Bay (horse)

Last updated
Bay
BayMare.jpg
A bay mare
VariantsBright reddish-brown to dark shades probably influenced by sooty or seal brown, points may be restricted in "wild bay" pattern
Genotype
Base colorBlack (E)
Modifying genes agouti gene (A)
Descriptionreddish-brown body coat with black point coloration
Phenotype
BodyReddish-Brown
Head and LegsBlack
Mane and tailBlack
SkinBlack
EyesBrown, unless modified by another gene
Other notesBlack ear edges

Bay is a hair coat color of horses, characterized by a reddish-brown or brown body color with a black point coloration of the mane, tail, ear edges, and lower legs. Bay is one of the most common coat colors in many horse breeds.

Contents

The black areas of a bay horse's hair coat are called "black points", and without them, a horse is not a bay horse. Black points may sometimes be covered by white markings; however such markings do not alter a horse's classification as "bay". Bay horses have dark skin — except under white markings, where the skin is pink. Genetically, bay occurs when a horse carries both the Agouti gene and a black base coat. While the basic genetics that create 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. The genetics of dark shades of bay are still under study. The genetic mechanism that produces seal brown has yet to be isolated. Sooty genetics also appear to darken some horses' bay coats, and that genetic mechanism is yet to be fully understood.

The addition of dilution genes or various spotting pattern genes create many additional coat colors, although the underlying bay coat color genetics usually manifest by a warm-toned red, tan, or brownish body color and the appearance of black points.

Color variations and terminology

The horses of the New South Wales Mounted Police show some of the typical variations in the bay color. RAS NSW Mounted Police muster.jpg
The horses of the New South Wales Mounted Police show some of the typical variations in the bay color.
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A very dark bay horse might appear to be almost black
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Dark bay or "brown" horses often have lighter hair around the muzzle, eyes, flanks, and elbow
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This horse is bay despite the fact that its black legs are masked by white markings

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 (or "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, and no black points.

Bay horses have black skin and dark eyes, except for the skin under markings, which is pink. Skin color can help an observer distinguish between a bay horse with white markings and a horse which resembles bay but is not.

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.

A partially body-clipped horse, showing the two-toned red hair shaft. Gelderlander trabend.jpg
A partially body-clipped horse, showing the two-toned red hair shaft.

The red areas of a bay coat usually have a two-toned hair shaft, which, if shaved 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. However, as the hair grows out, it will darken again to the proper shade. This phenomenon is linked to the genetics that produce red coloration in horses, but usually not seen in body-clipped darker shades of bay because there is less red in the hair shaft.

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.

The shades with the least amount of point coloration 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. Wild bay is sometimes 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]

Some breed registries use the term "brown" to describe darker bays, though modern genetics have resulted in some terminology revisions such as the use of "bay or brown." However, "liver" chestnuts, horses with a red or brown mane and tail as well as a dark brownish body coat, are sometimes called "brown" in some colloquial contexts. Therefore, "brown" can be an ambiguous term for describing horse coat color. It is clearer to refer to dark-colored horses as dark bays or liver chestnuts.

This foal was born bay but is starting to turn gray Arabian Simeon Stud(4428278721).jpg
This foal was born bay but is starting to turn gray

To further complicate matters, there apparently exists more than one genetic mechanism that darkens coat colors. One is a theorized sooty gene which produces dark shading on any coat color. The other is a specific allele of Agouti linked to a certain type of dark bay, called seal brown. The seal brown horse has dark brown body and lighter areas around the eyes, the muzzle, and flanks. A DNA test said to detect the seal brown (At) allele was developed, but the test was never subjected to peer review and due to unreliable results was subsequently pulled from the market. [2] [3]

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. 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

Mangalarga Paulista.jpg
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.
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Dark bay horse, showing lighter hairs around the eye
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Black horse with sun-bleached forelock, showing solid black hairs around the eye, even though forelock is reddish

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 Poulain de race ardennaise 1.jpg
Bay foals, like this one, sometimes have pale hairs on their legs and in their mane and tail until they shed their foal coats

The bay color is created with two colors of melanin pigment, the black eumelanin, which gives the black color of the mane, tail, and lower legs, and the "red" pheomelanin, which gives the body its red-brown color. Unlike the point coloration of Siamese cats and Himalayan rabbits, the points on horses are not produced by an albinism gene. Instead, two genes called extension and agouti interact to create this pattern.

