The Silver (AKA Silver Dapple) Gene
Silver is a dominant gene in the dilution category. (Remember, dominant means you only need one gene to get a visible effect, and dilution type genes are those that cause the color to be lightened in some way.) It is a simple dominant; there is no visual difference whether the horse has one Silver gene or two. The symbol for this gene is "Z" (nobody seems to know why that letter was chosen, but "S" would have been confusing since many colors begin with that letter, and maybe just about everything else was taken). The gene was isolated in 2006, and there is now a test for it.
This color has been known for 30 years or more, but is only recently becoming better understood. The name Silver Dapple was originally applied to Shetland Ponies, in which the color is fairly common (at one time it was even thought that the gene only occurred in Shetlands), because it frequently has the extremely dappled, greyish body color with silver-white mane and tail in that breed. Now we know that not all (possibly, not even most) of them are dappled, so the name has been shortened from Silver Dapple to just Silver. The term "Silver" has been confusing to some, who expect to see a grey-toned horse perhaps, but it has been in use too long to change. In Australia the color is called "Taffy", but the term has never caught on elsewhere. In some of the breeds in which Silver is common in the USA, such as the Rocky Mountain Horse, it is simply called "Chocolate".
The Silver gene is interesting because, unlike other dilution genes such as Champagne and Dun, this one is what's called pigment-specific. Silver dilutes only black pigment. Thus, the Silver gene can be carried and "hidden" by a chestnut horse (since it has no black pigment to be diluted), and in this way it can appear to skip generations, even though, like any dominant gene, one parent must have the gene in order for the foal to have it.
How It Works
Silver on Black
Silver on a black base color is the shade that comes to
mind first when hearing the term "Silver Dapple". The body color is
diluted to a chocolate-brown or mocha-brown shade, sometimes light enough to
appear similar to a sooty palomino. The mane and tail are often near-white, a
striking contrast. The lower legs are usually lighter than the rest, almost
flaxen near the hoof, and the lower legs are often dappled (which is highly
unusual in other colors). The mane and tail often have dark roots. In a horse
with the "classic expression" of Silver Dapple, there will be very
distinct and strong dappling present, which, unlike most colors, does not appear
to be related to age or condition, but rather stays fairly constant throughout
the horse's life -- although they may vary with the seasons, appearing on the
summer coat but not the winter coat, usually. But not all Silvers show the
dappling. Some are a flat chocolate-brown color all year round. Silver on black
can be hard to tell apart from a dark flaxen liver chestnut, and in most breeds
they have indeed been registered as "chestnut" because nobody knew
what they were. Some clues to look for would be the dappling, a drastic change
in color from winter to summer, a bluish cast rather than a reddish tone, and a
silvery mane/tail rather than golden-hued flaxen. Still, it may be impossible to
tell the difference by looking. Thankfully,
there are now genetic tests that will tell for sure. The normal name for this
color is "Black Silver", but sometimes you might see them called
"Classic Silver Dapple", "Chocolate Silver",
"Chocolate", or just "Silver".
Silver on Brown
A seal brown
with the Silver gene will look similar to either a black silver, or a bay
silver, depending on how light or dark the brown's base color happened to be.
Most seal browns are mostly black, and this plus Silver would probably be very
hard to tell apart from black silver. The lighter seal browns with more tan in
the coat would give a lighter shade of Silver. The Agouti test may be needed to
tell apart black-based from brown-based dilute colors.
Silver on Chestnut
dapple color can, like any color, occur in combination with any of the various
other dilution (i.e. Cream, Dun, or Champagne) or spotting (i.e. pinto,
appaloosa, etc.) genes. In some
cases the combinations can make it difficult to identify the presence of the
Silver gene. When Silver and Cream
are both present, the effects of the Silver gene tend to be less obvious, or
even not really visible at all. This
would seem to be counterintuitive since Cream makes the mane and tail of a
palomino white, and Silver makes the mane and tail of a black silver white (or
nearly white, usually), but oddly enough they seem to almost cancel each other
out instead of doubling the dilution effect.
Breeds That Have This Color
is not frequently seen except in a very few breeds -- the Shetland, Mini, and
Icelandic have quite a few, and there are a few breeds in the USA which have
purposely selected for the color so that now many horses of those breeds,
perhaps even most in some cases, are silvers: the Rocky Mountain Horse, Mountain
Pleasure Horse, and Kentucky Mountain Saddle Horse.
Aside from those breeds, it is not a very common color, but it does occur
in the Welsh Pony, Welsh Cob, Quarter Horse, Paint, Morgan, Saddlebred,
Tennessee Walker, Missouri Foxtrotter, Bashkir Curly, Chincoteague Pony, and
likely in the Appaloosa, Mustang, Dutch Warmblood and Paso Fino. There are even
reports of it possibly occurring in the Arabian, but these have never been
proven. It is thought to have been
in the Friesian breed in the past, but no longer. It also is known to occur in
some draft breeds such as the Belgian, Breton, Comtois, Noriker, and Italian
There is an excellent website on the silver dapple colors at: http://www.silverdapplemorgansproject.com
Although focused on Morgans, the color info is applicable to any breed.
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