Everyone knows (or should know) about HYPP-- the genetic disease passed on to Quarter Horses and stock-type grade horses from the stallion Impressive. It's a scary disease that's caused the deaths of horses and riders. It's more scary that many QH owners are either unaware of HYPP or even deliberately breed for it, because the low-level seizures a horse experiences daily result in the heavy muscling desirable for halter classes.
But HYPP only affects stock horses, and only a small number of those. What about a disease that affects virtually every breed, and up to 86% of horses in some breeds may be susceptible?
PSSM or EPSM is polysaccharide storage myopathy. In plain English, muscle-wasting disease. Horses with EPSM can experience a wide range of symptoms, including muscle tremors, tying up, cramping, weakness, stiffness, shortened stride, inability to collect well, sore back and gait abnormalities. Many horses will fall ill with these vague symptoms periodically, but go undiagnosed and pass on the condition to their offspring. Some horses will experience so much muscle trembling that secondary kidney damage and death result. Other horses will literally waste away, their muscles reduced to nothing until they cannot walk.
EPSM is most scary because we know so little about it. Unlike HYPP and other diseases, we don't have a genetic test to identify it yet. Muscle biopsies are a good, if not 100% accurate, test for EPSM. However, by the time there's enough muscle damage to show up for the test, the horse has already experienced intense suffering. Finally, although all breeds are susceptible, each breed and individual horse seems to react slightly differently, making EPSM especially hard to diagnose.
EPSM can be treated-- by doing exactly the opposite of what most owners would instinctively do. EPSM causes a horse's body to improperly break down grains and sugars, thus causing the horse's muscles to break down instead. When an owner piles on the grain and treats to try to boost a weak-looking equine, the disease is made even worse.
Draft horses are the most susceptible, with up to 86% of some draft breeds in danger.
You can read more about PSSM/EPSM in the following articles:
Review of “Breed susceptibility in equinepolysaccharide storage myopathy”
Quarter Horses Among Breeds Susceptible to EPSM
Feeding Draft Horses: The EPSM Diet
Tip of the Week: EPSM...