We suggest half of the protein supplement as corn distillers with a minimum of one pound of soybean meal. If corn silage and corn grain are major feed sources, limit the corn distillers to one-third of the protein mix (lysine will become a limiting amino acid). Four to six pounds of corn distillers is considered to be the upper limit to feed per cow.
Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET