Electrolytes and the Exercising Horse

Exercising muscles generate heat via metabolic reactions. Heat produced must be dissipated to prevent overheating, thus the horse sweats and evaporative cooling dissipates the heat. The amount a horse sweats depends on environmental conditions, the type of work performed, and the horse’s fitness. Horses may lose 5 to 7 liters (1 to 2 gallons) of sweat per hour when trotting and cantering for one hour under mild temperatures. As the temperature and humidity increase, sweating rates have approached 10 to 12 liters (>2.5 gallons) per hour.

Sweat is composed of water, proteins and minerals. The primary minerals are sodium (Na), chloride (Cl), and potassium (K), collectively referred to as electrolytes. Electrolytes maintain fluid balance, circulatory function, facilitate muscle contractions, trigger nerve functions and help maintain the body’s acid-base balance. Electrolyte deficiencies can promote or aggravate conditions such as causing a horse to decrease food consumption and drink less water. Low water intake can then lead to dehydration and in severe cases impaction colic. Excess sweat loss can also lead to over-heating, tying up (a muscular disorder resulting in stiff and/or trembling muscles after exertion), fatigue, and muscle weakness. In severe electrolyte deficiencies, synchronous diaphragmatic flutter (commonly known as ‘thumps’) can occur, and the horse may collapse and die if not treated.

The sheer volume of sweat produced by horses causes a substantial loss of electrolytes. Sodium and Cl are lost in the highest amounts, followed by K, then calcium and magnesium. Electrolytes are not stored in the body requiring them to be provided in the diet. Table 1 lists the average percentage of K, Na, and Cl in legume hay, grass hay, mostly grass hay, and grass pasture. As shown, forages are a rich source of K, low in Na and variable in Cl concentrations. Whole grains such as corn, oats, and barley are low in all of the electrolytes.

Table 1. Average mineral concentrations in legumes and grasses

Data from Equi-Analytical Laboratory Services Interactive Common Feed Profiles Library

Most horses at maintenance to light work should receive enough electrolytes from a high forage diet with the addition of 1.75-2.1 oz. (10-12 g) NaCl per horse (1100 lb. body weight) daily (NRC, 2007). To put this into perspective, one level  tablespoon (tbsp) equals 0.5 oz or the horse would require the equivalent of two-level tbsp of salt daily. As sweating increases due to temperature, humidity, exercise or a combination of both the horse may require more salt – at least four tbsp of NaCl per day, divided between meals. White salt blocks can provide sufficient NaCl for maintenance to light work, provided the horse consumes enough of it on a consistent basis. A granulated or kosher salt can be mixed into feed or provided loosely if you think a horse isn't getting enough with the block. For maintenance and lightly worked horses receiving appropriate amounts of forage in their diet, the K requirement should be met and supplementation is not necessary. If the lightly worked horse receives a commercial grain mix with forage, their NaCl and K requirements should be met. As the horse’s workload increases and the humidity and temperature rise, more sweat and electrolytes are loss. In fact, they may require up to 6 oz. (170 g) of NaCl per day.

Horse licking what salt block

Electrolytes supplements are available in many forms (granular, liquid, paste, etc.). A good supplement would mimic electrolytes found in sweat, thus the three key electrolytes Na, Cl and K would be the main ingredients. The goal for using electrolytes is to replace electrolyte losses in equine sweat and to help encourage rehydration. Electrolytes can be supplemented by mixing them in grain, pelleted feeds, or by direct oral administration. Offering salt water during or immediately after exercise is another method, but some horses do not like the taste and drink less water.

Horses should begin a competition or race fully hydrated. Administration of electrolyte pastes with free access to water is an effective way to make sure horses are hydrated prior to competition, and for rehydration after exercise. Wait for the horse to have a drink before giving the electrolyte. Never give electrolytes to an already dehydrated horse as this may worsen the dehydration. Use the pinch test to evaluate if the horse is dehydrated. Take a pinch of skin at the point of the shoulder, release. The skin should flatten out immediately (0-1 seconds) if not dehydrated. If it takes 2-3 seconds the horse is dehydrated.

Remember these key points:

• Feed electrolytes according to the amount of work the horse is performing
• Start feeding electrolytes during training and not just on the day of a competition
• Avoid electrolyte supplements with a high sugar content
• Always ensure clean, fresh water is freely available
• Always have a salt lick available to allow your horse access to extra Na and Cl at any time.

Resources

1. Coenen, M. (2013) Macro and trace elements in equine nutrition. In: Geor, R., Harris, P. and Coenen, M., eds. (2013) Equine Applied and Clinical Nutrition. China: Saunders Elsevier, pp. 191-228.
2. Geor, R. and P. Harris. 2014. Nutrition for the equine athlete: above and beyond nutrients alone. In: Hinchcliff, K.W., Kaneps, A, J., Geor, R.J., eds., (2014). Equine Sports Medicine and Surgery 2^nd edition.
3. Jose-Cunilleras, E. (2014) Abnormalities of body fluids and electrolytes in athletic horses. In: Hinchcliff, K.W., Kaneps, A, J., Geor, R.J., eds., (2014). Equine Sports Medicine and Surgery, 2^nd edition.
4. NRC, Nutrient Requirements of Horses. 6th ed. ed. 2007