Erythrocyte indices in relation to hydration and electrolytes in horses performing exercises of different intensity

Exercise induces changes in hydration and electrolytes status that might affect volumetric properties of erythrocytes. This research analyzes the modifications induced for different type of exercises on volumetric indices in horses in relation to plasma electrolytes, total plasma proteins, heart rate, and lactate. One hundred sixty-four healthy sport horses were studied, divided into six groups: A (16 racing Angloarabians), B (12 jumping Angloarabians), C (45 endurance horses), D (18 Andalusians), E (65 draft horses), and F (eight eventers). In groups A, C, E, and F, blood samples were taken before and after competition. The horses of groups B and D were subjected to an exercise test and blood samples were taken before and after the test. The parameters analyzed were: packed cell volume (PCV), mean cell volume (MCV), mean cell hemoglobin (MCH), mean cell hemoglobin concentration (MCHC), Na, K, Cl, heart rate, total plasma proteins, and plasma lactate concentrations. PCV increased in all the groups, MCV decreased in group D, MCH increased in groups D and F and decreased in group E, and MCHC increased with exercise in groups A and F. The only significant correlation between plasma electrolyte and volumetric indices was found between plasma Na concentrations and MCV. It is concluded that, although volumetric indices change with exercise in horses, their modifications are somewhat erratic and do not show a direct correlation with hydration, electrolyte status and exercise intensity, but red blood cell size is partially dependent on plasma Na concentration.