Responses for blood morphological indices in a 60-km horse endurance race depending on the season

The aim of this study was to find whether the magnitude of changes in blood before and after horse endurance competitions was the same at the beginning and the end of the season and if the studied indices could be useful in assessing the impact of such changes on the length of the endurance racing season. The study was conducted on 36 clinically healthy horses. Blood samples were taken during 60-km endurance competitions in 2014, three times in total. The study revealed an increase of lymphocytes (× 1.89–2.05; P < 0.001), red blood cell count (× 1.11–1.12; P < 0.001), and a decrease in the mean corpuscular haemoglobin concentration (× 1.20–1.27; P < 0.001), red cell distribution width (× 1.11; P < 0.01), platelet concentrations (× 1.33–1.40; P < 0.05), when compared at the beginning and in the end of the horse endurance racing season. During the entire season, haematocrit values significantly increased after the race but were at their lowest in the mid-season period. The results proved a significant increase in the white blood cell and granulocyte counts following the finish of a 60-km endurance race, when comparing the values at the beginning and in the end of the horse endurance racing season, and a significant reduction in lymphocytes when comparing the values at the beginning (35.7%) and at the end (29.7%) of the season. The endurance competition season highly influences haematology indices in horses’ blood, however, to determine the season’s impact on the results of the race, additional studies must be conducted