Predicting Muscle Problems

Competitive endurance riders know that horses lose fluids and electrolytes during strenuous rides. Calcium and magnesium are also lost during prolonged aerobic exercise. Low blood calcium (hypocalcemia) allows sodium to enter nerve cells, leading to hyperirritability of nerves, muscle twitching, cramping, and even paralysis. The
addition of low blood magnesium (hypomagnesemia) can produce signs ranging from lethargy to synchronous diaphragmatic flutter (thumps), increased respiratory and heart rates, ataxia, and even death. In humans, electromyography (EMG) is often used to predict the onset of severe muscle contractions and tetany (sustained muscle contraction). A study was conducted at Utrecht University in the Netherlands to investigate the usefulness of EMG in detecting these muscle changes in horses.

Dutch warmbloods were studied, and each was examined using EMG in a series of muscles. The horses were then treated with ethylene diamine tetra acetate (EDTA, a chemical that lowers blood calcium and magnesium), and an EMG was repeated while the horses were monitored for signs of neurological or musculoskeletal distress. Interestingly, none of the horses showed any classic signs of hypocalcemia or hypomagnesemia, despite confirmation by blood measurements. However, all of the horses had EMG results consistent with hyperirritability of nerves in the muscles examined.

Therefore, it's possible for horses to have hypocalcemia and hypomagnesemia for some period of time without demonstrating clinical signs. It might be useful to integrate this finding into the monitoring of horses during intense aerobic exercise.

Wijnberg, J.D.; van der Kolk, J.H.; Frannssen, H.; et al. American Journal of Veterinary Research, 63(6), 849-856, 2002.

About the Author

Susan Piscopo, DVM, PhD

Susan Piscopo, DVM, PhD, is a free-lance writer in the biomedical sciences. She practiced veterinary medicine in North Carolina before accepting a fellowship to pursue a PhD in physiology at North Carolina State University. She lives in northern New Jersey with her husband and two sons.

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