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Q: Do I need to supplement my stocker steers with urea if I am already supplementing them with distillers' grains?

A: Protein supplementation of forge diets can increase forage intake, and improve ADG if a protein deficiency exists. There is some speculation about the need for ruminally degradable intake protein (i.e. urea) in cattle fed high forage diets even when supplementation of distillers' grains is sufficient to meet crude protein requirements. Because of the symbiotic relationship of the ruminant animal and the rumen microorganisms, the protein requirement of a ruminant can be separated into the needs of the microorganisms to maximize rumen digestion and the needs of the animal itself for protein synthesis. Therefore, both requirements must be met in order to maximize animal performance. Most rumen fibrolytic bacteria use ammonia-nitrogen (a product of urea breakdown in the rumen) as their primary nitrogen source. Distillers' grains contain relatively high levels ruminally undegraded intake protein (approximately 65%) that is not converted to ammonia in the rumen. Therefore, one might assume that supplementation of forage diets with distillers' grains alone would cause a deficiency in available nitrogen for the fiber digesting rumen bacteria. However, Stalker et al. (2007) fed heifers a diet of 58% corn cobs, 12% sorghum silage, and the remaining 30% was one of five DDG based supplements with increasing levels of urea from 0 to 1.6% of diet DM. No effects of urea level were observed for ADG, DMI, or G:F. The amount of DDG consumed in that trial was approximately 0.52% of the initial BW. In another trial presented in the same paper, Stocker et al. (2007) observed no effects on performance in response to the addition of 45 grams of urea to a DDG supplement that was fed at 0.67% of BW to heifers fed grass hay (7.4% CP). Similarly, Martin et al. (2007) fed developing heifers either 0.59% of BW DDG or 0.78% of BW control supplement that did not contain DDG, but contained 2.3% urea (DM basis). Supplements were formulated to be isoenergetic and no differences in heifer gains were observed. Although the NRC model would predict a ruminally degradable intake protein deficiency in several grazing situations where distillers' grains are supplemented, the research doesn't generally support the addition of urea to those diets. This may be because the NRC model overestimates the ruminally degradable intake protein requirements of forage fed cattle, because urea recycling into the rumen is sufficient in cattle fed distillers' grains to meet any predicted deficiency, or both.