Splash White 1

Description

Splashed white horses look as though they were dipped in white paint, feet first. Typical features are a large blaze or bald face, white legs, white on the belly that may extend up the sides, and often blue eyes. The edges of the white areas are crisp and well defined, unlike the roaned edges of sabino. In some horses the white is minimal and cannot be told apart from ordinary markings, so testing is the only reliable way to identify carriers.

Several different mutations cause splashed white. Splash White 1 (SW1), a variant in the MITF gene, is the most widespread. It is thought to have arisen several hundred years ago, before the modern breeds were founded, which is why it is found across so many breeds. This test detects SW1.

One copy or two

SW1 is incompletely dominant. Horses with one copy (n/SW1) show splashed white markings to a varying degree, from a large blaze and white legs to minimal white. Horses with two copies (SW1/SW1) usually show more extensive white, typically a bald face, blue eyes and white extending up the legs and belly. SW1/SW1 horses are healthy; the homozygous state is not lethal.

Other splash white types

• Splash White 2 (SW2) — a PAX3 variant found in certain Quarter Horse and Paint lines.
• Splash White 3 (SW3) — a rare MITF variant in certain Quarter Horse lines. Two copies are suspected to be lethal, so two SW3 carriers should not be bred together.
• Splash White 4 (SW4) — a rare PAX3 variant reported in Appaloosas.

A horse can carry more than one splash white type, and together they usually produce more extensive white.

Hearing

Splashed white genes can affect pigment cells in the inner ear, which are needed for normal hearing. Some splashed white horses, particularly those with extensive white on the head and blue eyes, are deaf. Most splashed white horses hear normally, but owners of horses with extensive head white should watch for signs of hearing loss, such as not responding to voice or being easily startled from behind.

Possible results

Breeds Affected

American Quarter Horse, American Paint Horse, Appaloosa, Miniature Horse, Shetland Pony, Icelandic Horse, Trakehner, Welsh Pony, Morgan, Mustang, Thoroughbred

Reference

Mutations in MITF and PAX3 cause “splashed white” and other white spotting phenotypes in horses.

Novel variants in the KIT and PAX3 genes in horses with white-spotted coat colour phenotypes.

Related Tests

• Splash White 2 — a second splash white type in Quarter Horse and Paint lines
• Splash White 3 — a rare type suspected to be lethal in two copies
• Sabino1 — a white pattern often confused with splash

The Splash White Panel covers SW1, SW2 and SW3 together.