1. Institute of Animal Breeding, Wroclaw University of Environmental and Life Sciences, 51-630 Wroclaw, Poland
2. Department of Surgery, Wroclaw University of Environmental and Life Sciences, 50-366 Wroclaw, Poland
3. Center for Statistical Analysis, Wroclaw Medical University, 50-368 Wroclaw, Poland
4. Equine Clinic, Brno University of Veterinary and Pharmaceutical Sciences, 612-42 Brno, Czech Republic