1. Former postdoctoral research associate, visiting assistant professor, and professor, respectively, Department of Agricultural Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. Mention of product or trade names does not imply endorsement by the University of Illinois.
2. Corresponding author. Present address: USDA/ARS/ERRC, 600 E. Mermaid Lane, Wyndmoor, PA 19038. E-mail: vsingh@arserrc.gov
3. Professor, Department of Veterinary Biosciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801.