1. Itra-ULE, INDEGSAL, University of León, 24071 León, Spain
2. Animal Reproduction and Obstetrics, Department of Veterinary Medicine, Surgery and Anatomy, University of León, 24071 León, Spain
3. Cellular Biology, Department of Molecular Biology, University of León, 24071 León, Spain
4. Anatomy, Department of Veterinary Medicine, Surgery and Anatomy, University of León, 24071 León, Spain