July 2011


One of the guest horses at BreyerFest this year was the palomino dominant white stallion Sato from Blazing Colours Farm. Sato comes from the dominant white family of Puchilingui.

So far each of the identified dominant white families have been a separate mutation, and in most cases the originator is recent enough that they are known individuals. The version of dominant white that originates with Puchilingui, W5, is known for producing a pretty wide range of sabino-like patterning as well as truly white horses.

With horses like these, it is easy to understand why breeders use the term sabino when advertising their horses, rather than their technical classification. Mare owners looking to produce pinto patterned foals know what a sabino looks like, and dominant whites of this type produce what looks like a sabino. The “proper” genetic term can be, at least in that kind of setting, unintentionally confusing.

In informal settings, it is likely that dominant white horses will continue to be referred to as sabinos. That is what they look like, and that is the term many horse people understand. They are very different though, so in formal settings where genetics are being discussed they deserve their separate names. That topic probably deserves its own post, though.

Another quick note about Sato, though. The close-up at the top of the post shows the blue segment in his eye really well. Although dark eyes are more common, a number of the dominant whites have had blue eyes. This happened with some of the sabino white Walking Horses, too, though it appeared to be less frequent.  (The topic of blue eyes in Walkers is pretty complex, so that will have to wait for the volume that covers light breeds.)

Advertisements

Before I talk about Dominant White, it might be helpful to pull one of the archived posts from my studio blog. I still need to finish pulling the posts that deal with horse color over here to the Tapestry blog, but since this one is relevant I’ll repost it now.

(Previously posted on August 30, 2007)

Exciting News in the World of Horse Color

One of the downsides to publishing your theories is that you stand the chance of later being proven wrong. Or at least missing the mark by a bit.

Ten years ago I wrote an article entitled A Study of White Horses – Not What They Seem, where I questioned the existence of Dominant White in horses. My skepticism was based on my own research into the backgrounds of as many white-born horses as I could find. From that I came to believe that most of the horses designated as Dominant White were more likely to be extremely marked sabinos. I failed to find horses that fit the profile for Dominant White, so I began to suspect that the color did not exist – or perhaps no longer existed since there were anecdotal stories of horses that had fit the profile in times past.

It appears that my speculation was wrong, at least in terms of whether or not there was such a gene in horses. Not only are there real, live Dominant Whites, but the Swiss team that identified them has been able to test for it. So eventually we will know for sure which horses carry the gene. (It is thought that the gene is extremely rare, so it is likely that many of the white-born horses are still just sabinos.)

Other things are in the works, too. A Swedish team found the mutation for grey, though a test is not yet available. UC Davis has been working on dun, and of course there is the ongoing research on the appaloosa patterns. Pretty soon there won’t be anything left to guess about when it comes to horse colors!

That blog post was made in 2007. The article I wrote ended this way:

Given the breeding records of the aforementioned “white” horses, I have come to wonder if Dominant White really does exist. But it is clear that even if it does, the majority of white-born horses are probably sabino whites.

Much of the research for the original article was done between 1992 and 1995, when I had access to the archives at the Tennessee Walking Horse Breeders’ and Exhibitors’ Association. Looking through old show catalogs and registry records, I found a lot of horses that looked like the horse above, Silver Sultan. (Photo from the TWHBEA archives)  Even more were recorded in the early stud books.

(Don’t worry – the highlighting was done on the image, not the book itself! The only way I mark my books is with post-it-notes, which are visible there on the pages behind this one. Those all mark sabino-patterned or white horses that are recorded as having blue eyes so that I can enter them in my notes. There aren’t any post-its closer to this page because those have already been entered. I am perpetually behind with formal records like these.)

I had a complete set of Walking Horse stud books, which were a gold mine of information because breeders submitted (and the registry printed) detailed color descriptions. Because I was interested in how sabino might work, I developed an elaborate numerical system for evaluating just how much white the horse had, and then set about assessing how horses with different amounts of white produced when crossed with mates with differing amounts of white. In hindsight, it was probably far less useful than the time spent justified! But the one take-away was that the white horses all had two sabino parents, and in almost all cases the numerical value of the parents was pretty high.

