Equine coat color

basic information on equine coat colors

Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them. While most horses remain the same color throughout life, a few, over the course of several years, will develop a different coat color from that with which they were born. Most white markings are present at birth, and the underlying skin color of a healthy horse does not change. Some Equine coat colors are also related to the breed of horse, like the Friesian breed for instance. The basic outline of equine coat color genetics has largely been resolved, and DNA tests to determine the likelihood that a horse will have offspring of a given color have been developed for some colors. Discussion, research, and even controversy continues about some of the details, particularly those surrounding spotting patterns, color sub shades such as "sooty" or "flaxen", and markings.

Several different genetic allelic families produce colors that are lighter versions of the base colors, caused by dilution genes.

Cream dilution is an incomplete dominant gene that produces a lightened or "partial dilute" coat color when one copy of the allele is present and a fully dilute (or "double dilute") with two copies. The double cream dilute phenotypes overlap regardless of base coat color and often cannot be distinguished visually. Sometimes the creme allele is combined with an unrelated dilution gene from another family, which creates a cremello like coat. Such coloration is called a "pseudo double dilute." These distinctions usually require DNA testing to verify which alleles are present. Cremello: A horse with a chestnut base coat and two cream genes that wash out almost all color until the horse is a pale cream or light tan color. Often called "white", they are not truly white horses, and they do not carry the white (W) gene. A cremello usually has blue eyes. Buckskin: A bay horse with one copy of the cream gene, a dilution gene that "dilutes" or fades the coat color to a yellow, cream, or gold while keeping the black points (mane, tail, legs). Palomino: chestnut horse that has one cream dilution gene that turns the horse to a golden, yellow, or tan shade with a flaxen or white mane and tail. Often cited as being a color "of twenty two carat gold", palominos range in shades from extremely light, almost cremello, to deep chocolate, but always with a white or flaxen mane and tail. Perlino: similar to a cremello, but is genetically a bay base coat with two dilute genes. Eyes are usually blue. Mane, tail and points are not black, but can sometimes be darker than the body coat, generally a reddish or rust color, though not to be confused with a red dun. Smoky black: A horse which visually appears to be only black, but actually has a black base coat and one copy of the cream gene. Smoky Cream: Virtually indistinguishable from a cremello or perlino without DNA testing, a horse with a black base coat and two copies of the cream gene.

Dun is Yellowish or tan coat with primitive markings, sometimes called "dun factors": a darker colored mane and tail, a dorsal stripe along the back and occasionally faint horizontal zebralike stripings on the upper legs and a possible transverse stripe across the withers. There are several variations:
Grulla, or Blue Dun: A horse with a black base color and the dun gene. Coat is a solid "mouse colored" gray or silver (can also be almost brownish gray) with black or dark gray primitive markings. Red Dun: A chestnut base coat with dun factors. Coat is usually pale yellow or tan with chestnut (red) primitive markings. "Bay Dun" or "Zebra dun" are terms sometimes used to describe the classic dun color of yellow or tan with black primitive markings, used when necessary to distinguish it from red duns or grullos. "Buckskin dun" or "Dunskin" describes a bay dun that also carries the cream gene dilution and has a coat of pale gold with a black mane, tail, legs and primitive markings. Mixtures of dliution genes produce colors such as "dunalino" — a red dun that also carries a single cream gene and thus has a pale gold coat, white mane and tail, and very faint primitive markings.

Champagne: Produced by a different dilution gene than the cream gene. It lightens both skin and hair, but creates a metallic gold coat color with mottled skin and light colored eyes. Champagne horses are often confused with palomino, cremello, dun, or buckskins. Mushroom dilutes red based horses to a pale tan colour, so far found only in Shetland ponies or ponies with Shetland influence. Pearl: Also called the "barlink factor", A dilution gene that when homozygous, lightens red coats to a uniform apricot color, often also resulting in horses with blue eyes. When combined with cream dilution, it may produce horses that appear to be cremello or perlino. Silver or silver dapple: Caused by a dilution gene that only acts upon black hair pigment, it lightens black body hair to a chocolate brown and the mane and tail to silver in most cases. The gene may be carried but will not be visible on horses with a red base coat. Silver horses have informally been called Chocolate, Flaxen, or Taffy.

These patterns all have white hairs and often pink skin, varying from a fully white horse through the pinto patterns and smaller white markings to roan which only adds a few white hairs spread throughout the coat. These patterns can occur on top of any other color. The base color determines the color of the colored hairs, while the white patterns determine where and how many white hairs are present. Biologically the white comes from a lack of pigment cells. There are many different genetic alleles that create these patterns.

