1. Biosystems and Agricultural Engineering, Oklahoma State University, Stillwater, OK 74078.
2. Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
3. Animal Sciences, University of Missouri-Columbia, Columbia, MO 65211.
4. Veterinary Pathobiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
5. Corresponding author. Phone: 217-265-0697. Fax: 217-244-0323. E-mail: krausch@uiuc.edu