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Is this cause for concern?

Mare has had this weird line in her muscles since I’ve owned her on both sides. I’ve tried researching it on my own, and while I think I have identified the muscle, I can’t seem to find any info on what this could signify? Is it muscle atrophy or some sort of tightness?

a picture would help a lot. What kind of line? What muscle?

Sorry it didn’t want to upload! Posted

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Oh, your picture comment posted as I was replying

What breed is she? Lines like that can be indicative of some PSSM2/MIM myopathy


She’s a paint

Is she having any issues? If so, what, if anything have you tried to do to help? What’s the whole diet?

She was NQR in July and I pulled her out of work. She has a lameness exam in August and her X-rays were perfect but she was lame to the right on gravel and flexed positive the first time we did flexions somewhere on the RF but the vet couldn’t nail it down. When we did flexions a second time she wasn’t lame. That vet and nowhere within a 5hr radius of me has an US so the vet told me to take her out of work until the spring and see what she looks like then.

I didn’t do anything with her for ~2 months, she just lived outside 24/7. We started hand walking trails in September. In October I target trained her to do long/low walking and stretches, which we have done 4x a week since. She’s on a 5 week trim cycle and i rasp her toes every week. She gets a massage once a month. Today I hand walked her over ground poles for the first time since July.

Once a day she gets:

  • 2lb alfalfa
  • 4oz California trace plus
  • 2000iu VE in a homemade chia seed/ spirulina/ oat/ carrot/ molasses cookie
  • 90g SmartTendon
  • 3 tablespoons red mineral salt

Briefly skimming some symptoms of PSSM2: she was reluctant to go forward under saddle this summer but I attributed it to our ex trainer pushing her way too fast :confused: she is extremely chill by nature

“Extremely chill by nature” is also a red flag for PSSM.


Given her symptoms, which is the only reason I recommend this test, it’s worth testing with Equiseq to see which variant(s) of MIM she may have. You can start targeting her diet based on the results.

I’m now at a point with PSSM that a positive response to targeted dietary and exercise requirements gives me a “positive” diagnosis. Equiseq’s testing can be helpful, especially when trying to tailor diet very specifically, but I’ve seen such dramatic changes from just making changes in diet and exercise regimens that PSSM jumps to the forefront for me when I read posts like this.

Wow I’m feeling quite scared by this possibility. Could you please elaborate (with as much detail as you are willing to provide) what you mean by this comment and changing diet/exercise?

I don’t disagree! With all the variants I’ve seen enough differences that tend to work better for one variant over another, that it’s not a bad starting place, rather than just picking something out of the mix. But I agree, there are some reasonable dietary changes that could be made as a starting point

MIM tends to benefit from more, and higher quality protein. For some, it’s more alfalfa. For many, it’s adding whey isolate protein (like human supplement powder). For some, it’s pea protein/split peas. “Alcar”, acetyl-l carnatine, works well for some.

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Think of the PSSM horse as needing a kind of Keto approach to life…

Long stem greenery good in form of hay, and older pasture. No complex carbs, no grain, etc.

We got my guy managed by feeding mainly hay, was on a grass Alfa mix, he was fine with beet pulp, as long as no molasses, restricted grazing during high sugar in the grass. When working got a high fat, low carb cube, and we added, Vitamin E and Potassium to his feed. He also got Camelina oil. Very susceptible to cold, so blanketed all winter.

Once we got him working more, we gradually dropped the E and Potassium, he still gets the beet, high fat ration, and Camelina oil.


Ok. So start feeding something like UltraCruz Equine BCAA? I’ve been thinking for a bit anyway that I wanted to add a protein supplement because she’s always had a poor topline. But if she does have this, how do I balance rehabbing from a soft tissue injury with adequate exercise to keep the MIM/PSSM in check?

What were symptoms you were seeing in your horse before you got him tested? How long did it take to get him managed?

Type 1, yes. MIM (formerly PSSM2), not really. I’m only making an assumption more of MIM than PSSM1 because MIM really tends to make those muscle striations. It COULD be PSSM1, and thankfully there’s a simple hair test for that

That’s a good start yep. Get a big container of human whey isolate (important) protein powder and see if you can work up to 1/4-1/2c. I’ll ask a friend what she found works for her guy.

It’s going to be tough to balance rehab, but focus on the diet and rehab first. Once you get a diet dialed in (still assuming some kind of PSSM or MIM) then work will be easier, and that could take the entire time you’re in rehab

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Thank you very very much. In your experience, what are signs that they’re reacting positively to a diet change w/o riding them to determine their forwardness? She isn’t going back in under saddle work until the spring at the earliest. I’m feeling pretty horrible because if she does test positive then this would definitely explain a lot, like almost her entire demeanor. I’m going to buy the EquiSeq test.

I thought EquiSec had been discredited by vet community? Are they really legit? I’d be curious to see their results on my guy but had seen/heard from multiple sources there was question about them.

I did a biopsy to confirm PSSM2 and one very positive change I’ve noticed of late is adding both ALCAR and BCAAs - his muscles have noticeably softened. I also test my hay and could see the lysine in my hay was good and my KIS Trace supplies more lysine, along w methionine and threionine.

I’d have to look at the date but both started in the last 30 days. Until of late, I would feel beef jerky-like quality (dry, tight tissue) to hind end muscling and he did not want bodywork.

Since making sure Lysine, Methionine and then ALACAR and the BCAAs it’s like wow. He’s also getting better about me being back there and loosening that tissue. Thanks to the other thread I’ve got a Posture Prep now and gently moving tissue and he likes it. That is wild.

He’s also mostly reluctant to move - super chill, need to crack the whip on the lunge to get trot, mostly explodes if asked to canter on the lunge so mostly we don’t. Just being started under saddle.

What a shitty diagnosis. I also keep him blanketed to keep his muscles warm.