Long Term Physiologic and Behavioural Effects of Housing Density and Environmental Resource Provision for Adult Male and Female Sprague Dawley Rats

Simple Summary: The effect of housing on rodent well-being has received increasing scrutiny in recent years in North America in an attempt to define adequate standards of animal care. Typically, the adequacy of cage size is determined by species and body weight, with little consideration being given to the cage complexity and impact on animal welfare. Further, most studies evaluate different caging methods over relatively short periods of time, which may not be realistic for typical colony settings. Inappropriate housing may lead to boredom, aggression, and the development of abnormal behaviour and function, which in turn may affect animal responses during research protocols. In this study, we evaluated the impact of group housing rats by sex in double wide cages with the addition of polyvinyl chloride (PVC) tubes for shelter, a nylon chew toy, and a piece of food enrichment given three times weekly over the course of five months. These groups were compared to rats that were single or pair-housed by sex in standard cages provided only with a nylon chew toy. We found that group-housed rats were more active and continued to engaged in positive social behaviours, such as grooming, for the duration of the study, with minimal impact on other aspects of animal function. Abstract: There is considerable interest in refining laboratory rodent environments to promote animal well-being, as well as research reproducibility. Few studies have evaluated the long term impact of enhancing rodent environments with resources and additional cagemates. To that end, male and female Sprague Dawley (SD) rats were housed singly (n = 8/sex), in pairs (n = 16/sex), or in groups of four (n = 16/sex) for five months. Single and paired rats were housed in standard cages with a nylon chew toy, while group-housed rats were kept in double-wide cages with two PVC shelters and a nylon chew toy and were provided with food enrichment three times weekly. Animal behaviour, tests of anxiety (open field, elevated plus maze, and thermal nociception), and aspects of animal physiology (fecal corticoid levels, body weight, weekly food consumption, organ weights, and cerebral stress signaling peptide and receptor mRNA levels) were measured. Significant differences were noted, primarily in behavioural data, with sustained positive social interactions and engagement with environmental resources noted throughout the study. These results suggest that modest enhancements in the environment of both male and female SD rats may be beneficial to their well-being, while introducing minimal variation in other aspects of behavioural or physiologic responses.