Gray horse

Gray is common in many breeds. Today, about one horse in 10 carries the mutation for graying with age. The gray coat color makes up about 3% of Thoroughbreds. 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==

with suckling foal. The mare has a white hair coat, but the underlying black skin confirms that she is gray and not white. The light hairs around the foal's muzzle and eyes indicate that it will gray like its mother. Not all foals show signs of graying this young. A gray foal may be born any color. However, bay, chestnut, or black base colors are most often seen. As the horse matures, it "grays out" as white hairs begin to replace the base or birth color. Usually white hairs are first seen by the muzzle, eyes and flanks, occasionally at birth, and usually by the age of one year. Over time, white hairs replace the birth color. The changing patterns of white and dark hairs have many informal names, such as "rose gray," "salt and pepper," "iron gray", or "dapple gray." As the horse ages, the coat continues to lighten, often to a pure white. Some horses develop pigmented reddish-brown speckles on an otherwise white hair coat. Such horses are often called "fleabitten 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 white horse), while a horse in its teens usually is completely grayed out. One must also be careful not to confuse the small amount of gray hairs that may appear on some older horses in their late teens or twenties, which do not reflect the gray gene and never cause a complete graying of the horse. 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. 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. 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. ==The genetics of gray==

The gray gene (G) is an autosomal dominant gene. The gray gene does not affect skin or eye color, so grays typically have dark skin and eyes, as opposed to the unpigmented pink skin of white horses. 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. 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. Gray is controlled by a single dominant allele of a gene that regulates specific kinds of stem cells. Homozygous grays turn white faster, are more likely to develop melanomas, and are less prone to develop the "fleabitten" speckling than heterozygous grays. 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. Growth rate depends on the type, and many are slow-growing, but over time, many develop into a melanoma. 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. ==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 white horses have pink skin and some have blue eyes. A horse with dark skin and dark eyes under a white hair coat is gray. However, a gray horse with an underlying homozygous cream base coat color may be born with rosy-pink skin, blue eyes and near-white hair. In such cases, DNA testing may clarify the genetics of the horse. 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 dun hair coat known as a "blue dun", grullo, or "mouse" dun appear to be a solid gray. However, this color is caused by the dun gene acting on a black base coat, and horses who are dun have all hairs the same color; there is no intermingling of white and dark hairs. Also, dun horses do not get lighter as they age. Horses that are a light cream color are also not grays. These are usually cremello, perlino or smoky cream horses, all colors produced by the action of the cream gene. However, if a gray parent passes on the gene, the hairs will turn white like any other gray. Another cream-colored dilution, the pearl gene or "barlink factor", may also create very light-coated horses. Similarly, the champagne gene can lighten coat color, often producing dappling or light colors that can be confused with gray. In spite of its name, the silver dapple gene has nothing to do with graying. It is a dilution gene that acts only on a black coat, diluting the coat to a dark brown and the mane to a flaxen shade. Horses that express the silver dapple gene (and do not have the gray gene) are born that color and it will not lighten. However, again, if one parent passes on the gray gene, the gray gene will again be dominant. ==Mythology==

Throughout history, both gray and white horses have been mythologized. As part of its legendary dimension, the gray horse in myth has been depicted with seven heads (Uchaishravas) or eight feet (Sleipnir), sometimes in groups or singly. There are also mythological tales of divinatory gray horses who prophesy or warn of danger. ==See also==