Splash White 2

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. 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 2 (SW2) is a variant in the PAX3 gene, a gene involved in the development of pigment cells. Unlike the widespread Splash White 1, SW2 is found only in certain Quarter Horse and Paint Horse lines. This test detects SW2.

Breeding two SW2 carriers

Horses with one copy of SW2 (n/SW2) show splashed white markings to a varying degree and are healthy. No living horse with two copies (SW2/SW2) has been reported, and two copies are believed to be lethal before birth. For that reason, two SW2 carriers should not be bred together. Breeding a carrier to a non-carrier gives each foal a 50% chance of inheriting SW2 with no risk of an SW2/SW2 pregnancy.

Other splash white types

• Splash White 1 (SW1) — an MITF variant, the most widespread type, found across many breeds. Two copies are not lethal.
• Splash White 3 (SW3) — a rare MITF variant in certain Quarter Horse lines. Two copies are also believed to be lethal.
• 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

Reference

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

Related Tests

• Splash White 1 — the most common splash white type
• Splash White 3 — a rare type also believed to be lethal in two copies
• Lethal White Overo (LWO) — another white pattern where two carriers should not be bred together

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