At agouti, the dominant, ancestral A allele limits the location of black pigment to the points, seen in the bay color. The recessive a allele allows black pigment to cover the whole body, resulting in a fully black horse. [4]

At extension, horses with the dominant, ancestral E allele are able to produce either red or black pigment, and depending on agouti genotype horses with E can be bay or black. The recessive e alleles replaces all black pigment in the coat with red, creating a solid red chestnut coat regardless of agouti genotype. To be bay, a horse must have at least one E at extension and at least one A at agouti. [5]

The extent to which a bay passes on its color varies. Two bay horses heterozygous for E (Ee x Ee) have a 25% statistical probability to produce a chestnut. Similarly, bay horses heterozygous for A (Aa x Aa) may produce a black foal.

Because chestnut's e at extension is recessive to bay's E, two chestnut horses can never have a bay foal. Likewise, because black's a at agouti is recessive, two black horses cannot have a bay foal either. However, it's possible for a chestnut horse and a black horse to produce a bay foal, if the chestnut horse is AA or Aa at agouti. The foal can inherit the A allele from its chestnut parent and the E allele from its black parent, resulting in a bay color.

The genetics behind the different shades of bay are still under investigation. A genome wide association study identified a region of equine chromosome 22 that appears to correlate with the extent of black pigment on bay horses. This region includes the 5' end of the agouti gene as well as another gene called RALY , both known to affect coat color in other species. Further research is needed to pinpoint the causative mutation. [6]

Origin

Some bay horses have a faint dorsal stripe, which may be caused by the non-dun 1 allele. Countershading stripe.jpg
Some bay horses have a faint dorsal stripe, which may be caused by the non-dun 1 allele.

The oldest known horse coat color is bay dun, a tan color with a black mane, tail, dorsal stripe, and lower legs. The legs may sometimes have zebra-like black stripes; these, along with the dorsal stripe seen on all dun horses, are called primitive markings. Over 42,000 years ago, a mutation called non-dun 1 appeared, which allowed horses to be bay. Non-dun 1 replaces the tan dun color with the darker brown of bay, but keeps the primitive markings seen on dun. Later a second mutation to the dun gene, called non-dun 2, was able to remove the primitive markings altogether to create the non-striped bay color common today. [7] [8]

Bay-family colors

The effects of additional equine coat color genes on a bay template alter the basic color into other shades or patterns:

See also

Related Research Articles

Roan (color)

Roan is a coat color found in many animals, including horses, cattle, antelope, cat and dogs. It is defined generally as an even mixture of white and pigmented hairs that do not "gray out" or fade as the animal ages. There are a variety of genetic conditions which produce the colors described as "roan" in various species.

Palomino Genetic color in horses

Palomino is a genetic color in horses, consisting of a gold coat and white mane and tail; the degree of whiteness can vary from bright white to yellow. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a "red" (chestnut) base coat. Palomino is created by a genetic mechanism of incomplete dominance, hence it is not considered true-breeding. However, most color breed registries that record palomino horses were founded before equine coat color genetics were understood as well as they are today, therefore the standard definition of a palomino is based on the visible coat color, not heritability nor the underlying presence of the dilution gene.

Dilution gene

A dilution gene is any one of a number of genes that act to create a lighter coat color in living creatures. There are many examples of such genes:

Buckskin (horse) Equine coat color

Buckskin is a hair coat color of horses, referring to a color that resembles certain shades of tanned deerskin. Similar colors in some breeds of dogs are also called buckskin. The horse has a tan or gold colored coat with black points. Buckskin occurs as a result of the cream dilution gene acting on a bay horse. Therefore, a buckskin has the Extension, or "black base coat" (E) gene, the agouti gene (A) gene, which restricts the black base coat to the points, and one copy of the cream gene (CCr), which lightens the red/brown color of the bay coat to a tan/gold.

