Abstract
1 School of Veterinary Studies, Murdoch University, Murdoch, Western Australia 6150, Australia
2 Physiopathology Research Unit, National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Ames, Iowa 50010
3 Department of Veterinary and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska 68583-0905
4 Department of Anaerobic Microbiology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0305