ASD in Minis.

[Lizzie]

I'm starting this message, because Rabbitsfizz brought it up in the Grey thread.

I think we probably all know, that the gene for spotting in Appaloosas, has shown some linkage with the tendency to develop uveitis or 'moon blindness', an inflammatory disease of the eye.

In silvers, there has been a massive and ongoing study for many years, regarding ASD (Anterior Segment Dysgenesis) On the Gypsy Horse forum, we have spoken and discussed this a great deal, connected with Gypsies, since the colour is widespread in the breed. While those in the US, might consider the Gypsies to be rare compared to other breeds, in truth there are hundreds of thousands of them across the world. Many of these are silvers. I know that many are the result of silver x silver breeding. So far, not one case of ASD has been reported.

It is my opinion and the opinion of many others, that ASD has mostly shown up, only in Rocky Mountain Horses. This is the only breed I know of, which was part of the massive study. Personally, I think it all became so widespread in that breed, was because of the first famous silver horse, to whom many bred. I think he probably had ASD. I would say I'm almost certain of it. Breeders flocked to him and he was known to have many silver daughters, granddaughters and ggranddaughters, bred back to him. Hence my thinking it is why the problem spread so quickly and widespread in that colour and in that breed.

Knowing silver is a popular colour in Minis, I wonder if any cases of ASD have been reported. I have not heard of any. I don't know of any studies made, in Minis or other breeds. All info on silver related ASD has come from Rocky Mountain Horses only and (I believe) it has been wrong, for us to believe it is occurring or has be found in all breeds which contain silvers. In fact, ASD has been reported in breeds where silver does not exist. I know one book on the subject has been widely touted, but again, I and others, do not agree with the authors findings, since it was only studied in Rocky Mountain Horses.

Lizzie

 

[Minimor]

I believe there have been a few cases in minis--or at least I have been told that there are Minis that have this condition, I haven't personally known any that do.

There are those who will come out with the warning that breeding silver to silver will cause ASD but I don't believe that is quite accurate. I don't believe that breeding silver to silver will cause ASD any more than breeding silver to non-silver or non-silver to non-silver will--because not all silver horses have ASD. If there is no ASD in the pedigree then a horse isn't going to have ASD even if his pedigree is full of silvers. Some people don't seem to quite get that concept--that breeding silver to silver cannot make ASD appear out of the blue. It's not silver x silver breedings that cause a horse to have ASD, it is breeding ASD x ASD.

 

[Lizzie]

Exactly Minimor! That is the reason I think Dr. Sponenberg is all wet.

It goes along with inbreeding. Inbreeding does not 'cause' problems - they were there all the time.

Sorry about the spelling in the title. It is 'dysgenesis". I was unable to change it.

Lizzie

 

[Mona]

What are the symptoms and is there testing available to the general public?

 

[Lizzie]

I believe there is still no actual test to confirm ASD. However there is an eye exam that can be performed to identify the 'cysts' and can also confirm that horse does not have ASD. It should be noted that the eye exam is not 100% to determine normal since it is a visual exam and cysts can be very difficult to see. In such circumstances, some horses have been known to be silent carriers as they have produced cysts or ASD foals when bred. In most cases, one wouldn't even know a horse had ASD. Blindness is not a feature of this disease. It doesn't show up as a horse ages for example.

Lizzie

 

[Lewella]

To add to this - what Dr. Ramsey called "ASD" is not truly ASD. What the Rocky Mountain Horses have that is linked to silver in that breed (and yes it is believed to be a founder effect tracing to one stallion) is termed in newer research as multiple ocular anomalies. Dr. Grahn in Canada published a paper in 2008 that disputed some of the conclusions reached by Dr. Ramsey. The only flaw I can find with Dr. Grahn's research is that it could have been taken a step further and all horses in the study could have been tested using the then brand new siver zygosity test. My guess is that they could not get funding for the color testing though since they were already well into the research when the test was made publically available.

