THIS PROPOSAL WAS DEVELOPED IN COLLABORATION WITH A COMMERCIAL BEEF FEEDYARD, WITH THE GOALS OF ENHANCING SUSTAINABILITY AND MINIMIZING ECOLOGICAL FOOTPRINT IN BEEF PRODUCTION. COMMINGLING OF CALVES FROM DIFFERENT SOURCES PRESENTS BIOLOGICAL AND BEHAVIORAL STRESSORS, AND IS ASSOCIATED WITH INCREASED RISK FOR BOVINE RESPIRATORY DISEASE. SOCIAL BUFFERING REFERS TO THE PHENOMENON OF ENHANCED RECOVERY FROM DISTRESS IN THE PRESENCE OF A CONSPECIFIC, WITH KNOWN NEUROENDOCRINE MECHANISM. IN THIS PROPOSAL WE EXPLORE WHETHER PREFERENTIAL RELATIONSHIPS AMONG BEEF FEEDER CATTLE PRODUCES SOCIAL BUFFERING, WITH POSITIVE ANIMAL WELFARE, HEALTH AND PERFORMANCE OUTCOMES. IN OBJECTIVE 1, WE WILL EXAMINE SOCIAL DYNAMICS OF PASTURE-REARED BEEF CALVES ASSOCIATED WITH WEANING AND CHANGES IN HEALTH STATUS. PREFERENTIAL RELATIONSHIPS AMONG CALVES WILL BE IDENTIFIED USING SOCIAL NETWORK ANALYSIS. IN OBJECTIVE 2, DETAILED BEHAVIOR AND ENDOCRINE OBSERVATIONS WILL BE USED TO EXPLORE EFFECTS OF FAMILIARITY ON PREFERENTIAL RELATIONSHIPS IN SMALL PENS OF COMMINGLED BEEF BULLS. CALF RESPONSES TO COMMON STRESSORS (COMMINGLING, ROUTINE PROCESSING AND CASTRATION) WILL BE COMPARED TO DETERMINE SIGNIFICANCE OF SOCIAL BUFFERING ON CALF STRESS AND PAIN RESPONSES. IN OBJECTIVE 3, IMPACTS OF SOCIAL BUFFERING ON BEHAVIOR, HEALTH AND PERFORMANCE OF COMINGLED LIGHTWEIGHT CATTLE ON A COMMERCIAL FEEDLOT WILL BE DETERMINED. FAMILIAR CALVES, SOURCED AS GROUPS FROM THE SAME FARM, AND SOLITARY CALVES SOURCED SINGLY FROM FARMS, WILL BE FOLLOWED THROUGH THE FEEDING PERIOD, AND HEALTH, PERFORMANCE AND BEHAVIOR OUTCOMES COMPARED TO EVALUATE EFFECTS OF SOCIAL BUFFERING IN COMMERCIAL CONDITIONS. RESULTS FROM THIS PROJECT WILL PROVIDE NEEDED GUIDANCE ON COMMINGLING PRACTICES IN U.S. BEEF OPERATIONS.