Dun is one of the dilution genes that affects both black and red pigment. Unlike Silver or Cream, it has the ability to change the physical appearance of all Black, Bay or Chestnut based horses to some degree. Because Dun does not cause the horse to look any different when it's in present in one dose or two, this gene would not be considered an incomplete dominant.

Dun is found in many breeds such as Quarter Horses, Spanish Mustangs, Miniature Horses, Icelandic Horses and many European pony and draft breeds. Fjords and the Sorria are exclusively Dun and in some breeds such as the Arabian and Thoroughbred, Dun doesn't exist at all.

Since Dun closely resembles Buckskin when it's present on a Bay base color, it's common to hear the term Buckskin and Dun used to describe any horses that have a tan colored body with black points whether there are primitive markings present or not. The difference between this gene and the Cream dilution gene is that Dun also causes primitive markings to be present on the horse. These are a shade or two darker than the body color and include the following traits.

Dorsal Stripe

Wide dorsal stripe on a Bay Dun Mustang. ©Mustang

This is a dark line that goes from the base of the mane to the base of the tail. Sometimes it goes through the middle of the mane, tail or both giving the horse a dark streak through the middle of each. This trait is always present on a Dun horse and should not be confused with the more subtle dorsal stripes caused by countershading. Terms associated with this Dun trait are: eel stripe, list, lineback and backstripe. You may hear people call Dun colored horses, "lineback Duns".

Mock dorsal stripe on a dark Bucksin Miniature Horse foal. ©Equine Color

Many times foals are born with a dorsal stripe (and other primitive markings) that usually disappears or becomes less visible after they shed their foal coat. These are not "true" Duns, this is like camouflage, similar to fawns or baby lions having spots that fade as they get older. The only way a foal can be a true genetic Dun is if one of the parents is also Dun. This may be hard to determine if the parent(s) are very dark or have white patterns superimposed over the topline and/or legs.

Zebra Stripes
Another trait caused by the Dun gene is horizontal marks on the legs of the horse. These range from above the hock or knee to below and usually fade into the dark part of the leg. These lines are commonly called Zebra or Tiger stripes. These can be very dark like in the photo or so light they are hardly visible. These marks may not appear on all Dun horses and it is sometimes very hard to see them on darker shades.

Cobwebbing on a Bay Dun Mustang. ©Mustang

Cobwebbing
Some Dun horses have darker rings or stripes on their foreheads. This is commonly called cobwebbing or spiderwebbing.

Sulphur's Chance Sulphur Springs Mustang* Courtesy of Nature's Mustangs

Bay Dun

Just as with all dilution type genes, Dun dilutes the the base color and as Dun can dilute both black and red pigment the Dun dilution causes different types of Dun.

As Bay is probably the most prevalent color in horses, Bay Duns are probably the most common type of Dun. This group is caused by the Dun gene on Bay and as Bay comes in many shades, so does Bay Dun. The Dun gene seems to be more concentrated in diluting the body of the horse than the mane, tail, legs and head. This would explain why the points on Duns are a darker shade or in the case of Bay Duns, the mane, tail and legs do not seem to be diluted much at all.

The body coat of a Bay Dun will be a shade, ranging from dark to light, of tan or yellow. Horses this color usually have heads or a face "mask" that is a shade darker than their body color. The head of a Buckskin will be the same color as the body.

The terms used for this group of Duns will vary with shades and terms used for these various shades and will also vary with people's own descriptive terms and opinions. The most common name for the Bay Dun color is Zebra Dun.

Some people use the term "silver" in conjunction with Dun, whether they call it a "Silver Dun" or "Silver Grullo". This may cause some to believe that the horse also carries the Silver gene. When using descriptive terms it's usually just best to stick to the term that best fits what the horse is genetically, then there is no cause for confusion. That is why horses on this site are referred to as Bay Dun, Chestnut Dun or Black Dun.

All Bay Duns, regardless of shade, or the term you personally use to describe it, will have black legs although on some the black may be faded to a chocolate color and also faded at the coronary band. The mane and tail will also be black but just like on a Black or Bay it is subject to sunburn and fading from the weather.

Tibbs Cougar Dunn Miniature Horse Courtesy of Tibbs Family Miniatures

The only exception to this rule is if the horse also carries other genes which dilute or modify the legs, mane and tail. The horse below is an example of a Bay Dun that has a light colored mane and tail and sooty colored lower legs. This is caused by the Silver gene. This dilution gene only dilutes black pigment, it turns the black pigment in manes, tails, legs and bodies to a brownish chocolate, sooty, or light silvery color. How do we know that the horse below is not a Palomino with the Dun gene? Because she has produced several Bay based foals by Chestnut or Chestnut based stallions. If she was Palomino her base color would also be Chestnut and following the centuries old rule of Chestnut to Chestnut will only make Chestnut, she would only produce Chestnut based foals when bred to Chestnut based stallions. Included at the left is a photo of one of her foals whose sire is Palomino. His Bay base color proves that her base coat cannot be Chestnut.

Chestnut Dun

I'm All Better Now - AQHA Photo Uploaded to Photo Albums by joe@buckskinquarterhorses.com

This group of Dun colored horses are from the red based color Chestnut. Since they come from red based colors they do not have the black points. This group is generally referred to as Red Dun. On this site we call them Chestnut Duns so as not to be confusing their base color.

A Chestnut Dun's body coat will be very similar to that of a Chestnut but it may be a shade or two lighter and will be accompanied by the primitive marks in a darker red shade. Likewise the head will also be a darker shade of red.

The shades of a Chestnut Dun range from dark to light, many times the light shades will be called Claybank Dun. Some believe the genetics for a Claybank Dun are different than a regular Chestnut Dun. The genes of all red based Dun horses are the same, just as the genes for all red based horses without the Dun gene are the same. It's just the shade of the base color and the amount of dilution the Dunning gene does to that base, that differs. As with Bay Dun, regardless of the term you personally use to describe this color, all Chestnut Duns will not have black points.

Flicka - Unregistered AQHA Courtesy of Dean & Sally Babcock

Skippas Dun Smokin - AQHA Courtesy of Southern Comfort Ranch

Black Duns are more commonly called Grullo (GREW-yo). This is the most rarely seen shade of the Dun gene group. Since it is a Spanish word, females are referred to as Grulla (GREW-ya) and males as Grullo. This color is caused by the Dun gene on a Black.

Grullos are generally a smoky or bluish color and can vary from light to dark. Grullos consistently have black points and usually have a dark or even black head, which is an identifying characteristic of the Grullo group. The primitive marks on Grullos are characteristically black.

Just as with all colors shades of Grullo can vary from light to dark.

Jaz Ta Little Luck - AQHA Courtesy of Gail Lyon

As with Buckskins and Bay Duns a Grullo will have the black legs but they may fade slightly at the coronary band. The mane and tail will also be black.