Enhancing cage space utilization for laboratory rats (Rattus norvegicus) : evaluation of two enrichment structures

Abstract: The rearing environment of laboratory rats has a tremendous effect on their behaviour and cognitive skills. Rats housed in an enriched environment have been shown to be more resilient and better able to cope with challenges in the future. Their problem solving skills are enhanced, and rats will even exert a certain degree of physical strength to access an enriched environment. The majority of rats at AstraZeneca, Gothenburg, are group housed in the Enriched Rat Cage (ERC) system, with a very good size and enrichment standard compared to large parts of the laboratory animal science community. However, the height and overall large space, is not fully utilized. The aim of this study was to evaluate two enrichment structures with a potential to improve the cage space utilization. A shelf and a PVC tunnel was mounted to the back wall of the ERC. Six female rats were placed in pairs in one ERC rack, containing three cages. A surveillance system was set up with one camera for each cage. Recordings were performed in four 24-hour cycles, with the first cycle on day 1, starting directly after introducing the rats to the modified ERC. The following recording cycles were on day 8, 15 and 22. Analysis of behaviour was performed during 5 minutes, every other hour, totalling for 240 minutes, using The Observer XT 11.5. The behaviour and in cage location was recorded for each cage, containing two rats, along with duration for each behaviour (n=3). The results show a more frequent use of the tunnel than the shelf. The duration of each interaction was also longer for the tunnel than for the shelf. The mean duration for tunnel increased from 0.6 ± 0.3 seconds on day 1, to 287.0 ± 43.1 seconds on day 22. Mean duration on shelf did not differ much over the four recording cycles; results were between 1.9 ± 1.2 seconds and 7.5 ± 1.6 seconds. Both structures were used throughout the course of the day, where most interactions with the shelf occurred during the night, the rat’s active period, and the tunnel was used more during the day, the more inactive part of a rat’s day. The tunnel, as well as the shelf, fulfil the goal of better cage space utilization. This serves to enhance cage complexity, which is argued to be of more importance for rat well-being than a larger cage. The conclusion is that both the tunnel the shelf was used by the rats and should be studied and developed further, and, in the future, implemented in all ERC racks at AstraZeneca, Gothenburg.