Turner, P. V., Ovari, J., Pinelli, C. et al. 2010. Long-term effects of housing and enrichment on affective behavior and responsiveness of Sprague-Dawley rats. American Association for Laboratory Animal Science [AALAS] Meeting Official Program, 658-659 (Abstract #PS12).

Most rodent studies evaluate different caging paradigms over short periods of time, which may not be realistic for typical colony settings. Inappropriate housing may lead to boredom, aggression, stereotypies, and altered metabolism, which in turn may affect experimental responses. In this study, we evaluated the effect of single (n = 8/sex), pair (n = 16/sex), and enriched group (n = 4/cage, 20/sex) housing on the behavior and affective state of male and female Sprague–Dawley rats over 5 mo of age. Parameters included body weight, food consumption, monthly behavioral scoring, fecal corticoid levels, and nociceptive responses, object recognition, elevated plus maze testing, and CRHR1 mRNA (pituitary) and CRH mRNA (hypothalamus) levels. There were no differences in food consumption or body weight between housing paradigms within each sex. By the end of the study, singly housed males were less active (P < 0.022) and less well-groomed, with more porphyrin staining. Significant mild to moderate dominance-related ritualized aggression occurred in paired males (P < 0.017), and less barbering and alopecia was noted in group-housed animals. Group-housed animals used nylon chew toys enrichment and engaged in more allogrooming and exploratory cage behaviors than single or paired rats, and significantly increased abnormal behaviors, such as bar-biting, were noted over time in single and paired female rats (P < 0.002). Housing paradigm had no effect on elevated plus, object recognition or hotplate latencies; however, hotplate responses were significantly more consistent and rapid for group-housed animals than single or paired rats. Mild blunting of dark phase fecal corticoid levels occurred in all groups over time with no consistent differences in total fecal corticoid levels. There were no differences in hypothalamic CRH mRNA expression for either sex; however, pituitary CRHR1 mRNA levels were significantly increased in single male rats (P < 0.007) and paired female rats (P < 0.006). The results of this study suggest that low density group housing of Sprague–Dawley rats may be a preferred husbandry method resulting in more consistent physiologic responses and less stereotypic behaviors.