Enriched cages for groups of laboratory male rats and their effects on behaviour, weight gain and adrenal glands.

We investigated if there were any negative effects on the behaviour and physiology of rats housed in groups of five in two types of enriched cages and compared them with paired-housed rats housed in traditional cages. Eighty-four male Wistar and Sprague-Dawley rats were housed in an enriched rat cage (ERC), a rebuilt rabbit cage (RRC) or a Makrolon III cage (MC) system from 5-16 weeks of age with access to different enrichments. Recordings of behaviour and cage use (3 × 24 h video recording), weekly weighing, measuring food consumption four days/week and water consumption two days/week, were carried out. The rats' muscle strength was assessed using the 'inclined plane' at the end of the study, and after euthanasia the adrenal glands were removed and weighed. Being in the shelter was the most common behaviour in the ERC and RRC groups. In the MC group, which lacked a shelter, rats performed the highest percentage of lying, grooming, rearing, play fighting and manipulating paper shreds. Rats in the RRC had the highest percentage of standing and manipulating gnawing sticks. Water consumption was higher in MC than in ERC and RRC rats. Rats from the RRC managed to remain at a steeper angle on the 'inclined plane' than rats from the MC. There were no significant effects of cage type on weight gain, food consumption or relative weights of adrenal glands. In conclusion, male rats kept in groups of five in larger enriched cages benefited from the enrichments, and no negative effects were found in the larger groups.