Taffy/silver/eye abnormalities (MCOA/silver)
Silver (taffy) coat colours include the eye-catching black silver (aka silver dapple) and bay silver.
The silver gene alters the distribution of black pigment but does not affect red. This means that the effect of the silver gene is not visible on chestnut horses and other colours that have no black, such as palomino.
In addition to its effect on colour the silver gene is thought to cause eye abnormalities in some silver horses (not all). These are referred to as multiple congenital ocular abnormalities (MCOA). These abnormalities can affect vision. Horses with two copies of the silver gene are substantially more likely to show signs of MCOA than those with one copy of the gene.
Gene or region and technical reference
Gene: PMEL (causative). Reference: Brunberg et al., 2006
n. Test developed using animal controls.
Z. Test developed using animal cases.