Silver Horse

Silver Horse

Silver coat colour dilution, known as Silver Dapple, is caused by a mutation that inhibits the production of the dark pigment (eumelanin) in the horse’s hair. This results in black and bay horses having a silvery-grey or flaxen/white mane and tail. Silver Black horses have a dark brown body, while silver bay horses have a body coat that is similar to chestnut, but dark lower legs or dark ear tips can help distinguish between a flaxen chestnut and a silver bay.  Chestnut horses can be heterozygous or homozygous for silver without showing the trait.

Silver is a dominant trait, caused by a mutation to the gene for premelanosome (PMEL17), and it is found in multiple breeds. In Rocky Mountain Horses it may be called Chocolate, or in Australia the colour is often called Taffy.

There is no relationship between Silver dapple and Dapple Grey, which can be s a stage of progressive greying caused by G-Locus Grey

MCOA

Horses with the Silver mutation are at risk for Multiple Congenital Ocular Anomalies (MCOA, also known as Anterior Segment Dysgenesis and as Congenital Aniridia).

MCOA can cause a range of eye defects such as uveal cysts, cornea globosa, iris stromal hypoplasia, abnormal pectinate ligaments, cataract and iris hypoplasia.

MCOA has an autosomal incomplete dominant mode of inheritance, meaning that horses with one copy of the variant (N/Z) may only have cysts hard to distinguish without ultrasound of the eyes. Horses with two copies of the variant (Z/Z) have a much more severe presentation of the condition. Chestnut horses will also be affected, even though they do not express the coat colour.

Relevant tests

• P784