A visual guide to equine colors and patterns
The Mushroom Dilution
Chestnut with the mushroom dilution (Mayflouwer Ester v.d. Toom, Shetland Pony mare). Photo by Anna Gamsgaard Frederiksen.
Bay with the mushroom dilution (Kaitlynn of Duke Stable, Shetland Pony mare). Photo by Anna Gamsgaard Frederiksen.
Silver dilutes the black pigment on the body of the horse to a silvery chocolate color, and turns the mane and tail flaxen. This means that black horses show the effect most strongly. Bay horses have their black legs diluted and flaxen mane and tail, but their red body remains unchanged. Because they do not have black hair to dilute, chestnut horses that have the silver dilution do not show the effect. Because chestnuts with the silver dilution can have self-colored manes and tails, it does not appear that silver alters their manes and tails to flaxen.
Silver-diluted black can vary in color from a pale taupe to a deep chocolate that approaches black. Seasonal changes are common, with winter coats tending to be paler. As they age, the flaxen manes and tails tend to darken, starting at the roots. Black silvers sometimes show dappling. This is especially vivid when the horse is clipped. Paler silvers sometimes have a dark face mask similar to that seen on dun horses.
When combined with cream, silver-diluted black pigment tends to lose its cool, silvery tones and look more like milk chocolate. Black silvers with cream, sometimes called silver smokies, often lack the contrast in their manes and tails seen in ordinary black silvers.
A pale shade of mushroom (Shady Acres Cute Cupcake, Shetland Pony mare). Photo by Anna Gamsgaard Frederiksen.
A dark shade of mushroom (Zilver Sun v.d. Nijkamphoeve, Shetland Pony mare). Photo by Anna Gamsgaard Frederiksen.
Silver smoky (black silver cream) - notice the warmer tone compared to the two horses above (Positively Charmed, purebred Morgan)
A clipped black silver showing vivid dappling with longer coat is visible at the base of the tail (Miniature Horse)
Silver can be difficult to identify reliably without genetic testing. Darker silvers, liver chestnuts and sooty palominos can all look very similar. The difference in leg color on clear bay silvers can be subtle, especially in winter, leading them to be misidentified as chestnut. Sooty chestnuts where the dark hairs are concentrated on the legs can be mistaken for bay silvers. Some wild bays have very pale, silvery points and some otherwise ordinary bays have flaxen manes and tails. Black silvers and chestnut-based mushrooms also look very similar.
Bay horse with a silver tail
Sooty chestnut with dark legs and mixed flaxen mane and tail (grade pony)
Mushroom is recessive, so it can hide for generations until two carriers are bred together. Also, because it dilutes red pigment, base colors with little or no red hair do not show it, or may not show it in an obvious way.
Silver is caused by a mutation to the PMEL17 gene, also known as SILV. Commercial tests to identify silver horses are available. Research on ancient remains suggest that the mutation dates back to at least to the Iron Age.
The mutation for silver is associated with Multiple Congenital Ocular Anomalies (MCOA), formerly known as Anterior Segment Dysgenesis (ASD). Homozygous silvers are believed to be at higher risk for these eye defects.
So far the only breed where mushroom has been observed is the Shetland Pony. A few Miniature Horses have been identified as carriers. Shetland Ponies were used in the development of that breed so it is assumed to have come from there. It is also possible that the mutation is present in the American Shetland Pony since it also shares common ancestry with the Shetland Pony, but without widespread testing that would be hard to confirm.
The mushroom mutation dilutes red areas of the coat to a color between pale taupe and sepia brown. It amplifies black countershading in bay ponies. Because they do not have red areas or variation in the amount of black in their coat, black ponies effectively hide the mushroom dilution even when homozygous. Black silver, palomino and buckskin can mimic mushroom. The mutation is not known to be associated with any defects.
Halstock Shetlands - mushroom breeding program
Halstock Superstar - dark mushroom tobiano stallion
Halstock Sienna - dark mushroom with a self-colored mane minimal tobiano mare
Halstock Swiss Cappucino - very dark mushroom tobiano, dark mane and tail
Twyford Pepsi - mushroom tobiano stallion
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