The way I scored the horses actually skewed this, because I grew up in the Tennessee Valley and I knew that many horsemen called a horse with indistinct body spotting “roan”. Taking that into account, if the horse had enough points based on markings – if I could be pretty sure it was not a dark-headed roan – then it got extra points if roan was used in the description. Many of the horses probably didn’t have body spots, or at least weren’t as patterned as their number value would suggest, but I was weighing a trait that was tied to the white even if I didn’t know it at the time. That is because the gene that causes sabino-white, Sabino1, tends to produce really roany horses, even when they are not very spotted. This old-fashioned Walking Horse mare is a good example.

Finding that link between white-born horses and sabino in both parents was why I wrote the article. Still, there were horses that did not fit my theory. In the article I speculated that in some breeds sabino might be linked in some way to the chestnut gene. There was no apparent link in the Walking Horses, which inherited spotting without any real difference related to base color that I could tell. I did know, though, that in some breeds (like Arabians) there was a noticeable difference in the amount of white a chestnut horse might inherit compared to a bay or black horse. I wondered at the time if this might play a role in the white-born horses that had parents with low numerical values (ie., little to no white), since in most of those cases the parents were bay or brown.

The biggest limitation was that most of the white-born horses I could find were long gone, and in many cases only partial records remained. I published what I had, and hoped that the article might flush out a bit more information. If your heart is truly in research, you really do want those corrections, because where you are wrong is where you learn.

My correction didn’t come for another ten years, but it did come. Almost all the horses that didn’t fit my theory quite exactly right were found to be Dominant White. R Khasper. White Beauty. Puchilingui.  Those that weren’t in the study fit the pattern for being Dominant White.

Tomorrow I will post pictures of Sato, the palomino Dominant White Thoroughbred stallion from one of those identified families. I was fortunate enough to see him in person in Kentucky, and talk to his owner, April Wayenberg. He is particularly interesting because he is more colored than a lot of Dominant Whites. He is also extremely photogenic, so I took hundreds of photos.

I have mentioned before that I try to be careful about copyrights when including pictures in posts. I get permission before I include photos in the posts, or I link. When photos come from other people, I include that information in the text. More recently I’ve been trying to remember to mark my own photos with a copyright notice, just so it is clear where the images originated. If the images aren’t credited, it is pretty safe to assume I have taken them even if I haven’t marked them.

I usually take pictures for my own reference and with an eye to images that can help illustrate ideas. They are meant for education – mine or others. For that reason, I don’t usually mind someone using them for the same kind of purpose, but please do ask before posting them somewhere.

Also, most of the pictures are uploaded to this site much larger. The images shown in the posts often degrade due to compression, too. Clicking on the image will often take you to a better, larger picture.

And finally, if you have taken photos of interesting colors, I am always eager to see them. Clicking on the sabino horse under the “Contact Me” will give you the necessary email address.

 

I know I said I’d post about the Dominant White, but I wanted to share this photo sent by my friend Jackie Arns. This is a rescued pit bull that Jackie saw as a patient. Much like Domino, the Cocker in the previous post, she has a high percentage of color, but she had the abnormal pupils of a double merle. As these pictures show, she has merling that effects her red pigment. (By red I mean the pigment color as horse people understand it, not the color many dog people call red but that is the result of the brown (b) gene. Dog people would call the color “yellow” rather than red.)

These are great photos of what I thought I had seen in a few other dogs. I have seen speculation that the presence of sable allows merle to act on the red pigment, though I am not aware of any formal research on this. I also do not know if it is possible to find a clear, non-sabled red (yellow) dog with visible merling. It is also possible that the fact that this particular dog is homozygous plays a role in the merling of the red pigment. This gal is a sable, though she only has a bit of smudging on her ears and face.

