Sharp, J. L., Zammit, T., Azar, T. A. et al. 2003. Stress-like responses to common procedures in individually and group-housed female rats. Contemporary Topics in Laboratory Animal Science 42(1), 9-18.

Mean resting HR values in the mornings prior to human contact were significantly (P < 0.05) lower in rats housed four per cage than animals housed alone or with one cage mate, whereas MAP during this period was lowest in rats housed two per cage. Nocturnal HRs were highest in rats housed two per cage, whereas nocturnal MAP did not differ significantly between housing groups. When rats were subjected to acute husbandry and experimental procedures, HRs increased 80 to 180 beats per min (bpm) above a baseline of 300 to 325 bpm and were significantly (P < 0.05) increased for periods of 30 to 90 min after the procedures. MAP showed increases that were proportionately the same as those in HR. Group housing often, but not always, reduced these cardiovascular responses. Procedure-induced arousal behaviors occurred in all housing groups after the acute husbandry and experimental procedures, but the occurrence of these behaviors was less frequent and of shorter duration in group-housed rats than rats housed alone. In light of these results, we conclude that under resting conditions group housed rats were somewhat less stressed than were rats housed alone. Further, we conclude that common procedures induce significant stress-like responses in female rats, and the magnitude and duration of these responses are reduced by group housing.