The three base colors
Bay
A bay horse has brown to reddish-brown hair on its trunk and neck, with a black mane, tail and lower legs. Some bays are light brown; others are very dark, almost black.
Bay: how the color works and is inherited
Two genes explain this arrangement. MC1R allows the horse to produce black pigment. ASIP largely restricts that pigment to the mane, tail and lower legs, leaving the trunk and neck brown or reddish.
A foal inherits one version of each gene from each parent. Several combinations produce bay. Two bay parents can therefore have a bay, black or chestnut foal, depending on the versions they pass on.
Bay: origins and the role of breeding
Bay existed in wild horses before people began breeding horses. Ancient DNA reveals the genetic variants that allow this color in prehistoric populations. Bay did not originate with the creation of a modern breed or a recent cross between breeds.
Choosing bay breeding horses has made bay more common in some populations. Crossing two different breeds is not necessary for a foal to be bay.
Bay: photographs of horses
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A bay Ardennes stallion with black mane and reddish-brown hair.
Buddy, a bay mustang with black lower legs and mane.
A free-ranging bay mare on Shackleford Banks.
A bay horse grazing at Kencot, England.
A very dark bay: brown hair contrasts with the black mane.
A bay horse in its winter coat in Transylvania.
Photograph credits
Photographs have been resized. Photographs within scientific figures have been separated by cropping. Colors are preserved.
- A bay Ardennes stallion with black mane and reddish-brown hair. — Marie-Claire · CC BY 3.0
- Buddy, a bay mustang with black lower legs and mane. — Mwirig · CC BY-SA 4.0
- A free-ranging bay mare on Shackleford Banks. — Bonnie Gruenberg · CC BY-SA 3.0
- A bay horse grazing at Kencot, England. — Acabashi · CC BY-SA 4.0
- A very dark bay: brown hair contrasts with the black mane. — Acabashi · CC BY-SA 4.0
- A bay horse in its winter coat in Transylvania. — Emőke Dénes · CC BY-SA 4.0
Bay: telling similar coats apart
On a very dark bay, look for brown or red hairs around the muzzle, flanks and inner thighs. A black horse’s colored hair starts out black, although sunlight can fade it to brown.