The question then is why do dogs like this pit bull show merling in the red areas, while Lily (the sable merle Collie from the first post) and most others do not?

Another friend, Cindy Dalton, included this link in the comments.  The dog, a Border Collie named Psycho, does have reddish patches on what looks like an extremely dark liver (recessive brown, b) background. He has the paler, redder patches because he is what is called a tweed merle. That is the other modified form of merle besides harlequin. Where harlequin strips out the silver coloring, making the merled areas white, tweed takes the dark areas of the merle and dilutes them to a different tone – or a lot of different tones. In some dogs the diluted patches are rather reddish, while in others they look more pewter or slate.  The effect on Psycho is easy to see in this picture. (His cool parti-colored eyes can be seen in this one.)

My Aussie mix, Emma, is a tweed merle. In her case the diluted patches range from a slate gray to a pale brownish gray.  The largest one, which runs down her chest to her upper right leg, is visible in the picture I posted of her earlier. The same area on the other side is diluted, though the patches are intermixed with true black rather than being one large area. Her lower legs and muzzle all have smaller dilute patches, which give her legs and face a warmer tone than the colder silver on her back.

Here are close-ups of the areas that shows the two different tones really well.  Because the warmer dilute patches were concentrated on her legs and her muzzle, I originally wondered if she might be some odd black and tan color under her merling, but the black and tan patterns have red (yellow) pigment trimming the black. Sometimes the tan (red) pigment is really pale, almost white, but that isn’t what she is. Her lighter areas are quite obviously a dilute of black pigment.

Tweed was first identified in Aussies and is thought to be dominant. What isn’t clear is whether all the variations are the same gene. Some merles just have a few diluted spots. Others have many patches of many different colors. Still others have white patches mixed among the colored ones. Those are often called harlequins – a term not especially helpful since it is already used for the modifier found in Danes. They might all be tweed, or they might have different genetic causes.  There was an initial study done by Dr. Sponenberg on tweed in 1995, but I don’t think any further ones have been done.

And for those with a more technical bent, the original study that identified merle is available here. (As technical papers go, it is very clearly written.)  The study that located the (Great Dane) harlequin gene is available here.

As I mentioned in a previous post, I was fortunate enough to get some wonderful comparison shots while I was in Kentucky. It seems a good time to share this one since I touched on the topic of merle in dogs in the last few posts. This is Lily, a sable merle Collie. Here she is with her ordinary sable companion.

As I had mentioned in a previous post about merle in dogs, the merle gene effects black pigment. This is why the sabled areas on head are muted on Lily compared to her friend. With only a small amount of black pigment present, the effect is pretty subtle. From a distance Lily looks a little washed out and pale. Her blue eye is quite a giveaway for the merle gene, since those happen even with merles that are completely red pigmented. Her ears, which are often the blackest area on a sable Collie, are the other giveaway.

Her other ear and the colored area along her back skull are all visibly merled.

I should also clarify that she is what Collie breeders call a color-headed white with a single merle gene. She is extensively white because she is homozygous for the color-headed gene, and not because she has two copies of the merle gene.

Here is a typical (non-merle) color-headed Collie. (Photo from Wikimedia.)

Unlike double merles – and the white Boxers in the previous post – the gene responsible for this pattern usually leaves the head, nose and ears dark.

Here is my friend Andrea Caudill’s merle Cocker Spaniel, Domino. (Thank you, Andrea, for letting me use pictures of your sweet boy!)

Domino is probably a double merle. Although many double merles are very white, especially on the face, some carry enough color that they could be mistaken for a dog that had a single merle gene and one of the more extensive piebald patterns.

Since posting about the fact that merle acts on black pigment, several people contacted me about red dogs that were merle. In some breeds, red is used to describe liver, which is a form of black pigment. The people writing were not talking about liver red. In these cases, what was meant was truly red (or yellow) pigment. Some of the dogs did in fact look red, or had what looked like merling in their red-pigmented areas as well as their black. It was often less extensive, but still it was enough to make me wonder how absolute the connection was to black pigment.

