You've probably seen brindle dogs, but have you ever seen a brindle horse? I haven't, but they are out there! They are rare and there's not a lot of information out on the Net about them, but I've included some links to an excellent Web site, by Sharon Batteate, which includes lots of information on the coat coloring as well as some great photographs. Research is going on right now into ways in which the brindle phenotype may occur.
It should be noted that the Brindle Horse is not a breed, but a phenotype which displays the distinguished brindle coat coloration.
In Sharon Batteate's Historical References to Brindle in Horse she notes that the earliest recorded appearance of the brindle coat pattern was seen in a Russian cab horse in the 1800's that was preserved and displayed in the Zoological Museum in Leningrad.
The main distinguishing feature in brindle horses is the striking coat pattern, which looks like someone has drizzled a darker color paint over the horse. The coloring is sometimes confused with Dun Factor markings -- the dorsal stripe and stripes on the legs. The brindle coloration has appeared in various breeds, such as the Arabian, Tennessee Walking Horse, Russian horses and others, as well as donkeys and mules.
Brenda Batty Atty, dark bay brindle mare owned by Sharon Batteate. Photograph used with permission.
According to research, it seems there are two ways in which the brindle phenotype can appear in horses. In some horses, the pattern seems to be inherited, indicating that one or more genes are responsible. In other horses, the pattern is not inherited, possibly due to mosaic or chimeric origin, similar to that seen in tortoiseshell cats.
Since the brindle coloration crops up (albeit rarely) in a variety of breeds, uses of the Brindle Horse are varied.