1. Present address: Faculty of Veterinary Medicine, Lilongwe University of Agriculture & Natural Resources, Lilongwe, Malawi
2. School of Veterinary Science, Hopkirk Research Institute, cnr University & Library Rds Massey University, Palmerston North 4442, New Zealand
3. Food Systems Integrity, Hopkirk Research Institute, cnr University & Library Rds, AgResearch Ltd, Palmerston North 4442, New Zealand
4. Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, PR China