Managing Polysaccharide Storage Myopathy (PSSM) in Your Horse

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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,

So that everyone knows what we’re talking about, let’s start from the beginning! PSSM (or EPSM, depending on whose lab you’re following) is a form of “tying up,” or, exertional rhabdomyolysis, which literally 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, warmbloods and other breeds 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. A grazing muzzle is a nice option here, because it limits the amount of grass eaten but still allows for turnout. I’m glad to see you’ve pulled your horse off traditional fortified 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. Choices for providing the correct ratio of vitamins and minerals include low-starch grain such as you’re using, a ration balancer, or a 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 he had been using for energy, you need to replace it with another source of energy that’s more available and less problematic: 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 one pound of fat a day, but some horses do just fine on a half pound. Just be sure and add the fat to the diet gradually to give your horse’s GI system a chance to learn to digest and absorb it.

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

Lydia F. Gray, DVM, MA SmartPak Staff Veterinarian and Medical Director Dr. Lydia Gray has earned a Bachelor of Science in agriculture, a Doctor of Veterinary Medicine (DVM), and a Master of Arts focusing on interpersonal and organizational communication. After “retiring” from private practice, she put her experience and education to work as the American Association of Equine Practitioner’s first-ever Director of Owner Education. Dr. Gray continues to provide health and nutrition information to horse owners through her position at SmartPak, through publication in more than a dozen general and trade publications, and through presentations around the country. She is the very proud owner of a Trakehner named Newman that she actively competes with in dressage and combined driving. In addition to memberships in the USDF and USEF, Dr. Gray is also a member of the Illinois Dressage and Combined Training Association (IDCTA). She is a USDF “L” Program Graduate and is currently working on her Bronze Medal. Find Dr. Gray on Google+

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41 comments on “Managing Polysaccharide Storage Myopathy (PSSM) in Your Horse
  1. Jane E Meyer says:

    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?

    • Christine says:

      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.

  2. Susan says:

    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.

  3. rhea says:

    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.

  4. Sue says:

    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

  5. Marie says:

    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?

    • Ellie says:

      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?

      • SmartPak SmartPak says:

        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!

    • Cathy McGhee says:

      I have a paint quarter horse who was diagnosed 1 year ago with EPSM. I’ve had him since he was 7 and has never had an episode until 2 yrs ago. He is now 17 yrs ago. So he did not have any signs of it when he was younger. Yes they are born with it but my vet told me the horse may not show signs of it until later. My friends Appaloosa is 5 yrs old and she just started to have some episodes. She just had her DNA tested and she definetly has EPSM.
      So as you can see not all horses have episodes from birth.

  6. Kelly Moore says:

    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

    • SmartPak SmartPak says:

      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.

  7. Meagan says:

    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!

    • SmartPak SmartPak says:

      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.

    • Jess says:

      Megan,

      I have sort of the same problem with my horse. In the summer the weather is just too much for him so I have to put him on stall board. But in the winter he’s pasture boarded. I wait a few weeks after the frosts have set in so the pastures aren’t super sugary from being flash frozen. If your horse can handle it, try talking to the manager and do a 1/2 and 1/2. My horse’s back end freed up amazingly and just comfort level when we kicked him out for the winter. I also live in the south though.

  8. Laura Rencher says:

    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.

  9. Judy says:

    I tried the high fat diet for a week–then my horse refused to eat it. I am now using (successfully) Al-Car. I would appreciate hearing more about Al Car diet as an alternative to added fat, which, as I understand it, might be a risk factor for developing IR. I learned about AL Car from the yahoo group for PSSM/EPSM horses. BTW, my horse tested negative for PSSM type 1. I am awaiting biopsy results for type 2 PSSM. It is important to realize that if a horse is negative for type 1, it may still have a form of PSSM.

  10. Lisa says:

    My warmblood mare has Type 1 PSSM that we have been able to bring completely under control with diet and exercise. The greatest lesson I have learned from this is that “low carb” grain is not necessarily low *enough* carb. You need to know the NSC (non-structural carbohydrate) value of everything you feed your horse (even supplements!) and use that number to control the starch intake.

    I am having great luck with Blue Seal Carb Guard (allegedly the lowest NSC value on the market), E-Se-Mag from Smartpak, and Ultimate Finish fat supplement (recommended by the lab at the Univ of Minnesota). My vet also suggested that we not feed her any processed treats or candy (like peppermints or her very favorite root beer barrels), to further reduce the sugars.

    It’s a condition that will always effect the ability of her muscles to recover from work, but it is managable and has not slowed us down with our goals (once we got it under control).

