Kansas State University Graduate Research Assistant June 1973 - June 1975 University of Nebraska Graduate Research Assistant August 1975 - August 1978 University of Illinois Assistant Professor May 1978 - August 1982 University of Illinois Associate Professor August 1982 - August 1997 University of Illinois Full Professor August 1987 - August 2009 University of Nebraska Lincoln Professor Ruminant Nutrition August 2009 - Present