White Horses and Genetics
The history of white horses is given a little illumination today, in a study released in Nature Genetics on July 20, 2008.
A picture of the late actor Clayton Moore in his Lone Ranger costume with his stunt horse Silver. Hi ho Silver! Away!
Photo Credit: Online USA / Getty Images
White horses undoubtedly have a special place in ancient history. The pure white horse has been associated with magic and kings and heroes and even the good guy in cowboy serials of the 1950s. Mythical versions of white horses are found in the flying horse Pegasus from Greek mythology and unicorns from the Babylonian epic of Gilgamesh. An early reference to white horses is found in the writings of Herodotus, who reported that white horses were held as sacred animals in the Achaemenid court of Xerxes the Great (ruled 486-465 BC).
White Horses are Gray Horses?
White horses don't start out that way. They are born with dark hair that fades to white as the horse matures; the hair of such horses turns pure white between about 6-8 years old. White horses are often called gray horses because the coloration is an aging process. Normal skin coloration of horses is black, and the white hair gives the horse a gray visual appearance. Many gray horses have skin discolorations; some are speckled and some have red blotches called "blood marks."
Gray horses occur in various percentages among several horse populations of the world, including Arabian horses, Shetland ponies, Icelandic ponies, and of course the famous dancing Lipizzaner horses, among others. According to a new study led by Leif Andersson of Uppsala University and reported in Nature Genetics on July 20, 2008, the gray/white coloration is caused by a specific genetic mutation recognized in all gray/white horses, and never seen in any non-gray horse. This means that all the grays descended from a single ancestor horse, probably an Arabian horse and at least 1,000 years ago--at any rate, before Iceland's ponies were developed as a separate horse population.
That the selection for white hair was intentional seems likely, given the deep historic cross-cultural mythology associated with white horses. Research by Andersson and colleagues bolsters this argument, providing data that shows that the pigmentation variations within the horses is associated with melanomas--skin cancers. Between 70 and 80% of gray horses older than 15 years have melanomas, shortening their lives by several years. The existence of white horses in many different populations, despite their propensity to develop skin cancer and die young, is certain evidence of human interference.
Source and Further Information
See More on White Horses for information on white horses in ancient history.
Rosengren Pielberg, Gerli, et al. 2008 A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse. Nature Genetics Advance Online article published 20 July 2008. DOI doesn't appear to be working as of yet. See Nature Genetics
Comments
Being a city girl transplanted to a country town, I once showed my “ignorance” at a county fair by exclaiming,
“What a beautiful white horse!”
I was promptly informed that there is no such thing as a “white” horse, there are only gradations of grays, up to and including “blacks”.
Not knowing whether I was being “guppied” again, I said nothing and moved on.
BTW, here, being a “guppy” means you’ll swallow anything!
So, was I being “guppied”????
Well, I guess it depends. Because, yes, that’s right, that white=gray, and the coloration is a combination of white hair + skin color and it varies between white and gray. And it seems apparent that the white/gray ones are genetically different than other colors.
Then they were only partly putting me on? Because, surely, the white/gray gene wouldn’t/couldn’t include black. I would (how I hate this word) assume that black would be a gradation of a brown horse. Or even have been bred purposely for it’s color as well.
I’m so confused!
You know, I just don’t know. I think the hair and skin are related; but I don’t know for sure. There definitely are white horses—but they aren’t born that way, so you could say there weren’t any white horses, they just age into the job description.
There ARE true white horses. They are not all grays! They have dark eyes, PINK skin, and they are *born white*. Grays are born dark and turn “white”, but retain dark skin for the most part. Currently, there are two different (known) genetic causes for true white horses. One gene was identified and is currently called the Sabino 1 (or Sb1) gene. For a horse with this gene to be pure white, they must be homozygous for the Sb1 gene. The study was published in 2005. They are born white, have dark eyes and pink skin.
Then more recently (late 2007) genetic researchers identified 4 different mutations for horses born white with pink skin and dark eyes. These are 4 mutations of the same gene and they are all referred to as Dominant White genes. Each mutation occurs in a different breed and are suspected to be spontaneous mutations. The 4 different breeds are Thoroughbred, Camarillo White (which seem to be descended from the original white horses from the White Horse Ranch troop), Franches-Montagnes, and Arabian (a friend of mine has 2 of the Arabians, both sired by the same white, not gray, stallion). Horses with a Dominant White gene are so far only found to be homozygous for the mutation. It is suspected that homozygotes are embryonic lethal (fetus not viable). A Dominant White horse will produce 50% white offspring.
From color photos that I’ve seen of The Lone Ranger’s horse, Silver, he was a true white … NOT a gray. He had dark eyes and pink skin. He most likely was of breeding from the original White Horse Ranch horses, which were true white (dark eyes, pink skin, born white). Though he could also have been a homozygous Sb1. But with that pink skin, he was definitely not an aged gray.
For Susan … gray horses are born any and all colors … black, brown (brown is a black horse modified by the “At” gene), bay (a black horse modified by the “A” gene), chestnut, palomino, buckskin, dun, etc, etc.). Just as humans can have various colors of hair that eventually turns gray, the same is true of horses. It’s a gradual depigmentation of the hair. The skin remains dark, however. I cannot recall the scientific explanation of how this happens off the top of my head, though. To better understand horse color genetics, one needs to study it on a good, reliable forum, as most of the books are incredibly out-dated or just plain inaccurate in some places. Even some color genetics forums and web sites are dangerous because they are run by individuals who may not be up-to-date on the topic. This particular web page on white/gray horses, for instance, is inaccurate, sadly. Because there ARE true white horses, yet this site/page says this isn’t so. It identifies The Lone Ranger’s horse as a horse gone gray, when that is not accurate. It definitely requires a commitment to try to keep up with the latest research findings, which is not always easy to do.
Correction to my first comment!! Where I wrote:
“Horses with a Dominant White gene are so far only found to be homozygous for the mutation.”
It should read:
“Horses with a Dominant White gene are so far only found to be HETEROZYGOUS for the mutation.”
Sorry! I didn’t proof read very well before posting it
(
i need to know what color of a horse is most likley to get skin cancer and why? and what breeds they normaly are mosty common to get sikin cancer? WHY?
Re; Nancy’s post (5)
I have a Spanish Colonial [Spanish Mustang] mare who has tested SB1/SB2 for the sabino gene. She is solid white with blue spotting and freckling on the skin with pink skin regions.
Interesting site as I’m trying to find out more about whether the Spanish horses that cae with the conquistadors to the New world in the early 16th century would have had any with pink skin or did this evolve later.