1. Institute for Animal Science and Technology Universitat Politècnica de València 46022 Valencia Spain
2. MRC Human Genetics Unit MRC Institute of Genetics and Molecular Medicine University of Edinburgh Crewe Road, Edinburgh EH4 2XU United Kingdom
3. Roslin Institute and Royal (Dick) School of Veterinary Studies University of Edinburgh Midlothian EH25 9RG United Kingdom
4. Division of Animal Sciences Department of Agricultural and Food Sciences University of Bologna 40127 Bologna Italy
5. Departament de Ciència Animal Universitat de Lleida–Agrotecnio Centre E-25198 Lleida Catalonia, Spain