Archive | January, 2013

Little white dots

Birdcatcher

In the previous post, I included an image of a really interesting Greyhound with white dots on his coat. In horses, small white dots on a colored background are often called Birdcatcher Spots. They are not usually as large or as abundant as the spots on that particular dog, which is probably why they go unmentioned in most registry applications. The horse above is a good example of this kind of spotting. You might want to click on the image to get the larger version, and even then the small spots on his hindquarters, barrel and neck are easy to miss if you are not looking for them.

Here is a close-up of some similar spots. Both the horse above and this one are Saddlebreds, where the trait is not uncommon.

Birdcatcher2

To my knowledge, there have not been formal studies on Birdcatcher Spots. My own experience has been that they are more often seen on chestnuts than any of the black-based colors. (A reader did share an image of a dark bay with very prominent white spots on our Facebook page back in late December.) The spots also seem to occur more often in the “thin-skinned” breeds with finer coats – breeds like Thoroughbreds, Arabians and Saddlebreds. Some have noted that horses with these flecks are more prone to getting white hair growing back over skin abrasions. The horse above did have what appeared to be a few minor abrasions that were growing white hair. A similar tendency might also explain why some roans become covered in dark lines and specks, since injuries on roans tend to grow back with dark hair rather than white.

That does not seem to be the explanation for all cases, however. Here is another Saddlebred from the same show, with unusual white spots on her face. One is just visible on her right ear in this image, and another just behind the browband. A third can be seen in front of the cavesson, and there was another on the left tear bone (not visible here). When asked, her owner said she had always had odd spots like this. Other than her broken blaze, she was a seal brown horse with no other white markings. (She was a very striking horse with a slightly baroque head shape that reminded me of some of the older images of carriage horses I saw while writing my book, and I would have happily taken her home with me!)

Whitedots1

Here is another instance of random white spots, this time on a tobiano.

Whitedots2

Although this fellow had roan hairs around the edges of his pattern, a bit like the horse at the top of this post, and he did have the kind of blaze that might suggest that one of the sabino patterns was present, these were the only round spots like this on his coat so they seemed almost out of place there.

It seems likely that there are multiple causes, either environmental or genetic or some combination, that cause white spots. Reports of how the spots appear, and whether or not they are permanent, vary. Some owners report that their horse was solid colored and then became spotted with a single shedding. Others report that the spots appeared over time. Some say the placement of the spots shift with each shedding. Still others seem to have spots that get progressively larger and more roaned over time. Unfortunately with subtle color variations like these, it is often hard to assemble enough information to draw firm conclusions.

Continue Reading

White ticking on dogs

ChubariGreyhound

Elvis Brown posted this very interesting Greyhound to the blog’s Facebook page, and was kind enough to give me permission to share him here. Mr. Brown says he owned the dog from age three, and that he had always had the white spots, though at that time he was black. He is thirteen in this picture, and the greying is due to age. Mr. Brown also mentioned that someone from the Greyhound society had previously seen an Irish-bred Greyhound with a similar pattern.

These are somewhat reminiscent of Tetrarch Spots – sometimes called chubari spotting – in horses. Those take their name from the famous Thoroughbred, The Tetrarch, who was well-known for the unusual white spots on his coat. His daughter Mumtaz Mahal and (to a lesser extent) granddaughter Mumtaz Begum were similarly marked.

the_tetrarch_813

This kind of spotting in horses is associated with progressive greying, but progressive greying in dogs is different. In dogs grey is strongly associated with black pigment (eumelanin). It is most often seen in longhaired breeds, like the Bearded Collie, or in breeds that do not shed, like the Poodle and the Bedlington Terrier. Greyed dogs tend to be lightest where their hair is the longest, like on the topknot of some of the terriers, and darkest where the hair is short, like on the ears. This suggest that the hair loses pigment as it grows longer, rather than with each shed like a horse. Another interesting aspect of greying in dogs is that while it lightens black pigment, if the gene for black masking is present, it does not alter the black there. That is why Kerry Blue Terriers are born black and turn blue-grey while their face remains dark. The black mask, which would not otherwise be visible on a black dog, is revealed by the greying.

KerryBlue

Whatever caused the white ticking on this Greyhound, it does not sound like it is related to greying. In size and placement, the white spots actually look a bit more like Birdcatcher Spots, which are more common on red horses than black ones. Quite a few horse owners report those as increasing in number with age, so they could be considered progressive, though the various kinds of white ticking in horses is another under-researched topic. I have some images to post for that, as well as an update on a related horse from a previous post, for tomorrow.

Continue Reading

Leopard Complex (Lp) test now available

Thumper2013

The official Leopard Complex test is now available for $25 from UC Davis. A paper detailing the causative mutation is expected in the near future. Congratulations to Sheila Archer, Dr. Rebecca Bellone and the Appaloosa Project on the discovery!

For more information on Leopard Complex, including some older posts that explain how it works together with patterning genes to produce the variety of appaloosa coat patterns, can be found by clicking on “Appaloosa” under the Categories menu to the right of this page.

Continue Reading