    • SmartPak SmartPak says:

      Exactly right, there are two different types of PSSM–Type 1 (which is diagnosed with a genetic test on hair or blood) and Type 2 (which is diagnosed with a muscle biopsy). The Neuromuscular Diagnostic Laboratory at the University of Minnesota Equine Center College of Veterinary Medicine can perform both these tests and is a great source of information on this condition: http://www.cvm.umn.edu/umec.
      Although there doesn’t appear to be any scientific research to date on the use of ALCAR (acetyl L-carnitine) specifically in horses with PSSM, anecdotally many people are reporting good results from this naturally occurring amino acid which helps the body mobilize fat for energy. – SmartPaker Lydia (aka Dr. Gray)

      • Andree says:

        Hi,
        I would also like to know more about this Alcar, from what I understand(and correct me if I’m wrong), this amino acid allows glucose to metabolize in the mitochondria without converting to glycogen? How is this fed? With minimal research on it, is there an equine supplement or just human form until it is proven? And with feeding Alcar, I have read that you have to wean horses off the EPSM high fat diet before introducing alcar? It sounds concerning, and I apologize for all of the questions but my gelding has been symptomatic recently on the high fat diet so I am just exploring my options. Any input will be greatly appreciated! Thank you!

        • Cynthia Bancale says:

          I have had tremendous results with my mare and the ALCAR supplement. I could not be happier with the response. My mare is now able to hold her feet up without trembling, has more energy and seems to be back to her old self…not lethargic like before. I did try the high fat diet and did not see that much improvement. With the ALCAR, there was a vast difference within a week and within two weeks, symptoms were almost completely gone. If you have a horse with EPSM I highly suggest you give this a try. I am so grateful for this treatment and my horse is a lot happier and more comfortable. You can get more specific information through Dr. Eleanor Kellon. You can find her on the web.

    • Ros Nightingale says:

      Hi there
      I am very interested in researching more about the PSSM in horses particularly in the Warmblood but need to know the bloodlines of the Warmbloods and what draught horses they go back to. Can you please let me have the bloodlines of your horse that has PSSM? You dont have to give me the name of the horse just the sire and dam will do.
      Many thanks, I appreciate any help.
      Regards
      Ros

      • Barb C. says:

        My guy is Belgian/TB/Standardbred.
        The University of Minnesota has some breed statistics on their PSSM page as well.

  11. Sarah says:

    Looking for some advice on selling my draft cross with PSSM, I didn’t know he had it when I bought him, and now that I have decided to move on to a horse that would be better for showing and jumping, I am finding it impossible to sell him. I really don’t want to have to give him away, he has had excellent training and is a great horse. I keep getting people interested in him and then they talk to their vets who tell them they shouldn’t buy him. He is very well managed and other than a mild tying up incident a year ago has had no major issues with it. At that point we removed him from grain, he gets canola oil and vitamin E and selenium. He looks and feels great, but I just can’t convince people to even come out and try him. He went on a 12 mile hunter pace last fall and was absolutely fine… Also people want him to be able to go out on pasture, he is out on grass, but it is not rich pasture so I don’t know how he would do on it. I just lost a buyer because her vet told her he would not be able to go out on her pasture… I am at a loss for how to get him sold to a good home, I am always completely up front about it with people, and I would never not tell someone he has it, but pretty much I am at a complete loss as to what to do.

    • SmartPak SmartPak says:

      Hi Sarah, thanks for your question. As riders ourselves, we SmartPakers know just how tough it can be to part ways with a great equine partner, when you add in people’s misunderstandings about a condition like PSSM, it can get even harder. While we aren’t able to provide recommendations on how to sell your horse, we can refer you to an awesome community of riders who own and love horses with PSSM: http://sports.groups.yahoo.com/group/EPSM/ This group might definitely knows where you’re coming from, and some of the riders may be able to offer some helpful advice. Good luck and have a great ride! – SmartPaker Sarah

    • Valerie says:

      Sarah Although it it difficult 2 sell a horse with any pre existing medical condition, my horse that has epsm is out on grass with no problems for years. A simple diet change alfalfa pellets, rice bran pellets and carb guard along with 5,000 iu of vitamin E and a cup of corn oil has made him better! Hopefully, you can find someone that will buy him for a pleasure horse. Best regards, Valerie

  12. Andree says:

    Hi everyone. I have a 17 year old Appendix gelding who was diagnosed in 2006 with mild EPSM. I have been successfully managing it with this diet! He gets 2 cups of Performance Pak 100% dried fat supplement, 2 QTs of Kent feeds Omegatin, Smartflex resilience, Smartgut Ultra, about a pound of soaked Timothy cubes and lastly 5 flakes of mixed hay twice daily. I understand the exact diet doesn’t work for every horse with EPSM, however, I thought I would throw it out there for those who are just as stumped as I was when I had to figure out a combination. It took us a long time to get there, slowly introducing and increasing his rations but now that we have it all together he has been great! He does best with as much turnout and exercise as possible. He is at a boarding farm and is turned out every other day (weather permitting) so on the off days I make sure I am there to get him out of his stall. He also wears a grazing muzzle when he is out on grass, that thing is worth it’s weight in gold! He gets out to stretch and exercise while controlling the amount of grass he consumes. I hope this helps my fellow EPSM horse moms and dads! It can be frustrating but with the right diet combination and patience, they will bounce back to normal!

