The yearly production capacity of ethanol in the United States is expected to be more than 6 billion gallons by the end of 2006 (Loy et al., 2005). Up to 80% of the byproducts of this production are fed to ruminant animals (Lardy, 2003). One of these byproducts, sorghum wet distiller’s grains plus solubles (SWDG) provides a source of both energy and crude protein, in finishing diets for beef cattle. Sorghum wet distiller’s grains plus solubles contain large portions of undegraded intake protein (UIP) compared with other feedstuffs (50% UIP; Tjardes and Wright, 2002).
The most frequently fed processed grain in feedlot diets in the High Plains region is steam-flaked corn (SFC). Because SFC is such a readily available source of starch, it is quickly and comprehensively fermented in the rumen. This process results in high microbial protein production, resulting in an increased supply of degraded intake protein (DIP) being needed to maintain microbial synthesis. Thus, in diets containing SWDG substituted for SFC, UIP is increased at the expense of DIP. This exchange of UIP for DIP might result in decreased performance of the animal. The objective of this research was to determine whether additional DIP, added in the form of urea, would compensate for the potentially negative effects of increasing levels of SWDG in the diet on animal performance.