To quote Dr. Grahn - “We don’t think it’s the same gene, but another gene close by on the same chromosome. We have a black horse with the condition that isn’t considered silver dapple, although some people think this classification must

be a mistake. I don’t agree. We also have a silver dapple horse that’s clear [of ocular abnormalies] and there may be others. We need to extend the pedigree.” http://blogs.usask.ca/EHRF/HHL.FALL08.EYE.ANOMALIES.pdf

 

[Lizzie]

Lots of these things come down to funding or lack of it, don't they Lewella. UC Davis has no funding for CPL now either. Something close to my heart and vital knowledge for anyone with a feathered breed. However, my friend who studies it in England, does come over to the US occasionally, to offer them her new findings.

What breed/s was Dr. Grahn studying?

Lizzie

 

[Margo_C-T]

I lost all of my saved 'favorite' sites due to recent computer problems, but speaking from memory(which may not be exact!)--- one 'clue' to whether a horse might have ASD was a visual exam of the degree of 'outward bulge' of the eyeball, with a more-than-usual bulge being a sign of possible ASD. As I recall, it was presumed that a breeding of ASD-carrying silver to ASD-carrying silver would or could produce ASD in the offspring...which I would seem to mean that the gene(s)? that cause ASD was somehow linked to silver(but NOT PRESENT in ALL horses carrying the silver gene). As Minimor said, it wasn't the silver gene, but whether the ASD gene was (also) present that would determine whether ASD might occur in an offspring.

As I said, just what I recall from one or more websites I found several years back when searching for further info on ASD; verifiable knowledge/research on the subject may or may not have been 'advanced' since then. I do recall that I came to believe that it probably DOES occur occasionally in minis.

Margo

 

[Lizzie]

I think, since the studies have only been done seriously in the Rocky Mountain Horses, we should consider that any horse carrying or who has ASD - regardless of colour and in any breed, should not be bred.

From the time I first looked into this several years ago, I still firmly believe that it is so widespread within silvers in RMHs, purely because the first known/famous silver horse in that breed, had the problem. He was bred back to his descendents countless times to produce silver. In Gypsies, one breeder in the UK, bred silvers for years 'and' bred his stallion back to his daughters and granddaughters. Not one case of ASD has shown up yet and it is spoken of at length within the Gypsy community.

ASD has been known to have shown up in several breeds and some which don't have silver at all. Certainly something to be aware of, but not have fits over, if one breeds silvers.

I have been led to believe Margo, that those with ASD or the cysts, show no outward signs. Only an eye examination can tell and even then, apparently the condition is very difficult to see.

Lizzie

 

[Jill]

I'm not sure that's ever been found to be at large problem miniature horses, a breed of horse in which the silver gene is extremely common and of which there are far more individuals than in any other breed that carries silver. While we do not breed on a large scale, H and I do own quite a few horses that carry silver. We do plan in the future to cross silver mares to our real nice silver stallion

 

[rabbitsfizz]

It is not ASD that is the problem, it is MCOA(multiple congenital ocular anomolies )

See this thread for more details...

http://colorgenetics.info/equine/forum/colour-related-blindness

Don't be put off by the title- the colt in question was blind due to something else, and be warned there are graphic images of eyes, but this is pretty much proven now, and it is related to Silver....in fact it can be used to "diagnose" Silver in Chestnuts.

 

[Lizzie]

Danni, the lady who started the thread on the colour forum, is an old friend of mine. She lives in Australia and has Gypsies and Shetlands. She and I have discussed ASD and MCOA for several years now.

It is thought, that the causative mutation for MCOA is actually the same mutation that causes the silver coat color. However, this hypothesis has been challenged by the fact that MCOA-type ocular abnormalities are not known to be present in those horses who have no silver at all in the breed, yet have shown to have the eye problems. It has also been shown in dogs (no silver) and even in humans. (obviously no silver gene)

I do (still) believe it to be of a genetic indication in all mammals. Not necessarily a colour indication. I suspect, that if an intensive study were done, in a breed where no silver existed, but ASD and MCOA were found, the results might indicate (for example) that all bay horses were culprits for the problems. This of course, if it were concluded that most horses with the problem, had one common ancestor. My feeling would be that it was he who passed on the problem, regardless of colour.

All very interesting isn't it.

Lizzie