A bay horse has a reddish-brown body coat with black mane, tail, lower legs, and ear edges

Bay is a hair coat color of horses, characterized by a reddish brown body color with a black mane, tail, ear edges, and lower legs. Horses exhibit a diverse array of coat colors and distinctive markings. The horse ( Equus caballus) is a hoofed ( Ungulate) Mammal, one of eight living species of the family Equidae. The tail is the section at the rear end of an Animal 's Body; in general the term refers to a distinct flexible Appendage to the Torso. Bay is one of the most common coat colors in many horse breeds.

The black areas of a bay horse's hair coat are called "black points," and without them, a horse cannot be a bay. Black points may sometimes be covered by white markings, however such markings do not alter a horse's classification as "bay. Note This article is about individualized markings on any breed type or color of horse and does not discuss coat colors generally " Bay horses have dark skin, except under white markings, where the skin is pink.

Bay is genetically a base color and the addition of other genes creates many additional coat colors. While the basic concepts behind bay coloring are fairly simple, the genes themselves and the mechanisms that cause shade variations within the bay family are quite complex and, at times, disputed.

Color variations and terminology

Dark bay or "brown" horses often have lighter hair around the muzzle, eyes, flanks, and behind the elbow

Detail of a dark bay horse, showing lighter hairs around the eye

There are many terms that are used to describe particular shades and qualities of a bay coat. Some shade variations can be related to nutrition and grooming, but most appear to be caused by inherited factors not yet fully understood.

Bay horses range in color from a light copper red, to a rich red blood bay (the best-known variety of bay horse) to a very dark red or brown called dark bay, mahogany bay, black-bay, or brown (occasionally "seal brown"). The dark, brown, shades of bay are referred to in other languages by words meaning "black-and-tan. " Dark bays/browns may be so dark as to have nearly-black coats, with brownish-red hairs visible only under the eyes, around the muzzle, behind the elbow, and in front of the stifle. Dark bay should not be confused with "Liver" chestnut, which is also a very dark brown color, but a liver chestnut has a brown mane, tail and legs; no black points. Chestnut is a hair coat color of Horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat

The pigment in a bay horse's coat, regardless of shade, is rich and fully-saturated. This makes bays particularly lustrous in the sun if properly cared for. Some bay horses exhibit dappling, which is caused by textured, concentric rings within the coat. Dapples on a bay horse suggest good condition and care, though many well-cared for horses never dapple. The tendency to dapple may also be, to some extent, genetic.

Bays often have a two-toned hair shaft, which, if shaved too closely (such as when body-clipping for a horse show), may cause the horse to appear several shades lighter, a somewhat dull orange-gold, almost like a dun. A Horse show is a judged exhibition of Horses and ponies. Many different horse breeds and equestrian disciplines hold competitions worldwide The dun gene is a Dilution gene that affects both red and black pigments in the coat color of a Horse. However, as the hair grows out, it will darken again to the proper shade. This phenomenon is part of bay color genetics, but usually not seen in darker shades of bay because there is less red in the hair shaft. (See: "Inheritance and expression," below)

This horse is bay despite the fact that its black legs are masked by tall white markings

The palest shades, which lack specific English terminology found in other languages, are called wild bays. Wild bays are true bays with fully-pigmented reddish coat color and black manes and tails, but the black points only extend up to the pastern or fetlock. The pastern is a part of the horse between the Fetlock joint and the Hoof, or between the wrist and forepaw of a Dog. Wild bay is often found in conjunction with a trait called "pangare" that produces pale color on the underbelly and soft areas, such as near the stifle and around the muzzle. ^[1]

Bay horses have black skin and dark eyes, except for the skin under markings, which is pink. Note This article is about individualized markings on any breed type or color of horse and does not discuss coat colors generally Skin color can help an observer distinguish between a bay horse with white markings and a horse which resembles bay but is not.

Ambiguity of "brown"

Some breed registries (including the Jockey Club Thoroughbred registry) use the term "brown" to describe dark bays. The Thoroughbred is a horse breed However, "liver" chestnuts, horses with a red or brown mane and tail as well as a dark brownish body coat, are also sometimes called "seal brown" in some colloquial contexts. Chestnut is a hair coat color of Horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat A colloquialism is an expression not used in formal speech, writing or Paralinguistics. Therefore, "brown" can be an ambiguous term for describing horse coat color. It may be clearer to refer to dark-colored horses as dark bays or liver chestnuts.

