1. Animal Science, Auburn University, Auburn, Alabama, USA.
2. Livestock Issues Research Unit, USDA ARS, Lubbock, Texas, USA.
3. Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas, USA.
4. Animal and Dairy Science, University of Georgia, Athens, Georgia, USA.
5. College of Agricultural Sciences and Natural Resources, Texas Tech University, Lubbock, Texas, USA.