1. Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, University of Illinois, Urbana, IL 61801. Mention of brand or firm names does not constitute an endorsement by University of Illinois above others of similar nature not mentioned.
2. Veterinary Diagnostic Laboratory, University of Illinois at Urbana-Champaign, University of Illinois, Urbana, IL 61801.
3. Corresponding author. Phone: 217-333-9510. Fax: 217-244-0323. E-mail: vsingh@uiuc.edu