Effect of gray gene

Some foals are born bay, but carry the dominant gene for graying, and thus will turn gray as they mature until eventually their hair coat is completely white. A foal is a Horse that is one year old or younger More specific terms are colt for a Male foal and Filly for a Female foal Gray or grey is a coat color of Horses characterized by progressive silvering of the colored hairs of the coat Foals that are going to become gray must have one parent that is gray. Some foals may be born with a few white hairs already visible around the eyes, muzzle, and other fine-haired, thin-skinned areas, but others may not show signs of graying until they are several months old.

Colors confused with bay

A black horse, even with a sun-bleached hair coat (as seen with the forelock of this black horse) will have solid black hairs around the eye.

A liver chestnut is distinguished from a bay by a lack of black points. The mane and tail are the same color as the body, or lighter.

For description of other coat colors, see Equine coat color. Horses exhibit a diverse array of coat colors and distinctive markings.

• Chestnuts, sometimes called "Sorrels," have a reddish body coat similar to a bay, but no black points. Chestnut is a hair coat color of Horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat Their legs and ear edges are the same color as the rest of their body (unless they have white markings) and their manes and tails are the same shade as their body color or even a few shades lighter.
• Black are occasionally confused with dark bays and liver chestnuts because some black horses "sunburn," that is, when kept out in the sun, they develop a bleached-out coat that looks brownish, particularly in the fine-haired areas around the flanks. Black is a hair coat color of Horses in which the entire hair coat is black However, a true black can be recognized by looking at the fine hairs around the muzzle and eyes. These hairs are always black on a black horse, but are reddish, brownish, or even a light gold on a bay or chestnut.

Bay-family colors

Bay is considered to be one of the "hard" or "base" coat colors in horses. The two others in this category are chestnut and black. Chestnut is a hair coat color of Horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat Black is a hair coat color of Horses in which the entire hair coat is black The effects of additional equine coat color genes on a bay template alter the basic color into other shades or patterns:

• Buckskin horses have a black mane and tail, but instead of a red or brown coat, they have a cream or gold coat. For other meanings of buckskin see Buckskin (Disambiguation Buckskin is a hair coat color of Horses referring Though once called a "Sandy" bay in older texts on horse color, the genetic distinction created by the cream gene is significant. The cream gene is a Dilution gene expressed in Horses and produces lighter colors They are a bay horse that is also heterozygous for the dominant creme (CCr) allele. Zygosity refers to the genetic condition of a Zygote. In genetics zygosity describes the similarity or dissimilarity of DNA between Homologous The black pigment remains largely unchanged, but any red pigment in the coat is diluted to gold. Buckskins are seldom mistaken for bays because their coats are significantly lighter and have no hint of a red or orange tint.
• Perlinos are bay horses who are homozygous for the dominant creme (CCr) allele. Perlino is a color in Horses created by a Dilution gene, also known as the Creme gene acting on an underlying Bay coat color Zygosity refers to the genetic condition of a Zygote. In genetics zygosity describes the similarity or dissimilarity of DNA between Homologous Both black and red pigment are diluted to some shade of creme, though the formerly-black points often have a stronger reddish cast. The skin is a slightly pigmented pink and the eyes are blue.
• Bay duns are bay horses with at least one dominant dun allele. The dun gene is a Dilution gene that affects both red and black pigments in the coat color of a Horse. An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms Red and black pigment at the extremities remains largely unchanged, but on the body, black pigment is diluted to slate and red pigment is diluted to a dustier shade. The effect is similar to buckskin, but the coat of a bay dun is a flatter tan rather than bronze, and all duns have some form of "primitive" marking, that include a dorsal stripe along the backbone, and sometimes faint horizontal striping at the back of the front legs.
• Amber champagne refers to a bay horse with at least one dominant champagne allele. The champagne gene is a gene that occurs in Horses that produces a golden coat color and other distinctive features Black pigment is diluted to warm brown and red pigment to gold. The effect is similar to buckskin, but the points of an amber champagne do not remain black, and the skin is mottled. Amber champagnes also have hazel eyes rather than brown.
• Silver bays are bay horse with at least one dominant silver (Z) allele. The silver dapple ( Z) gene is a Dilution gene that affects the black base coat color. Red pigment is unaffected, but black pigment in the short coat is diluted to dark, flat, brown-gray while the longer hairs are diluted to silver. The overall effect on a bay is that of a chocolate-colored horse with a pale mane and tail.
• Bay Roan horses are bays with at least one dominant roan (Rn) allele. Roan is a coat color found in many animals notably Horses Cattle and Dogs It is defined generally as an even mixture of white and pigmented hairs that The roan gene creates an effect of white hairs intermingled with the red body coat. This color was formerly lumped together with chestnut or "strawberry" roans and called "red roan. "
• Bay pintos are bay horses with any number of white spotting genes, including but not limited to tobiano, frame or splash overo, and so on. A Pinto horse has a coat color that consists of large patches of white and another color Tobiano is a spotted color pattern commonly seen in Pinto horses produced by a Dominant gene. Overo refers to several genetically-unrelated pinto coloration pattern of white over dark body markings in Horses Overo is a Spanish word originally meaning “like The pattern has no bearing on whether or not the horse is bay. Pinto horses also may have a bay base coat overlaid by white spots. A Pinto horse has a coat color that consists of large patches of white and another color Sometimes the term Skewbald or "Tricolor" is used, especially in the UK, to refer to bay pintos. For the band of the same name see Skewbald (band Skewbald is a color pattern of Horse. Tri-coloured (archaic oddbald) refers to a horse with three different coat colours in a pinto spotting pattern of large white and dark patches usually
  • Sabino is a color pattern in the pinto family, but in some cases, the gene may be minimally expressed in the form of very bold white markings or slight body spotting and such horses will be registered by their owners as "bay," particularly in breed registries that do not have a category for pinto. Sabino is a color spotting pattern in Horses that is usually recognized as a form of Pinto horse color Note This article is about individualized markings on any breed type or color of horse and does not discuss coat colors generally A breed registry, also known as a stud book or register, in Animal husbandry and the Hobby of Animal fancy, is an official list of
• Bay Leopards are horses that carry the leopard (Lp) gene or gene complex characteristic of the Appaloosa and other breeds. Leopard is a term used to describe a spotted color pattern particularly in the hair coat or skin of Animals but also used to describe spotting patterns in Plants This gene also produces secondary characteristics that include mottled skin, a white sclera around the eye, and striped hooves. The sclera, called the white or white of the eye, is the opaque (usually white though certain animals such as horses and lizards can have black sclera fibrous A horse hoof is a structure surrounding the distal phalanx of the 3rd digit (digit III of the basic Pentadactyl limb of Vertebrates evolved into a single
• A few bay horses may carry the rabicano gene, which either produces faint roaning on only some parts of the body or can cause some white or cream hairs to appear in the mane or tail, sometimes creating a "skunk" effect. Rabicano, also called white ticking, is a Horse coat color characterized by limited roaning in a specific pattern interspersed white hairs most dense Most bays with rabicano are registered as either bays or as bay roans.

