Electrolytes are an extremely important consideration for horses that are doing fast work endurance and cross country eventing. Especially in hot weather conditions where they can become dehydrated.

Electrolytes are one of the most abundant compounds in the body after water. The major electrolytes include sodium, potassium, chloride, calcium and magnesium. All compound feeds and forages contain some electrolytes but a grass/hay and/or commercial feed diet will generally only supply adequate amounts of the different electrolytes for horses at pasture or in light work and the one electrolyte that will always be deficient is sodium (salt).

Electrolytes are not evenly distributed throughout the body. For example, potassium is high in red blood cells and nerve cells but low in the plasma. Calcium is low in plasma, but high in bone and muscle cells. When it comes to hydration, sodium is the most important electrolyte. Not all the electrolytes consumed by a horse will be absorbed. However, for major electrolytes like sodium, potassium and chloride the absorption is very high (probably 90% or more).

Why are Electrolytes important for a horse?

Horses at rest lose electrolytes on a daily basis in faeces, urine and breath. During training and competition the event horse will also lose electrolytes through sweating. 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.

Eventers in regular work need supplemental electrolytes to perform optimally and to avoid problems such as poor performance or digestive disturbance, or clinical problems such as synchronous diaphragmatic flutter (also known as “thumps”; a condition where the chest twitches in time with the heartbeat due to stimulation of the diaphragm) or some forms of tying-up. A diet low in electrolytes is also a common and often undiagnosed cause of horses not performing to expectation.