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Q: Do I need to include urea in finishing cattle diets containing distiller's grains?

A: Properly formulating rations to meet the protein requirements of both the cattle and the microbes in the rumen of the cattle can have an impact on your bottom line. With the high levels of distillers' grains in some of today's finishing cattle diets, the crude protein requirement of those cattle is often met or exceeded without supplementation. However, due to potential deficiencies in other nitrogen containing substances such as urea, supplementation may be needed. Within a ruminant animal the protein requirement can be broken down into the protein needs of the animal itself and the protein needs of the rumen microbes to support optimum microbial growth and therefore ruminal digestiblity. Protein for the animal is supplied by the protein from the feed that escapes degradation in the rumen and the protein contained within the microbial cells escaping the rumen. Once out of the rumen these proteins are then digested by the animal and are used for various functions in the body. The rumen microbes however, require a mixture of true protein (from amino acids) and ammonia. Ammonia is a product of protein and urea breakdown in the rumen and sufficient ruminal ammonia is necessary to support optimal microbial activity in the rumen. However, ammonia production in the rumen from urea is more efficient than ammonia production from true protein. Therefore, one function of dietary urea supplementation is to ensure that there is sufficient ammonia produced in the rumen to support microbial growth and activity. To apply some of these concepts to your situation it may be useful to review some of the research that has been conducted looking at urea supplementation in finishing diets. In diets containing no distillers' grains, corn processing method appears to affect the optimum level of urea supplementation. Research from the University of Nebraska suggests that in diets without distillers' grains, urea should be added at higher levels in diets based on high-moisture corn and steam-flaked corn than in diets based on dry-rolled corn (Cooper et al., 2002). Researchers from the University of Nebraska also fed finishing heifers dry-rolled corn based diets containing 10 and 20% (dry matter basis) dried distillers' grains (Vander Pol et al., 2005). To address possible deficiencies, urea was added to the 10 and 20% dried distillers' grains diets at 0.80 and 0.63% (dry matter basis), respectively. The addition of urea to the diets did not statistically improve feed efficiency, although a numeric improvement (3.3%) in feed efficiency was observed with the addition of urea to the 10% dried distillers' grains diet. The authors suggested that a conservative application of the data would be to add a small amount of urea to diets containing 10% distillers' grains or less. Additional urea might be needed as well in steam-flaked corn and possibly high-moisture corn based diets that contain distillers' grains. Researchers from Kansas State University observed depressed ruminal ammonia concentrations in steers fed steam-flaked corn based diets containing 25% (dry matter basis) dried distillers' grains plus solubles (Uwituze et al., 2008). The authors speculated that the reduced ammonia concentration could limit nitrogen availability in the rumen, thus reducing ruminal digestibility because of inadequate microbial growth. A recent study from West Texas A&M indicated that in steam-flaked corn based diets optimum feed efficiency was achieved when urea was included between 1.5 and 3.0% of the diet dry matter when diets contained 15% wet distillers' grains plus solubles. In that same study, optimum feed efficiency was achieved when urea was included at 1.5% of the diet dry matter or less when steam-flaked corn diets contained 30% wet distillers' grains plus solubles. Several factors other than corn processing method will dictate specific protein and urea requirements in different feeding situations, and working with your nutritionist to ensure that you are meeting those requirements can help improve the profitability of your operation.