It's been a matter of debate over the years how much distillers grain can be used in the ration.

Some reports have placed the ceiling at 10 percent (on a dry-matter basis), while others say it is OK to go up to 20 percent or beyond. A study in this month's Journal of Dairy Science suggests somewhat of a middle ground: 15 percent. Researchers from the University of Nebraska, Texas A&M University and Dakota Gold Research Association looked at a 15-percent inclusion rate for various corn-milling co-products, including dried distillers grains plus soluble, dehydrated corn germ meal and high-protein dried distillers grains. When included at 15 percent of dry matter, the co-products did not adversely affect dry matter intake, milk yield or components — in fact, performance was similar when cows were fed those diets compared to a control diet with no co-products.

"This experiment indicates that dairy rations can be successfully formulated to include 15 percent of diet DM as corn-milling co-products while maintaining yields of milk and milk components," the authors wrote in the JDS article. The researchers did not look at any other inclusion rates besides 15 percent.