The five major electrolytes: sodium, chloride, potassium, calcium and magnesium; are key nutrients required for nerve and muscle function, maintenance of normal hydration and normal function of the digestive system, kidneys, lungs and heart. Sub-optimal electrolyte intake can lead to muscle problems and poor performance, therefore horses in work require extra electrolytes to replace those lost in sweat, faeces and urine. The harder the horse works, the hotter the horse gets. The longer a horse works and the warmer the weather, the more sweat and therefore the more electrolytes a horse will lose. One litre of horse sweat contains around 3.5g of sodium, 6g of chloride, 1.2g of potassium and 0.1g of calcium. A horse can easily lose 5 litres of sweat each hour on a normal day at a moderate pace which equates to the loss of around 50g of electrolytes. This amount would not be replaced by the horses' normal daily hay and hard feed alone.