Shelved cages impact affective behavior in Sprague Dawley rats – implications for animal welfare

Laboratory animal welfare has received increasing attention in recent years as housing protocols move toward favoring environments that allow natural behaviors. Within this study, the effects of housing male and female Sprague Dawley rats in standard cages versus taller cages with an upper shelf were investigated. To determine differences in behavior and physiology based upon cage type, home-cage assessment of ultrasonic vocalizations and analysis of fecal corticosterone metabolites, as well as various behavioral tests, were performed. Rats in shelved cages produced significantly less 50 kHz calls, demonstrated better working memory in the spontaneous alternation task and had higher concentrations of fecal corticosterone metabolites. No differences were observed in the open field, elevated plus maze or light-dark box. While no significant treatment differences were found in the ultrasonic vocalization playback paradigm, results confirmed previous evidence of approach behavior upon 50 kHz call playback. The observed differences in behavior and physiology as a consequence of housing conditions inevitably have implications for experimental reproducibility as comparing studies across laboratories may be difficult if different housing parameters are utilized. The results of this study can also be used in guiding future animal welfare protocols given that certain cage modifications such as increased vertical space and/or the presence of a shelf might improve welfare. Investigation of additional parameters and strains of rodents will enhance our understanding of optimal laboratory animal housing conditions.