1. Clinic for Cattle, University of Veterinary Medicine, 30173 Hannover, Germany.
2. Department of Animal Biology, Faculty of Veterinary Science, University of Zulia, Maracaibo, Zulia 44011, Venezuela.
3. Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca NY 14853, USA.
4. Anatomy Unit, University of Veterinary Medicine, 30173 Hannover, Germany.
5. Immunology Unit, University of Veterinary Medicine, 30173 Hannover, Germany.
6. Clinic of Reproductive Medicine, Vetsuisse Faculty, University of Zurich, 8057 Zurich, Switzerland.