Housing and Welfare in Laboratory Rats: Welfare Implications of Isolation and Social Contact Among Caged Males

Abstract

AbstractMale laboratory rats (Rattus norvegicus; Wistar, Alderley Park) were housed as singletons or groups of three in units of two joined, but divided cages. Units were divided by different types of barrier that allowed different degrees of social contact across the barrier. Singletons were established either with another singleton as a neighbour on the other side of the barrier, or with a group of three as neighbours. Relative to group-housed animals, singly-housed rats showed reduced activity and a greater incidence of self-directed behaviours and behaviours apparently related to escape or seeking social information. Pathophysiological evidence was consistent with Baenninger's (1967) suggestion that tail manipulation in singletons is a surrogate social response, but was also consistent with an overall increase in self-directed activity, reflecting elasticity in time budgeting. Variation in the degree of increase in self-directed activity among singletons and the negative correlation between self-directed activity and organ pathology may have reflected differences in the ability of individuals to avoid an activity limbo. While reduced corticosterone concentration and organ pathology compared with grouped rats implied that separation may remove social stress, responses to contact with neighbours, and correlations between behaviours and organ pathology suggested that rats may actively seek social interaction. Broad differences in stress responses between single and grouped housing conditions may therefore be an inadequate yardstick to the animals’ welfare. However, exposure to neighbours reduced the aggressiveness of singly-housed males when they were eventually introduced into an unfamiliar group, suggesting that a degree of exposure to neighbours (separation, but not isolation) may have some welfare benefits for laboratory-housed rats, depending on procedures.