I want to breed silver sports horses and I had read sometime ago that ASD was linked to silver Rocky Mountain Horses/partbreds. Recently I read a study (an 08 study) that said other breeds were now tested and it is not related to only RM horses/partbreds but all silvers no matter the breed.
Can you please fill me in on the current information. I want to be a responsible breeder. I was planning on putting my silver colt over my silver mare next year. These horses do not have Rocky Mountain breeding (aussie horses and the silver is from aussie breeds). If breeding ZZ horses is not recommended by reliable sources, not just within the RM horse breed, than I won't be doing it.
I have only seen the correlation in RMH, but haven't seen anything more recent than about 8 or so months ago. Even in the RMH study, they showed many silvers that had no ASD and some non-silvers that had ASD so it is not a complete link. I will dig up what I can.
.
Thank you Monsterpony, I would really appreciate it!
The essential joy of being with horses is that it brings us in contact with the rare elements of grace, beauty, spirit, and fire. ~Sharon Ralls Lemon
~I have seen it in a mini filly that was imported but I don't think they knew what it was then.
You could see her eyes were buldging as in ASD otherwise she was fine.
www.alamanda.co.uk
Was she a silver?
The essential joy of being with horses is that it brings us in contact with the rare elements of grace, beauty, spirit, and fire. ~Sharon Ralls Lemon
Yes a silver black.
www.alamanda.co.uk
I've seen many silver stock horses and ponies with silver over the years in Australia, and none had eye problems. I own a homozygous silver shetland with normal eyes. Heaps of silvers in the gypsy horses with no ASD, and many have been checked since they were in the US. So if ASD can link to silver it's certainly not all the time. I think the horse or breed has to have ASD before it can possibly link to silver. If that makes sense. Thus with no known eye problems I quite confidently breed silvers, including silver to silver. :)
http://www.flickr.com/photos/gypsycobs/ http://www.gypsyhorsesaustralia.com/
Dr. David Ramsey, who did the massive Michigan state study that defined ASD, declares it is present in all breeds who carry silver. ASD Syndrome is a collection of developmental conditions associated with the anterior segment of the eye; however, only one of the multiple conditions possible will affect vision - a subluxated lens. Dr. Ramsey stated that only 5% of the RMH population is homozygous for ASD, and of those only about 30 of them have problems with vision; only 2 were blind (that he stated). Statistically, there is a 25% probability of breeding a homozygous ASD horse when breeding 2 silvers together. There should be a 10% chance of one of them having a subluxated lens, leaving an overall chance of 2.5% with a vision problem.
The RMH is the only breed that has been extensively studied for ASD, and it is probably the only breed so heavily inbred as a population with the silver allele. So it is not unusual, considering the relative rarity of the condition, and the fact that most heterozygous carriers go completely unnoticed without an extensive opthalmic exam, that is has not been truly noticed in other breeds.
Bottom line - don't breed two silvers together if you want to avoid having an homozygous ASD horse with inherited eye abnormalities that may or may not affect the horse's vision.
This paper will probably answer a lot of your questions:
http://www.biomedcentral.com/1471-2156/9/88" onclick="window.open(this.href);return false;
It is actually not widely believed that all silver horses carry ASD. The Icelandic horse, which has a great deal of silver, has never had a documented case. While research is still ongoing, it is most likely that some silver horse, who was a founder of the RMH and perhaps had influence on other breeds as well, was also a carrier of ASD and spread it, along with the color, through breeds that show silver. But that does not mean that all silver horses will have ASD. However, as the paper states, the mutation for ASD is not yet known, and we only know that it maps to the same region as silver...so they could, in fact, be the same mutation.
Thank you for your responses.
My colt has silver from (part) stockhorse breeding and my silver mare from waler breeding. So I would think less chance of breeding a homozygous ASD foal. Mmm it's food for thought.
The essential joy of being with horses is that it brings us in contact with the rare elements of grace, beauty, spirit, and fire. ~Sharon Ralls Lemon
is this the most recent info on this problem , id it a problem in homzygous minis ?
1http://www.doaj.org/doaj?func=abstract&i...
www.celticmistminiaturehorses.com
As far as I know personally that's the most recent published research. At this point it is safe to say that all horses with the silver mutation are capable of expressing MCOA/ASD.
Even if the silver mutation itself isn't causing the eye issues, but instead a very close linked gene, this research proves that the MCOA/ASD mutation is so old that all silver horse breeds have it.
http://www.virtualpwnies.blogspot.com/
That would probably be the most recent considering the publication date is 26 May 2011. Thanks for posting it. I wasn't aware of it.
After reading through the article I would say there is a very high probability that MCOA would be a problem for ANY breed where silver is present.
Just a few highlights I found interesting.
Link above not working for me? :-(
Diane
I had my miniature stallion tested just before christmas and he came back as homozygous for silver , should I be worried about this problem and should I be getting him tested for anything ?
www.celticmistminiaturehorses.com
From http://www.horse-genetics.com/silver-dap...
Anterior segment dysgenesis is a genetic eye defect of the horse. Affected horses may have a variety of abnormalities of the eyes, including lesions and cysts, with defects in the iris, cornea, lens, and eyelids (Ramsey et al, 1999, Ewart et al, 2000). They do not respond normally to light, but affected horses don’t usually seem to have significantly impaired vision. Vets had noticed that anterior segment dysgenesis is more common in horses with the silver dapple gene than it is in other horses.
