Effects of a complex semi-natural cage system on Sprague Dawley rat welfare using behaviour, faecal glucocorticoid metabolites and selected organ weights as indicators

Abstract

The primary objective of using animals for research is to collect reliable data that is reproducible and translatable to the intended species. Sometimes, it is difficult to obtain reliable data because the animals are exposed to stress from experimental manipulation, or from housing environments that may not meet their species-specific requirements. This issue is especially important in rodents, which are housed in cages that are structurally different from their natural environments as most rodent housing systems are designed on economic and ergonomic factors with little consideration to the environmental needs of animals. One approach towards improving rodent housing environments is to include environmental enrichment. One idea of enriching laboratory rat cages is adding physical structures to their enclosures to create complex environments that mimic their natural habitats. For this study, we designed a complex caging system (semi-natural cages) furnished with different types of enrichment items together with increased cage space to determine if this could promote species-specific behaviour as a means of reducing stress and improving laboratory animal welfare. The study utilised previously described methods for welfare monitoring in animals namely change in home cage behaviour, monitoring of faecal glucocorticoid metabolites and monitoring changes in body weights and selected organ weights. Twenty-four female Sprague-Dawley rats were randomly allocated to either semi-natural or standard cages (each cage housing four rats), and evaluated weekly for six weeks. Behaviour data was collected via date-stamped video footage that was randomly scored using scanning and focal methods. A competitive enzyme immunoassay was used to determine the faecal glucocorticoid metabolite concentrations. The results show that animals in the semi-natural cage expressed normal rat behaviour, showed increased natural locomotory activity and were leaner than those in standard cages; characteristics that define healthier animals with improved welfare. An unexpected finding in the study was elevated faecal steroid concentration in the animals in the semi-natural cages, which will require further investigation. Basing on the outcomes of this study, we recommend semi-natural cage housing when room space and the study design allow for their use.