1. The School of Veterinary Medicine and Science, The University of Nottingham, Sutton Bonington Campus, Sutton Bonington, Leicestershire LE12 5RD, United Kingdom, Institute for Animal Health, Compton, Berkshire RG20 7NN, United Kingdom, and Nuffield Department of Clinical Laboratory Sciences, Oxford University, John Radcliffe Hospital, Headington OX3 9DU, United Kingdom