*Department of Poultry Science, Center of Excellence for Poultry Science, University of Arkansas, Fayetteville, Arkansas 72701; and †Cobb-Vantress, Inc., Siloam Springs, Arkansas 72761-1030 (Key words: broiler, complex activity, feed efficiency, glutathione, oxidative stress) 2005 Poultry Science 84:782–788 782 2005 Poultry Science Association, Inc. Received for publication September 14, 2004. Accepted for publication January 31, 2005. 1 2