1. a Institute of Veterinary, Animal and Biomedical Sciences , Massey University , Private Bag 11222, Palmerston North 4442, New Zealand E-mail:
2. b Department of Animal Science , Iowa State University , Ames, IA, 50011-3250, USA
3. c Faculty of Veterinary Science , University of Sydney , Private Bag 3, Camden, NSW 2570, Australia
4. d NSW Department of Primary Industries , PMB 8, Camden, NSW 2570, Australia
5. e Central Tablelands Rural Lands Protection Board , PO Box 20, Bathurst, NSW 2795, Australia