1. University of Illinois, College of Veterinary Medicine, 2001 South Lincoln Ave., Urbana, Illinois 61802, USA
2. Current address: University of Tennessee, College of Veterinary Medicine, 2001 South Lincoln Ave, Urbana, Illinois, 61802, USA
3. University of Tennessee, College of Veterinary Medicine, 2407 River Dr., Knoxville, Tennessee 37996, USA
4. Eli Lilly and Company, Lilly Research Laboratories, PO Box 708, Greenfield, Indiana 46140, USA
5. University of Florida, College of Veterinary Medicine, PO Box 100126, Gainesville, Florida 32608, USA