Chestnut/Sorrel Horse Color
Also known as sorrel, chestnut is the most recessive equine color. Different shades of chestnut may be given different names in different parts of the world or in different breeds, but since every red horse has the same genetic makeup, we will stick to one term: Chestnut.
Every chestnut has these two genes: ee. This allele of the Extension gene makes the horse produce red pigments, instead of black (E produces black). All chestnuts are homozygous-- they have two e genes. This is why a chestnut crossed with a chestnut will always produce a chestnut.
Since this basic rule is understood by almost all breed associations, non-chestnut foals from two chestnut parents are not given recognition... it's obvious someone was mistaken as to the foal's parents, or one of the parents was misidentified as a chestnut.
While breeding two chestnuts always produces chestnuts, this is not the only way to produce a chestnut horse. Other colors, such as bay, black, palomino, buckskin, and brown, can also produce Chestnut foals.
If two non-chestnuts produce a chestnut foal, then this is proof that both parents carry the 'e' gene. Each parent gave their e gene, resulting in a foal that is ee-- chestnut.
The different shades of chestnut are many and varied. They can range from an intense red to palomino-colored, to almost black.
All attempts to classify the shades of chestnut by their genotype has failed. It is sometimes difficult to classify a horse by his phenotype because of changes in color due to season, nutrition, or other factors. However, you can get a pretty good idea of what shade your horse is and pick the term you best suits him-- usually horses are evaluted when they are well-groomed and in summer coat.
The shade of chestnut is also influenced by the F gene (flaxen), which makes the horse's mane and tail ligher, and may lighten the legs or entire body. The Pangarè gene will also lighten a chestnut's muzzle/flanks. The Sty (sooty) gene may scatter dark hairs throughout the horse, making him darker, giving him dapples, or seasonally changing him to a false liver chestnut.
Haflingers are a good example of very light chestnuts. The flaxen and mealy coloration is so distinct in the Haflinger breed that these horses are often mistaken for palominos. There are no palominos, only chestnuts, in this breed.
Friesian stallion is a dark chestnut. Although famous for their
pitch black color, the occaisonal extremely rare chestnut friesian
does occur. This is because, although visually black, a heterozygous
black horse carries a red gene. When two heterozygous black horses
are bred, there is a 25% chance of getting a chestnut. Therefore
both Fire Magic's sire and dam must have been heterozygous blacks,
and if bred again, could produce another red friesian.
This Morgan is a liver chestnut. The term "liver chestnut" is often used for chestnuts that have a chocolate brown coat. I have also heard the term "chocolate chestnut" used.
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