# KHP is listing their new "rare" white TB



## farmpony84 (Apr 21, 2008)

I can't see the video from here. I'll have to pull it up when I get home. There is such a thing as a true white, it's not common:

http://en.wikipedia.org/wiki/White_(horse)

*White horses* are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white (_W_) genes, are rare. Most horses that are commonly referred to as "white" are actually "gray" horses whose hair coats are completely white.[1]


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## bubba13 (Jan 6, 2007)

Video link does not work, but I found this: Video: Rare White Thoroughbred Arrives at KHP | discoverhorses.com

Yes, white (dominant white) is a real color. Sometimes it produces a pure white horse with dark eyes, and sometimes the horse looks more like a pinto/sabino. There are many different DW genes. All are lethal in the homozygous form, similar to OLWS.


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## LuvMyPerlinoQH (Jun 21, 2011)

Ha learn something new everyday


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## smrobs (Jul 30, 2008)

There is no "white" gene persay so there are truly no "white" horses. What there are is pinto horses with maximum expressed white markings. Other than that, the closest you can get to "white" is cremello.


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## farmpony84 (Apr 21, 2008)

bubba13 said:


> Video link does not work, but I found this: Video: Rare White Thoroughbred Arrives at KHP | discoverhorses.com
> 
> Yes, white (dominant white) is a real color. Sometimes it produces a pure white horse with dark eyes, and sometimes the horse looks more like a pinto/sabino. There are many different DW genes. All are lethal in the *homozygous form*, similar to OLWS.


And if a horse tests positive for the homozygous gene that means that it will produce a lethal white?


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## LuvMyPerlinoQH (Jun 21, 2011)

smrobs said:


> There is no "white" gene persay so there are truly no "white" horses. What there are is pinto horses with maximum expressed white markings. Other than that, the closest you can get to "white" is cremello.


I googled it and apparently there is is just very rare(I hate using that word)


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## bubba13 (Jan 6, 2007)

farmpony84 said:


> And if a horse tests positive for the homozygous gene that means that it will produce a lethal white?


If you breed a white horse to a non-white horse you have a 50% chance of a healthy white foal and a 50% chance of a healthy, non-white foal.

If you breed a white horse to another white horse, you run a 25% chance of a healthy, non-white foal, a 50% chance of a healthy, white foal, and a 25% chance of a lethal foal. Though in the case of dominant white, as opposed OLWS, I think the lethal form more frequently ends in abortion and late-term pregnancy termination rather than a live birth which soon dies.


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## Quixotic (May 22, 2009)

Dominant White is mapped onto the KIT gene, which is the same gene where Roan & Tobiano are found. I believe they've currently identified 11 different varieties of Dominant White. Many horses (especially Arabs & Thoroughbreds) who were believed to be maximum Sabino have since been identified as Dominant White.


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## alforddm (Oct 1, 2010)

Homozygous DW horses are terminated very early in the pregnancy. The mare can generally be rebred the same year. 

I think the current count of DW mutations is up to 12. There was one discovered several months ago in a foal that carried a new spontaneous DW mutation. Unfortunately the foal didn't live long a few weeks I think. The researchers believed the new DW mutation he carried was the cause of his death. There may have been more discovered since then but if so I'm not aware of them.


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## Allison Finch (Oct 21, 2009)

Thank goodness my white horse was a grey!!

he was homozygous for grey so ALL of his babies were all shades of grey.


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## bubba13 (Jan 6, 2007)

That's the sad and unfortunate thing about grays, though, too--the melanoma...


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## farmpony84 (Apr 21, 2008)

seems wierd that the color would be an issue... When you see homozygous for black it means you'll have the black gene right? And no health issues... White is the only color associated with issues?


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## bubba13 (Jan 6, 2007)

The KIT gene, which is where DW is located, also has some sort of function in the development of the gastrointestinal tract (keep in mind that many genes have multiple functions, and it's way more complex than how we always oversimplify genetics). dominant white in horses
This is why homozygous DW is lethal.

Although frame overo is on a different gene, it is still associated with incomplete development of the gastrointestinal tract.


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## LuvMyPerlinoQH (Jun 21, 2011)

I'm glad I started this I am loving all of this info.


