Genetic testing before breeding

[Marigold4]

Sorry - yet another question.

I am going to send off a hair sample of my mare to check for PSSM because its a dominant gene. Is there anything else I should ask the lab to test for? Mare is a small warmblood by Royaldik (oldenburg x TB with a dash of Arab); out of an ISH also with a little Arab. Sire of foal will be a Connemara who has tested neg for HWSD.

Am I right in thinking that all the Warmblood genetic disorders like WFFS are recessive and need both parents to carry the gene for it to be passed on to the foal, so I don't need to test for these? Is there anything else dominant I should look for?

Thanks in advance for any advice.

 

[Littlewills]

Are you testing for type 2 PSSM? She is very unlikely to have type 1. This is the list of tests offered with some specifically flagged for warmbloods

https://www.animalgenetics.eu/Equine/Genetic_Disease/Disease_Index.asp

 

[Marigold4]

Are you testing for type 2 PSSM? She is very unlikely to have type 1. This is the list of tests offered with some specifically flagged for warmbloods

https://www.animalgenetics.eu/Equine/Genetic_Disease/Disease_Index.asp

So type 1 is rare but type 2 more common in warmbloods? I would need a muscle biopsy, so not worth doing as I don't have any suspicion that she has it?

 

[DabDab]

So type 1 is rare but type 2 more common in warmbloods? I would need a muscle biopsy, so not worth doing as I don't have any suspicion that she has it?

My gelding has PSSM1 from his warmblood dam, so it's worth testing for.

There are some pssm2 hair follicle tests about, but I have no idea on accuracy etc do you would have to research to see if it was worth it.

I like the sound of what you are planning to breed

 

[Littlewills]

So type 1 is rare but type 2 more common in warmbloods? I would need a muscle biopsy, so not worth doing as I don't have any suspicion that she has it?

Type 1 is very rare in TBs and warmbloods but not unheard of. Type 2 is terrifyingly common sadly. Theres a hair test for type 2. Its not peer reviewed yet so some people are wary of it, but anecdotally I've not heard of a false positive. You can speak to the people working on the test and they are pretty open with info. One of the universties in America is currently doing a huge research project, so hopefully it will become more mainstream in due course. Although given how many breeding warmbloods have it, I have my doubts!

I would not breed from anything under any circumstances without doing both tests. Type 2 is nasty, they rarely stay sound and in work and it gets worse and worse over time. It can also show up fairly late in life which means its not picked up on.

The details are here:

http://equiseq.com/pssm-faq

 

[Marigold4]

Thanks for this information. I will investigate type 2 testing. Do you happen to know how difficult to do the muscle biopsy is? Do they have to take much muscle? Is it expensive? I will also look into the type 2 hair test. Thanks again.

 

[Littlewills]

Thanks for this information. I will investigate type 2 testing. Do you happen to know how difficult to do the muscle biopsy is? Do they have to take much muscle? Is it expensive? I will also look into the type 2 hair test. Thanks again.

The problem with the biopsy is that it does fairly often show false negatives, its also a fairly nasty, invasive test. Its not so much difficult, more unpleasant and leaves a hole punched out of the muscle.

I know there are people researching bloodlines. It might be worth asking on one of the facebook groups with your mare's breeding and making quiet enquiries about any stallions you may want to use. It clearly doesnt rule it out, but it may rule it in with a lot more certainty if you see what I mean

 

[Marigold4]

The problem with the biopsy is that it does fairly often show false negatives, its also a fairly nasty, invasive test. Its not so much difficult, more unpleasant and leaves a hole punched out of the muscle.

I know there are people researching bloodlines. It might be worth asking on one of the facebook groups with your mare's breeding and making quiet enquiries about any stallions you may want to use. It clearly doesnt rule it out, but it may rule it in with a lot more certainty if you see what I mean

Thanks so much for this. Do you know which facebook group I should approach please? Do I just search for a PSSM group?

 

[Marigold4]

My gelding has PSSM1 from his warmblood dam, so it's worth testing for.

There are some pssm2 hair follicle tests about, but I have no idea on accuracy etc do you would have to research to see if it was worth it.

I like the sound of what you are planning to breed

I have found the place for the hair test and downloaded the form. Very expensive - but worth it if it avoids an even more expensive PSSM tragedy.

Thanks also for your comment on the breeding plan. I have been over-thinking this for two years!

 

[Gloi]

I got my pony tested for a wide range of things here
https://etalondiagnostics.com/pages/order
It was easy and came back quickly.

