My horse was just diagnosed with Equine Polysaccharide Storage Myopathy, he is now on Poulin Grain Carb Safe. Can you explain more about this, and how to keep the total carbohydrate level at 12% or below. Thank you. SK, Vermont
Dear SK,
I’m so glad someone finally asked a question about Polysaccharide Storage Myopathy (PSSM or EPSM, depending on whose research you read). Because my own horse has this, I’ve done quite a bit of research on it, and might be able to shed some light on this relatively new disorder in horses for you.
So that everyone knows what we’re talking about, let’s start from the beginning! PSSM is a form of “tying up,” or, exertional rhabdomyolysis, which means “muscle breakdown with exercise.” Some classic examples of this are the working draft horse that gets Sunday off then develops “Monday morning sickness,” the thoroughbred who “ties up” after a race or three-day event, and the Arabian who develops this painful cramping of muscles during an endurance competition. While PSSM is related to these other forms of “tying up,” it is a unique, inherited condition in quarter horses, draft horses and warmbloods that has to do with how sugar (glucose) is taken up and stored in the muscles for energy.
Here’s the current theory: First, PSSM horses are very efficient at pulling glucose out of the bloodstream and putting it into muscles because of heightened insulin sensitivity. Second, because of a mutated gene, the enzyme that transforms glucose into glycogen (the storage form of glucose) is faulty and instead transforms glucose into a different polysaccharide, one that is abnormal and unusable. Therefore managing a PSSM horse involves 1) limiting the amount of sugars and starches he eats, 2) providing fat for energy instead, and 3) keeping the horse’s muscles moving so abnormal polysaccharides don’t build up.
As you’re finding out, performing these three tasks well is not easy! Current recommendations for the maximum amount of sugars and starches range from 10 to 20% of the total daily calories. To achieve this, you’ll probably need to have your hay analyzed (www.DairyOne.com and www.Equi-Analytical.com are good choices), then stick with that one hay source, if possible. If not, you may want to purchase hay cubes in bags, which have a more predictable composition. You’ll also have to be careful allowing your horse access to pasture, as there are certain times when the sugars and starches in grass are very high. Visit www.safergrass.org to learn when grazing is safe and when it’s not. I’m glad to see you’ve pulled your horse off grain (sweet feed, corn, oats, etc.) and are using a low-starch alternative. That’s important, because these horses still need a complete and balanced diet—not just forage—especially if they are being asked to perform. For people who can’t find a low-starch grain in their area, I recommend feeding a ration/forage balancer or multi-vitamin/mineral supplement.
You don’t mention if you’re providing your horse with extra fat, but this is the next step in managing a PSSM horse. Because you’ve taken away much of the sugar and starch they had been using for energy, you need to replace it with another source of energy: fat. Some commercial feeds have added fat, other companies make high-fat products to go along with their feeds, or you can use vegetable fat in a powder or oil to supply these calories. Note: additional Vitamin E (an anti-oxidant) should be fed to horses receiving high fat diets as the increased aerobic metabolism associated with such diets may result in oxidative stress (free radicals). Some experts recommend feeding up to 1 pound of fat a day, but I’ve found a half pound works just fine in my own horse. I feed him four ounces of Cool Calories AM and PM, with SmartE in the morning and MSM in the evening.
Finally, it’s important to provide lots of exercise to PSSM horses. The worst thing you can do is put them in stall! Twelve hours max is the rule. In addition to as much turnout as possible, these horses do best if worked (lunged, ridden, driven) every day. In fact, some experts recommend two shorter bouts of exercise per day! Take your time warming up and cooling down, and if your horse has an extended layoff for any reason, start back very very slowly with him, adding on just a few minutes of additional exercise a day until he’s back at the former level of work.
For those of you reading this who are concerned your horse might have PSSM, here is a list of the other, more subtle signs PSSM horses can have, besides full-blown episodes of “tying up,” which can be as mild as shortened strides or as severe as an inability to move:
- Gait abnormalities
- Mild colic (pawing, rolling, sweating, not eating)
- Muscle wasting or atrophy
- Decrease in level of performance
- Painful and firm back muscles
- Reluctance to collect and engage the hindquarters
- Poor rounding over fences
- Tucked up abdomen
- Difficulty backing
- Difficulty holding up limbs for the farrier
- Muscle trembling
- Muscle weakness
- A “shivers”-like gait
To learn more, visit the University of Minnesota College of Veterinary Medicine Neuromuscular Diagnostic Laboratory website: www.cvm.umn.edu/umec/lab/home.html.
