Gray horse
Gray horse | |
---|---|
Other names | Grey |
Variants |
|
Genotype | |
Base color | Any |
Modifying genes | Graying gene (G) dominant when single allele present |
Phenotype | |
Body | Born any color, lightens with age until fully white, may develop pigmented speckles |
Head and Legs | Head may be first part of body to lighten, legs may be among last parts of body to lighten |
Mane and tail | May not gray at same rate as body, can be lighter or darker |
Skin | Usually black, except under white markings present at birth. |
Eyes | Usually dark brown, unless affected by other genes which lighten eye color |
Other notes | When gray gene is present, horse will always become gray, may be masked by white genetics |
A gray horse (or grey horse) has a coat color characterized by progressive depigmentation of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike some equine dilution genes and some other genes that lead to depigmentation, gray does not affect skin or eye color.[1] Gray horses may be born any base color, depending on other color genes present. White hairs begin to appear at or shortly after birth and become progressively more prevalent as the horse ages as white hairs become intermingled with hairs of other colors. Graying can occur at different rates—very quickly on one horse and very slowly on another. As adults, most gray horses eventually become completely white, though some retain intermixed light and dark hairs.
The stages of graying vary widely. Some horses develop a
Gray horses appear in many breeds, though the color is most commonly seen in
People who are unfamiliar with horses may refer to gray horses as "white". However, a gray horse whose hair coat is completely "white" will still have black skin (except under
While gray is classified as a coat color by
Prevalence
Gray is common in many breeds. Today, about one horse in 10 carries the mutation for graying with age.
Gray also affects spotting patterns of pintos and leopard complex horses such as Appaloosas. Its effects wash out the contrast of the markings of these patterns, sometimes colloquially described as "ghosting."
Changes in the color of gray horses
A gray
Different breeds, and individuals within each breed, take differing amounts of time to gray out. Thus, graying cannot be used to approximate the age of a horse except in the broadest of terms: a very young horse will never have a white coat (unless it is a true
This change in hair color means that the same gray horse will appear to be a different color over time, sometimes resulting in a need to change the color noted on breed registry papers.[5] Other times, people traveling with gray horses who have a pure white hair coat have encountered problems with non-horse-oriented officials such as police officers or border guards who are unclear about a horse who has papers saying it is "gray" when the horse in front of them appears white.[6]
To further complicate matters, the skin and eyes may be other colors if influenced by other factors such as white markings, certain white spotting patterns or dilution genes.
Name | Image | Description |
---|---|---|
Foals | Horses in their first year begin to show a few white hairs as their foal coat sheds. Some foals show gray hairs around their eye, muzzle and other "soft" areas at birth, others do not show white hairs until they are almost yearlings. | |
Young gray horses | An intermediate stage typically seen in young horses in the early stages of turning gray is when white hairs are mixed with the dark birth color. In horses born black or dark bay, the horse shows mostly black and white hairs intermingled on the body. This is sometimes called "salt and pepper", "iron gray", or "steel gray." This is the most common intermediate form of gray, which can give a silvery look to the coat. A reddish tinge, called a "rose gray", describes this intermediate stage for a horse born a chestnut or bright bay. Young horses just starting to gray out are sometimes confused with roans, but a gray continues to lighten with age, while a roan does not. Roaning also causes fewer white hairs on the legs and head, giving the horse the appearance of dark points, which is usually not true of gray. | |
Dapple gray | Light and dark areas form a dappled pattern of dark rings with lighter hairs on the inside of the ring, scattered over the entire body of the animal. Not all grays dapple, and it is an intermediate stage, usually seen in young adult horses, often considered highly attractive. The horse will continue to become lighter. Dappled grays should not be confused with the slight dappling "bloom" seen on horses of other colors that are in excellent condition, as "bloom" dapples disappear should the horse lose condition. | |
Late stage graying | As grays become lighter with age, a few areas, especially around the flanks and legs, retain some color | |
Complete depigmentation | Nearly all hairs are white. A horse at this stage may be done changing color, or may begin to develop fleabitten pigment. Gray horses with a completely white coat can be distinguished from a white horse by their underlying black skin, particularly around the eyes, muzzle, and genital area. | |
Fleabitten gray | Flea-bitten gray is a color consisting of a white hair coat with small pigmented speckles or "freckles". The flea-bitten pattern is seen primarily in heterozygous Grays.[7] Most horses who become flea-bitten grays still go through a brief period when they are pure white. The amount of speckling varies between individuals and density of speckling may increase as the horse ages. Some horses may appear almost pure white, with only a few speckles observed on close examination. Others may have so many speckles that they are occasionally mistaken for a roan or even a type of sabino. | |
