1. Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, 1089 Veterinary Medicine Drive VM3B, Davis, CA 95616
2. Department of Pathobiology and Department of Poultry Science, Auburn University, 302J Poultry Science Building, 260 Lem Morrison Drive, Auburn, AL 36849
3. Department of Animal Sciences, College of Agriculture, University of California, Davis. One Shields Avenue, Davis, CA, 95616