1. School of Veterinary and Life SciencesMurdoch University 90 South Street Murdoch WA 6150 Australia
2. Landcare Research P.O. Box 69040 Lincoln 7640 New Zealand
3. Department of Food and Resource Economics and Department of Veterinary and Animal SciencesUniversity of Copenhagen Rolighedsvej 25 DK‐1958 Frederiksberg Denmark