February 2012

This five year-old Saddlebred mare was recently listed on Craigslist, and her owner has allowed me to use her photos here. Longtime readers of the blog might remember the unusual greys that were discussed here (“Ponies Don’t Read”) and here (“Another Unusual Grey”). When I saw those horses, they reminded me of some a handful of unusual roaned Morgans that I had seen, though they were definitely not greys. This mare, however, is a lot more like the Morgans. You can see their pictures on the Morgan Colors site. The one most like this mare can be seen here:
Sleepys Select Rose
Sleepys Select Rose (winter coat)

I have seen a handful of other horses a bit like this one, all with roaning on the body that tends towards dappling or reverse dappling, dark legs and white on the face. I’ve tended to categorize them as some kind of odd sabino roan, simply because right now just about anything that produces roaning and white markings gets lumped into that category. Of the existing categories, it was the closest match. But it is much more likely that what we call “sabino” is a lot of different things. What seems to be true of horses like this mare is that they are usually connected – when their backgrounds can be determined, at least – to sabino roan families of a certain visual type. Those are horses that look quite a lot like true roans, only they are more uniformly roaned over their entire body. They usually have dark legs and some white on the front of the face, rather than the wrap-around blaze typical of ‘flashy white’ sabinos.

I have inquired about this particular mare’s background, to see if there are similar connections, and will post any information I receive. In the meantime, if readers have horses with extensive roaning and white on the face but not the legs, but that are not true, dark-headed roans, I would love to see them.

UPDATE: The mare’s name is Wing’s Sable Sky. Her owner is in the process of getting larger pictures taken, so hopefully I can share those in the near future.

I am a big believer in the benefit of grouping images of horses of a specific color or pattern as a way to develop a solid mental image of the different colors. For those of us that paint horses, it is the single best way to develop your eye. Back before there were many horse sites on the internet, I kept clipping files. The down side was that my ability to collect images outpaced my ability to clip them from magazines and sort them into scrapbooks. I still have boxes of unsorted images from that time! With the computer, it was much easier to sort images into folders and I assembled hundreds of thousands of references.

What I have not been able to do is share them. As anyone who has followed this blog for a while knows, I am a stickler for intellectual property rights. I stick with pictures that I have taken, that are in the public domain, or that I have been given specific permission to use. I would love to share my sorted images, but I do not own most of them. Keeping a library of images for personal reference is quite different from posting those same images on a public website. Which brings me to Pinterest.

Pinterest has been described as a virtual corkboard, but really it is a social media site for the sharing of links. The site allows users to assemble groupings of links by topic, and then uses a thumbnail as a visual for that link. Most people use it to share images of products and ideas that they like. For me, I saw it as a great way to put together some color sorting files that linked directly to the source (ie., the owner or farm that had the horse), while still giving an overview of the range in a particular color or pattern. The image above comes from a board I started with images of homozygous tobianos. What I was specifically interested in was the range of face markings, because I had noted that even in breeds not inclined to face markings, the homozygous horses often had a fairly high level of white on the face. Looking at a lot of them, from a lot of breeds, might be helpful to see any trends. I also have a board for tested SW1 splashes, tested Sb1 sabinos, and the Bald Eagle line that has tested negative for splash. Eventually I hope to add more boards for other colors and characteristics, because I think this might be a particularly good way to share visual information.

For those that are not currently using Pinterest, here is a good overview of how the site works. You’ll notice that you do have to request an invite, since the service is actually still in Beta mode. This can take a few days, in my experience.

(Oh, and I must apologize that I have not found a way to separate out my personal Pinterest boards from the horse color ones. So beware that there are boards for recipes and craft ideas and pretty artwork all completely unrelated to the topic at hand!)

More information keeps coming in from the new Splashed White tests being offered by UC Davis. Horses that have tested positive for the second version of the splash mutation (SW2) have been identified. Only a few have been made public,  but links to those have been added to the Splashed White Project page. So far the positive results have been consistent with the rumor that the SW2 mutation is present in the Gunner line of Paint Horses.

For many, the biggest surprises with the new tests have been how many horses have tested negative. I had suspected that might happen, because I knew that blue eyes were not a reliable indicator that a horse could or would produce the classic pattern. Finding horses without the classic pattern testing negative was something I expected. What I didn’t expect at all was to find horses that tested negative with the classic pattern. And now that is exactly what has happened.

Those that have read Jeanette Gower’s book Horse Color Explained may remember the Australian splash line of Bald Eagle. Several horses from this family are pictured in the book, and more can be seen at the Dunsplashin Stud website. They have classic splash patterns, but so far they have all tested negative for all three genes. What is even more interesting is that, speaking to breeders, it is clear that this particular family show this pattern with just one copy of their gene. Unlike the SW1 mutation, which presents as a classic pattern when it is homozygous, the Bald Eagle horses have the classic pattern – and produce it – with only one gene. One breeder stated that it was thought that the color was homozygous lethal, which is what is thought to be true of SW2 and SW3.

