1. Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, S1 076, Schurman Hall, Ithaca, NY 14853, USA
2. Rodney Shearman Endocrinology Laboratory, Royal Prince Alfred Hospital, Missenden Road, Camperdown, NSW 2050, Australia
3. Department of Veterinary Clinical Sciences, The Queen Mother Hospital for Animals, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Herts AL9 7TA, UK