Ewart et al (2000) performed a study to determine wether anterior segment dysgenesis was inherited (Ewart et al., 2000). They studied the eye phenotypes and pedigree information from 516 horses in an extended Rocky Mountain Horse family. They found that anterior segment dysgenesis was inherited in a codominant manner in these horses. They concluded that it was being caused by a single gene, with cysts expressed in heterozygous horses and complex lesions expressed in the homozygous horses. Only in homozoygous horses was the disorder potentially a problem. Such horses should be bred to non Taffys to avoid passing the condition on to their foals. Nonpenetrance of the cyst phenotype appeared to occur in a small number of heterozygotes, and was associated with a particular lineage (i.e. not all heterozygotes showed eye abnormalities).
It would appear that either the silver gene can cause eye abnormalities (i.e. it has pleiotropic affects), or that (in some Rocky Mountain Horses) it is tightly linked to another gene that causes them. Horses with the palest manes and tails were most affected, possibly indicating that homozygous horses are also more diluted in color than heterozygous ones. Anterior segment dysgenesis does occassionally occur in horses of other colors. This might well mean that the gene for it is separate from the silver dapple gene (but closely linked to it). However it is also possible that another gene is involved in these cases.
We now know that there are probably two or more causative silver mutations in the Pmel17 gene. It is possible that one or other of these, or another mutation in the same gene, is associated with ASD.
References
Brunberg E, Andersson L, Cothran G, Sandberg K, Mikko S and Lindgren G. 2006. A missense mutation in PMEL17 is associated with the Silver coat color in the horse. BMC Genetics 7:46.
Ramsey DT, Ewart SL, Render JA, Cook CS, and Latimer CA. 1999. Anterior megalopthalmos and megalocornea of Rocky Mountain Horses. Vet Opthalmol 2, 47-59.
Reissmann, M. Bierwolf, J. and Brockmann, G. A. 2007. Two SNPs in the SILV gene are associated with silver coat colour in ponies. Animal Genetics 38: 1-6.
Ewart SL, Ramsey DT, Xu J-F, and Meyers DA. 2000. The horse homologue of congenital aniridia conforms to semidominant inheritance. Journal of Heredity 91, 93-98.
Be careful googling it...there seems to be a ton of "not-quite-understood" information out there on websites (including one that says that ASD is another gene that is linked to eye problems, like the one that links Lp to uveitis...not the actual CSNB that has been linked)
This link looks promising: http://www.wcrmhc.com/page9.html
Scroll down to Question #13: http://www.aaep.org/ask_the_vet_question...
thanks , that was helpful , we really do need a test , my foals will all carry at least one copy of silver and potential buyers are bound to ask about it at some stage , Id like to be able to give them a proper answer
www.celticmistminiaturehorses.com
Here's a link to the full text NZ
http://www.biomedcentral.com/1746-6148/7/21
As your stallion is already several years old it is most likely that he shows minimal symptoms. You could have his vision tested if your worried about it.
I feel that, especially in light of this article, it will eventually be proven that the silver coloration and MCOA are caused by the same mutation. As the mentioned article stated If you breed you stallion to non-silvers you will
Thanks Admin!
Homozygous silver cause congenital conditions, meaning they are born with them as the condition causes problems during development of the eye as an embryo. You will most likely be able to detect any problems when they are young. Only a small percentage of the ocular anomalies that occur with homozygous silver actually cause vision deficits most homozygous silvers have no obvious problems.
.
Im not worried at all about his sight , he is nine years this year and his eyes look to be a normal shape ( no bulging )and as far as I can tell he has good vision , Im more concerned about his foals , I have a mare that he has bred that is reg as red pinto well Ive just found out that her dam ..who is visually the exact same colour has been tested as silver bay and so its possible that she is too )Ill post her in a separate thread) I also have a another silver black mare that I have bred ( I didnt know about this problem at time of covering) so I have at least two mares due to foal that could be homozygous , I also have the worry of covering chestnut mares that could carry silver too
www.celticmistminiaturehorses.com
double post
www.celticmistminiaturehorses.com
I have a homozygous silver stallion as well, his eyes are basically normal. Well I assume he'd have the cysts, but there is no obvious abnormalities. Of his het silver foals, some of them have fractionaly more poppy looking eyes than others, I wonder if they are the ones with more cysts? I don't like the cysts but I think it's certainly a given they are associated with silver, so I can live with them. The further abnormalities that have been found worry me, I'm not sure it would totally stop me breeding silver to silver with horses that have eyes that basically look normal. I don't know, I would certainly think about it more now anyway. It's good they are doing futher studies and it would be great if it proves one day that it's possible to breed for less severe problems. The extreme abnormalities in the homo silvers still seem very rare, I wonder what makes them so severe at times, and at others no different to the het silvers..
http://www.flickr.com/photos/gypsycobs/ http://www.gypsyhorsesaustralia.com/
That was interesting, I wonder how old that answer is?
http://www.flickr.com/photos/gypsycobs/ http://www.gypsyhorsesaustralia.com/
June 2011, I think.
I wonder when they've done the research if they've taken note of how many are inbred or line bred?
The essential joy of being with horses is that it brings us in contact with the rare elements of grace, beauty, spirit, and fire. ~Sharon Ralls Lemon