If you look closely at Lily (the images link to larger pictures), the area at the corner of her blue eye, running towards the blaze, is roaned. Here is a sable Dachshund with an even more merling in the red areas of his face. (For comparison, here is a sable Dachshund puppy with the merling mostly confined to his sable areas.)

It is also true that merle, when paired with the harlequin (Harl), will effect red pigment. In Danes these dogs are called fawnequins. (Image from Wikimedia.)

The harlequin gene has much the same effect on brindles that inherit the merle gene, which are known as brindlequins. Compare that to a more typical brindle merle here, where the red/yellow pigment is not especially altered.

So it appears that the link between merle and black is not absolute. I know I’ll be looking at merles with red pigment more closely in the future. I am curious to see how common this is, and why it happens in some red dogs but not most.

(I promise to return to horse colors with the next post, which will have the Dominant White stallion Sato!)

As anyone who is friends with me or my family members on Facebook can probably tell, we play a lot of games at our house. The guys play ruthlessly, so we often joke that it’s not a real game unless someone cries. As the mother, and resident peacemaker, this has made me keenly aware of the concept of game mechanics. Those are the factors that make a game hard enough to be a challenge without being needlessly frustrating.

The card above comes from the French game Milles Bornes. It was a game I played with my siblings as a child, but somehow I missed the fact that the game had terribly bad mechanics. Certainly they do not work for my own family! That’s because this card unbalances the game. It did not take long for my children to figure out that once you have this card, it is almost impossible to lose. So someone finally draws the Right of Way, and someone else cries. Whenever someone suggests this game, most of us just groan because we know what is coming. What we need to do is experiment with altering the rules to make the game more fair, but somehow we always end up using the traditional rules.

I have often wondered why people in the animal fancies – that is, the hobbies devoted to breeding and showing purebred animals – don’t question their own game mechanics.

I suspect that is because many are unaware that the “rules” the activity has are exactly that: game mechanics. Why do the spots have to be just so big, and just so regularly spaced? Why can the tail end be white but not the feet? Why does it matter if the white collar circles all the way around the neck? Do any of those things actually matter to the well-being of the animal? Do they contribute to his ability to do the job he was originally bred to do? Are they tied to an agreeable temperament?

The answer is usually no. What they are about is game mechanics. The game, which in this case is competitive exhibitions of animals, has to be difficult enough to keep the interest of the participants. By adding color requirements to the list of desirable traits, the game is made more challenging. The more specific the requirements, the greater the challenge.

Breeding to a standard is already a challenge. The head on a Collie, which is one of the most important aspects of type in that breed, is required to have very specific angles. The parameters of this are outlined in detail in the breed’s illustrated standard. (The Collie Club of America has one of the most instructive standards in this regard.)  Unfortunately the desired head shape fits between two norms that the canine skull structures tend to take.

The middle image is the ideal Collie head. The heads to either side represent the extremes, with the “Borzoi” type roman nose to the left and the “Farm Collie” dished face to the right. One of the challenges to breeding Collies is getting that elusive middle image. If you are breeding Collies, that is part of the game.

For some animals color and markings are part of the challenge. Yet color is different in one significant way. Compared to something like the angles of the skull, color is pretty easy to predict. Take Boxer markings, for example. Boxer breeders like flashy white markings like the ones seen on these dogs.

In most breeds of dog, this kind of pattern where the legs, belly and collar are white is thought to be recessive. It is most often called Irish spotting, though in Danes it is called Mantle. Boxers are different in that while the white occurs in much the same areas, the pattern is incompletely dominant. Dogs with one copy look like the pair above. Dogs with two copies look like this.

Puppies like this are called White Boxers or Check Boxers (if there are significant patches of color inside the white). White and check Boxers cannot be shown. This is the American Boxer Club position on white Boxers.

