PSSM is not the only condition that leads to muscle soreness, horses can also have acute or recurrent exertional rhabdomyolysis. Acute ER is most commonly caused by overtraining and exercising horses beyond their capacity, which leads to leading to straining of muscles. For example endurance horses racing in hot climates will lead to excessive sweating, loss of electrolytes and eventually muscle dysfunction and damage because electrolytes are essential for muscle function.
Other factors that may trigger an acute episode of ER can be viral infections or dietary imbalances. For example when the diet does not meet the requirements for essential nutrients for the level of exercise the horse is doing, like energy, Vitamin E and Selenium.
Therefore the best way to avoid acute ER is to ensure that the horse has a balanced diet that matches is exercise intensity accordingly.
Chronic ER or recurrent ER is a condition often seen in Thoroughbreds, Arabians and Standardbreds and is caused by a genetic defect leading to abnormal Calcium regulation in the muscle. This abnormal Ca regulation has nothing to do with dietary Ca deficiency but simply how the intramuscular Ca is metabolized. So it cannot be fixed by simply feeding more calcium. This disease is common in breeds with more nervous temperament and an episode of muscle spasms and tremors in these horses is typically induced by stress.
In the dietary management of these horses it is important that all nutritional requirements are met for the level of training. There is also evidence that lower NSC intake reduced the occurrence of RER episodes. However, as this condition is most common in horses with an already nervous behavior that typically get fed large amounts of sweet feed like the Thoroughbred, it is not clear whether the effect of feeding low NSC diets results from lower glucose spikes or simply a more calm demeanor and less stress.
If you do have to feed a diet higher in NSC, make sure to feed it in small meals throughout the day, together with plenty of forage. Other ways to increase energy intake in these performance horses is to replace some of the calories from NSC with those from fat.
Make sure all vitamin and mineral requirements are met, as it is essential for the horse to be getting these nutrients which are critical for muscle health. Such horses might also benefit from a little extra supplementation if needed during competition season.
Lastly, as an episode is typically triggered by stress, it’s important to reduce stress and nervous behavior in these horses. Provide plenty of turn out always to help bring excessive stress down and gradually adapt the horse to any changes in routine.