When the black gene is present, the agouti gene restricts the black color to the mane, tail and legs. This creates the color we call "bay."
It is an extremely pervasive gene, and is dominant, so very few horses are free of it. This is why there are so few solid black horses.
At this time it is believed that its effect cannot be seen on a red horse; at any rate, a red horse has no black pigment for it to affect.
There is some speculation that it may affect the shade of red the horse appears (i.e. bright chestnut vs. liver chestnut). More research needs to be done in this area.
A bay horse has a black gene plus a bay ("agouti") gene "A", which confines the black to the "points": the mane, tail and lower legs. Some "sooty" bays look nearly black. The "sooty" gene can also produce shading or dapples, as at left. But these are still, basically, a red horse with black points.
Text © 2000-2009 by Julia Lord and horsecolor.com
All photos © by photographer and are used with permission.
If you'd like to have your horse's picture considered for use as an example on this site, you may submit it to us as an email attachment.