Importance of Nitrogen Recycling to Beef Cattle Grazing Low-Protein Forages

To maximize digestion by cattle, ruminal microbes require adequate nourishment. For cattle consuming poor-quality forages, nitrogen (N) is the nutrient that is typically most limiting for the microbes (Köster et al., 1996). The total amount of N required by the microbes would minimally be the amount of microbial N flowing from the rumen and to the small intestine, but an additional amount of N equal to that lost from the rumen as ammonia would also be needed. Level 1 of the NRC (1996) model sets the microbial requirement for degradable intake protein (DIP) as 13% of TDN intake, which would be the predicted amount of microbial crude protein (MCP) leaving the rumen.