Splashed white (SW 1-4)

Splashed white is a variable white spotting pattern characterized primarily by extremely large blaze, extended white markings in legs, variable white spotting in belly, and often blue eyes. Some, but not all, splashed white horses are also deaf. Recent research has identified 4 mutations – SW-1, SW-2, SW-3 and SW-4 - that cause splashed white phenotypes in horses. SW-1 has been found in several breeds - Quarter Horse, Paint, Trakehner, Miniature Horse, Shetland Pony and Icelandic Horse – and may be present in other breeds as well. Horses homozygous for SW-1 (SW1/SW1) have been identified, which suggests that this mutation is not homozygous lethal. SW-2 and the rare SW-3 occur exclusively in certain lines of Quarter Horses and Paints. Based on predictions from other species, SW-2 and SW-3 may be homozygous lethals and thus matings of two horses that carry SW-2 or SW-3 should be avoided. The rare SW-4 mutation has been identified in the Appaloosa breed and may cause a splashed white or a broad blaze.
Horses that carry combinations of the splashed white mutations, tobiano or lethal white overo can display extensive white patterning or be white.