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## bubba13 (Jan 6, 2007)

On the subject of grays, I wrote this with another poster from a different horse forum--I've done a lot of research on the subject. The mechanism, as I hypothesize, has to do with the syntaxin intron's (the location of the gray allele) regulatory properties:

*While Pielberg et al. suggest a likely mechanism for the whitening of the coat and development of melanoma in gray gene-carrying horses, the hypothesis is far from a complete explanation and does not explain the process fully. The researchers propose that the mutation leads to a proliferation of melanocytes and thus a predisposition toward dermal melanoma. This proliferation early in life, however, depletes the lifetime supply of the stem cells necessary for hair follicle pigmentation. This is why gray horses are initially born a darker shade of their adult base color, and this also explains why the coat turns white within a few years. No causative mechanism linking genotype to phenotype was proposed, however. Perhaps the duplication in STX17 leads to overexpression of NR4A3 not just in tumor cells, but throughout the body (or at least the melanocytes) of the animal. The increase in this gene could interfere with the cell cycle of melanocytes, thus leading to the cascade effect explained above. *


*Gray Horse Melanoma*

*Description: *
Though the complete details of the process are not fully understood, the gray gene in horses causes a proliferation of melanocytes (skin and hair follicle cells) which eventually deplete and cause the underproduction of pigment in the hair. This causes horses to go prematurely gray in color and leads to an increased risk of melanoma (tumors). Tumors most often occur around the anus and on the tail. Internal tumors can also occur and are more dangerous. Tumors around the head and throat are often more deadly and aggressive in formation. Most tumors are often considered cosmetic blemishes. The melanomas may metastisize to vital areas of the horse’s body and cause death. Though this is not common it may still occur.

*Lethal: *
Potentially yes. Gray horses who have severe melanoma may lose function and die if it spreads into vital areas.

*Inheritance:* 
Gray is a simple dominant trait. Though not all horses who have gray will eventually develop melanoma. Homozygous grays are at higher risk for melanoma formation than heterozygous grays. Horses lacking functional agouti (the genes that cause black horses to be bay/brown) are at a higher risk for melanoma formation in general regardless of color. Therefore grays who have some form of functional agouti (regardless of underlying color) have a decreased risk of melanoma compared to those who lack it.

*Affected breeds:* 
Any breeds or individuals who possess gray have the potential for Gray Horse Melanoma. (Mules/Hinnies can also inherit gray though melanoma has not been studied in them)

*Statistics: *
Approximately 10% of all horses have the gray gene. Approximately >75-80% of gray horses over the age of 15 will have developed melanoma caused by the presence of gray.

*Available Tests:* 
There is a direct test for the gray allele, but this will not detect if a horse has melanoma. Only veterinary examination will determine its presence after a horse has already developed it. Research is being done to identify factors that reduce the risk of melanoma formation.

*Treatment:* 
Most gray horses with melanoma can live normal lives without human intervention to attempt removal of the tumors. Tumors that ulcerate are often treated with freeze therapy. Tumors are often only removed if they interfere with the horse’s normal function. Consult a vet.

*Prevention:* 
There is no way to proactively prevent melanoma in a gray horse. Not breeding for gray is the only form of preventing a foal which may develop the disorder. Since melanoma affected horses often live normal productive lives, most breeders do not proactively avoid using grays.

*Links: *
http://www.myhorse.com/melanoma-deadly.html 
http://www.cvm.umn.edu/equinegenetic...noma/home.html


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## smrobs (Jul 30, 2008)

^^And that is exactly why Dobe will likely be the last gray horse I ever own. I had 2 melanomas taken off him a couple of years ago and now there are 4 more that need to go (one of which is right in the middle of his back where the bars of my saddle sit). He's only 9 years old so I am hoping, but not counting, on having him until his elder years.


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## Faceman (Nov 29, 2007)

But with that being said, it is also important what is not said. Melanoma in greys is far less serious than in other horses because mealanoma rarely metastisize in greys...they have a natural defense against it. In those instances when it does metastisize, of course it is very serious, just as with any metastatic cancer. Because grey horses have a natural defense against melanoma, they are and have been under study for potential human applications.

I mention this only because some people are hesitant to have grey horses due to potential melanoma, when in fact non-grey mostly white horses, particularly those with pink skin are in far more danger from lethal metastatic melanoma, even though the incidence of non metastatic melanoma may be higher in greys.

