1. Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
2. Fermentation Biochemistry Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, USDA, 1815 North University Street, Peoria, IL 61604.
3. Animal Sciences, University of Missouri, Columbia, MO 65211.
4. Corresponding author. Phone: 217-265-0697. Fax: 217-244-0323. E-mail address: krausch@illinois.edu