Base Modifiers – The Silver Gene

The silver gene (Z) dilutes the black base coat with or without the Agouti gene (bay). It does not affect the red base coat. Horses with one or both Z genes will dilute their coat color, which is an autosomal dominant gene. The gray autosomal dominant gene supersedes the silver gene in that, over time, the silver dilution will eventually become all gray as depigmentation increases.

With the silver dilution, the normally black mane and tail will become flaxen with a “sooty” appearance versus the flaxen mane of a palomino. The unique coloration is because there is some black in the diluted hair, whereas a palomino (a dilution of the red base coat) has no black. The hair coat will become chocolate brown, often with dapples.

Common names for this dilution are “silver dapple” and “bay dapple,” while Australians may call this “Taffy.”

Liver chestnut horses with a flaxen mane and tail are actually light bay horses (black base coat with the Agouti bay gene) with the silver dilution. Chestnut horses will retain red to yellow tones, while a silver-diluted black or bay will retain gray, black or brown undertones. Diluted chestnuts with the cream gene will also have a slightly lighter eye color, while the silver gene of the black base coat does not lighten the eye color.

Common American breeds that carry the silver gene include the Rocky Mountain Horse, the Miniature horse, Morgan, American Saddlebred, Missouri Foxtrotter, Tennessee Walking Horse and the Quarter Horse. Also, carriers are the Icelandic, Nordic Pony, Shetland pony, Welsh Mountain Pony, Welsh Pony, Swedish Warmblood and the Finnhorse.

Some horses with the silver gene also have Multiple Congenital Ocular Abnormalities (MCOA) that include cataracts, uveal cysts, hypoplasia of the iris and globe enlargement. It may also be the cause behind some retina detachments.

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