Polysaccharide storage myopathy (PSSM) in horses is a condition with an excessively abnormal glycogen accumulation, the standard form of sugar stored in muscle. This condition could lead to incidents of muscle stiffness and pain after exercise. This is also known as “tying up.” Affected horses may refuse to move and display symptoms like sweating, lameness, and muscle tremors.This article explores the leading causes and types of PSSM in horses and their management tips for horse owners.
Causes and Types of PSSM
Type 1 PSSM
Type 1 PSSM occurs due to a genetic mutation that affects glycogen synthesis. This mutation leads to excessive muscle glycogen production and storage, interfering with exercise energy generation. Horses with PSSM1 can have signs associated with tying-up (muscle stiffness, sweating and reluctance to move). During an episode horses may seem lazy, tense up in their abdomen and develop tremors in their flank area. Incidents often are seen in horses when put in to initial training or after a lay-up period when they have had minimal turnout/exercise.
Type 2 PSSM
The genetic cause of Type 2 PSSM is still unknown, but it can occur in various horse breeds. Diagnosis requires a muscle biopsy. Horses with Type 2 PSSM show similar symptoms to those with Type 1, such as muscle stiffness and exercise intolerance. Contributing factors to PSSM include inadequate exercise, respiratory diseases, and dietary deficiencies in sodium, vitamin E, selenium, or calcium-phosphorus imbalance.
Symptoms of PSSM
Horses with PSSM often display the following symptoms:
- Muscle Stiffness: Persistent muscle stiffness, especially after light exercise.
- Pain and Cramping: Episodes of muscle pain and cramping.
- Sweating: Excessive sweating during or after exercise.
- Lameness: Difficulty moving and lameness.
- Muscle Tremors: Visible muscle tremors.
- Reluctance to Move: Unwillingness to move forward or engage hindquarters under saddle.
- Exercise Intolerance: Poor performance and intolerance to physical activity.
Treatment of PSSM in Horses
Managing PSSM involves dietary changes and regular exercise. The nutritional needs of horses affected by PSSM can vary and be complicated. Seeking advice from an equine nutritionist is highly recommended.
Dietary Adjustments
- Low sugar and starch diet: Reduce or limit concentrates (commercial feed) and start feeding fats such as rice bran or vegetable oils. This helps blood sugar levels stabilize and provides fat for energy requirements.
- The diet should be based on forage such hay and alternative sources such as pellets and cubes made from grasses with a NSC level less than 12%.
- A high-fat feed source can be incorporated if additional energy or calories are needed. Rice bran or vegetable oils can help stabilize blood sugar.
- Beet Pulp is a good source for additional calories if needed.
- Protein and/or amino acids can be added to the diet to help support muscle function. Good sources include alfalfa hay, soybean meal, wheat bran, flaxseed meal, and whey protein.
Exercise Regimen
Exercise should be gradually introduced and tailored to the individual horse and condition.
Medical Interventions
In severe cases, sedatives, analgesics, muscle relaxants, and/or non-steroidal anti-inflammatory drugs (NSAIDs) can be given to help minimize pain.
Ingredients that may lend support
Vitamin E and Selenium are important antioxidants that support healthy muscle function and recovery as well as has help to neutralize free radicals that can be generated from a high fat diet often associated with PSSM. Magnesium is also a key ingredient as it supports glucose metabolism and helps to maintain normal/healthy blood sugar levels.
Prevention and Breeding Considerations
Since PSSM is hereditary, breeding affected horses is not recommended. Avoid using PSSM-affected horses for breeding to prevent the condition in future generations.
Conclusion:
Polysaccharide Storage Myopathy in horses is a metabolic disorder that has no medical cure but can be managed carefully through diet and exercise to help reduce the severity of symptoms (ie. Tying Up).Providing a diet low in sugar and starches is key to avoiding the build-up of glycogen in the muscle tissue. Managed exercise routines and the addition of nutrients such as Vitamin E, selenium and magnesium can also be beneficial in helping to manage PSSM in horses helping to improve overall health and performance.
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