ABC policy strictly forbids registering white Boxers with the American Kennel Club, as well as selling white Boxers or breeding white Boxers. The ABC also requires that white puppies not be included in the count on the AKC litter application form. The ABC has never condoned or encouraged the culling of white puppies.

Yet breeders know this is what they will get. It is entirely predictable. If breeders are using white trimmed dogs in their breeding programs (and trends that I have observed suggest that most are), then this is the fate of  25% of all Boxer puppies born in show breeding programs. If the average litter is eight puppies, then each breeding produces two “waste” puppies right out of the gate, before any other aspects of quality are going to be assessed. What if the hoped-for improved quality for that litter happened to fall to one of those white puppies? The parent registry requires that you not even retain the dog for breeding. That makes eight “waste” puppies – and another two additional ones that will be white the next time.

There are worse situations where the color requirements produce a lot of predictable culls. Harlequin Danes are the result of the merle gene and a modifier that strips away the silver color so that the background is white. Merle without Harlequin is not an acceptable color, but Harlequin is a homozygous lethal so all living Harlequins are heterozygotes. That means half the litter will not have the harlequin modifier and will be merle – a color not permitted. It gets even more complicated because merle causes defects (and the wrong coloring) in its homozygous form. That means ethical breeders will be crossing to non-merles, so only half of the puppies will inherit merle. If the breeder is lucky, most of those will be the ones that get the harlequin gene, too, but that’s not a given. To stack the deck even further, the Harlequin gene is “leaky” so undesirable merle patches sometimes show through. The potential for a lot of “pet quality” colors is pretty high.

Those are the rules of the game as it is currently played. Many of these rules date back to the founding of registries. Yes, that makes the limitations traditional, but it also needs to be understood that the men (and it was largely men) making those rules lived in a different world, and looked at animals differently. How easy is it to place a half-dozen off-colored puppies that will one day grow to giant size today, when many families cannot even fit a regular dog into their lifestyle? And are we comfortable with a built-in percentage of “waste” in a world where perfectly healthy animals go begging for a home?

Games only work if there is a challenge. The downside to this kind of challenge is that, depending on how hard it is to get it right, you are going to have a certain amount of misses. With animals, that means offspring that have no future within the fancy. Obviously we all expect fanciers to behave responsibly in regards to the excess animals they produce, and many breeders go above and beyond in this regard. But still the structure of the game ensures that some portion of the animals created will not have a place. When those undesirable animals are the sure outcome of something that is desired, then maybe it is time to reassess the rules of the game in light of the world as it is now, and our modern understanding of animals as fellow beings rather than objects. We do have the power to write new rules.

Update: It has been brought to my attention that the American Boxer Club website page on white Boxers does not have current information. In 2004 it was voted to amend the Breeder’s Code of Ethics so that breeders could offer Limited Registration papers and recoup medical expenses when placing white puppies. It should also be noted that until 1985 the Code of Ethics did not allow for placement of white puppies, which meant that while the statement that culling was never encouraged is technically true, the only action officially allowed was that the breeder keep every white puppy born.

(Boxer photos from Wikimedia Commons, Collie illustrations from the CCoA Breed Standard.)

(Photo by Tereza Huclova, provided for the upcoming book by the Kladruber Stud)

Several people have commented about the convex profiles of the Kladrubers and how they are visible even in the foals. I thought I would share this photo since it illustrates the characteristic so well. The extent of the arch varies from horse to horse, but it does seem especially pronounced in the black horses. As someone who grew up around Walking Horses when this type of head was not uncommon, I find it very appealing.

I also received a number of responses about genetic diversity and closed registries, so I thought I would include some links and reference material for those with an interest in the subject.

As Sarah Minkiewicz-Breunig mentioned in her comment, I like to recommend the book Bred for Perfection by Margaret Derry.

In the book Derry explores how culture, economics and the (then new) science of genetics shaped the world of stud books and animal breeding. She doesn’t shy away from the less appealing aspects of that history – namely the close association with eugenics and social Darwinism – but she does so in a less sensationalistic way than many.

