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Getting Informed…
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Although other breeds exhibit dun factor, this article is written in the context of quarter horses.
Dun factor is patterns of primitive black or dark brown markings on a diluted body. In the quarter horse world, dun factor is always present on duns, red duns and grullos. Dunalinos (palominos with dun factor) are sometimes registered as palomino. Roans and grays may also have a dun factored base color "under" the roan or gray coat. Bays, blacks, true browns, buckskins, sorrels, true palominos and chestnuts do not carry dun factor and do not have the ability to pass the factors on to their offspring.
History of Dun Factor in the
Quarter Horse
Dun factor has been passed on through ancient times to horses of
today. Because dun factor is a dominant characteristic that may not be
hidden through generations, some modern breeds have chosen to breed dun
factor out of the standard. Quarter horses received the majority
of their ancestral influence from Thoroughbreds with many crosses to other
breeds such as Draft, Morgan, Arab, and most importantly for the dun factor
world, Mustangs. Many, including this author, believe the Mustang gave
dun factor back to the quarter horse. The world's oldest Equus horse
fossils were discovered in the central United States, but the horse became
extinct about 8,000 years ago due to climate change and over-hunting.
In the 1500s, Spaniards reintroduced horses to the Americas through their
Spanish Mustangs. Descendents of these horses run wild in parts of the
western U.S. today. Many mustangs carry dun factor. Being it is
a dominant trait, it was easily inherited into the quarter horse.
The Dun Gene
The dun gene dilutes a horse's normal body color to a lighter shade by
narrowing the pigment flow through the hair shaft. It also stamps
certain "dun characteristics" throughout a horse's body. The dun gene
is not associated with the creme gene which creates buckskins, palominos and
cremellos. Although a dun factored horse may carry the creme gene, it
is not required and may not be visible to the eye. Buckskin dun and
dunalino are exceptions.
The Dun Factors
There are nine "officially" recognized dun
factors:
The Dorsal Stripe
The
dorsal stripe extends from the base of the mane to the tip of the tail.
On rare occasion, there may be a lightly lighter dorsal at the base of the
mane for a maximum of 6-8 inches. Dorsals are defined on the horse's
body and the "main" dun factor. In order to be considered a dun
factored horse in the AQHA (American Quarter Horse Assn), a horse must have
a dorsal stripe.
The Transverse Stripe
The transverse
stripe is a dark patch on each side of the whither. It may be solid or
stripes. Many non-dun factored horse exhibits signs of a transverse,
but it is commonly called "shadowing".
Zebra Stripes
Zebra, or leg
striping is darker lines horizontally across the legs. Another
variation looks almost like speckles on legs.
Face Mask and Cob Webbing
Dun factored
horses commonly have a darker face. The bridge of the nose is a "face
mask" and above and between the eyes is "cob webbing".
Frosted Mane and Tail
Frosting is lighter hairs overlaying the mane and
tail. Most dun factored horses exhibit this trait.
Neck Barring
Neck barring is dark striping vertically on a horse's
neck. It is in front of the transverse stripe. Although I
suppose it is possible, I have never seen a horse have a neck bar without
having a dorsal.
Tipped and Lined Ears
A dark edging along the ear and stripes horizontally
across. Most dun factored horses exhibit this trait.
Mottling
Dark speckles seen on lower part of neck, shoulders
and hips.
Rare Horizontal Tail Marking
Considered a rare marking, seen only on duns.
This is not widely seen in the quarter horse breed.
Breeding for Dun Factor
In order for a horse to pass dun factor onto it's offspring, it
must exhibit dun factor. Roan and gray modifiers may make dun factor
harder to see, but it would have shown through when the horse was a foal and
it's base coat was visible. Two non-dun factored horses may NOT
produce a dun factored foal and dun factor may not be hidden.
Sometimes horses are extremely dark, as in the case of Lobo grullos, where
it is near impossible to distinguish the body coat from the dun factor.
However, all horses show their dun factor at certain times of the year (gray
and roan are an exception). Dorsal stripes are always passed on to
offspring. The other dun factors may or may not be. Dun
factor does not appear to be passed on as a "group", meaning if both sire
and dam have a transverse stripe, the resulting dun factored foal carrying a
dorsal stripe may not. Likewise, there is evidence that a sire and dam
may produce a dun factored foal with additional exhibited dun factors that
neither parent exhibits. Dun factor genes are not mapped yet,
therefore they may not be tested for using DNA.
"Wishful Thinking" Dun Factor
Many foals are born with some dun characteristics such as a faint
dorsal or transverse stripe. These traits are commonly seen on bays
and some buckskins and palominos. Unfortunately, this isn't true dun
factor, but a phenomenon called "counter-shading" or "shadowing".
Horses exhibiting these traits are no more likely to produce dun factored
foals than those that do not. Normally counter-shading fades into
adulthood, but some horses carry it throughout their lives.
Learn more about the evolution of the horse at: http://www.pbs.org/wildhorses/wh_origin/wh_origin.html#
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