Abstract
Sarcocystosis is a widespread protozoan disease of sheep caused by intracellular parasites of the genus Sarcocystis. The infection is characterized by a predominantly chronic course and often develops without pronounced clinical signs, which complicates early diagnosis and control. Despite the frequently subclinical nature of the disease, sarcocystosis can lead to significant economic losses in sheep farming due to decreased productivity, reduced weight gain, deterioration of meat quality, and increased veterinary management costs. Hematological parameters are considered informative indicators of the physiological and pathological processes occurring in the host organism during parasitic infections and may reflect inflammatory reactions, metabolic disturbances, and adaptive responses. The aim of this study was to evaluate hematological changes in sheep naturally infected with sarcocystosis and to identify hematological parameters that may reflect the influence of the parasitic invasion on the organism. Peripheral blood samples were collected from sheep with confirmed sarcocystosis during field investigations. A total of seven blood samples (n = 7) were analyzed. Blood was obtained from the jugular vein using standard aseptic procedures and placed into tubes containing EDTA as an anticoagulant. Hematological analysis was performed using an automated hematology analyzer and included evaluation of leukocyte, erythrocyte, and platelet profiles, as well as erythrocyte indices. The results showed deviations in several hematological parameters compared with established physiological reference ranges. Functional changes in leukocyte distribution suggested activation of the immune response. The most notable alterations were observed in the erythrocyte profile, including increased red blood cell counts and decreased erythrocyte indices (MCV and MCH), while MCHC values were elevated. Variability in platelet parameters and an increased proportion of large platelets were also detected. These findings indicate that sarcocystosis may lead to systemic hematological changes reflecting inflammatory and adaptive processes in infected sheep.