2007 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research project is to determine time-series differences in blood urea nitrogen and cortisol concentration levels in varying genotypes and genders of stocker cattle to determine the usefulness of these blood parameters as indicators of adaptation to and animal performance on cool-season and warm-season forages. 1b.Approach (from AD-416) Differences in blood urea nitrogen and cortisol concentration levels in varying genotypes and sex of stocker cattle will be determined in cattle grazing both warm-season and cool-season forages. Relationships of these parameters to time of adaptation to novel forages and to grazing animal performance will be determined using multiple linear regression. Standard laboratory procedures will be used in estimating serum cortisol and blood urea nitrogen. 3.Progress Report This report serves to document research conducted under a non-funded cooperative agreement between ARS and University of Arkansas, Fayetteville. 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 production, but calves gain little weight during the first 4 weeks of the grazing season. During this adaptation period the animal’s physiological system may be stressed due to the change in diet. As a result, blood concentrations of cortisol are increased due to sub-clinical stress. Sub-clinical stress can reduce the rate of body weight gain. Blood samples will be collected from animals grazing wheat pasture in the falloff 2007 to determine is cortisol concentrations for the first 4 weeks of the grazing season. The ADODR uses conference calls to monitor the activity of this agreement.