We hypothesized that post-exercise rehydration using a hypotonic electrolyte solution will increase the rate of recovery of whole body hydration and that this is associated with increased muscle glycogen and electrolyte recovery in horses. Gluteus medius biopsies and jugular venous blood was sampled from 6 exercise conditioned Standardbreds on 2 separate occasions, at rest and for 24 h following a competitive exercise test (CET) designed to simulate the speed and endurance test of a 3-day event. After the CETs horses were given either water ad libitum (Control) or a hypotonic commercial electrolyte solution (Electrolyte) via nasogastric tube followed by a typical hay/grain meal, or a hay/grain meal alone. The CET resulted in decreased total body water and muscle glycogen concentration of 8.4 ± 0.3 L and 22.6 %, respectively, in the Control trial, and 8.2 ± 0.4 L and 21.9 % in the Electrolyte trial. Electrolyte resulted in an enhanced rate of muscle glycogen resynthesis and faster restoration of hydration (as evidenced by faster recovery of plasma [protein], maintenance of plasma osmolality and greater muscle intracellular fluid volume) during the recovery period compared to Control. There were no differences in muscle Na, K, Cl or Mg contents between the 2 treatments. It is concluded that oral administration of a hypotonic electrolyte solution after prolonged moderate intensity exercise enhanced the rate of muscle glycogen resynthesis during the recovery period compared to Control. It is speculated that post-exercise dehydration may be one key contributor to the slow muscle glycogen replenishment in horses.