Sławomir Gonkowski1, Jaroslaw Calka2. 1. Departement of Clinical Physiology, Faculty of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, ul Oczapowskiego 13, 10-718, Olsztyn, Poland. slawomir.gonkowski@uwm.edu.pl. 2. Departement of Clinical Physiology, Faculty of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, ul Oczapowskiego 13, 10-718, Olsztyn, Poland.