 

[Littlewills]

PSSM & MFM Awareness is one of the better ones

 

[Marigold4]

The problem with the biopsy is that it does fairly often show false negatives, its also a fairly nasty, invasive test. Its not so much difficult, more unpleasant and leaves a hole punched out of the muscle.

I know there are people researching bloodlines. It might be worth asking on one of the facebook groups with your mare's breeding and making quiet enquiries about any stallions you may want to use. It clearly doesnt rule it out, but it may rule it in with a lot more certainty if you see what I mean

I've got my mare's test results back now and she's N/N for PSSM1 and WFFS. The test for PSSM 2 is well over £200 and not yet peer reviewed. I think you think it would still be worth doing as you haven't heard of a false positive - do you know many who have used this test?

Also, can you recommend a facebook group please where I could ask about her breeding and PSSM please?

Thanks very much for your help.

 

[Littlewills]

Have a chat with the people on here. They are the experts. The lab who does the testing have a rep who answers questions as well if you wanted to speak to him.

https://www.facebook.com/groups/pssmandmfmawareness

 

[Marigold4]

Have a chat with the people on here. They are the experts. The lab who does the testing have a rep who answers questions as well if you wanted to speak to him.

https://www.facebook.com/groups/pssmandmfmawareness

Thanks. That's really helpful. I have joined and posted my question.

 

[paddy555]

Also, can you recommend a facebook group please where I could ask about her breeding and PSSM please?

Thanks very much for your help.

if you search FB for sharalee worms (yes she really is a person) I guess she will be the one to either help with bloodlines or point you in the right direction.

 

[ycbm]

Given another thread on here today about the heritability of kissing spines, I would want a set of back x rays if money was no object, to check for proximity of the DSPs

 

[paddy555]

Given another thread on here today about the heritability of kissing spines, I would want a set of back x rays if money was no object, to check for proximity of the DSPs

interesting comment. Just before coming on here I was on FB on "PSSM forum" there is a post 19 hrs ago by Candy Beauchamp about KS and PSSM and I guess the link quoted. Haven't had time to read the comments yet but could be helpful to you Marigold.

 

[Marigold4]

The KS spine thing is certainly interesting but it would be useful to know if the gene causing it is dominant or recessive.

 

[Marigold4]

if you search FB for sharalee worms (yes she really is a person) I guess she will be the one to either help with bloodlines or point you in the right direction.

Thank you. I will have a look.

 

[FinnishLapphund]

Type 1 is very rare in TBs and warmbloods but not unheard of. Type 2 is terrifyingly common sadly. Theres a hair test for type 2. Its not peer reviewed yet so some people are wary of it, but anecdotally I've not heard of a false positive. You can speak to the people working on the test and they are pretty open with info. One of the universties in America is currently doing a huge research project, so hopefully it will become more mainstream in due course. Although given how many breeding warmbloods have it, I have my doubts!

I would not breed from anything under any circumstances without doing both tests. Type 2 is nasty, they rarely stay sound and in work and it gets worse and worse over time. It can also show up fairly late in life which means its not picked up on.

The details are here:

http://equiseq.com/pssm-faq

In one place in that link it says "Because some genetic variants are not fully penetrant, some horses that are n/P2, n/P3, n/P4, n/P8, or n/K1 will not develop exercise intolerance."
And it continues with "This means that the tests are not completely predictive. P2/P2, P3/P3, P4/P4, P8/P8, and K1/K1 horses are much more likely to be affected."

I'm not sure if the last part is badly worded, or if it's me who interpret it wrongly, but to me it sounds as if they're saying that even a horse with a double copy does not have to develop exercise intolerance, even though they are much more likely to do so. Which isn't the same as what I've read on one of their other pages
http://equiseq.com/learning_center/health/polysaccharide-storage-myopathy-pssm .

On that page it says that a horse that carries 2 copies of either P2, P3, P4, P8, or K1 "is expected to develop symptoms of exercise intolerance."

Further down on that page it says that P2, P3, P4, P8, and K1 is semidominant, but P5, and P6 is recessive.
Horses with one copy of the recessive N/P5 or N/P6 is not expected to develop exercise intolerance, but horses with one copy of the semidominant n/P2, n/P3, n/P4, n/P8, or n/K1 "may develop exercise intolerance".

I presume the semidominant part means that may = it is likely, but doesn't have to, develop.


Then I read one of their other pages (http://equiseq.com/blog/p2-p4-linkage) about horses potentially carrying both P2, and P4. Very interesting, but partly I still feel a bit confused.

