Many people think their horse needs electrolytes during the summer. Provided the horse is conditioned properly and is consuming a properly balanced diet, supplemental electrolytes probably are not necessary. However, during extremes of temperature and humidity, the horse may need an electrolyte solution, but it should not be needed or given on a daily basis. If you think a solution is needed, make sure the horse has a choice between the solution and plain water.
A horse that is working hard and sweating profusely will be able to maintain its electrolyte balance provided it is fed a balanced diet, has unlimited water, and is conditioned properly. Neither diet nor supplemental electrolytes will prevent symptoms if the horse has been inadequately trained or conditioned. A properly conditioned horse will sweat more efficiently, losing less electrolytes per volume of sweat. The kidney is thought to become more efficient in conserving electrolytes as the horse becomes conditioned.
Use electrolytes when you think your horse may be experiencing electrolyte depletion. This may occur even in the conditioned horse when the sum of the temperature and humidity exceeds 150.
Commercial electrolyte solutions are available, but a simple solution can be made of one part limestone (CaCO3) and two parts light salt (NaCl/KCl mix). This mix should be added at the rate of four tablespoons per gallon of water. It is important to offer the horse two buckets of water, one with the electrolyte solution, and the second with plain fresh water.
Commercial electrolytes that contain bicarbonates should not be used for the exhausted, sweating, and dehydrated horse. These types of electrolytes are designed for use in diarrheal diseases and will only aggravate the problem in exhausted horses.