If that conflicts with your research, Bubba, let me know...


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## LadyDreamer (Jan 25, 2008)

Then what is the White Fox. I worked on the farm where he was stood. He was a gorgeous individual and a camera hog. 
Patchen Wilkes' white Thoroughbreds - The White Fox, Patchen Beauty, Precious Beauty & Late 'n White - Images | Barbara D. Livingston

http://www.bloodhorse.com/horse-racing/articles/tag/the-white-fox


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## coffeegod (May 6, 2011)

Pretty horses but the first thought I had was 'Gah, what a PITA to keep clean!'


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## bubba13 (Jan 6, 2007)

Faceman, I don't know that I've ever read any statistics about the rate of grays actually _dying_ from melanoma, but it's common enough to be disconcerting. I knew a mare who had it internally, causing horribly diarrhea and weight loss until she had to be euthed. A friend's horse had it so that it cut off her airway, again leading to euthanasia. I've heard of it strangulating the bowel and causing fatal colic, or causing horrific (thus fatal) neurological damage by butting up against the spinal cord. There is a mare in my vet's practice--if she hasn't died yet--who has them all over her body, just subdermal. There's a football-sized lump at her throat. She had to have a permanent tracheotomy. It's horrible. Some of these horses, oddly enough, never displayed the outward signs of lumps and bumps before dying of internal cancer. I really _don't_ know how it works, or what causes it to be harmless in one horse and deadly in another. All I know is that in terms of getting it in the first place, homozygous grays are at an increased risk, as are horses in general who do not possess a copy of the A agouti gene.

With pink-skinned horses, I always thought the dominant cancer to watch out for was squamous cell carcinoma? I may be wrong, but I've seen several cases of that on the eyes and genitals of some Appaloosas I know.

Oh, and Faceman, I believe they've all but given up on using gray horses as models of human melanoma, unless they've recently found some new application. The inheritance and expression of the cancer is quite different between the species, which is not what they'd hoped to find.

LadyDreamer, I believe those are dominant whites.


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## trailhorserider (Oct 13, 2009)

smrobs said:


> ^^And that is exactly why Dobe will likely be the last gray horse I ever own. I had 2 melanomas taken off him a couple of years ago and now there are 4 more that need to go (one of which is right in the middle of his back where the bars of my saddle sit). He's only 9 years old so I am hoping, but not counting, on having him until his elder years.


Can anyone show me what melanomas look like in the very, very small stages? I've had 3 grays (two adults, one is still a yearling) and I have yet to see a melanoma, although my Fox Trotter does have two tiny, tiny mole-looking lumps, about 1/2 the size of a pea. One is where the cinch goes and one is on her shoulder. Both are covered with hair (for the most part, the cinch one gets rubbed a bit). Anyway, I don't know if they are melanomas or just benign moles or blemishes.

I showed one to my vet and he didn't think anything of it and said that if she got melanomas they would likely be under her tail, vulva, face or jawline. She has no lumps or skin blemishes in any of those areas. So maybe I am worried for nothing, but hey, it's in my nature to worry! She is 17 years old.

My other adult gray was a 24 yr old Arabian that died of re-occuring colic. If he had any tumors they were internal, because I never saw any blemishes on him either. And I groom my horses pretty thoroughly, so I think I would have noticed even the smallest lump.

Now I did have a Paint gelding in his late 20's that developed cancer in his sheath/penis, but that is a whole 'nother topic I suppose.

So, do melanomas start out small and covered with hair? Smrobs, are Dobe's hair covered? When I Google the subject, I just get all these horrible pictures of tumors under the tail and such. :shock:


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## bubba13 (Jan 6, 2007)

Usually I see them depicted, yes, as those dark, hairless nodules around the anus. The subdermal ones I saw on the poor mare I described were all covered with hair, but huge and covering a good percentage of her body (and also obviously not part of the skin). Do you have pictures? Could very well just be sarcoids, though naturally it doesn't hurt to keep an eye on them for growth.


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## trailhorserider (Oct 13, 2009)

bubba13 said:


> Usually I see them depicted, yes, as those dark, hairless nodules around the anus. The subdermal ones I saw on the poor mare I described were all covered with hair, but huge and covering a good percentage of her body (and also obviously not part of the skin). Do you have pictures? Could very well just be sarcoids, though naturally it doesn't hurt to keep an eye on them for growth.


