The answer to that question depends on a couple of different factors. First is the level of sulfur in the distillers' grains. Feedlot cattle can tolerate 0.3 percent sulfur in the diet on a dry matter (DM) basis. The combination of the sulfur contributed from distillers' grains and other feed ingredients and water must all be considered. If the sulfur is not problematic, research would suggest that 30 percent is the maximum level of distillers' grains that should be included. However, the second factor that should drive the decision is economics. Generally, distillers' grains are an economical protein source but may or may not be a more cost-effective energy source than corn. If they are cheaper than corn on an energy basis, include the distillers' grains at 30 percent of the diet DM. If corn is cheaper, use distillers' grains to balance protein requirements then use the more economical energy source.