    • SmartPak SmartPak says:

      Hi Andree, that is SO fantastic! Your horse is lucky to have one awesome mom! We’re thrilled that some of SmartPak’s products and articles are helping you take the best care of your horse. – SmartPaker Casey

  13. Dr Elizabeth Kellon seems to be an excellent authority on PSSM in horses. She states that she sees far too many horses whose owners follow the fat diet become laminitic and develop insulin resistance. She therefore recommends ALCAR otherwise known as Acetyl L-Carnitine. I hope this helps!

  14. holly says:

    Does smartpak have a supplement for acetyl L carnitine?

    • SmartPak SmartPak says:

      Hi Holly, thanks for your question! Currently SmartPak does not carry a supplement that solely provides high levels of acetyl l-carnitine. – SmartPaker Casey

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  16. aleks and mickey says:

    I am currently using l-car and not alcar as a supplement is there any benefit to using the alcar over plain l car I was told that if your horse is eating a high oil diet ( my highly symptomatic appy boy gets coconut oil and copra as he pretty much cannot eat anything else )they should have l-car and if they are not eating as much oil they should get alcar please clarify if you can :)

    • SmartPak SmartPak says:

      Hi Aleks & Mickey, thanks for your question! To date, much of the information available about supplementation with Acetyl L-Carnitine in horses with PSSM is anecdotal, and so there is simply no established protocol for the use of this nutrient. I would recommend you continue to seek out the advice of your veterinarian in determining the best approach for supporting your horse through nutrition, good management, and supplements where appropriate. – Dr. Lydia Gray

  17. Wendy says:

    I just got me results back from aqha. Nn for pssm. I asked if he could have epsm. She said no. That is not what I read. Do you know what is right are pssm and epsm the same thing, Or different?

    I am seeing a vet tomorrow because there is something wrong with me gelding. That I have always assumed was epsm 2. So he has been on low sugar high fat for about 6 months. But I have not been able to exercise him everyday. He lives in a large paddock in and out.
    Wendy

    • SmartPak SmartPak says:

      Hi Wendy, we’re sorry to hear about your gelding’s condition. EPSM and PSSM are two different names for describing the same general muscle dysfunction in horses. EPSM stands for Equine PolySaccharide Storage Myopathy while PSSM stands for PolySaccharide Storage Myopathy. Think of the tomato, tomaaato…potato, potaaato saying.
      For the sake of consistency, I’m going to simply refer to it as PSSM. However, there are different types of PSSM that effect different types of horses, and can also present a different set of signs in the horse. Because determining IF your horse has PSSM, as well as what TYPE of PSSM is quite complex, the best advice I can give is to continue working closely with your veterinarian. Diet and management are essential for these horses, and it’s great that you’ve worked with your veterinarian to make appropriate adjustments to your horse’s nutrition program. – Dr. Lydia Gray

  18. Sydney says:

    I have a horse that was tested negative for type one but has strong symptoms so im thinking she has type 2. I’ve been doing a lot of research and found chia seeds. The benefits of chia seeds are everything that a PSSM horse needs and am just wondering if anyone else has tried this and if it works/helps. Also wondering if there are any negative affects of the chia seed because I do not want to make my horse worse. Any insight would be greatly appreciated, Thanks!

    • SmartPak SmartPak says:

      Hi Sydney, thank you for your comment! PSSM can be a really tricky condition in horses, and it’s excellent that you’re working toward finding ways to help support your horse. I would encourage you to work closely with your veterinarian when it comes to making adjustments to your horse’s nutrition program like adding chia seeds. Your veterinarian will be the expert when it comes to strategies to help manage your horse, so I would get him or her involved sooner rather than later. – Dr. Lydia Gray

  19. Janice says:

    Hi!

    I recently found out that my paintmare’s mother and brother has PSSM and I’m now going to test my mare to. She’s now 4 yo and has never shown any symptoms. Shes been on grassrich pastures 3-4 months every summer and here feed is not very low on starch. If i turns out that she has PSSM, how radical a change do I have to do? I’ll of course cut the starch (as much as possible) from her feed, but the summerpasture… Do I have to keep her in a nuzzle (is it called that? English isn’t my first language)even if she doesn’t show any symptoms? Can the fact that she’s able to go outside 24/7 been hiding any eventual symptoms?

    • SmartPak SmartPak says:

      Hi Janice, I’m sorry to hear about your mare’s situation. At this point, I would encourage you to keep working closely with your veterinarian during and after diagnostic testing. Pending the results of the tests, it may be determined that you’ll have to make some adjustments to your horse’s nutrition program and daily management. The best resource you have is your veterinarian, who can help you develop a plan for the best way to support your horse’s wellbeing after diagnosis. – Dr. Lydia Gray

  20. MT says:

    Since you live in VT and use Poulin Grain Carb Safe as feed, I urge you to contact Poulin Grain… a rep. will come to your farm & test your hay for you and give you nutritional advice to balance your horse’s ration. They will provide you will a balanced ration analysis… I too have a horse with EPSM and feed Carb Safe, some MVP, hay pellets, and vegetable oil (I get it a Costco) as well as supplementing with Vitamin E and electrolytes.

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