Effects of Alternative Housing Systems on Physical and Social Activity in Male Sprague Dawley and Spontaneously Hypertensive Rats

Two alternative rat cages and their effect on home cage physical and social activity were evaluated in male Sprague Dawley (SPD) and Spontaneously Hypertensive (SH) rats for 10 weeks. Rats were housed strain-wise in pairs in ST cages, in groups of eight in Enriched Rat Cage System (ERC) equipped with a shelter and wall-hung ladders, and in groups of eight in four interconnected Scantainer(NOVO) cages (NOVO), equipped with shelves. Home cage activity was assessed through direct observations and effects were studied in exercise tests, parameters related to physical activity and in the Elevated Plus Maze (EPM). Effects of within-group variation on the minimum sample size needed to detect a treatment effect were calculated for the different cage types. The home cage activity was highest in NOVO cages, followed by the ERC cages. This was supported by the higher locomotor and exploratory activity in the EPM and an improved performance in the last exercise test, compared to ST-caged rats. Aggressive and submissive interactions were higher in NOVO cages compared to ST cages. The design of the NOVO cages, if connected, might induce both a higher activity level and more aggression. The hypertension and insulin resistance typical of the hypertensive rat model were not influenced by an increased home cage activity. No major effects of alternative cage types were found on within-group variation. The activity was not enough to create a distinct training effect but prevented exercise-related parameters from deteriorating during the study and is therefore still relevant for the health and welfare of the animals. Additional benefits of the alternative cages are qualitative, since they stimulate a wider range of behaviours, social interactions and offer possibilities for the rats to control their situation.