Equine

A palomino mare with the tobiano pattern. Photo courtesy of CheyAut Ranch

Tobiano is probably the best recognized of all the white patterns. It almost always leaves the legs white. It will cross the top line at the shoulders and hip before other areas and fights to leave the chest, flanks and head colored. It commonly results in a solid head and white tale head. Some theorize that Tobiano doesn't add face white but whether this is true or not is still open for conjecture. When Tobiano is mixed with other patterns we can get a solid white or nearly white horse but rarely, if ever, does Tobiano express to that extent alone. When Tobiano is very minimal (sometimes called Crypt-Tobiano). It will usually express as four white stockings or socks, sometimes with a wither or neck spot. In miniature horses, it's expression can found at it's most minimal, at times leaving only the back two feet white.

The color brown in horses has long been a source of ambiguity. Some registries handle brown as a separate color, while others consider all browns to be dark bay. Adding to the confusion, researchers, even as late as 2003, theorized that the darkest brown horses were actually black horses with mealy. It became apparent however, when the recessive allele at agouti (a) was located, that these dark horses with brown noses and flanks didn’t test as black but as bay. Because no other agouti alleles were located, at the time, it was generally accepted that brown (even the almost black variety) was just a darker version of bay. This changed when Pet DNA Services of Arizona isolated the mutation that causes brown.

Frame is a white pattern in horses that puts white on the barrel and the face of a horse. It tends to leave white markings with jagged edges but no "halos" (areas of dark skin under white hair) or roaning. Frame can cause blue eyes and face white but prefers to leave the legs solid. Horses positive for frame can have leg white, but it must be added by a separate white pattern. Any color horse can be a frame carrier and frame's expression can very greatly from a "solid" animal to one who is wildly marked. Frame will rarely cross the top line of the horse without another white pattern being present. Because of frame's wildly varying expression, as well as its ability to "blend" with other patterns, it can be very difficult to tell if a horse carries frame simply by visual inspection. Frame is the gene responsible for Lethal White Overo Syndrome. It is therefore important, for everyone who may breed a frame positive horse, to understand how frame is inherited and how it affects foals.

A dun filly displaying her clearly defined dorsal vs the smudged look of countershading. Photo donated by Cascabel Ranch Performance Arabians

It's quite common for countershading to be confused with dun markings. What is countershading? It's not known what causes countershading type markings but they are believed to be a type of camouflage. Countershading is more common on foals but can appear on adult horses as well. Countershading markings that can closely resemble dun are false dorsals, shoulder bars, and stripes or mottling on the legs. It is usually possible for a trained eye to distinguish between the two even on foals but at times even experts can be fooled. The most important thing to remember is that a dun foal must have a dun parent. It is sometimes possible for dun to "hide" in that it can be covered by gray or white patterns but generally speaking if the horse has no dun in its near pedigree then it's not dun but countershading.

All mammals produce two types of pigment, and horses are no exception. Eumelanin is black pigment and pheomelanin is red/yellow pigment. These two pigments work together to provide the basis of all horse colors. They are controlled by two genes, Extension (MCR1) and Agouti (ASIP).