Dun is considered to be one of the most primitive horse colours. This is believed because of the primitive horse breeds come in Dun. Recent discoveries of a nearly intact horse hide from the extinct wild Yukon horse shows hints that this breed was likely Dun. At one time there appeared to be three different genetic mutations of Dun, however, recently an announcement was made by Animal Genetics Inc stating that they have found the Dun allele and breeds across the three theorized Dun categories test positive for this allele, showing that there is only one Dun mutation.

Dun Allele Genetics

The Dun mutation proved to be one of the hardest mutations to map. Animal Genetics Inc found the Dun mutation in 2014 resulting in a true DNA test is available for the Dun allele by Animal Genetics Inc. Other labs still offer the less accurate Dun zygosity test. The Dun allele is dominant.

Dun Phenotype

Dun tends to lighten the body colour and leave the head, lower legs and mane and tail alone, this is seen on both red based, black based as well as Agouti combos however the degree of difference in shade does depend on the individual horse. Dun horses have what are called Dun Factors. These are specific traits seen specifically with Dun horses. Most notable is the Dorsal Stripe, a marking that all Duns must have to be considered a Dun. A horse with the Dun allele and no other genes will have black skin and dark brown eyes.

Dun Factors

There are a large list of Dun Factors; markings and patterns that are associated with Dun. One factor, the Dorsal Stripe is mandatory for the Dun allele. If the horse doesn’t have a Dorsal Stripe, it’s not a Dun. However, this doesn’t mean that all horses with Dorsal Stripes are Dun; horses that are not Dun with a stripe have what is called a False Dorsal Stripe (this is often created by the Sooty gene). Other then the Dorsal Stripe a Dun may have any collection of Dun Factors, from a large many to a rare few. The intensity of the Dun Factors can vary largely as well. The Dun Factors are as follows:

Dorsal Stripe: All Duns have dark stripe down the horse’s spine.
Leg Barring or Zebra Stripes: These are dark stripes that appear on the legs, generally around the knees and hocks.
Cob Webbing: Dark lines that appear around the horse’s forehead which can resemble spider webs.
Frosting: This is when sections of the hairs in the mane (usually on the sides) are lightened to white or cream. This is best seen in the Fjord breed.
Face Mask: A darker cloud of hairs on their face
Guard Hairs: White hairs at the base of the tail. This is best seen on the Fjord breed.
Dorsal Barbs: Little spikes of dark hair come off of the dorsal stripe.
Ear Tips and Bars: Dark spots on the tip of the back of the ears, as well as dark bars across the back of the ears.
Dark Points: Where the front of the knees and cannon bone, etc, are darker then the back.
Mottling: Not to be confused with the term Mottling of the skin, give the appearance of ‘reversed dappling’ or dark circling patches found on the horses legs and/or shoulder areas, it is only visible on the sleeking summer coat of the horse.
Neck Shadow/Stripes: Dark areas on the neck either in a large splotch resembling a shadow or in large stripes.
Shoulder Stripe/Shadow: A stripe coming off of the dorsal stripe running across the withers or a large dark area around the same area.

Basic Dun Colours

Below is a chart to help show what the basic colours of the Dun allele are. A basic Dun colour is when the Dun allele is combined with Extension and Agouti colours. On the left we see those basic Extension and Agouti colours and on the right we see what those colours are when the Dun allele is present. Arguably more then any other dilute, Dun has the most names given to a single coat, I have chosen to use the most basic names for the coats in attempt to keep the chart universal.

Alternative Names

Red Dun: Chestnut Dun, Claybank Dun, Norwegian Fjord: Rodblakk

Black Dun: Blue Dun, Mouse Dun, Grullo, Grulla, Norwegian Fjord: Gra

Seal Brown Dun: Brown Dun

Bay Dun: Dun, Zebra Dun, Norwegian Fjord: Brunblakk

Check out the Dun Horses album to see pictures of Dun horses!