1. Department of Veterinary Medicine, University of Cambridge, Cambridge, CB3 0ES, United Kingdom.
2. Royal (Dick) School of Veterinary Studies and The Roslin Institute, The University of Edinburgh, Edinburgh, EH25 9RG, United Kingdom.
3. Bristol Veterinary School, University of Bristol, Bristol, BS40 5DU, United Kingdom.
4. Department of Clinical Sciences and Services, Royal Veterinary College, London, AL97TA, United Kingdom.
5. Department of Pathobiology and Population Sciences, Royal Veterinary College, London, AL97TA, United Kingdom.
6. Department of Small Animal Clinical Studies, Texas A&M University, College Station, TX 77843-4474, USA.