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Electrolytes and Muscle Function: What's the Connection?By Kentucky Equine Research Staff · September 27, 2017

Electrolytes are necessary for normal muscle contraction and relaxation. “When electrolytes become depleted or imbalanced, fatigue and muscle cramps can result,” says Catherine Whitehouse, M.S., a nutritionist with Kentucky Equine Research (KER).

Muscles contract with the help of an electrical charge. This contraction, in physiological terms, is called an action potential and is essential to create movement. Electrolytes are electrically charged minerals that facilitate action potentials. Electrolytes can carry a positive (cation) or negative (anion) charge, and dissolve in body water to create a solution that can conduct electricity, although the solution itself is electrically neutral. Sodium is the major cation found outside of cells, while potassium is the primary cation found inside of cells, along with calcium and magnesium. Major anions in the body include chloride, bicarbonate, and phosphates. The body tightly regulates the concentration of each electrolyte. Because electrolytes help conduct electrical charges, balance is a key component of proper muscle function.

A horse’s sweat is heavily concentrated with electrolytes (sodium, potassium, calcium, and magnesium). For this reason, heavily sweating horses lose substantial amounts of electrolytes during prolonged exercise. If losses are great enough, a disruption in the balance of electrical charge both inside and outside of a muscle cell can upset normal contraction and relaxation processes. For example, excessive losses of calcium and magnesium can cause the main nerve to the diaphragm to fire in sync with the heart, a condition known as “thumps.” Thumps occurs in extremely dehydrated horses. In addition, significant loss of potassium can contribute to muscle cramps.

“Proper diet and supplementation are the best ways to help a horse stay in electrolyte balance and recover from strenuous exercise,” says Kathleen Crandell, Ph.D., longtime nutritionist for KER. Studies have shown that horses that received an electrolyte supplement prior to endurance-type exercise drank more water, lost less weight, and maintained higher blood sodium and chloride concentrations compared to unsupplemented horses.*

Key feeding strategies include providing a horse with plenty of water alongside the regular diet. If exercise is to take place during hot, humid conditions, provide electrolytes and extra water the night before the event. Electrolytes can be top-dressed on feed or mixed into a paste (try water, applesauce, or yogurt). This will help the horse start off fully hydrated. If exercise is prolonged (over several hours), additional electrolytes can be given at regular intervals. Electrolytes are water soluble, so feeding too much at once will simply result in excess being excreted. For this reason, Restore SR was developed with a time-release formula to ensure maximum absorption and electrolyte replenishment.

KER developed Race Recovery, an electrolyte designed specifically to counteract the diuretic effects of furosemide (Lasix). Race Recovery provides horses exercised on furosemide targeted electrolyte supplementation.

Remember to always provide a salt block and plenty of fresh, clean water. Hydrated horses in electrolyte balance are much better able to maintain exercise, control body temperature, and perform compared to dehydrated horses.

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*Düsterdieck, K.F., H.C. Schott, S.W. Eberhart, K.A. Woody, and M. Coenen. 1999. Electrolyte and glycerol supplementation improve water intake by horses performing a simulated 60 km endurance ride. Equine Veterinary Journal Suppl. 30:418-424.