1. Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, MI 48824, USA
2. Center for Comparative Epidemiology, Michigan State University, East Lansing, MI 48824, USA
3. Veterinary Services, Animal and Plant Health Inspection Service, United States Department of Agriculture, East Lansing, MI 48823, USA
4. Animal Industry Division, Michigan Department of Agriculture and Rural Development, Lansing, MI 48909, USA