What is Brindle?
Brindle colouration in horses is rare and it is not yet known exactly how it is inherited. There appears to be a few different manifestations of the brindle colouring: The chimeric form is very obvious but does not appear to be inheritable. Other more subtle forms have been bred for successfully from parents showing the phenotype. A lot of work has been done by Sharon Batteate
The Brindle pattern consists of a watery or drippy looking striping (sometimes just partial striping) over the body of an animal. It is more commonly seen in dogs or cattle. In horses, the pattern is extremely rare. Brindle has occurred in such diverse breeds as Arabians, Thoroughbreds, Mustangs, Quarter Horses, Tennessee Walking Horses, German and Bavarian Warmbloods, Russian Horses, Spanish Horses, and also in Donkeys and Mules.
The first record of the Brindle Pattern in Horses seems to be by J.A. Lusis, in the publication Genetica vol.23, 1942. In the article on "Striping Patterns in Domestic Horses", he details a Russian cab horse from around the 1800's, that was preserved and put in a museum. Reports of Brindle or Brindle Dun patterns from the 1860's to 1870's in the Criollo horses of South America have been documented by writers such as Marrero, Pereyra, Solanet, and Odriozola.
Many people confuse the Brindle pattern with Dun Factor markings (stripe down the back, barring on the legs, and occasional regular-spaced striping down the ribs). At one time, it was thought Brindle was a just a variation of Dun Factor. Indeed, there have been many examples of horses that were probably carrying both Dun Factor and Brindle.
Brindle horses also have texturing in their coat, similar to that seen in some Appaloosa horses. The pattern seems to be inheritable, especially in terms of coat texturing, but the expression of the darker or more intense pigment to make the pattern visible is highly variable, and even varies with individual horses seasonally / yearly. Sometimes the pattern seems to be composed of dark hair (black or brown), sometimes of white hair (roan or gray).
Information collected since 1990 on Brindle horses is now shedding some light on the Brindle pattern. It now appears there may be two ways in which a Brindle phenotype (outward appearance) can occur. In some horses, the pattern has not been inheritable, pointing to a possible mosaic or chimeric origin, such as seen in tortoiseshell cats. In other horses, the pattern has been shown to be inheritable. However, there could be several genes involved, producing similar patterns (much as pinto/paint spotting can result from several different genes).
The most recent book mentioning the Brindle Pattern is Jeanette Gower's book Horse Colour Explained, 1999, Kangaroo Press, available thru 20 Barcoo Street, East Roseville NSW 2069. Another book is Phil Sponenberg's book on Equine Color Genetics, 1996, Iowa State University Press, Ames, Iowa, 50014. Another good book on genetics, is Ann Bowling's new book Horse Genetics, 1996, CAB International, available thru Oxford University Press, 2001 Evans Rd, Cary, North Carolina, 27513.