1. Department of Surgery, Faculty of Veterinary Medicine, Wroclaw University of Environmental and Life Sciences, Plac Grunwaldzki 51, 50-366 Wrocław, Poland
2. Institute of Animal Breeding, Wroclaw University of Environmental and Life Sciences, Chelmonskiego 38C, 51-630 Wrocław, Poland
3. Center for Statistical Analysis, Wroclaw Medical University, Marcinkowskiego 2-6, 50-368 Wrocław, Poland
4. Department of Anatomy, Physiology and Animal Sciences, University of Forestry, 1797 Sofia, Bulgaria