None of our horses at R2 Ranch carry this genetic disorder


What is it: Polysaccharide storage myopathy (PSSM1) is characterized by the abnormal accumulation of the normal form of sugar stored in muscle (glycogen) as well as an abnormal form of sugar (amylase-resistant polysaccharide) in muscle tissue. By definition horses with PSSM1 have a distinctive genetic mutation in the gene.

Can you ride a PSSM horse? Yes, You must be mindful of their exercise routine.

Do you have to do anything different with them? Yes, diet is a little bit more strict. Low carb and high fat.

Is it prevalent in the rocky breed as it is in AQHAs? NO

What brought this into our breed? Many theories exist. It is thought many wider bred or drafty breeds carried this disorder from before horses existed in the Americas- possibly a common Spanish ancestor for both AQHAs and RMH and possibly Drafts as well. It has prevailed through the creation of many American breeds we now have today.

Is there a common ancestor? Yes, some may have noticed it was a Yankee bred horse within the RMH but it is very exclusively KING'S BLONDE and most likely RIP in his line that carried PSSM1.

Are all offspring from these horses 100% possible to be carriers? No- only genetic testing for the gene will tell you. Usually the offspring are only passing the gene 50% of the time unless they carry 2 copies of the gene.

Our Notes on PSSM1