1. Gastrointestinal Laboratory, Department of Small Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843-4474, USA.
2. Department of Biomedical and Diagnostic Sciences, College of Veterinary Medicine, The University of Tennessee, Knoxville, TN 37996-4542, USA.
3. Department of Medicine, Section of Gastroenterology, College of Medicine, The University of Chicago, Chicago, IL 60637, USA.