Blood marks | One unique form of gray, genetically related to flea-bitten gray, are "blood marks" or a "bloody shouldered" horse. This is an animal that is so heavily pigmented on certain parts of the body, usually the shoulder area, that it appears as an irregular, almost solid pattern—as if blood had been spilled on the horse, hence the name. Blood marks can change size and shape as the horse ages. Arabian horse breeders claim the Bedouin people considered the "bloody shoulder" to be a prized trait in a war mare and much desired.[8] |
The genetics of gray
The gray gene (G) is an autosomal
In 2008, researchers at Uppsala University in Sweden identified the genetic mutation that governs the graying process. The study revealed that all gray horses carry an identical mutation that can be traced back to a common ancestor that lived at least two thousand years ago.[2] The discovery that gray can be linked to a single animal provides an example of how humans have "cherry-picked" attractive mutations in domestic animals.[7]
Gray is controlled by a single dominant
Researchers suggest the pigmented speckles of the "fleabitten" gray, as well as more intense reddish-brown colored areas called "blood" markings, may be caused by a loss or inactivation of the gray allele in some of the somatic cells as that would explain why the speckles are more common on heterozygous grays than homozygotes.[7]
Melanoma in gray horses
The identification of the gray mutation is of great interest in of medical research since this mutation also enhances the risk for
The study of gray genetics has pointed to a molecular pathway that may lead to tumour development. Both STX17 and the neighboring NR4A3 gene are overexpressed in melanomas from gray horses, and those carrying a loss-of-function mutation in ASIP (agouti signaling protein) had a higher incidence of melanoma, implying that increased melanocortin-1 receptor signaling promotes melanoma development in Gray horses.[7] Some studies indicate as many as 66% of melanomas become malignant, though other studies have found much lower rates, and in one case, zero.[12]
Horse coat colors sometimes confused with gray
White horses
Many people who are unfamiliar with horses refer to a gray horse as "white". However, most
Roan
Some grays in intermediate stages of graying may be confused with a roan or a rabicano. Some heavily fleabitten grays may also be confused with roans. However, roans are easily distinguishable from grays: roan consists of individual white hairs on a dark base coat, usually with the head and legs of the horse darker than the rest of the body. Rabicanos also have intermixed white hairs primarily on the body with a dark head. With gray horses, the head is often the first area to lighten, especially around the eyes and muzzle. Also, roans do not lighten with age, while grays always do.
The varnish roan is another unusual coloration, sometimes seen in Appaloosa horses, that, like gray, can change with age, but unlike gray, the horse does not become progressively lighter until it is pure white. Varnish roans are created by the action of leopard complex within breeds such as the Appaloosa and are seldom seen elsewhere.
Diluted colors
The dilution genes that create dun, cream, pearl, silver dapple and champagne coloring may occasionally result in confusion with gray.
Some horses with a particular type of
In spite of its name, the
Mythology
Throughout history, both gray and
See also
Notes
- ^ PMID 12354140.
The progressive loss of colour in the hair of grey horses is controlled by a dominantly inherited allele at the Grey locus (G^G). Foals are born any colour depending on the alleles present at other colour determining loci. The progressive loss of color in the hair of gray horses is controlled by a dominantly inherited allele at the Grey locus (GG). Foals are born any color depending on the alleles present at other color-determining loci. After birth, horses carrying the GG allele begin to show white hairs that are intermixed with their original hair color. Although the rate at which horses will turn gray is variable, the amount of white hair increases with age until the coat is completely white at maturity. Pigmentation of the skin and eyes is not affected by GG. Dark skin distinguishes the grey phenotype from that of pink-skinned cremello and white horses.
- ^ a b "Edited Press Release. "Genetics of the Gray Horse Unraveled." Article # 12468". The Horse, Online edition. August 7, 2008. Archived from the original on 2 December 2017.
- PMID 12354141.
All grey Thoroughbred horses trace back to the Alcock's Arabian (b1700).
- ISBN 0-8131-1477-2.
- ^ "Jockey Club Interactive Registration". Jockey Club. Retrieved 20 April 2020.
- ^ "Equine Identification". USDA APHIS. May 25, 2017. Retrieved 20 April 2020.
- ^ S2CID 6666394.
- ^ "The Legend of the Bloody Shouldered Mare". www.babsonarabians.com. Retrieved 30 April 2020.
- ^ "Gray - Horse Coat Color DNA Testing." Animal Genetics, Incorporated.' Archived 2010-10-25 at the Wayback Machine. web page accessed August 29, 2008
- ^ Pascoe, Elaine. "Equine Melanoma: Harmless Bump or Time Bomb?". Expert how-to for English Riders. Retrieved 18 April 2020.
- ^ Tannler, Bria (2013). "Equine Melanoma: It's not just black and white!" (PDF). Equine Health Update. Purdue University College of Veterinary Medicine. Retrieved 18 April 2020.
- PMID 24196087.
References
- "Introduction to Coat Color Genetics" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008