Do horses really need electrolytes?

Electrolytes the tiny molecules that we cant live without. The astoundingly delicate balance of water and electrolytes in the horses body is essential to keep them healthy and performing well. 
What are electrolytes?
Water accounts for the majority of the horses bodyweight as in humans. This water is present both inside the cells in intracellular fluid and outside the cells in extracellular fluid. It moves between the intracellular and extracellular compartments as needed to keep the water balance or osmolality steady. Electrolytes are the salts dissolved in this water. The main ones are potassium in intracellular fluid and sodium and chloride in extracellular fluid. Others are phosphorus calcium and magnesium. Electrolytes are key for normal cell functions and the proportions of water and electrolytes in and around the cells affect how well these processes work. The proportions can alter with exercise but also with illness. 

Its important for horse owners to be aware of electrolytes and what maintaining the normal electrolyte balance means for their horse particularly in the case of performance horses.
Why worry about electrolytes?
Well they are essential for essential everyday processes such as muscle contraction and generating energy for use in the cells. This is especially important when we think about our performance horses. Knowing that electrolytes are needed to sustain activity we can understand how electrolyte alterations can impact performance. We can also then appreciate the importance of keeping the horses electrolyte and water balance in check. Additionally when the horse is unwell we often see abnormal changes in electrolyte levels. This may be from excess losses dehydration or reduced intake. This is the reason for supplementing the horse with intravenous fluids in many medical disorders to restore correct water and electrolyte balance in the body. 
It has also been thought that an altered intracellular level of calcium could play a part in recurrent exertional rhabdomyolysis tying up a painful condition that causes muscle damage and can lead to kidney failure. 
Sweating and exercise
During exercise the horse can lose litres of water particularly during long periods of low intensity exercise like endurance rides the animal can lose up to 15 of its bodyweight in water. The water lost through sweat evaporates from the skin surface taking heat with it. This is an important mechanism by which the horse regulates its temperature during and after exercise. 
The loss of water through sweating and its use by cells during exercise