When your horse sweats, he loses sodium and chloride (which combine to form salt) along with potassium and trace amounts of calcium and magnesium-simple inorganic compounds that are collectively known as electrolytes. These substances dissolve in the horse’s body fluids and regulate many chemical processes that occur both in and between the cells. The kidneys are the primary organs involved in regulating electrolyte levels, conserving or excreting the elements as necessary to maintain a stable state of equilibrium (homeostasis) within the horse’s body.
For the most part, a balanced diet supplies ample amounts of electrolytes for a moderately worked horse. Grain is high in phosphorus, and legume hays are excellent sources of calcium. The soil, in which grain and hay are grown, however, largely determines the feed’s mineral content. Your state department of agriculture can provide specific information about locally grown crops, and in many states, it’s possible to receive a complete nutritional analysis of your horse feed.
Only if your horse sweats heavily and frequently he is likely to require supplemental electrolytes. Salt is the exception, since horses virtually always need more than they can acquire from grain and hay. Give your horse free access to a trace-mineralized salt block (it isn’t advisable to add salt to his feed or water).
He will generally consume no more and no less than his body needs one half-pound per week is average for an adult horse.