Mare has been ‘tested’ for PSSM “!”. negative. Now? beyond that testing current vets suggest only the muscle biopsy for PSSM 2, as in not ‘trusting’ the hair pulling testing results I guess since not ‘verified’ as conclusive yet. Seems some new study is going on to determine this. Anyway. this horses’ symptoms seem to be more defined as PSSM 2, etc…vs. PSSM 1 anyway. But have any of you worked WITH your vets that do suggest this hair pull analysis as a diagnosis and treatment plan? I am indeed trying to read all the groups who are helping each other in specific diets and supplements and exercise, blanketing, etc. but— its all over the map for ‘this type’ or that type. Not ‘ready’ to self diagnose this young mare, so i don’t want to poo poo what the vets working with her believe in. 
Have you also checked Vitamin E and magnesium levels in your journey?
have not ‘specifically’ but I can ask. 
What symptoms does she have?
You can always make the diet appropriate for a Type 2 horse - higher protein, add whey protein powder, etc - and see if things change, and “diagnose” by treatment
JB - can you link or tell us more about whey? My research must be out of date as I haven’t seen that. Any specifics you could provide would be gratefully appreciated!
https://cvm.msu.edu/research/faculty-research/comparative-medical-genetics/valberg-laboratory/type-2-polysaccharide-storage-myopathy
“Ensuring adequate protein content in the diet is an additional recommendation for PSSM2 horses especially those with loss of muscle mass. Whey based formulations are recommended at the manufacturers recommended amount. Progressive’s topline Xtreme or Purina’s Supersport are two such supplements. Feeding within 45 min of exercise may enhance development of muscle mass.”
I do know several people who buy straight whey protein, but I have no idea how much they add - probably a bit of guessing to find what works best for their specific horse.
