Tag Archives | silver

An important correction

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Louis XIV as the Roman Emperor in the Carrousel du Roi, by Israel Silvestre the Younger, c.1662. The depiction of his mount, and a similar one for the Duke d’Anguein, suggest that the silver dilution might once have been present in the Spanish horse population. 

A few years ago, I reported that a Pura Raza Espanola (PRE) mare has tested positive for silver. This was significant since a previous case of what appeared to be a bay silver stallion had been called into question, regarding both a reported test and registration status. Unlike the stallion, the mare in question was not visibly silver – she was chestnut – but was said to be a carrier. Unfortunately, she has since proven to be negative for the dilution. It appears that while the owners used standard testing notation, what they were doing was what the dog geneticist, Sheila Schmutz, refers to as “guessotyping“. More often when people guess the color of a horse, they use the name of the color. This is especially true when a new and interesting color with an appealing name (champagne, pearl) comes to light. Most of the time there are other clues that the owner is guessing, though that was not true with this particular case, where the particulars were a little unusual.  With the proliferation of websites and forums dedicated to the discussion of horse color, and the more widespread use of testing notations in the descriptions of horses,  this is likely to be an increasingly common problem going forward.

From the standpoint of this blog, I have tried to keep a balance between verifying information and being unnecessarily antagonistic with owners and breeders. In the past, owners of horses with unexpected colors or test results have encountered very aggressive – and at times outright rude – questioning from color enthusiasts. What is often lost in these exchanges is an awareness that breeders do not owe enthusiasts copies of test results. Certainly a potential buyer, or a mare owner interested in breeding to a stallion, have every right to ask to see results if the true color of a horse is in question. But what we are often asking is that someone satisfy our curiosity. Owners and breeders are a valuable resource for anyone interested in horse color. Unlike the situation with the model animal for coat color, the mouse, it is not feasible to breed large, expensive animals as part of a research program. Breeders are doing the work, and paying the bills, for that. What’s more, they are in a unique position to observe nuances of color that people less directly involved with the individual animals might miss. Maintaining a positive atmosphere encourages an open exchange of information, and reduces the chance that someone with a unique horse feels burned by the research community.

That said, it is clear that testing notations cannot be assumed to represent an actual test. As much as it would be a good idea if people did not use them without test results in hand, because they are more widely understood than in the past, the temptation to use them as shorthand for a guessotype is there.

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More on founders

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Fascination, a son of Trot by Trot’s grandson Chestnut

In the previous post I talked about how novel colors are the result of a mutation that occurs in a single, founding animal. I wanted to use a couple of different colors to illustrate this idea, and talk about what that means for anyone researching color in a given breed. In this post, I’ll talk about the search for the founder of the silver dilution. 

The silver dilution first came to the attention of researchers through the work of the early geneticist W. E. Castle. Castle had authored a number of articles that appeared in the American Shetland Pony Journal, and in 1953 he published the paper “Silver Dapple, A Unique Color Variety Among Shetland Ponies” in the Journal of Heredity. In that article, Castle concludes that silver originated with the American Shetland mare, Trot 31.

The first pony known to have shown this color (doubtless a mutation) was the mare Trot 31, born in 1886, the color being described as “fawn”.

It was reasonable for Dr. Castle to draw the conclusion that Trot was the founder for the mutation, because he had been told that her color had never been seen before, and that only her descendants possessed it. Since a study of her offspring and their production records already proved that the color was dominant, then the logical explanation for its sudden appearance was that she was the source for the mutation. This conclusion was flawed, in part because the interaction between the base colors (black, bay and chestnut) was not well understood. Castle and others had concluded that chestnut was the equivalent to Brown, a recessive version of black in mice and dogs. But there was another problem: the breeder was not entirely truthful about his ponies. In the same article, Dr. Castle quotes Mr. Bunn, the owner of Trot.

[Trot] was the only pony of this color in America and was also a beautiful color… However, every one of the ponies you now see of this color was the produce or descended from Chestnut. His granddam Trot was the only mare ever known to have that color of all the Shetlands ever bred or known.

Castle then adds that those who study genetics “call such abrupt origins mutations”. But Trot was not as unique as the previous quote might suggest. Her breeder had a full brother, Baron Keithsburg, who was also silver. When a horse has a sibling with the same color, that is proof that the color did not originate with them, and attention has to turn to one of the two parents. In the case of Trot and Baron Keithsburg, their sire Jeff was said to be of the same color. But perhaps Mr. Bunn did not lie outright, because Jeff was not actually a Shetland Pony. By multiple accounts, including Mr. Bunn himself, Jeff was an imported Welsh Pony.  (Jeff is discussed briefly in the chapter on Hackneys in Volume I of Equine Tapestry, and more of his story will come up in Volume II, which covers the pony breeds.)

