Evaluate the Total Amount of Corn-Derived Protein in Diets When Considering Using Distillers Grains

Dr. Bill Weiss, Dairy Nutrition Extension Specialist, The Ohio State University 

Variety is not only the spice of life, it also can increase milk yields and concentrations and yields of milk protein.  Researchers at Michigan State University (Hollmann et al., 2007, J. Dairy Sci. 90: 2022-2030) recently conducted a statistical analysis of multiple experiments evaluating corn distillers grains when fed to dairy cows.  Across the individual studies, diets contained 0 and 42% distillers grains (DM basis), milk yields ranged from about 50 to 100 lb/day and milk true protein concentration ranged from about 2.6 to 3.2%.  The forages were mainly corn silage and/or alfalfa, ground corn was the primary starch source, and soybean meal was the primary source of supplemental protein (at least in the diets without distillers grains).  The concentration of crude protein (CP) in the diets averaged 16.7% and ranged from about 14 to 20%.  Overall, control diets were fairly typical Midwestern diets. 

Dietary CP was divided into corn CP (the protein provided by corn silage, corn grain, distillers grains, and other corn byproducts if they were fed) and non-corn CP (protein from alfalfa, soy products, wheat midds, grasses, brewers grains, etc.).  Protein from corn products is a biologically low quality protein because of its amino acid profile.  The protein is quite low in lysine and many other essential amino acids.  The Michigan State study determined that when the concentration of non-corn CP in diets decreased below 6.5 to 8.5% of dietary DM, milk protein concentration and yield of milk and milk protein decreased.  Ensuring diets contain a minimum of about 7.5% non-corn CP can be used to set maximum inclusion rates for distillers grains.

For the following examples, corn grain was 9% CP, corn silage was 8% CP, distillers grain was 29% CP, alfalfa was 20% CP, and soybean meal was 54% CP.


Diet 1


Diet 2


% of Diet DM

CP, % of Diet DM


% of Diet DM

CP, % of Diet DM

Corn silage






Alfalfa silage






Corn grain






Soybean meal (SBM)












Total CP






Non-corn CP (alfalfa+SBM)






Desired non-corn CP1












1When the concentration of non-corn CP is less than 6.5 to 8.5%, yield of milk and milk protein can decrease.
2Difference = Non-corn CP minus Desired non-corn CP.

In diet 1 (high corn silage), you could replace up to 3.7 percentage units of non-corn CP with corn CP without likely affecting milk protein or milk yield. To maintain diet total CP at 17%, then for every 1 percentage unit of distillers grain added you need to remove 0.55 percentage units of corn grain and 0.45 units of soybean meal. The CP in that mix is approximately 24% non-corn CP and 5% corn CP.  To estimate maximum inclusion of distillers that can be used without negatively affecting milk yield or milk protein, divide the difference value in the table (3.7 for diet 1) by the “apparent” non-corn CP concentration in distillers (24%, not 29% because both corn grain and soybean meal will be removed as distillers is added).  For Diet 1, maximum distillers would be 3.7/0.24 = 15.4% of dietary DM (the amount of corn grain would be reduced by 15.4 x 0.55 = 8.5 units and SBM would be reduced by 6.9 units).

For diet 2 (high alfalfa), maximum inclusion is 5.3/0.24 = 22% (corn grain would be reduced by 12.1 units and soybean meal would be reduced by 9.9 units).  Since the original diet only contained 5% SBM, you would have to increase the concentration of total dietary CP if you wanted to use the maximum amount of distillers grains.  Potential changes in feed costs would have to be considered before making that decision.

The bottom line is that using a variety of feedstuffs derived from different plant sources (corn, soybean, and alfalfa) provides a blend of different protein sources which is needed to maximize milk protein yields.  Diets typically fed in Ohio already contain substantial amounts of corn protein from corn silage and corn grain, and this may limit the inclusion rate of distillers grains.