1. Swine Medicine Education Center, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA
2. Nebraska Veterinary Diagnostic Center, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
3. Veterinary Preventive Medicine, College of Veterinary Medicine, Ohio State University, Columbus, OH 43210, USA
4. Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA
5. Department of Statistics, Iowa State University, 1121 Snedecor Hall, Ames, IA 50011, USA