I'm curious about genetic testing

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LostandFound

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Who tests their mares and stallions and what for? I know there are a few dwarf genes that can be tested for, LWO, and of course the eye issues related to silver dapple. Is there anything I'm missing? They come up with new things so often. And how many people really bother with testing?
 
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elizabeth.conder

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My stallion is tested for all four dwarfism genes (he’s negative). He’s also had some color testing done (tested silver bay tobiano). He hasn’t been tested for frame yet but by pedigree he really shouldn’t even have a chance at being a carrier. My mares are the same. No overo in their lineage as far as I can trace. That’s on my to do list just to confirm. Because honestly it’s so simple to make sure and can prevent lethal white foals. My goal is for all my mares to be tested for dwarfism eventually. Frame isn’t a big deal as long as one is tested negative. But I’d like to be sure I don’t have any dwarfism carriers. There is a lot of hypothetical guessing on the silver gene and eye problems. It’s online connected to homozygous silver. But it hasn’t been confirmed to be an issue in minis there are some people who have had issues but those cases are quite rare from what I’ve read. There are a bunch of homozygous silvers that don’t have issues. It’s like night blindness in Appaloosas.
 

LostandFound

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Unless there is new research that I haven't seen that isn't correct. If your horse has silver dapple, he has MCOA. And if he is homozygous for LP (appaloosa) he is night blind. They used minis for some of their studies, as well as rocky mountain horses, because the gene is common in them. If you want to test for mcoa they actually just test for silver dapple at this point. The reason you see a lot of people saying there is no issue is that there is a fairly wide range in severity, and only homozygous horses with the most severe cases are ever likely to have a problem.
 

elizabeth.conder

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Silver is the gene, silver dapple is strictly a black base + silver. But red and bay bases carry silver too. They can carry the gene without being effected. There’s a lot of debate about this in some of the genetics groups I’m in.
 

elizabeth.conder

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I think we’re basically saying the same thing. It’s typically more of an issue in Kentucky mountain saddle horses and Rocky Mountain horses. Minis definitely can and do carry it. But according to the breeders/researchers I follow that don’t find as many issues in minis. But it’s like night blindness in appys. Sometimes it causes major issues and sometimes it’s not a big deal. But people don’t stop breeding those colors. It’s not like LWO that would result in a lethal foal.
 

LostandFound

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I don't think it's much of an issue in the rocky mountain horses. 5 or 6 years ago if you asked a breeder about it, they would look at you funny and tell you they don't have eye problems in their horses. I'm not sure that has changed. It seems rare to have a real problem with it, even though they almost all have it. It's more something to be aware of than anything else.
 

arrelle

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I haven’t been breeding my minis - but I’ve bred my APHA horses for years and used to stand an AQHA stallion.

LWO has always been a very important test in both breeds simply because it can hide- I know several people with phenotypically solid horses (one has solid/breeding stock APHA papers actually) but they’ve tested positive for LWO. The association has made some changes to give full papers to genetic carriers, since it wasn’t their fault the pattern didn’t show but they’re still an asset to the breed.

I say all of that to say, we have the tools and it is SO important to use them. There are several genes that are absolutely fine to have single copies of, but are lethal in the homozygous form. There are also many genes where a single copy is problematic - I know one poor lady who unknowingly purchased a n/PSSM1 colt and now is going to have problems with him the rest of his life, since he became symptomatic at 3. Some people are willing to take those risks, others are not - but the key is the knowledge so that the choice CAN be made.
 

LostandFound

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APHA is now giving regular papers to LWO horses, or AQHA was denying them? I have been out of the stock horses for a while, so I'm not up to date. I have noticed that one of the big problems with "hidden" spotting is that the definition and the reality are often not the same. I can look at my new boy and tell you he is solid but he has some sort of overo pattern. I remember talking to someone years ago who was a pro at picking out "solid" horses with a pinto gene and was crossing them to get incredibly spotted horses.
 

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