Effects of the housing system and environmental enrichment on social dominance in laboratory male rats

Abstract

In laboratory rats, dominance manifests as agonistic behaviour that damages social bonds between individuals. In this study, the effect of the housing system and environmental enrichment on the social dominance in male Wistar rats was assessed in the social dominance tube test. Rats were housed in different housing systems (individual vs. social housing, with or without enrichment) from weaning and tested at the age of 7 weeks. In each test, two rats from different housing systems were released into opposite ends of a narrow tube and the rat that forced its opponent out of the tube was declared the winner (the more dominant animal). In this way, all possible combinations of housing systems were tested and number of wins were recorded and percentage of the total number of matches was calculated. The results show that environmental enrichment suppresses (P < 0.001) dominant behaviour in individually housed rats while no such effect was seen in socially housed male rats (P = 0.532). However, social housing combined with enrichment was more effective in reduction of dominant behaviour compared to only providing enrichment for individually housed rats. Reduction of variability in the manifestations of dominant behaviour is important in animals used for experimental purposes from the perspective of greater homogeneity of animals, which ensures obtaining valid research results and at the same time better living conditions for laboratory animals.