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The hair of chestnut horses can also fade; in such cases, a horse may look like he is covered with dust.
Chestnut foals are born red color with whitish legs and underbelly. Guard hair is often light. The foals become darker with age.
Chestnut color is common, surpassed in frequency only by bay. It is prevalent in the Arabian, Thoroughbred, Hanoverian, Budyonny, and Karabakh breeds, and some breeds have a characteristic chestnut shade, including Suffolk Punch and Russian Don horses. Chestnut color is encountered extremely rarely in Friesians, Percherons, Cleveland Bay, Orlov Trotters, Exmoor ponies, and Andalusians.
INHERITANCE OF BASE COLORS
Base colors in horses (black, bay, seal brown, and chestnut) are controlled by two genes: Extension and Agouti. The gene corresponding to the Extension locus is called MC1R (melanocortin-1 receptor). The “Wild” allele of this gene, designated “E,” is dominant and codes for the intact, normal receptor for the melanocyte-stimulating hormone. Upon binding of the hormone, the receptor leads to the synthesis of the black pigment eumelanin in melanocytes.