershading on the mane and/or tail.
For horses where dun is suspected but believed to be masked by other color genes, there is a genetic test offered by various agencies. To find a testing facility, check out my post on equine DNA testing labs.
The dun gene is represented in genetic tests by a capital “D” when present and a lowercase “d” when absent. There are three possible test results for all horses:
- DD – Homozygous Dun: Horse carries two copies of the dun gene.
- Dd – Heterozygous Dun: Horse carries one copy of the dun gene.
- dd – No Dun: Horse is not dun; it does not carry any copies of the dun gene.
Dun Horse Characteristics
Horses with the dun gene typically express “wild” type characteristics, including:
- Dorsal Stripe
- Leg Barring
- Mane / Tail Highlights
These color features evolved to help keep wild animals safe from predators. In fact, the most extreme form of this type of color defense in the wild is in zebras.
But we can also see it in other wild animals like the okapi and even wild goats.
Granted, these are far less prominent in the horse, but it is interesting to note the similarities.
Common Shades of Dun
A red dun occurs when the dun gene is layered on an otherwise red horse.
The dun gene causes the body of the horse to lighten while the mane and tail typically stay their normal dark red color. The dorsal stripe is typically easily visible; however, leg barring may not be as visible.
A red dun horse, if genetically tested, will come back with one of the following gene patterns:
- ee DD – homozygous red, homozygous dun
- ee Dd – homozygous red, heterozygous dun
On this red dun mustang below, you can see black lines above his front right knee; this is the leg barring from his dun gene.
Chestnut / Sorrel vs. Red Dun
Below you can see the difference between a red horse without the dun gene and the horse above with it.
You can see how the body is notably lighter than the mane for the red dun horse but mostly the same color for the sorrel horse on the left:
Sometimes it isn’t as easy to tell. Some horse owners may body clip or shave their horse’s long winter coat to help keep them cool when riding.
Sorrel horses who are body clipped will appear to be red dun, but they will be missing the leg barring and dorsal stripe.
Additionally, even in summer, some sorrel horses may just naturally have a little bit lighter body color. When in doubt, a genetic test can always tell you for sure if your horse has the dun gene or not.
Bay Dun / Zebra Dun
The color bay dun is also sometimes called classic dun or zebra dun. For this color horse, the bay color is diluted slightly by the dun gene but the horse maintains their beautiful black mane.
If DNA tested, a bay dun horse will come back with one of the following eight gene sequences:
- EE AA DD – homozygous black, homozygous agouti, homozygous dun
- EE Aa DD – homozygous black, heterozygous agouti, homozygous dun
- EE AA Dd – homozygous black, homozygous agouti, heterozygous dun
- EE Aa Dd – homozygous black, heterozygous agouti, heterozygous dun
- Ee AA DD – heterozygous black, homozygous agouti, homozygous dun
- Ee Aa DD – heterozygous black, heterozygous agouti, homozygous dun
- Ee AA Dd – heterozygous black, homozygous agouti, heterozygous dun
- Ee Aa Dd – heterozygous black, heterozygous agouti, heterozygous dun
The grulla color tends to be a very popular color, especially in the quarter horse breed. This is partially due to the fact that it is one of the rarer colors in most breeds.
A grulla horse is a horse that was born with a solid black base and the dun gene.
This dun gene, when added to a true black horse, causes the body color to dilute to a beautiful mousy grey color. The mane, tail, and legs stay a dark black which creates a beautiful color contrast.
The genetic makeup of a grulla horse would be one of the following:
- EE aa DD – homozygous black, no agouti, homozygous dun
- EE aa Dd – homozygous black, no agouti, heterozygous dun
- Ee aa DD – heterozygous black, no agouti, homozygous dun
- Ee aa Dd – heterozygous black, no agouti, heterozygous dun
One thing to note is that a grulla horse can hide the cream gene as well. In that case, the horse would be considered a smoky grulla.
