Silver dilutes black pigment whilst not affecting red pigment
Alternate names
Silver Dapple, Taffy
Symbol
Z
Breeds known to carry this mutation
Icelandic Horses, Morgan Horses, Gypsy Cobs, Shetland Ponies, Welsh Ponies, Australian Stock Horses, Quarter Horses and related breeds, Paint Horses, Rocky Mountain Horses
Inheritance pattern
Silver has an autosomal dominant effect on black pigment. The Multiple Congenital Ocular Anomalies (MCOA) associated with silver are incomplete dominant.
Description
Silver dilution only affects black pigment. A black horse will show a flaxen or silver grey mane and tail and a chocolate-coloured coat, often with dapples, accounting for the ‘Silver Dapple’ name. A bay horse will have a solid red coat with lighter legs and a flaxen/silver mane and tail.
Silver is also associated with a range of ocular defects known as Multiple Congenital Ocular Abnormalities (MCOA) syndrome. If a horse has one copy of silver (Z/n) they will have fewer and less severe eye abnormalities than a homozygous silver (Z/Z) horse.
While silver does not have a noticeable effect on a chestnut horse, if they have two copies of silver they are still susceptible to MCOA.
Interpretation of results
n/n: Horse does not carry the silver dilution allele.
Z/n: Horse is heterozygous for the silver dilution allele. It should pass on the silver mutation to half its offspring.
Z/Z: Horse has two copies of the silver dilution allele. It will pass the silver mutation on to all its offspring and will likely have more severe Multiple Congenital Ocular Abnormalities (MCOA).
Reference
Brunberg et al. A missense mutation in PMEL17 is associated with the Silver coat color in the horse. BMC Genetics 2006; 7:46. doi: 10.1186/1471-2156-7-46