Izzy's are a part of her skin. If she wasn't a gray, I would assume the one in the cinch area was a bit of scar tissue from a past cinch sore or something. 

The one of the shoulder is normally covered with hair, but one of the last times I rode her it got kind of scabby and then the scabbed sloughed. So I've been putting a little antibiotic ointment on it. I don't have pictures, but if I remember I can get them tomorrow. 

They look almost identical to the ones in this post, particularly the photo with the fingernails in the picture.

http://www.horseforum.com/horse-health/mysterious-lump-92666/

Actually, I just went back and looked at the above link. They are not that dramatic on Izzy. I will have to try to get photos.


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## smrobs (Jul 30, 2008)

THR, this is what Dobe's look like. When they are smaller, they appear to have hair on them but don't really. They are just small little lumps that are hard and don't seem to cause any pain.

The smaller ones on his face right now.









And here are the larger ones that he had on his butt a couple of years ago.


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## bubba13 (Jan 6, 2007)

I see the big one below the anus--is that dot on the left side of his rump a tumor as well? Why did your vet advise you to remove them, and what method did you use?


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## smrobs (Jul 30, 2008)

Yep, the smaller one to the left is a tumor as well. The vet didn't advise it, really, he said he would remove them if I wanted him to or he would leave them, it was up to me. I wanted it done because both were growing quickly (grew to that size in just a few months). Because they were both just on the skin, the surgical removal was relatively easy. Vet just cut through the dermal layer around them in sort-of an elongated diamond pattern and when they were off, he just sewed it up. This was after, just before the stitches were taken out.









And now, other than a small scar where the one on the left was, you can't even tell they were there and I've found no more around the incision area.


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## trailhorserider (Oct 13, 2009)

Thanks Smrobs for the photos, they are very helpful. The ones on his face are similar to what Izzy's look like. 

Do they ever peel or anything? The one on her shoulder she's had since I bought her (almost 2 years now) and it has never caused an issue but I did a 13 mile trail ride and the lump is under the saddle blanket. Not where the saddle actually sits, but under the corner of the blanket, and so after the long ride it appeared to scab and slough the top layer. That was the first time it's ever done that. 

Your vet did a nice job of removing them. If my vet wanted to do that I would be all for it (I've had a couple of moles removed on myself in a similar fashion) but my vet just kind of shrugged it off. Maybe in the spring when he comes out again I can bring it up again and see what he says. Luckily (so far) they don't seem to be growing in a noticeable fashion. Unless the one that scabbed over doesn't heal well or something.

Thank you Bubba13 for all great information too!


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## Starlite (Jan 25, 2011)

There is a woman in my area who breeds paints and TB'S, and claims she has "rare white tb's"...infact, she had a white stud colt that sold at keenland a while back for somewhere around 900,000 (for accuracy sake, I am basing the amount on memory, can't find it on her website to verify the actual amount.) He wasn't fast enough, and I heard he was sold to a Hollywood animal trainer subsequently.

Anyway, here is her website (it's pretty bad, she is an older lady and my guess maintains her website herself.)

Bubba, out of curiosity, what are you in school for? You are so well written 


http://www.painteddesert.net/images/4_whites_bl.jpeg


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## bubba13 (Jan 6, 2007)

Is that so? Well, thank ya kindly for the compliment. I'm a senior pre-vet student.


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## Quixotic (May 22, 2009)

LadyDreamer said:


> Then what is the White Fox. I worked on the farm where he was stood. He was a gorgeous individual and a camera hog.
> Patchen Wilkes' white Thoroughbreds - The White Fox, Patchen Beauty, Precious Beauty & Late 'n White - Images | Barbara D. Livingston
> 
> http://www.bloodhorse.com/horse-racing/articles/tag/the-white-fox


The Patchen Beauty line carries W2, one of the Dominant White mutations. This link shows pictures & descriptions of some of the White variations.
http://www.duncentralstation.com/PDF/KITGeneMutations-Castle.pdf


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## Allison Finch (Oct 21, 2009)

bubba13 said:


> That's the sad and unfortunate thing about grays, though, too--the melanoma...


Oh, he has had several removed...all benign. I was referring to the lethal white problem in breeding.


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## nicole25 (Jun 24, 2011)

He is gorgeous.


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