Genetics

Bay foals, like this one, sometimes have pale hairs on their legs and in their mane and tail until they shed their foal coats

Main article: Equine coat color genetics

The various shades of bay may be genetically produced by multiple factors, but a simple explanation of bay genetics is that "red" color, seen in the chestnut horse, represented by the recessive "e" allele; and black color, represented by the dominant "E" allele, are the two most basic coat color genes. Equine coat color genetics determine a Horse 's coat color All horses begin genetically with a base coat of "red" ( chestnut) or "black Chestnut is a hair coat color of Horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat Black is a hair coat color of Horses in which the entire hair coat is black All other colors are produced by the action of additional alleles acting on these two base colors.

A bay horse carries both the Extension (E) allele and a suppression gene known as the agouti gene (A). The melanocortin 1 receptor (also known as melanocyte-stimulating hormone receptor or Mc1r) is one of the key Proteins in regulating hair and skin color Agouti signalling peptide, also referred to as Agouti is a Peptide which acts as an antagonist at Melanocortin receptors specifically MC1. The agouti gene, dominant over the black gene, limits or suppresses the black coloring to black points, allowing the underlying red coat color to come through. Unlike other types of "point" coloring, such as that seen in Siamese cats, the black points characteristic of bay coloring are not produced by a dilution or albinism gene. Point coloration refers to animal coat coloration with a pale body and relatively darker extremities i The Siamese is one of the first distinctly recognised breeds of Oriental Cat. Dilution gene is a popular term for any one of a number of Genes that act to create a lighter coat color in living creatures Albinism (from Latin albus, "white" see extended etymology) is a form of hypopigmentary Congenital disorder, History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance

Because the extension (E) gene and agouti (A) gene can be either heterozygous or homozygous, the extent to which a bay passes on its color varies widely from one horse to another depending on its genotype and that of its mate. Also, a chestnut may carry the Agouti gene, which will be "masked" or not manifest until the horse is bred to a horse with the E allele and produces offspring with both genes.

