1. Department of Animal Science, Raleigh, NC 27695-7621
2. Zoology, North Carolina State University, Raleigh, NC 27695-7621
3. Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
4. Durham VAMC and the Department of Medicine, Division of Gastroenterology, Duke University Medical Center, Durham, NC 27710