Housing Environment and Enrichment for Laboratory Rats - Refinement and Reduction Outcomes

Laboratory rats (Rattus norvegicus) are usually housed in polycarbonate, polypropylene or stainless steel solid bottom cages (SBCs) with bedding, although grid floor cages (GFCs) without contact bedding are also used. When housing rodents in laboratory conditions group housing and environmental enrichment are generally recommended. Due to the large number of rats used in biomedical research each year, it is important to offer them a proper housing environment thus satisfying their physiological and behavioural needs and ensuring their welfare. In order to evaluate the effects of housing environment and environmental enrichment on the physiology and behaviour of Wistar rats, SBCs, GFCs and three different enrichment items were used. The extent of the use of items was assessed and the effects of group size, cage level in rack, litter and gender on the physiology and behaviour of rats were measured. The effects of housing environment and enrichment on the variability of research results and hence on the number of animals needed in an experiment were assessed with n-values obtained from SOLO Power Analysis and with Nratios (n larger / n smaller). Additionally, the effects of housing modifications on two of the 3Rs – refinement and reduction – were evaluated in the experiments. Smaller gnawing blocks were used effectively only in GFCs, suggesting a more enriching value in GFCs than in SBCs. Tubes and larger blocks enabled a wider range of behaviour patterns to be expressed and thus were more suitable enrichment items in SBCs than smaller gnawing blocks. Enrichment items had only minor effects on physiology and behaviour of rats. Cage type had more profound influence on physiology and behaviour of rats than cage level or group size. The results, however, do not indisputably suggest the superiority of SBCs over GFCs, but rather that cage type in general may have physiological and behavioural consequences in rats. Variation of research results may be influenced by housing modifications thus leading to more or less animals needed. Scientists should acknowledge these potential effects while designing animal experiments. Welfare of Wistar rats was not threatened by any of the environmental modifications studied and environmental enrichment may act as refinement. In general, both concepts – refinement and reduction can be applied simultaneously but in some cases one concept may interfere the application of the other. Universal Decimal Classification: 57.082, 612.012, 591.6, 159.929 CAB Thesaurus: animal welfare; animal behaviour; enrichment; rats; rattus norvegicus, animal housing; cages; stress; variation; reduction Satu Mering: Housing environment and enrichment for laboratory rats ____________________________________________________________________________________ Kuopio Univ. Publ. C. Nat. and Environ. Sci. 114:1-60 (2000). 4