Chestnut (horse color)

Source: Wikipedia, the free encyclopedia.

Chestnut
Flaxen, Liver chestnut
Genotype
Base colorRecessive extension "e"
Modifying genesnone
Descriptionreddish-brown color uniform over entire body other than markings
Phenotype
Bodyreddish-brown
Head and Legssame as body, occasionally lighter
Mane and tailflaxen to brown
SkinUsually black, may be lighter at birth in some breeds
EyesBrown, eyes may be lighter at birth

Chestnut is a

horse coat colors
, seen in almost every breed of horse.

Chestnut is a very common coat color but the wide range of shades can cause confusion. The lightest chestnuts may be mistaken for

better source needed
]

Chestnut is produced by a

black
, but on rare occasions still produce chestnut foals.

Visual identification

A chestnut horse with white markings

Chestnuts can vary widely in shade and different terms are sometimes used to describe these shades, even though they are genetically indistinguishable. Collectively, these coat colors are usually called "red" by geneticists.

  • A basic chestnut or "red" horse has a solid copper-reddish coat, with a mane and tail that is close to the same shade as the body coat.
  • flaxen
    mane and tail.
A liver chestnut
  • recessive mode of inheritance.[3]
This light, flaxen, mealy chestnut Haflinger might be mistaken for a palomino

Chestnut family colors

Chestnut is considered a "base color" in the discussion of equine coat color genetics. Additional coat colors based on chestnut are often described in terms of their relationship to chestnut:

A red dun has a light reddish- tan body and dark red primitive markings and points
  • Red duns have a chestnut base coat with the dun gene (one or two copies). Their body color is pale, dusty tan shade that resembles the light undercoat color of a body-clipped chestnut but with a bold, dark dorsal stripe in dark red, a red mane, tail and legs. They may have additional primitive markings, which distinguish a red dun from a light or body-clipped chestnut.
  • Gold champagnes have a chestnut base coat with the champagne gene (one or two copies). They resemble a palomino, or they may be an all-over apricot shade, but can be distinguished from other colors by amber or green eyes and lightened skin color with freckling.
  • Red or "strawberry" roans have a chestnut base coat with the classic roan gene (one or two copies).
  • A skewbald, "chestnut pinto" or "sorrel Paint" is a pinto horse with chestnut and white patches.

Combinations of multiple dilution genes do not always have consistent names. For example, "dunalinos" are chestnuts with both the dun gene and one copy of the cream gene.

Chestnut mimics

Bay horses have a red body but black "points"
  • Bay horses also have reddish coats, but they have a black mane, tail, legs and other point coloration. The presence of true black points, even if obscured by white markings, means that a horse is not chestnut.
  • Seal brown or dark bay horses are not chestnut but may be confused with a liver chestnut. Those unfamiliar with horse coat color terminology often call most horses "brown". including chestnuts. Brown, which may be difficult to distinguish visually from dark bay, is always accompanied by black points. Liver chestnuts, in particular, are mistakenly called brown or "seal brown".
  • Silver bay horses typically have chocolate- to red-brown bodies with silvered mane, tail, and legs. The flat reddish-brown color and lack of easily identified black points can confuse even knowledgeable horse persons. Silver dapple horses usually hint at black or dark gray pigment at the roots of the mane and tail, and where their silver points end on the legs. Silvers look a bit "off"-chestnut. To further confuse matters, some flaxen chestnuts have silverish streaks in their manes and tails. However, genetic testing can clarify matters.

Inheritance and expression

pheomelaninistic
characteristics of chestnut genetics. The skin will darken as the foal becomes older. Skin depigmentation is not always seen in chestnut foals.
A chestnut foal with body-clipped head and neck, showing two-toned hair shaft, lighter at the roots

The chestnut or sorrel color, genetically considered "red", is caused by one of two

bay and black coat colors, plus two mutations "e" and "ea", both of which are capable of causing the chestnut color. Each individual horse has two copies of the extension gene. If either copy is "E", then the horse will be bay- or black-based. But if the two copies are any combination of "e" and "ea" (e/e, e/ea, or ea/ea), then the horse will be red-based. Alternate extension "ea" is rare and there is no known difference in appearance between it and the more common "e".[5][6]

Because the red color is recessive, two bay or black parents can produce a chestnut foal if both carry "e" or "ea". However, two chestnut parents cannot produce a bay or black foal.

The extension

dominantly
and result in a black-based coat color ("E"), while mutated alleles that create "dysfunctional" MC1R are recessive and result in a lighter coat color ("e").

Normally MC1R would bind to the

pituitary gland[7] and stimulates the production and release of melanin in skin and hair. Red hair color in horses ("e") is created by a missense mutation in the code for MC1R,[8] which results in a protein that cannot bind to MSH. When only mutant copies ("e) of the gene are available, non-functional MC1R proteins are produced. As a result, no black pigment is deposited into the hair and the entire coat is red-based. However, the skin of chestnut horses is still generally black, unless affected by other genes. Some chestnut foals are also born with lighter eyes and lightened skin, which darken not long after birth. This is not the same as the blue eyes and pink skin seen at birth in foals carrying the champagne gene
. It is a genetic mechanism not fully understood, but may be related to the pheomelanistic characteristics of "e".

Though "E" allows the production of black pigment, it can also allow for red pigment in some parts of the animal as seen in

agouti signalling peptide
(ASIP), or agouti gene, which "suppresses" black color and allows some red pigment to be formed.

See also

References

  1. ^ "Foal Colors". Retrieved November 30, 2021.
  2. ^ "General Glossary". American Quarter Horse Association. Archived from the original on July 7, 2011. Retrieved December 25, 2010.
  3. . The statistical analysis of 1369 offspring from five stallions indicate, that darker shades of basic color phenotypes (dark chestnut, dark bay) follow a recessive mode of inheritance in the Franches-Montagnes horse breed.
  4. . The eyes and skin of palominos and buckskins are often slightly lighter than their non-dilute equivalents.
  5. ^ "Red Factor". UC Davis Veterinary Genetics Laboratory. Retrieved October 5, 2023.
  6. PMID 11086549
    . Within the tested chestnut coloured horse population, no association between both alleles e respectively ea and one of the variable chestnut phenotypes could be observed. Different individuals regarding to the shade of their chestnut coat colour were found in every group of the genotypes (e/e), (e/ea) and (ea/ea).
  7. ^ a b Online Mendelian Inheritance in Man (OMIM): MELANOCORTIN 1 RECEPTOR; MC1R - 155555
  8. S2CID 29095360
    .

Further reading

External links