The chestnut colour is defined by a completely red coat with red points (mane, tail, ear tips, lower legs). Though the most common shade is a normal red, it can range from yellow to nearly black.
The melanins in the cell are turned into pheomelanin by the e-allele of the extension gene. This pheomelanin is the red pigment that is responsible for the overal red coats of chestnut horses. The opposite, when the E-allele from extension is present, results in eumelanin, the black pigment. When other genes are present, they can influence this process and create different colorful outcomes. Due to the fact all horses have to have either the e or the E-allele creating red and black pigment, we call chestnut and black two of the base colours. As the e-allele is recessive to the black-pigment creating E-allele, it is also one of the easiest colours to breed for in a population with a lot of chestnut horses because it breeds pure.
Chestnut always has the genotype ee. Agouti (bay, brown) cannot influence it, as that gene requires black hair to be present. Other genes like grey and cream can influence it, but silver for example cannot as it too requires black hairs.
- ee = chestnut
- eeAA = chestnut
- eeAa = chestnut
Beside the common chestnut colour, flaxen chestnut is one of the best known shades of chestnut. The main coat is not too affected, but the most striking difference is the change in colour of the mane and tail. These can turn yellow or even a nearly pure white. The lower legs, especially when they are feathered to some degree, can also be altered to a lighter colour, though this is not always as profound as the mane and tail.
The cause behind the flaxen shift is not known, but it appears to be recessive in some form. Foals may be born with flaxen mane and tail, or with normal red mane and tail which will lighten as they age.
Flaxen is present in many breeds, ranging from rare to common. Flaxen chestnut is the only accepted colour in haflinger horses.
Liver chestnuts are chestnuts that are considerably darker than the common shades. They range from a dark red to chocolate and sometimes nearly black, making is very hard to visually distinguish it from true black horses. The key is to check the lower legs, which are usually a little lighter than the coat. Surprisingly, foals are born a more common red, but darken and lighten in several fases when they grow older.
The cause of this darkening is not known. In the past the terms 'sooty' or 'smutty' have been used, but they are mainly speculative. Liver chestnut can be combined with flaxen to give a spectacular effect. It is particularly loved in arabians and morgans, but appears in no breed as much as it does in the black forest horse.
It would be too much to describe all variants of the chestnut base colour, but if we have to compile a shortlist, palomino would be on it. This bright yellow or golden colour is a favourite among many breeders and owners. It is caused when a chestnut-based foal also receives one copy of the cream gene from one of its parents. The cream turns the red coat into yellow, ranging from a soft cream to bright gold.
As palomino horses already have white mane and tail, the flaxen genetics will not affect it. The colour may however, be influenced by what is likely the same mechanism as in liver chestnuts, sometimes resulting in uniquely black palominos.
Chestnut is caused by the e-allele of the extension gene. As it is recessive, it requires two copies of it. Chestnut horses always breed true, but black or bay based horses may occasionally produce a chestnut foal.
- Chestnut code: ee
- Black code: Ee or EE or eE
- Flaxen code: eeff (it's ff and not Ff or FF as flaxen is probably recessive)
- Palomino code: eeCRn (where CR means 'cream' and n stands for 'no cream')