Gray or grey is a coat color of horses characterized by progressive silvering of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike many depigmentation genes, gray does not affect skin or eye color.
Their adult hair coat is white, dappled, or white intermingled with hairs of other colors. 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 lighter as the horse ages. Graying can occur at different rates—very quickly on one horse and very slowly on another.
Gray horses appear in many breeds, though the color is most commonly seen in breeds descended from Arabian ancestors.
Some breeds that have large numbers of gray-colored horses include the Thoroughbred, the Arabian, the American Quarter Horse, the Percheron, the Andalusian, the Welsh pony, and the most famous of all gray horse breeds, the Lipizzaner.
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 markings that were white at birth) and dark eyes. This is how to discern a gray horse from a white horse. White horses usually have pink skin and sometimes even have blue eyes. Young horses with hair coats consisting of a mixture of colored and gray or white hairs are sometimes confused with roan. Some horses that carry dilution genes may also be confused with white or gray.
While gray is commonly called a coat color by breed registries, genetically it may be more correct to call it a depigmentation pattern. It is a dominant allele,
and thus a horse needs only one copy of the gray allele, that is, heterozygous, to be gray in color.
A homozygous gray horse, one carrying two gray alleles, will always produce gray foals.
Gray is common in many breeds. Today, about one horse in 10 carries the mutation for graying with age.
The vast majority of Lipizzaners are gray, as are the majority of Andalusian horses. Many breeds of French draft horse such as the Percheron and Boulonnais are often gray as well. Gray is also found among Welsh Ponies, Thoroughbreds, and American Quarter Horses. All of these breeds have common ancestry in the Arabian horse. In particular, all gray Thoroughbreds descend from a horse named Alcock’s Arabian, a gray born in 1700.
The gray coat color makes up about 3% of Thoroughbreds.
Gray also occurs in spotted horses such as pintos or Appaloosas, but its effects wash out the contrast of the markings of these patterns. For this reason, some color breed registries refuse or cancel registration of gray horses.
A gray foal may be born any color. However, bay, chestnut, or black base colors are most often seen. As the horse matures, 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 and the horse changes slowly to either a rose gray, salt and pepper (or iron gray), or dapple gray. As the horse ages, the coat continues to lighten to a pure white or fleabitten gray hair coat.
Thus, the many variations of gray coloring in horses are intermediate steps that a young horse takes while graying out from a birth color to a hair coat that is completely “white.”
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 can be confusing. Many new horse owners, not understanding the workings of the gray gene, are disappointed to discover that their dapple gray horse turns completely white a few years later.