Not sure how likely it is, but a horse that is n/P2 n/n or n/n n/P4 can be symptom free.
A horse that is n/P2 n/P4 is more likely to develop symptoms, and if that happens more severely, but by the sound of it, isn't guaranteed to develop symptoms?

If you have a horse that is n/P2 n/P4 it can either:
A have inherited n/P2 from one parent, and n/P4 from the other.
Or:
B inherited P2 + P4 from one parent, and n/n from the other.

On the page it talks about the probability for which gene combination horse A's sperm versus horse B's sperm will carry, and the mare's egg is always n/n, but I presume that is only to simplify things, and it could just as well be the other way around, the mare could be horse A or B, and the stallion n/n?

If horse A is bred to a horse that is n/n, the foal have 46% chance for each of n/P2 n/n or n/n n/P4, but only 4% of being the most desired outcome of n/n n/n. However in comparison to the next example, also only 4% risk for being n/P2 n/P4.

If horse B is bred to a horse that is n/n the foal have 46% chance of being n/n n/n, 4% each for either n/P2 n/n or n/n n/P4. however also 46% risk for being n/P2 n/P4.

But to know which chance/risk percentage that is relevant, you of course first have to know if the horse is an A or B example. Hypothetically, even though I really like the 46% chance of n/n n/n, I wouldn't think the 46% risk of n/P2 n/P4 would be worth it.


Anyhow, I presume that this is like in dog breeding, a lot of the blame lies in inbreeding, line breeding, and some males being over used.

By the way, does anyone knows what happened to P7?

 

[Marigold4]

In one place in that link it says "Because some genetic variants are not fully penetrant, some horses that are n/P2, n/P3, n/P4, n/P8, or n/K1 will not develop exercise intolerance."
And it continues with "This means that the tests are not completely predictive. P2/P2, P3/P3, P4/P4, P8/P8, and K1/K1 horses are much more likely to be affected."

I'm not sure if the last part is badly worded, or if it's me who interpret it wrongly, but to me it sounds as if they're saying that even a horse with a double copy does not have to develop exercise intolerance, even though they are much more likely to do so. Which isn't the same as what I've read on one of their other pages
http://equiseq.com/learning_center/health/polysaccharide-storage-myopathy-pssm .

On that page it says that a horse that carries 2 copies of either P2, P3, P4, P8, or K1 "is expected to develop symptoms of exercise intolerance."

Further down on that page it says that P2, P3, P4, P8, and K1 is semidominant, but P5, and P6 is recessive.
Horses with one copy of the recessive N/P5 or N/P6 is not expected to develop exercise intolerance, but horses with one copy of the semidominant n/P2, n/P3, n/P4, n/P8, or n/K1 "may develop exercise intolerance".

I presume the semidominant part means that may = it is likely, but doesn't have to, develop.


Then I read one of their other pages (http://equiseq.com/blog/p2-p4-linkage) about horses potentially carrying both P2, and P4. Very interesting, but partly I still feel a bit confused.

Not sure how likely it is, but a horse that is n/P2 n/n or n/n n/P4 can be symptom free.
A horse that is n/P2 n/P4 is more likely to develop symptoms, and if that happens more severely, but by the sound of it, isn't guaranteed to develop symptoms?

If you have a horse that is n/P2 n/P4 it can either:
A have inherited n/P2 from one parent, and n/P4 from the other.
Or:
B inherited P2 + P4 from one parent, and n/n from the other.

On the page it talks about the probability for which gene combination horse A's sperm versus horse B's sperm will carry, and the mare's egg is always n/n, but I presume that is only to simplify things, and it could just as well be the other way around, the mare could be horse A or B, and the stallion n/n?

If horse A is bred to a horse that is n/n, the foal have 46% chance for each of n/P2 n/n or n/n n/P4, but only 4% of being the most desired outcome of n/n n/n. However in comparison to the next example, also only 4% risk for being n/P2 n/P4.

If horse B is bred to a horse that is n/n the foal have 46% chance of being n/n n/n, 4% each for either n/P2 n/n or n/n n/P4. however also 46% risk for being n/P2 n/P4.

But to know which chance/risk percentage that is relevant, you of course first have to know if the horse is an A or B example. Hypothetically, even though I really like the 46% chance of n/n n/n, I wouldn't think the 46% risk of n/P2 n/P4 would be worth it.


Anyhow, I presume that this is like in dog breeding, a lot of the blame lies in inbreeding, line breeding, and some males being over used.

By the way, does anyone knows what happened to P7?

Gosh - now my mind is definitely boggled!