The cream gene doesn’t have any effect on the color, but the horse could potentially have palomino or buckskin foals. The horse below is a smoky grulla.
Other Dun Colors
The dun variations listed above are the most common. Those show how dun interacts with the three base horse colors: red, black, and bay.
Dun is just a modifier on those base colors and, as such, can occur in combination with a variety of other modifiers.
A dunskin is a buckskin horse who also has the dun gene. This color is sometimes called a buckskin dun as well. This color horse has a bay base with one copy of the cream gene and the dun gene (one or two copies).
This horse is typically much lighter in color than a normal buckskin and has noticeable leg barring and a dorsal stripe.
Here you can see the difference between a buckskin and a dunskin. Many dunskins will also have lighter-colored highlights in their mane and tail.
The difference between a dunskin and a smoky grulla is the agouti gene.
A dunskin is a bay horse with one or more agouti genes, the cream gene, and at least one dun gene. A smoky grulla is a black horse with no agouti gene, the cream gene, and one or more dun genes.
The genetic makeup of a dunskin is one of the following:
- EE AA DD Crcr
- EE Aa DD Crcr
- Ee AA DD Crcr
- Ee Aa DD Crcr
- EE AA Dd Crcr
- EE Aa Dd Crcr
- Ee AA Dd Crcr
- Ee Aa Dd Crcr
Grey is a common modifier and will cause a horse to eventually turn all white (or possibly flea-bitten). Because of that, grey horses can often “hide” the dun gene.
Keep in mind that a grey horse must have at least one grey parent.
The best way to tell if a grey horse is a dun is to get a DNA test done.
Grey dun horses can be any of the following:
- Red Dun + Grey
- Bay Dun + Grey
- Grulla + Grey
- Any of the above, plus any other modifier
The palomino dun, also called a dunalino, occurs when the dun gene and cream gene pair on an otherwise chestnut horse.
Just as with palominos, the actual final shade of a dunalino can vary from horse to horse. Palominos range in color from light (Isabella) to dark (chocolate), and so too will the color range for a palomino dun vary.
Sometimes it is hard to differentiate a palomino dun from a palomino without the dun gene. A DNA test can confirm if the dun gene is present.
The DNA report for a palomino dun horse will appear as one of the following:
- ee DD Crcr – homozygous red, homozygous dun, heterozygous cream
- ee Dd Crcr – homozygous red, heterozygous dun, heterozygous cream
The silver gene is another dilution gene that, like dun, affects the body color of the horse. The silver gene will also lighten the mane color, often turning the mane and tail nearly completely white.
This horse is a black silver horse (no dun gene):
The roan gene in horses causes small white hairs to appear scattered throughout the body. There is typically more white in winter and less in summer.
Roan can appear on any base color.
For non-dun horses, we would call these blue roan, bay roan, and red roan. When combined with dun, it’s often easiest to say “dun roan,” but here are some variations (Keep in mind this isn’t a comprehensive list!):
- Red Dun Roan: Red Dun + Roan
- Bay Dun Roan: Bay Dun + Roan
- Grulla Dun Roan: Grulla + Roan
- Smoky Grulla Roan: Grulla + Cream + Roan
- Palomino Dun Roan (Dunalino Roan): Palomino (Dun + Cream) + Roan
- Dunskin Roan: Dunskin (Bay Dun + Cream) + Roan
Champagne is a modifier that is common in some breeds, like Tennessee Walkers, and rare in others, like quarter horses. Depending on the base color, champagne can have a striking effect on the color of a horse.
The horse below is a quarter horse stallion I once owned. He is a red dun champagne.
While he may look “palomino,” he does not have a cream gene at all. The champagne gene dilutes the red color even further and also is responsible for the beautiful shine you see.
The dun gene can have such a fun impact on a horse’s color. It’s responsible for some of the most popular colors in the horse world and can be found in many breeds. The dun gene typically lightens a horse’s body color and adds both a dorsal stripe and leg barring.