Equine Exertional Rhabdomyolysis is a syndrome that affects the skeletal muscles, causing muscle pain and cramping associated with exercise. It causes the muscles to break down, which is generally associated with exercise and diet. It is characterized by muscle damage and the release of muscle proteins into the bloodstream, potentially affecting the kidneys.
Exertional rhabdomyolysis can be subdivided into Sporadic or Chronic forms. Horses that experience a single episode or infrequent episodes of ER are categorized as having sporadic ER, whereas horses that have repeated episodes of ER accompanied by increased muscle enzyme activity even with mild exertion are classifies as having chronic ER.
Types of Exertional Rhabdomyolysis
Chronic Exertional Rhabdomyolysis
Horses with chronic ER experience repeated episodes of muscle breakdown during exercise. Chronic tying up is linked to an underlying genetic abnormality affecting muscle cell function, such as polysaccharide storage myopathy.
Chronic equine exertional rhabdomyolysis can be divided into 2 main types: Polysaccharide storage myopathy (PSSM) and recurrent exertional rhabdomyolysis (RER)
Type 1 Polysaccharide Storage Myopathy (PSSM1)
PSSM1 is caused by a mutation in the glycogen synthase gene, leading to continuous glycogen production in the horse’s muscles. This results in difficulty for the horse when switching to burning glycogen for energy during exercise. Glycogen is a complex carbohydrate that serves as a primary storage form of energy for muscle cells in horses. It can be broken down into glucose during exercise when the body needs energy to fuel muscle contraction. The abnormal glycogen storage also makes the muscles more susceptible to damage, increasing the risk of ER following exercise.
It is commonly found in breeds such as Quarter Horses, Belgian Drafts, and some Warmblood breeds. However, any horse that can store excess amounts of glycogen, usually due to genetics, can develop this kind of ER.
Affected horses may exhibit stiffness, muscle cramping and soreness following light exercise due to impaired energy generation in their muscles. Some horses may show increased insulin sensitivity, which further contributes to glycogen storage in the muscles.
Type 2 Polysaccharide Storage Myopathy (PSSM2)
This is another muscle disorder in horses that also results in abnormal glycogen storage, potentially contributing to chronic ER. In cases of PSSM1, glycogen is always elevated and also found in an abnormal form. In PSSM2, glycogen may be elevated or normal, but is present in unusual locations.
It occurs in breeds such as Arabians, Morgans, and Thoroughbreds, some Warmblood breeds and some Quarter Horses.
Recurrent Exertional Rhabdomyolysis (RER)
This is a condition characterized by repeated episodes of muscle contractions and pain during and after exercise. Unlike sporadic cases of ER that might occur due to over exertion or dietary imbalances, it is a chronic condition that can affect horses even under regular training conditions.
The exact cause of RER in horses is not fully understood but It is believed to be caused by irregularities in calcium signaling within cells, calcium plays an important role in muscle contraction and relaxation. In horses with RER, abnormal calcium regulation disrupts these processes leading to uncontrolled muscle contractions and stiffness. RER episodes are often triggered by stress or intense exercise and require careful management to minimize recurrence.
Sporadic Exertional Rhabdomyolysis:
Sporadic Exertional Rhabdomyolysis is an occasional occurrence that typically affects horses subjected to unusual or excessive physical exertion beyond their normal level of training or fitness. This form is often seen in horses that are otherwise healthy and do not have an underlying predisposition to muscle disorders. Instead episodes are caused by external factors such as intense exercise or environmental stressors that contribute to muscle cell damage. All breeds of horses are susceptible to Sporadic Exertional Rhabdomyolysis.
Examples of external factors that can trigger Sporadic Exertional Rhabdomyolysis include:
- Overtraining and muscle strain: ER commonly occurs when horses are exercised beyond their conditioning level, especially after; long periods of rest followed by sudden increase in training.
- Nutritional deficiencies: Deficiencies in electrolytes or antioxidant nutrients such as selenium and vitamin E can cause ER. Horses may develop electrolyte imbalances during periods of prolonged exercise in hot weather. Dietary imbalances, particularly with deficiencies in sodium, potassium, and calcium, have also been linked to ER.
Symptoms of Exertional Rhabdomyolysis
- Muscle pain, stiffness and cramping, particularly in the hind quarters and lowerback
- Reluctance to move or a shortened silted gait
- Sweating, increased heart rate and rapid breathing
- Muscle tremors and visible muscle stiffness
- Dark brown urine in severe cases due to the presence of myoglobin released from damaged muscles
Management of Equine Exertional Rhabdomyolysis
Nutrition:
Proper nutrition is important for the recovery from ER episodes and the ongoing management of the condition. A balanced diet, along with a complete vitamin and mineral supplement such as Horse Guard, will help make up for any deficiencies. These nutrients are important in muscle repair, metabolic function, and electrolyte status,
kidney function, tissue healing and the immune system. Deficiencies in minerals and vitamins could slow down the recovery from episodes of ER and prolong the time it takes to return to performance.
For horses with PSSM and RER eliminate grains from the diet to reduce sugar and starch intake and feed a fat supplement if additional energy is required
Horses may benefit from additional antioxidant supplementation to protect muscle cells from damage caused by oxidative stress. Increasing selenium and vitamin E in the diet can support muscle function and recovery in those horses experiencing ER.
Vitamin E and Organic Selenium is a synergistic blend of Vitamin E and selenium that is
specially formulated to combat stress and promote optimal muscle and nerve function. These two nutrients work together to combat stress and enhance immunity. Vitamin E plays a crucial role in supporting nerve tissues, the circulatory system, and the immune system of horses. It provides antioxidant support to maintain blood and tissue levels, reducing oxidative damage and supporting overall health. On the other hand, organic Selenium serves as a muscle protein, ensuring horses have the strength to perform effectively. Each 2-ounce dose of this supplement provides 5,000 IU of Vitamin E and 3 mg of organic selenium.
Flaxen Eas-E Guard is formulated to help horses combat oxidative stress, boost
immunity, and optimize muscle and nerve function. With 1,000 IU of natural Vitamin E in a 1-ounce dose, you can adjust supplementation to your horse’s individual natural vitamin E needs. The natural vitamin E is carried in the beneficial base of flaxseed cake, which provides an additional benefit of anti-inflammatory properties from omega-3 fatty acids.
Electrolytes: Horses that are often exercised in hot weather may develop electrolyte imbalances. Offering free choice access to loose salt or salt blocks should be provided for these horses and fresh water should always be available
Our Certified Equine Nutritionist Dr. Kelsey Nonella is always happy to help you find the right well-balanced diet for your horse’s needs. You can contact her at horsenutrition@horseguard.com
It is also important to complete a proper warm-up and cool-down together with a gradual increase in exercise intensity and duration. Also, keep in mind to minimize stress and excitement that could trigger an episode.
*Disclaimer:
The information provided in this blog is for educational and informational purposes only and is not intended as veterinary or medical advice. Always consult with a qualified veterinarian or equine nutrition professional before making changes to your horse’s diet, supplement program, or health care routine. Individual horse needs may vary.
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