Feeding “George”: A Polysaccharide Storage Myopathy (PSSM) Horse

Previously, I introduced you to George, my ‘Heinz-57’ PSSM positive horse.  Though his test results came back positive for Type 1 PSSM, his diagnosis does not mean his athletic career is over. With some diligence and routine, George is able to lead a normal life as a successful working partner.

One key to managing his condition is maintaining consistency in his diet and routine. Remember, he would get sore every time the hay changed, particularly if it had alfalfa in it.  First I work to ensure that George’s total diet is properly balanced which starts with controlling the starch and sugar energy sources in his hay and grain ration.  I buy larger quantities of grass hay (no alfalfa) that will last awhile, a full year if possible. I also have my hay tested before buying it to make sure it isn’t too high in non-structural carbohydrates (12% NSC or less), and that the rest of the nutrients are within an acceptable range for good quality hay, as this is the bulk of his diet. The lower the NSC in the hay, the more room there is in the diet to add calories from fat. More on that below.

To balance his hay, he gets a controlled starch feed concentrate that is fortified with essential amino acids, complexed trace minerals, pre- and probiotics.  If I need to add calories to his diet to support higher levels of exertion during training and show season, I add a balanced fat supplement to the concentrate component of his diet.  To meet the total caloric requirement it is recommended that PSSM positive horses receive no more than 10% of the digestible energy from non-structural carbohydrates (starch and sugar), and 15-20% of the digestible energy should be supplied by fat.  Remember, this applies to the total diet, contributions from grain plus forage.  Working with a qualified equine nutritionist is a great way to figure all of this out.  In a nutshell, I control the sugars and starches in his total diet (low NSC grass hay and low calorie, controlled NSC grain) and add a nutritionally balanced fat source when extra calories are needed. The only supplement he gets is vitamin E, which helps boost his antioxidant status (helps fight oxidative stress), and supports muscle recovery after exercise.  Because his total diet is balanced for selenium, I don’t supplement this mineral to avoid potential toxicity.

Estimating his weight and doing a regular body condition score help me adjust his diet and exercise routine accordingly, so he maintains good muscle mass and avoids excess fat deposits.  In addition, I make sure to minimize stress as much as possible by keeping his routine consistent.  His daily ration is divided up into 3 meals to avoid one large grain meal and he has access to hay for most of the day.  He gets a minimum turnout of 8 hours every day with a buddy and limited access to fresh forage.  I also exercise him at least 6 days a week.  With this management routine, regular veterinary and farrier care, he has never “tied-up” on me, and continues to excel in dressage with the occasional hunter pace thrown into the mix. Providing good quality of life is a top priority, especially when it comes to managing even the most challenging horses, and I think George would agree, he is doing great!

7 Replies to “Feeding “George”: A Polysaccharide Storage Myopathy (PSSM) Horse”

  1. Have you ever soaked the excess carbohydrates from Georges hay? My PSSM positive horse has responded well to soaking the hay. The water drained off the hay smells SO sweet! How do you feel about top dressing with oils?

    1. Hi Brianna,

      Thanks for your questions and suggestions for managing horses with PSSM.

      Vegetable oils are energy dense and highly digestible. Top dressing oil is a great way to increase dietary fat if you are adding small to moderate amounts, and can be more economical compared to other options. On the other hand, oil is difficult to provide in large quantities, can be prone to spoilage particularly in warm weather, and can be pretty messy. Regular cleaning of feed buckets/pans is recommended if top dressing oil. Additionally, if supplementing large quantities of oil (up to 600 ml per day), it is important to make sure the other nutrients in the diet are provided in adequate amounts, particularly vit. E and other vitamins and minerals, in order to avoid dietary imbalances.

      Another option to increase dietary fat are rice bran supplements. Rice bran tends to be around 20% fat and can be a good source of vitamin E. Additionally, commercial preparations of rice bran tend to be more stable than oils, and typically are corrected to maintain the proper Ca:P ratio as well as other micronutrient levels in some products. It also comes in several forms (powder, pellets, extruded nuggets), giving owners options in the event their horse is picky. Along with lowering the non-structural carbohydrate content of a low calorie diet and an appropriate exercise program, adding anywhere from 1 – 5 lbs of rice-bran products to a PSSM horse’s diet, has been shown to help alleviate disease symptoms.

      As for soaking hay, I have not personally done this with George, as other less labor intensive strategies have been successful in alleviating his symptoms. I do agree that soaking it is an effective way to reduce the non-structural carbohydrate (NSC) content in forages, and can serve as one aspect of PSSM management. There are a couple things to consider when soaking forages, one being that it will spoil fairly quickly once water is added, so any hay that is not consumed in a few hours should be discarded along with the water it was soaked in. Also consider that significant amounts of dry matter, or other nutrients along with the NSC are also leached out with soaking, so be sure that your horse is getting enough of the soaked hay to meet his dietary requirements and/or that an appropriate ration balancer or grain concentrate is added to the diet to make up for any nutrient gaps.

      Please note, any dietary changes should be made gradually, and benefits of reducing NSC and increasing dietary fat are most beneficial when paired with turnout and daily submaximal exercise. Time to noticeable improvements in symptoms vary by individual horse, and typically occur within 1 – 6 weeks. Hope this helps. Please let me know if you have any further questions.

      Good luck and happy trails! ~ Emily ~

  2. Great piece. Just wanted to add some experience. I once worked with a customer who had a winning barrel horse with PSSM, and was experiencing some difficulties post racing and an extended recovery time. She was feeding a textured, but well balance reasonably high fat diet. We went to a high fat 7% Professional Breeders Formula which ultimately became Safe Choice. The pellet allowed us to breakdown the starch from 41% NSC to a 24% NSC. We also added some additional fat from a stabilized rice bran product. The result was less tying up and a quicker recovery period. Thanks for letting me add a bit of experience.

  3. My mare was just diagnosed with PSSM type 1 a few days ago. Reading this has really helped me!

  4. I’m looking at buying an 8 year old appy. He tested PSSM n/P1. He’s in good health with no issues right now. Do you think he might show symptoms at a later date? Any info greatly appreciated.

    1. Hi Terresa,
      Some horses never show clinical signs, some can develop them later under certain circumstances (change in activity, change in diet, etc.). If they occur, symptoms can be mild or debilitating, it just depends, and with ongoing symptoms these horses can be very high maintenance. If this horse is currently in good condition/health, with no clinical symptoms, then wouldn’t recommend changing anything and to ensure that the current management can be maintained. In other words, if its not broke, don’t try to fix it. However, being aware of what can trigger symptoms and what those symptoms look like would be wise, especially if change in exercise or management (including diet) is inevitable. (Continued) proactive management to prevent a scenario that could trigger clinical symptoms would be beneficial. There is a bunch of helpful information from Dr. Valberg’s laboratory at Michigan State University. http://cvm.msu.edu/research/faculty-research/valberg-laboratory
      Best of luck,
      Emily L.

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