There are also a lot of resources from the dog world, in part because rigidly closed registries have long been the norm within that community. One of the best sites for articles is the Canine Diversity Project.  Among the particularly good ones are:

The Poodle and the Chocolate Cake by Dr. John Armstrong  (a really good overview of the problem)
The Price of Popularity: Popular Sires and Population Genetics
by C. A. Sharp

The dog world has also had some interesting experiments with out-crossing. Closed registries are the norm for dogs, so these have all been very controversial. Among horses relatively few breeds maintain completely closed stud books, and fewer still are willing to pay for that choice in the way that dog breeders are.

The Backcross Project  (restoring proper uric acid levels to Dalmations)
Bobtailed Boxers – Part 1
Bobtailed Boxers – Part 2
Bobtailed Boxers – Part 3
Bobtailed Boxers – Part 4
Bobtailed Boxers – Part 5
Bobtailed Boxers – Part 6
(This series is worth reading just to see how quickly a breed reverts back to type when crossed on something really different, all extensively documented in pictures.)

There was also a great post on the Terrierman blog about the importance of provenance in selling breeds.
You Can Blame Garrison Keillor’s Grandfather
The Terrierman blog has a lot of great posts about genetic diversity, though that recommendation comes with two caveats: 1) the blog is routinely sprinkled with unrelated politics that readers might or might not appreciate and 2) temperance and diplomacy are not really the style there. (He also takes exception to the color merle, which of course is not going to fly around here at the House of Blue Dogs!) Still it is consistently an interesting read, and it is worth exploring the (vast) archives there.

There is also the BBC program “Pedigree Dogs Exposed” which one of the comments referenced. To say that the program ignited a firestorm would be an understatement, and in parts it is certainly sensationalized. Still, what it portrays is happening, and perhaps something like this was the only thing that would push people to look at the issues involved. Since it aired, studies have been conducted and some preliminary actions taken by the British Kennel Club.

So what does that have to do with horses? To some extent horses and horse breeds are in better shape because they have not had a uniform culture of closed registries. Still where there are small populations and closed breeding programs, the same kinds of issues arise. Here is a discussion of the Friesian stud book policy on genetic disorders. This statement shows the very real parallel with the problems facing the dog world:

For this reason, the KFPS believes that carrier stallions should remain in the breeding pool. In addition, it should also be possible to approve young carrier stallions on the condition that they possess extra qualities. If we do not implement this policy, 1 in 3 young stallions will automatically be rejected on the basis of DNA testing.

One in three. And what are they carrying? Dwarfism. Twelve of the current stud book stallions are carries of dwarfism. Hydrocephalic Foals. Sixteen of the current stud book stallions are carriers of hydrocephalism. The effective breeding population is too small, and the defective genes so widespread that culling the carriers would probably narrow the gene pool enough that new defects would appear. That is what has happened in many dog breeds. It is exactly what should concern horse breeders, particularly those working with rare breeds with limited populations.

That is why many rare horse breeds have actually relaxed their color restrictions. They may still have strongly worded preferences for colors or markings, but off-colored or mismarked horses are not automatically removed in many breeds. Ironically, one of the breeds that does do this is the Friesian, which does not allow chestnut carriers as breeding stallions. This puts the registry in the awful position of permitting damaging defects if the horse is otherwise “of good quality”, but banning something as inconsequential as color no matter how nice the horse. As with dog breeders, this kind of disconnect with simple animal welfare undermines the assertion that purebred breeders are guided by a higher standard of ethics than “backyard” breeders.

Were it possible to expand the gene pool, culling could be accomplished without raising the inbreeding level to still more dangerous levels. Even without outright culling of carriers, introducing an outcross line can dilute the overall incidence of the defective gene. The fact that there are animals breeders out there who will choose “purity of blood” over solving serious health issues is something that deserves more attention. It isn’t a particularly comfortable discussion for a lot of breeders, and it points to the need for a very different mindset when it comes to breed stewardship, but it is one I personally feel must happen.

Next Page »