At right is displayed the color traditionally called liver.

Point coloration Coloration of animal coat/fur

Point coloration refers to animal coat coloration with a pale body and relatively darker extremities, i.e. the face, ears, feet, tail, and scrotum. It is most recognized as the coloration of Siamese and related breeds of cat, but can be found in dogs, rabbits, rats, sheep, guinea pigs and horses as well.

Gray horse Coat color characterized by progressive depigmentation of the colored hairs of the coat

A gray 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. 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.

Cream gene

The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino if they are heterozygous, having one copy of the cream gene, or cremello, if they are homozygous. Similarly, horses with a bay base coat and the cream gene will be buckskin or perlino. A black base coat with the cream gene becomes the not-always-recognized smoky black or a smoky cream. Cream horses, even those with blue eyes, are not white horses. Dilution coloring is also not related to any of the white spotting patterns.

Champagne gene

The champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink at birth, respectively. The coat color is also affected: any hairs that would have been red are gold, and any hairs that would have been black are chocolate brown. If a horse inherits the champagne gene from either or both parents, a coat that would otherwise be chestnut is instead gold champagne, with bay corresponding to amber champagne, seal brown to sable champagne, and black to classic champagne. A horse must have at least one champagne parent to inherit the champagne gene, for which there is now a DNA test.

Silver dapple gene

The silver or silver dapple (Z) gene is a dilution gene that affects the black base coat color and is associated with Multiple Congenital Ocular Abnormalities. It will typically dilute a black mane and tail to a silvery gray or flaxen color, and a black body to a chocolaty brown, sometimes with dapples. It is responsible for a group of coat colors in horses called "silver dapple" in the west, or "taffy" in Australia. The most common colors in this category are black silver and bay silver, referring to the respective underlying coat color.

Equine coat color genetics Genetics behind the equine coat color

Equine coat color genetics determine a horse's coat color. Many colors are possible, but all variations are produced by changes in only a few genes. The "base" colors of the horse are determined by the Extension locus, which in recessive form (e) creates a solid chestnut or "red" coat. When dominant (E), a horse is black. The next gene that strongly affects coat color, Agouti, when present on a horse dominant for E, limits the black color to the points, creating a shade known as Bay that is so common and dominant in horses that it is informally grouped as a "base" coat color.

Dun gene

The dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene lightens most of the body while leaving the mane, tail, legs, and primitive markings the shade of the undiluted base coat color. A dun horse always has a dark dorsal stripe down the middle of its back, usually has a darker face and legs, and may have transverse striping across the shoulders or horizontal striping on the back of the forelegs. Body color depends on the underlying coat color genetics. A classic "bay dun" is a gray-gold or tan, characterized by a body color ranging from sandy yellow to reddish brown. Duns with a chestnut base may appear a light tan shade, and those with black base coloration are a steel gray. Manes, tails, primitive markings, and other dark areas are usually the shade of the undiluted base coat color. The dun gene may interact with all other coat color alleles.

Fjord horse Breed of horse

The Fjord horse or Norwegian Fjord Horse is a relatively small but very strong horse breed from the mountainous regions of western Norway. It is an agile breed of light draught horse build. All Fjord horses are dun in colour, with five variations in shade recognised in the breed standard. One of the world's oldest breeds, it has been used for hundreds of years as a farm horse in Norway, and in modern times is popular for its generally good temperament. It is used both as a harness horse and under saddle.

Grullo Color of horses in the dun family

Grulla or grullo, also called blue dun, gray dun or mouse dun, is a color of horses in the dun family, characterized by tan-gray or mouse-colored hairs on the body, often with shoulder and dorsal stripes and black barring on the lower legs. In this coloration, each individual hair is mouse-colored, unlike a roan, which is composed of a mixture of dark and light hairs. The several shades of grulla are informally referred to with a variety of terms, including black dun, blue dun, slate grulla, silver grulla or light grulla, silver dun, or lobo dun. Silver grulla may also refer to a grullo horse with silver dapple, regardless of shade. In the Icelandic horse, the grulla color is called gray dun, in the Highland pony it is called mouse dun, and in the Norwegian Fjord horse, grå or gråblakk.