Lydia F. Gray, DVM MA, currently serves as the Medical Director/Staff Veterinarian for SmartPak Equine. Prior to joining SmartPak, Dr. Gray served as the first-ever Director of Owner Education for the American Association of Equine Practitioners. She has authored numerous articles in publications such as The Horse, Horse Illustrated, Western Horseman and a variety of veterinary journals and magazines. Dr. Gray is also a frequent speaker at horse expos, veterinary conventions and other locations. After graduating with honors from the University of Illinois College of Veterinary Medicine and receiving her Master's Degree in Interpersonal and Organizational Communication, she practiced at the Tremont Veterinary Clinic for several years. Dr Gray is active in the American Veterinary Medical Association and Illinois State Veterinary Medical Association and enjoys training and showing her trakehner Newman in her spare time. Find Dr. Gray on Google+: Find Dr. Gray on Google+
I have a paint that I believe suffers from PSSM. My question is: can a muscle biopsy be preformed at any time or do you need to wait for an “episode” to get a true diagnoses?
They now have a genetic test for PSSM Type 1 by using hair root samples. I just had my Paint done by Animal Genetics and got the results super fast! Not the results I was hoping for but at least I now know what exactly is wrong with my horse.
The easiest thing is to put your horse on low carb, high fibre/hight oil conent diet(such as Happy Hooves-in Australia) and fluid balancing Electrolyte such a Equitec (Osmoplex) and Magnesium such as(Placid Rein) also from Equitec. I also have my horse on (Proflex)which contains MSM, from the same company. My horse has never ben better.
Can this disease also be in thoroughbreds? Ive got a boarders horse who exhibits almost all of these symptoms, except tying up and dark urine.
Hi Christine, my vet has diagnosed PSSM in my Quarter horse mare. We are now feeding, Speedibeet, & lucern chaff,and some sunflower seeds, added to this is Equi-Sure, Cell-Vital minerals. For fat content can I use Full fat Soy? or would this cause digestive upset too?
Sue
I would like to know if there is anyone else out there who had their horse tested for PSSM and got back a n/P1 result, but has never had any episodes of lameness or tying up. I had my horse tested for breeding purposes, never in 7 1/2 years has this horse ever exhibited any signs. Has anyone else seen this? Isn’t it apparent from birth if they have a problem?
I have the same questions as Marie. My family has raised Appaloosas for many years, and recently tested our stallion (age 20) for PSSM due to one of his get having tested positive for it. He has never had any of the symptoms listed on any of the sites I have found info on, nor have any of the 20+ of his get and grandget I have trained myself. Is there evidence that some horses are not affected even though they are n/p1?
Hi Ellie,
Yes, some horses have the genetic mutation although it may not be expressed because of the combination of diet, turnout, exercise and other management factors. And even though it is inherited as a dominant trait, one copy of the PSSM gene may not result in clinical signs while two copies will. So it is the combination of genes from your stallion and the mare he is bred to that determines the offspring’s health. We hope this helps!
What does the MSM do to help?My horse exibits signs and I just sent a hair sample to University of Minnesota for analysis.She has been on the high fat,(Healthy Glo nuggets,Grostrong mineral),low starch diet since May,2012 and grass hay,first cut.She has had 2 episodes,almost 4 weeks apart but her work schedule was lax from the holidays…I feel very responsible for that!!!I read a lot on this disorder and have not seen the MSM added yet….any info is greatly appreciated.Thanks Kelly
Hi Kelly,
Besides diet and exercise, there’s not a lot that has been researched to specifically help horses with PSSM besides fat, Vitamin E and possibly selenium. And while there have been numerous studies touting the benefit of MSM in various systems such as joints, respiratory, skin and hooves, papers are just coming out now about its effect on muscle tissue. In “The correlation of training times, thermography and serum chemistry levels to provide evidence as to the effectiveness of the use or oral MSM (methylsulfonyl methane) upon the musculature of the racing standardbred” veterinarian Ronald Riegel confirms the anti-inflammatory and analgesic (pain-relieving) benefits of this natural substance, with improved hoof growth, skin and coat health and recovery from exercise as a bonus.
Hi, My horse has EPSM and is fed alfalfa cubes, chia seeds, SmartShine Ultra, SmartTendon, and SmartVite performance. He does very well on this diet. However he is boarded at a show barn, and during the winter months, if the weather is not good, they do not get turn out. I am still in school so I cannot get out there more than once a day to allow for exercise. My only other option is to turn him out 24/7, but I am worried about his access to lush pasture in the spring. I am afraid the sugar and carbs in the grass will make him worse. What do you think is the better lifestyle for him? Thank you!
Hi Meagan, thanks for your question. It sounds like your horse is very lucky to have such a conscientious owner! We recommend that you discuss these turnout options with your veterinarian, as they are most familiar with your individual horse and will be able to provide the best recommendation, given his health condition.
Just wanted to had that the Yahoo group is an excellent source of information on this disorder. An alternative not talked about here, is the use of ALCAR or l-carnitine to help with the metabolizing of glucose. I have had excellent results using ALCAR with my horse as have most on the yahoo list.