The PSSM Situation in Our Breed

We are probably not the only Morgan owners who never really gave much of a thought to diseases like PSSM (Type 1 or 2), as it is not something typically associated with our breed.  However, a few months ago, on one of the Morgan Facebook pages, a stallion owner posted that their horse had tested positive for PSSM1.  They still would continue to breed him, but would make results of the PSSM tests known to potential buyers of their foals.  This particular stallion’s sire was very prolific, and is often found in the pedigrees of colorful Morgans.

In case you’ve never encountered PSSM, a brief explanation; PSSM is short for Polysaccharide storage myopathy.  It is a hereditary glycogen storage disease that results in the accumulation of abnormal complex sugars in muscle cells.  There are two types, PSSM1, and PSSM2.  PSSM1 presents as the genetic form of “tying-up,” with muscle damage, pain, weakness, and the inability to move.  PSSM1 can be tested the same way we record DNA results for AMHA, or look for color – hair with the root bulb still intact. It can also be tested via blood.  PSSM2 is a bit more complicated, while symptoms are similar, they do not have the same genetic markers and therefore there is no simple DNA test.  A muscle biopsy would be the only way to diagnose.

PSSM1 can be treated in part with diet.  We feed a forage-based diet here, with Custom Equine Nutrition’s ration balancer, Vermont Blend Pro the core of our program.  This is the kind of diet that can truly assist a horse suffering from PSSM (and a myraid of other issues, especially in easy keepers like Morgans).  Regular exercise (keeping the horse’s limits in mind), muscle relaxants, and other medication related measures may be necessary as well.  There is no cure, but some horses live a completely normal life, especially with dietary management.  

We were able to rule out two of our geldings – HJA Sundust (Jimmy) and BDS Silhouette’s Prestige (Sheldon) because of their ages and workloads; they would have shown signs by now.  While we likely could have ruled out our stallion, Declaration (Sparky) due to his rigorous competitive career, we went ahead and tested him so that breeders could feel confident, and he was thankfully negative.  We are a small breeding program, but we still felt that ethically, we had to test everyone.  We are very thankful that all of our horses came back N/N for PSSM1.  

One Morgan owner and breeder put a lot of hard work into creating the Morgan Horse Health Database. Morgan owners can submit their horse’s test results to this database, and if negative, photo evidence of the test will be included.  It can be done anonymously, though at this point it would be helpful just to know the positive horses.

Morgans are a small breed, and a small community.  Transparency can do so much to help contain and hopefully eliminate PSSM from the breed.