EFFECTS OF HYPERHYDRATION ON CARDIORESPIRATORY AND METABOLIC RESPONSES TO EXERCISE IN HORSES DURING A SIMULATED 2ND DAY OF THE 3-DAY-EVENT

We hypothesised that hyperhydration before prolonged exercise would in crease and maintain plasma volume (PV), assisting thermoregulation and cardiorespiratory function. In a cross-over design, 7 horses received approximate to 26 L (6% bodyweight) of isotonic fluid or nothing (con trol). Horses undertook 98 min of treadmill exercise at intensities el iciting 20-60% VO2max (24.5 degrees C and 60% RH) to simulate 2nd day of a 3-day event. Results (mean+/-sem, P<0.05) at the end of the test in the treated group when compared with control showed: a lower TP (69 +/-2 vs 77+/-2 g/L) indicating PV expansion; a higher HR but no differ ences in Q and SV; and lower venous pH, HCO3-. Core temperature remain ed unchanged despite higher bodyweight losses (25.7+/-1.7 vs 17.1+/-0. 9 kg), mainly as sweat. Hyperhydration does maintain PV during prolong ed exercise but does not assist thermoregulation and may adversely aff ect acid-base balance.