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Blood is an important and reliable medium for assessing the health status and performance level of horses. Variations in hematological parameters in horses are associated with several factors such as exercise and training, feeding, age, sex, breed, diurnal and seasonal variation, temperature and the physiological status etc. The objective of this study was to determine the influence of seasonality on hematological indices and osmotic resistance of erythrocytes in horses involved in recreational horseback ride before and after exercise. Thirteen healthy adult horses from Pomeranian regions in Poland (aged 9.5±2.4 years) were used. All horses participated in recreational horseback riding. Blood samples were taken once per season for one year – in spring (April) and summer (July). Blood was drawn from jugular veins of the animals in the morning, 90 minutes after feeding, and immediately after exercise. The blood samples were assessed for haematocrit (HCT) value, haemoglobin concentration (HGB), the red blood cells (RBC) amount, mean corpuscular hemoglobin concentration (MCHC), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), red cell distribution width (RDW), the platelets (PLT) amount, platelets distribution width (PDW) and osmotic resistance of erythrocytes before and after exercise. Our results confirm that hematological parameters in equines involved in recreational horse riding are subjected to seasonal variations. Significant increase of RBC amount and hemoglobin level after exercise both in spring and summer seasons were observed (p < 0.05). In spring, exercise caused enhancement of the hematocrit level, the mean corpuscular volume and the mean corpuscular hemoglobin levels (p < 0.05). At the same time, post-exercise MCH were higher in the spring (p < 0.05) compared to summer season. However, pre-exercise MCHC level in the summer was lower (p < 0.05) compared to the spring season. Higher percent of hemolyzed erythrocytes in spring season probably caused by the liberation of red blood cells from spleen and/or the increase of oxygen consumption.
Key words: horses, hematological parameters, seasonal variations, exercises