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Chestnut, grandson of the silver “founder” Trot

The article about Trot did prompt at least one reader to write to Dr. Castle to say the color was not unique to Trot or even to Shetlands. She pointed to a half-tone photograph of Skerryvore, a Highland Pony stallion pictured in Lady Wentworth’s Thoroughbred Racing Stock. Images of Skerryvore are fairly easy to find, since he was often held up as a model of “improved” pony type. Those familiar with the dappling on silver dilutes will probably recognize right away, even in a half-tone, that Skerryvore was an ordinary dapple grey. (The image in his entry for allbreedpedigree.com is even more telling of his true color.)

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Skerryvore, Champion of the prestigious Highland and Agricultural Society Show in 1909 and 1911

Perhaps Dr. Castle had further information about other Highland Ponies, because the color was present, if not with Skerryvore, among the ponies of his time. Rhum Laddie, the stallion found in the pedigrees of most modern silver dilute Highlands, would have been a contemporary of Skerryvore. Or perhaps other Shetland breeders had alerted him to the discrepancies in the story he was given about Trot. Either way, Castle published an addendum shortly after the original article, stating that the color probably had older origins. It seems few read this, because the idea that this was a color unique to Shetlands – and to American Shetlands in particular – persisted for decades. In fact, when the first Welsh Pony tested positive for silver, there were vocal accusations that his American breeders must have slipped in American Shetland blood.

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Rhum Mary V, modern silver dapple Highland Pony

That kind of situation, where a color becomes so closely associated with a specific breed, tended to muddy the waters before there were genetic tests. Testing has allowed researchers to determine if a color in one breed is in fact the same color in another. When the same color is found in separate breeds, then barring dishonest pedigree records, that is proof that the mutation dates back to a time before the two groups separated. This fact is used as a way to guess the age of some mutations. If the same mutation is spread widely across a group of breeds with no documented connection, like yesterday’s example with grey, then it is pretty safe to assume the mutation is quite old. This can also be used to guess at the possible origins of a mutation, if it predates recorded pedigrees. When a mutation clusters with a group of related breeds, then it tends to suggest that it arose in the animals that were used to develop those breeds. The pearl dilution, for instance, is suspected to have Spanish origins because so many of the breeds were it is found have Spanish blood. These are still guesses, since it is quite possible for a mutation to occur in one population, spread to a second area as an outcross, while the color in the original area dies out. Still, this type of hypothesis can be useful when trying to guess how likely a horse may carry a given mutation – and how worthwhile it may be to send out hairs for a test.

Using the oldest breed with a positive test for silver, the Icelandic, it can be proven that this particular mutation dates back to at least 982 AD, which was when Iceland banned importation of new horses. There is another avenue to investigate questions about original mutations, however, which has been discussed in previous posts on this blog. It is possible to test ancient remains for mutations. In a study that did just that, the silver mutation was found in Siberian remains dating back to the Iron Age. That date might get pushed back further, if earlier remains with the mutation come to light, but we will likely never know much about the founding horse or pony. The long span of time since he or she lived does explain why the color has spread to so many diverse breeds. Because it often produces a very deep color (something generally preferred in the modern stud book era), and two traits that have wide appeal (dappling and flaxen manes and tails), in many cases it has been spared the kind of selective pressure that has reduced the prevalence of the some of the other dilute colors. In the next post, I’ll talk about splash white, what we can guess about its origins, and how it managed to survive in so many populations.

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Possible new dilution

Charli

In the first volume of the Equine Tapestry series, I talked about two cases of unexpected dilute foals. The first was a Dutch Draft filly, Marinka van’t Heereind. The second was the Alt-Oldenburg filly Gaja. There is further information in the upcoming volume that covers the light breeds, where similar horses have been born to purebred Arabians. More recently, an entire family of Morgans has been documented that appears to have this same as-yet-unidentified dilution. Laura Behning has put numerous pictures up with photographic pedigrees on her Morgan Colors site. I highly recommend visiting her page!

Possible New Dilution in Morgans

There are also photos of the Arabian family with the similar dilution on the New Dilutions website.

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The color has been called “light black” for lack of any better term, since it appears to dilute the black hair more strongly than the red hair. Because both the Morgans and the two Arabians are closely linebred, and because none of the parents are unusual in color, it is believed that this might be a recessive dilution. It should be noted that these horses have all tested negative for the known dilutions. In appearance, many have looked like the Laura Behning’s Morgan mare, Positively Charmed (“Charli”), who is pictured at the top of this post. Charli is a tested smoky black with the silver dilution. That particular combination produces a body color like milk chocolate, while the skin tends to have a purplish cast. Many of these horses also have paler eyes, but I have not yet seen a silver smoky that had eyes quite as pale as those seen in this Morgan family.

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