Inheritance and expression

See also: Introduction to genetics

The bay family of coat colors is dependent on two autosomal simple dominant genes: Extension and Agouti. Genetics studies how living Organisms inherit many of the features of their ancestors &ndash for example children usually look and act like other people in their History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance The melanocortin 1 receptor (also known as melanocyte-stimulating hormone receptor or Mc1r) is one of the key Proteins in regulating hair and skin color Agouti signalling peptide, also referred to as Agouti is a Peptide which acts as an antagonist at Melanocortin receptors specifically MC1. The role of the Extension gene is to produce a protein called Melanocortin 1 receptor or Mc1r. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl The melanocortin 1 receptor (also known as melanocyte-stimulating hormone receptor or Mc1r) is one of the key Proteins in regulating hair and skin color Mc1r allows the black pigment eumelanin to form in hair. Melanin is a class of compounds found in the Plant, Animal and Protista kingdoms, where it serves predominantly as a Pigment. Closely tied to this process, the role of the Agouti gene is to produce Agouti signalling peptide Asip, which disables Mc1r, effectively allowing the red pigment phaeomelanin to "show through. Agouti signalling peptide, also referred to as Agouti is a Peptide which acts as an antagonist at Melanocortin receptors specifically MC1. Melanin is a class of compounds found in the Plant, Animal and Protista kingdoms, where it serves predominantly as a Pigment. " However, this disabling does not occur throughout the coat; it occurs only in pulses on the body coat and not at all on the extremities or points.

If a horse does not possess a functional, dominant copy of the wildtype E-allele at the Extension locus, then Mc1r cannot be produced. An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms Without this protein, the black pigment eumelanin cannot form in the hair. Such horses, having two copies of the recessive mutation, have eumelanin-free, phaeomelanin-rich coats; they are red, or chestnut. Chestnut is a hair coat color of Horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat In summary, unless a horse has at least one functional E-allele, it cannot be bay.

Similarly, if a horse does not possess a functional, dominant copy of the A-allele at the Agouti locus, then Asip cannot be produced. Without Asip, eumelanin is unreglated and the coat is wholly black. The regulation of black pigment, though, is dependent on its presence in the first place; a horse with the recessive Agouti genotype aa is indistinguishable from any other genotype in a horse with a eumelanin-free coat. When eumelanin is present, it is restricted in varying degrees by the action of Asip.

The action of Asip can be observed in horses which have their winter coats clipped. When shaved close, the black tip is shorn off leaving the phaeomelanic bottom of the shaft. This produces a dull, orange-gold appearance on the body coat which is lost with the spring shed. This is not usually seen in dark bays, which have little red in the hair shaft.

Agouti

The cause behind the various shades of bay, particularly the genetic factors responsible for wild bay and seal brown, have been contested for over 50 years. In 1951, zoologist Miguel Odriozola published "A los colores del caballo" in which he suggested four possible alleles for the "A" gene. He described an order of dominance between the alleles and the associated phenotypes:

• a, the least dominant, must be homozygous to be observed and is responsible for unrestricted black coat (non-agouti black),
• A^t, only visible in the homozygous form or when paired with a, is responsible for the black-and-tan seal brown coat,
• A, visible when homozygous or when paired with a or A^t, is responsible for the standard bay coat,
• A+, dominant, is responsible for the wildtype wild bay coat. ^[2]

This was accepted until the 1990's, when a new theory became popular. ^[3] The new theory suggested that shades of bay were caused by many different genes, some which lightened the coat, some which darkened it. This theory also suggested that seal brown horses were black horses with a trait called pangare. Pangare is an ancestral trait also called "mealy", which outlines the soft or communicative parts of the horse in buff tan.

The pale areas on this bay horse are due to the pangare trait

The combination of black and pangare was dismissed as the cause of brown in 2001, when a French research team published Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus). This study used a DNA test to identify the recessive a allele on the Agouti locus, and found that none of the horses fitting the phenotype of seal brown were homozygous for the a allele.

Since 2001, the mechanisms of the variations within the "bay" category remain unclear. Ongoing research suggests that Odriozola's theories may have been correct,^[4] evidenced by a parallel condition in mice. Mice have more than six alleles at the Agouti locus, including A^t which produces black-and-tan. ^[5]

It is still likely that to some extent, the "shade" of coat color may be regulated by unrelated genes for traits like "sooty", and that the phenotypes of sooty or dark bays/browns may overlap. ^[6]

See also

• Equine coat color genetics
• Equine coat color

References

• "Introduction to Coat Color Genetics" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008