Hydration and electrolyte balance in horses during an endurance season.

REASONS FOR PERFORMING STUDY

Limited information exists about the physiological training-induced changes in electrolyte balance of horses competing in long distance endurance races.

OBJECTIVES

To determine the effects of endurance training and racing on hydration and electrolyte balance in horses.

METHODS

Blood and urine were sampled at rest in 8 endurance horses before training and after two 11 week training periods (T1 and T2). Each training was followed by a 120 km endurance ride and horses were sampled before, during and 2 h after the rides. Blood was analysed for packed cell volume (PCV), total protein (TP), urea, creatinine and electrolyte concentrations. Urine was analysed for pH, specific gravity, creatinine and electrolyte concentrations, which allowed calculation of fractional excretion of electrolytes (FE). Changes associated with training and with the rides were assessed using a Student paired t test (P ≤ 0.05).

RESULTS

Plasma TP, urea, creatinine and sodium concentrations increased during T1 and PCV decreased significantly during T2. FE(Cl) increased during T1 then decreased. FE(K) increased significantly during both training periods. Other blood and urine parameters did not show remarkable changes with training. PCV, plasma TP, urea, creatinine and total Ca concentrations increased and plasma Na(+) and Cl(-) concentrations decreased during both rides. Urine concentrations of Na(+), K(+) and Cl(-), FE(Na) and FE(Cl) decreased during the rides while urinary creatinine increased. FE(K) increased during the first part of the rides then decreased.

CONCLUSIONS

These data contribute to the understanding of changes associated with training and prolonged endurance exercise.