Are "by-stander" female Sprague-Dawley rats affected by experimental procedures?

The objective of this study was to test the hypotheses that female rats are stressed by being in the same room as animals subjected to common husbandry and experimental procedures and that the level of stress is affected by housing density. Two commonly used indices of stress, heart rate (HR) and mean arterial blood pressure (MAP), were determined by using radiotelemetry for 2 h before and 3 h after rats witnessed the following procedures: decapitation, simulated decapitation, cage change, simulated cage change, restraint and subcutaneous injection, removal of rats to another room for injection, restraint and tail-vein injection, handling and weighing, and handling and vaginal lavage. In addition, home cage behaviors (sleeping, awake, moving, rearing, and grooming) were scored once each minute for 15 min before and 45 min after the procedures. Witnessing decapitation of six other rats induced small, but significant, increases in HR above undisturbed baseline values in animals housed alone, whereas responses in animals housed with one or three cage mates were slightly greater than those of rats housed alone. Witnessing a routine cage change induced significant increases in HR in rats which were equal to or greater than those induced by witnessing decapitations; however, housing density had little effect on the responses to cage change. HR did not significantly increase above baseline values in rats witnessing restraint and a subcutaneous or tail-vein injection of other rats or when witnessing other rats being handled and weighed. However, rats housed alone showed significant increases in HR when witnessing a vaginal lavage of other rats. Active behaviors (moving, rearing, grooming) in the home cage were significantly altered only in rats housed alone and then only when witnessing a cage change or a tail-vein injection. Considering primarily increased HR, we conclude that female Sprague-Dawley rats may be marginally stressed when present in the same room in which decapitation is being performed, but similar stress-like responses are induced by common husbandry and experimental procedures. Finally, group housing often, but not always, reduces the stress-like responses that can occur in female by-stander rats.