Plasma and sweat electrolyte concentrations in the horse during long distance exercise

Blood samples were taken from 20 horses competing in a 100 km endurance ride and plasma concentrations of sodium, potassium, chloride, bicarbonate and protein measured. Measurements were performed on samples taken before the ride (pre-ride), at the mid point and end of the ride and after a 30 min recovery period (post-ride). Sweat samples were collected from 6 horses competing in the endurance ride and 14 horses competing in a 3-day event competition and sweat concentrations of sodium, potassium and chloride measured. There were substantial decreases in plasma electrolyte concentrations, which were greater than previously reported. Decreases from pre to post ride samples of 5 mmol/1 of sodium, 1.2 mmol/1 of potassium and 16 mmol/1 of chloride were found. These losses appeared to be related directly to sweat electrolyte concentrations, where potassium and chloride had relatively greater concentrations than in plasma.