2006 Annual Report 4d.Progress report. This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Mississippi State University. Additional details of research can be found in the report for the inhouse project, 6604-32630-004-00D, Nutritional and Environmental Management to Reduce Stress, Improve Quality and Improve the Efficiency of Poultry Production. Further research has been conducted on effects of the major stress related steroid hormone, Corticosterone, in commercial broilers. These studies have provided mechanisms to compare classic hormone induced stress responses to those seen in birds subjected to differing lighting programs and stocking densities. In addition, studies have been completed comparing growth, performance and processing yields in commercial heavy broilers reared at differing stocking densities. Physiological adaptive responses as affected by stocking densities in commercial broilers, and the affects of stocking density on their intestinal microflora have also been examined and published.