There are a group of coat patterns caused by the leopard gene complex. Not every horse with leopard genetics will exhibit hair coat spotting. However, even solid individuals will exhibit secondary characteristics such as vertically striped hooves and mottled skin around the eyes, lips, and genitalia, plus a white sclera of the eye. Several breeds of horse can boast leopard spotted (a term used collectively for all patterns) individuals including the Knabstrupper, Noriker, and the Appaloosa. There are several distinct leopard patterns:
blanket: white over the hip that may extend from the tail to the base of the neck. The spots inside the blanket (if present) are the same color as the horse's base coat. varnish roan: a mix of body and white hairs that extends over the entire body—no relation to genetic roan. snowflake: white spots on a dark body. Typically the white spots increase in number and size as the horse ages. leopard: dark spots of varying sizes over a white body. few spot leopard: a nearly white horse from birth that retains color just above the hooves, the knees, "armpits", mane and tail, wind pipe, and face. frost: similar to varnish but the white hairs are limited to the back, loins, and neck.

Roaning adds white hairs to any of the other colors and, unlike gray, the color does not steadily lighten over the horse's lifetime, though there may be some minor color variation from year to year or especially between summer and winter coats. Classic Roan: a color pattern that causes white hairs to be evenly intermixed within the horse's body color. Roans are distinguishable from greys because roans typically do not change color in their lifetimes, unlike gray that gradually gets lighter as a horse ages. Roans also have heads that are either solid colored or much darker than their body hair, and do not lighten. Variations of roan include:
Red Roan: A chestnut base coat with a roaning pattern with the mane and tail being the same red as the body. Red roan is sometimes called Strawberry Roan, and the term Red Roan is occasionally used to describe a Bay Roan. Bay Roan: A Bay base coat with a roaning pattern (the mane and tail of the Bay Roan will be Black). Bay roans are sometimes also called Red Roans. There are no "albinos" in the horse world. Albinos, defined as animals with a white coat with pink skin and reddish eyes, are created by genetic mechanisms that do not exist in horses. In some cases, homozygous dominant white (W) is thought to be an embryonic lethal, though this does not occur with all W alleles.

White markings are present at birth and unique to each horse, making them useful in identifying individual animals. Markings usually have pink skin underneath them, though some faint markings may not, and white hairs may extend past the area of underlying pink skin. Though markings that overlie dark skin may appear to change, the underlying skin color and hair growing from pink skin will not. The distinction when white markings confined to the face and legs or a few small body spots become extensive enough to constitute a white spotting pattern is usually determined by breed standards set by registries. White markings generally are now hypothesized to be a minimal expression of certain genes in the dominant white (W) allelic series.

Brindle: One of the rarest colors in horses, characteristics are any base coat color with "zebralike" stripes, but the most common is a brown horse with faint yellowish markings. Usually linked to chimerism, but one heritable brindle pattern that affects coat texture and color in a family of American Quarter Horses has been named Brindle1 was announced in 2016. Sooty is a proposed genetic modifier not yet mapped that causes dark hairs to be dispersed within the coat, darkening the whole coat with age. Pangaré is a modifier that is the opposite of sooty, it causes individual hairs to lighten, causing lightened areas on the muzzle, flank and belly of a horse. "Flaxen" is used only to describe the lightened mane and tail of a chestnut, and has been proposed as a genetic modifier, particularly when it appears to be a trait of certain breeds. However, the genetic mechanism of this process has yet to be identified. Primitive marking variants sometimes called "bider markings" have been seen in Przewalski's horses and Mongolian horses.

Most horses have brown eyes with minor shade variations. Blue eyes are linked to the splashed white spotting allele, and cream dilution may produce a bluish green eye color. The champagne and pearl genes also produce lightened eye colors in the blue or green shades. The leopard complex produces a white sclera around an otherwise dark eye. The yellow or amber Tiger eye gene has been found only in the Puerto Rican Paso Fino and has two variants, Tiger eye 1 (TE1) and Tiger eye 2 (TE2), which are both recessive. There is no obvious link between eye shade and coat color, making this the first studied gene in horses to affect eye color but not coat color. Exterior hoof wall color is usually linked to coat color. Most horses have a dark grayish hoof wall unless they have white leg markings, in which case they will have pale colored hooves. The leopard complex gene will create a light and dark striped hoof, and many chestnut horses have brownish hooves that are somewhat lighter than the usual dark gray.

Registries have opened that accept horses (and sometimes ponies and mules) of almost any breed or type, with color either the only requirement for registration or the primary criterion. These are called "color breeds". Unlike "true" horse breeds, there are few if any unique physical characteristics required, nor is the stud book limited to only certain breeds or offspring of previously registered horses. As a general rule, offspring without the stated color are usually not eligible for recording with the color breed registry, although there are exceptions. The best known color breed registries are for buckskins, palominos, and pintos. Some horse breeds may have a desired coat color that usually breeds on as a characteristic that is part of the breed standard, in addition to distinctive physical characteristics and a limited stud book. They are not color breeds, and include the Friesian horse (must be uniformly black for mainstream registration), the Appaloosa (with Leopard complex patterns) and the American Paint Horse. In some of these breeds, though not all, offspring of animals registered in these stud books may be registered even if they do not have the desired color, sometimes with restrictions.