Chestnut (horse color) Horse coat color

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. Chestnut is characterized by the absolute absence of true black hairs. It is one of the most common horse coat colors, seen in almost every breed of horse.

Equine coat color Horse coat colors and markings

Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them.

Black horse Horse coat color

Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and it is not uncommon to mistake dark chestnuts or bays for black.

Seal brown (horse) Hair coat color of horses

Seal brown is a hair coat color of horses characterized by a near-black body color; with black points, the mane, tail and legs; but also reddish or tan areas around the eyes, muzzle, behind the elbow and in front of the stifle. The term is not to be confused with "brown", which is used by some breed registries to refer to either a seal brown horse or to a dark bay without the additional characteristics of seal brown.

Roan (horse) Horse coat color pattern characterized by an even mixture of colored and white hairs on the body

Roan is a horse coat color pattern characterized by an even mixture of colored and white hairs on the body, while the head and "points"—lower legs, mane, and tail—are mostly solid-colored. Horses with roan coats have white hairs evenly intermingled throughout any other color. The head, legs, mane, and tail have fewer scattered white hairs or none at all. The roan pattern is dominantly inherited, and is found in many horse breeds. While the specific mutation responsible for roan has not been exactly identified, a DNA test can determine zygosity for roan in several breeds. True roan is always present at birth, though it may be hard to see until after the foal coat sheds out. The coat may lighten or darken from winter to summer, but unlike the gray coat color, which also begins with intermixed white and colored hairs, roans do not become progressively lighter in color as they age. The silvering effect of mixed white and colored hairs can create coats that look bluish or pinkish.

The agouti gene, the Agouti-signaling protein (ASIP) is responsible for variations in color in many species. Agouti works with extension to regulate the color of melanin which is produced in hairs. The agouti protein causes red to yellow pheomelanin to be produced, while the competing molecule α-MSH signals production of brown to black eumelanin. In wildtype mice, alternating cycles of agouti and α-MSH production cause agouti coloration. Each hair has bands of yellow which grew during agouti production, and black which grew during α-MSH production. Wildtype mice also have light-colored bellies. The hairs there are a creamy color the whole length because the agouti protein was produced the whole time the hairs were growing.

References

  1. Sponenberg, Dan Phillip (2003). Equine Color Genetics 2e. Blackwell. ISBN   0-8138-0759-X.
  2. "The Enigmatic Brown Horse - Color Genetics". Archived from the original on 2016-04-08.
  3. Understanding Equine DNA and Agouti, at PetDNAServicesAZ; via archive.org; archived February 27, 2015
  4. "Agouti (Bay/Black)". UC Davis Veterinary Genetics Laboratory. Retrieved Nov 20, 2021.
  5. "Red Factor". UC Davis Veterinary Genetics Laboratory. Retrieved Nov 20, 2021.
  6. Corbin, Laura J.; Pope, Jessica; Sanson, Jacqueline; Antczak, Douglas F.; Miller, Donald; Sadeghi, Raheleh; Brooks, Samantha A. (2020). "An Independent Locus Upstream of ASIP Controls Variation in the Shade of the Bay Coat Colour in Horses". Genes. 11 (6): 606. doi: 10.3390/genes11060606 . PMC   7349280 . PMID   32486210.
  7. Imsland F, McGowan K, Rubin CJ, Henegar C, Sundström E, Berglund J, et al. (February 2016). "Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses". Nature Genetics. 48 (2): 152–8. doi:10.1038/ng.3475. PMC   4731265 . PMID   26691985.
  8. Ludwig A, Pruvost M, Reissmann M, Benecke N, Brockmann GA, Castaños P, Cieslak M, Lippold S, Llorente L, Malaspinas AS, Slatkin M, Hofreiter M (2009-04-24). "Coat Color Variation at the Beginning of Horse Domestication". Science. 324 (5926): 485. Bibcode:2009Sci...324..485L. doi:10.1126/science.1172750. PMC   5102060 . PMID   19390039.