With each new pattern test, it becomes more clear that there are a lot more pattern mutations that previously understood. Because the Bald Eagle line is a sizable family, it seems likely that their mutation – which may be unique to them – will be identified in time. But the discovery that they look so much like the SW1 horses, yet have some other mutation, is another sign that we probably have a lot more patterns than was previously thought, and a lot of them probably look a lot alike.

The last few posts about silver in horses, and merle in dogs, dealt with mutations that alter black pigment without changing red pigment. Those two pigments – red and black – are pretty straightforward in horses. In dogs, though, the term “red” can lead to confusion.

That is because red is used in some breeds, like Australian Shepherds and Dobermans, to refer to what is really an alternate form of black pigment. The same color is sometimes called chocolate (Labradors, Cocker Spaniels), liver (English Setters, Pointers), or brown (Newfoundlands). Although they can appear red-brown in color, the pigment involved is a form of black rather than red. That is why a brown-and-tan dog will have two different shades of red-brown on their body. The brown-and-tan Kelpie pictured above is a good example of this. The darker areas of his coat correspond with the areas you would expect to be black on a black-and-tan dog, while the brighter, copper areas are the places you would expect to be tan. That’s because he carries the mutation that changes the black pigment (called eumelanin) to brown. Because red pigment (called pheomelanin) is not changed by the brown (b) mutation, his copper markings stay the same color. Were this dog not carrying two recessive brown genes (bb), he would be the more familiar black-and-tan.

Red merle are the same kind of color as the Kelpie, only with the merle gene added. Here is a red merle Catahoula Leopard.

Like the Kelpie, genetically he is a black-and-tan dog with the recessive brown (bb) mutation. He also has the merle mutation, which has merled the brown areas (which have a black pigment, or eumelanin, base) but left the tan (which have red pigment, or pheomelanin) alone.

The brown mutation also alters the pigment in the nose, paw pads, lips and eyes, so that the dog takes on a fairly monochromatic brown appearance. Here is a darker brown German Wirehaired Pointer showing how the nose leather is changed. The dog behind him, although somewhat out of focus, shows that the lips are changed as well.

Brown dogs can vary a good bit when it comes to shade. Some are redder than others, while some are a lot closer to black. With darker brown dogs, like this Dalmation and this German Shorthair, it is perhaps easier to imagine that the brown color is really an alteration of black.

So far, all the dogs posted have been genetically black (or black-and-tan) with the brown mutation. Brown, unlike the silver dilution in horses, does change genetically red dogs, too. It doesn’t change their fur, which is red, but it does change their noses, paw pads, lips and eyes. The extreme piebald Ibizan Hound posted a few days ago is a red dog with the brown dilution.

See how his patches are more similar in color to the tan markings on the brown-and-tan dogs? That is red pigmented fur. His nose, lips and area around his eyes are pinkish because the brown (bb) changed what would normally be black to brown. Nova Scotia Duck Tollers are another breed that is genetically red with the brown mutation. They also have pinkish-brown leathers and paler eyes.

Contrast the nose and eyes with the typical Golden Retriever, and that is how brown changes a red-pigmented dog.

And finally, one more bit that tends to cause confusion with the term red in dogs. The Golden Retriever pictured above is a genetically red dog, but most people would not readily call that color red, either. Most genetically red dogs are actually yellow in appearance. That is why, when speaking of dogs, pheomelanin is sometimes called “red/yellow” pigment. In horses, that is not typically used. There diluted red often does look yellow, but that is not common enough that the term needs to be added. In dogs it can help to clarify what it meant by red – especially given the confusion with brown.

(The Kelpie, Catahoula and Golden Retriever pictures are all courtesy of Wikimedia Commons.)

The recent posts on eye defects in dogs reminds me that I meant to share a recent paper on eye defects in silver horses. The issue of eye defects first came to light within the Rocky Mountain Horse breed, where it was initially called Anterior Segment Dysgenesis (ASD). That name was recently discarded in favor of Multiple Congenital Ocular Anomalies (MCOA).

Since its discovery, questions remained about whether or not MCOA was directly linked to the silver dilution, or if it was a more recent mutation tied to one of the Rocky Mountain founders. The recent study, “Multiple congenital ocular anomalies in Icelandic horses“, tied the issue directly to the silver mutation.

In this study we have shown that the MCOA syndrome is segregating with the PMEL17 mutation in the Icelandic Horse population. This makes the hypothesis that the MCOA mutation has recently arisen unlikely.

The Icelandic population is significant because it has been isolated from other domestic horses since 982 AD. If silver Icelandics have the same problem as silver Rocky Mountain Horses, then it is far more likely that the silver mutation is involved.

One of the things that makes this interesting is that the silver dilution – which is linked to eye defects in horses – occurs in the same location as the merling gene in dogs. Both are  PMEL17 (SILV) mutations. Both also dilute black, but not red, pigment. Those are interesting parallels between two colors that have such a visually different appearance.

