2007 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research project is to determine the concentrations of acid detergent insoluble ash (ADIA) and indigestible acid detergent fiber (iADF) in mixed grain rations, wheat pasture, and calf fecal samples from calves grazing wheat pasture and calves consuming mixed rations; determine the apparent digestibilities of grain rations and wheat pasture in calves grazing wheat pasture or consuming mixed rations; determine the application of near infrared spectroscopy (NIRS) techniques and software to predict ADIA and iADF concentrations in wheat pasture, mixed rations, and fecal samples to reduce the time and costs associated with laboratory analysis; and determine the levels of blood urea nitrogen and associated influence on gain and digestibilities. 1b.Approach (from AD-416) Grain, forage, and fecal samples collected in 2002 and 2003 from a study evaluating postweaning performance of beef calves in feedlot and on wheat pasture will analyzed for ADIA and iADF. Estimates of ADIA and iADF will be used as internal markers to estimate digestibilities of mixed grain rations and wheat pasture forage. Samples will also be scanned by NIRS and laboratory results will be used to develop equations to predict ADIA and iADF from NIR spectroscopy. Blood samples collected in 2003 and 2004 will be analyzed for blood urea nitrogen and impact of blood urea nitrogen levels on animal performance and feed digestibilities will be evaluated. 3.Progress Report This report serves to document research conducted under a non-funded cooperative agreement between ARS and Southwestern Oklahoma State University, Weatherford, OK. Additional details can be found in the report for the parent project 6218-31630-004-00D, Improving Stocker Production in Sustainable Grazing Systems. In the southern Great Plains region, wheat pasture is a predominant cool-season forage for stocker cattle, but calves gain little body weight during the first portion of the grazing period. Wheat forage contains relatively high concentrations of digestible protein and many forms of non-protein nitrogen. Consumption of high levels of wheat forage may result in a sudden increase in blood urea nitrogen, which serves as negative feed-back signal to decrease food intake. Low forage intake may be a partial explanation for poor weight gains during the first 4 weeks of the grazing season. Blood samples from calves grazing wheat pasture will be collected to monitor blood urea nitrogen changes over time. The ADODR uses meetings with cooperators to monitor activity in this agreement.