Effect of physical exercise on cortisol concentration and neutrophil oxygen metabolism in peripheral blood of horses

The aim of the study was to evaluate the effect of regular physical exercise on cortisol concentration and oxygen-dependent bactericidal activity of neutrophils in peripheral blood in recreational and competitive sport horses (racehorses - Ra, trotters - T, jumping horses - J, driving horses - D). The study was conducted on 55 clinically healthy horses. Blood samples were collected from the external jugular vein three times: before exercise, immediately after exercise, and after 30-min rest. Blood samples were subjected to haematological examination, cortisol concentration was determined by radioimmunoassay (RIA) and neutrophil oxygen metabolism of neutrophils was determined using a chemiluminescence method. The analysis showed that cortisol concentration was significantly higher (P<0.05) post-exercise only in the blood of sport horses. This finding, along with a significant correlation (P<0.00005) with the heart and respiratory rates, suggests that the magnitude of cortisol secretion is associated with the intensity and duration of exercise. The relatively small post-exercise increase in cortisol concentration during different exercises of horses resulted in a transient increase of chemiluminescence activity of neutrophils, mainly in D (P<0.00001) and J horses (P<0.01). In the studied groups analysis of the correlation between cortisol concentration and other parameters showed significant correlation only in the case of the CL total in T (P<0.02) and D horses (P<0.004). It is therefore apparent that in a limited concentration, this hormone may stimulate the activity of these cells, although the effect of other neurohormonal factors cannot be excluded. This result confirms that regular and moderate training loads have a beneficial effect on the immunological status of horses.