In the previous post, defects in the eyes were used to help identify a homozygous merle. That is often a strong indicator, but there is one situation where that is not always helpful. Collies, and some of the closely related breeds, have a number of issues with their eyes that are unrelated to the merle gene. Compare the normal eyes of the merle Shetland Sheepdog, above, to the eyes on the merle Rough Collie below.

Like the Great Dane in the previous post, this dog has an eye that appears to be too small and set incorrectly. Her left eye, which is blue, also has a distorted pupil similar to the one seen on the Dane. It is more obvious when viewed from the front.

Although it might look like she is looking to the side in this shot, her pupil actually skewed over toward that corner, giving her a cross-eyed look.

She is not a double-merle. Her pattern is typical for a single merle with moderate white irish patterning. Whatever is wrong with her eyes, it is probably separate from her merle coloring. Her one blue eye makes the problem more noticeable, but chances are she would have had issues whatever color she happened to be.

And that is why distortions in the eyes on collie breeds are not necessarily proof that the dog is homozygous for merle. Fortunately for identification purposes, most double-merle Collies are quite dramatically white so they are unlikely to be mistaken for a heterozygous merle.

But dogs like this one also point to the reason why using double-merles in Collie breeding programs is a bad idea, even when someone else made the ethical compromises necessary to create the dog in the first place. Because two copies of the merle mutation damages the eyes, there is no way to know if a homozygous merle breeding animal had eye problems unrelated to the merle coloring. Dismissing eye problems with the assumption that the heterozygous offspring will not be affected could be a mistake, because there is no way to be sure that the homozygous parent has otherwise normal eyes.

With all the controversy surrounding the double-merle sire of the Westminster Best in Breed Collie, I thought it might be timely to finally get this post up about homozygous merles.

The motivation for posting this was a Great Dane I encountered at a dog fair this past fall. The dog was a homozygous merle, but the rescue worker was unaware because she believed that double-merles were “all white or nearly all white.” The dog at the top of this post is a good example of what people expect when someone says double-merle. That is often what they look like, especially in breeds that also have white patterning in addition to the merle.

This was the dog at the dog fair.

His handler did not believe he was a homozygous merle because he had more colored areas than white areas. She insisted that he was just a merle dog “marked with white.” She was unaware that some homozygous merles actually have a fair bit of coloring on them. In my experience, breeds that have solid merles (that is, merles without any white patterning) tend to produce homozygous merles with more color.

A close look at the placement of the white on this dog will show why it comes from a doubling up of the merle, rather than a white pattern. Here I’ve filled in his merled areas so that he looks like a black dog with white patterning.

Here are some white patterned dogs to compare, starting with a Shetland Sheepdog. He has the irish spotting commonly seen in herding breeds.

Here is a very similar kind of white spotting found in Boxers. (This was the pattern discussed indirectly in this post.)

And here is an Ibizan Hound with the pattern sometimes called extreme piebald.

Even though the edges on the last example are more ragged and irregular, it still looks quite different from the tinted image of the merle Dane. The placement of the color is wrong for any of these patterns. Here is what it does resemble.

These two patterns look much the same. That is because the only real difference is that the dog above has white areas where the Harlequin gene came and stripped the gray coloring away, leaving those areas white. The dog below (whose patches are actually gray) had this color stripped away by a second dose of merling. The white areas on both dogs have an outline and placement consistent with merle, not white patterning.

The white areas on this Dane do not make sense for any of the common white patterns found in dogs. Look at the difference between his two front legs, where one is white well up to the body and one is dark down to the end of his foot. His hind legs are similarly patched and uneven, just as might be expected with a merle, but not with an irish or piebald dog.

The other giveaway are his eyes. His handler believed his eyes were fine, and that they just looked odd because his one eye was particolored. Particolor eyes can make it hard to assess eyes, but the problems with his eyes can be seen despite their coloring. This first photo shows how the black pupil of the right eye has “bled” down into the lower part of the eye. This is common among homozygous merles. His left eye, meanwhile has an unusually small pupil, which is why the eye appears so very blue in this picture.

If you look carefully at that first eye picture, you might notice an odd angle to his eye. I suspect from this shot, it is something more likely to jump out at those of us who sculpt animals. These next pictures show it more clearly.

If the nature of his pattern was not enough of a clue that he was a double-merle, his eyes would give him away. Defects like this are typical.

This is also one of the reasons why the production of homozygous merles tends to generate some very emotional reactions. This particular dog has eyes that certainly look “wrong”, but his appearance – as double-merles go – is actually pretty mild. The eye deformities in many other homozygous merles are quite frankly disturbing to see. It is not just that homozygous merles are often blind and deaf, but that fact that hey look maimed is particularly upsetting. This probably contributed to rules in many countries that merle to merle breeding is abusive and therefor not permitted. Unfortunately, in the United States the Rough Collie registry has no such rule.

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