Impact of environmental conditions on the levels of stress and breeding performance in Wistar rats: conventional environment versus environmentally controlled housing.

It has been established that providing comparable and standard environmental conditions to house experimental rats is of high importance. However, there is growing evidence that rats prefer higher temperatures owing to their thermoneutral zone that lies between 28-34°C. This experiment validates the stress levels of Wistar rats of both sexes housed in conventional conditions about 24-31°C and a relative humidity of 70-92% in a tropical animal facility when compared to rats housed in controlled temperatures of 20-24°C with humidity maintained between 30-70%. Adequate air-changes to maintain ammonia-free environment was provided with a power-exhaust system in a conventional setup and with the individually ventilated caging system in the environmentally controlled group. To assess stress, faecal corticosteroid metabolite assay was done in naïve animals and in a set of animals that underwent retro-orbital bleeding under general anaesthesia. Mothering ability, fecundity and preweaning mortality were also compared between animals housed in two different conditions. Results showed no differences in stress hormone levels between the groups. However, faecal weights differed between males and females in both naïve and orbital bled groups. Animals housed in controlled environment clearly had better breeding data with lesser preweaning mortality in comparison to the conventionally housed rats. Further studies are required to elucidate whether the results are comparable when conducted during all seasons of the year at different locations across the globe.