HOUSING AND WELFARE IN LABORATORY RATS - WELFARE IMPLICATIONS OF ISOLATION AND SOCIAL CONTACT AMONG CAGED MALES

Male laboratory rats (Rattus norvegicus; Wistar, Alderley Park) were h oused as singletons or groups of three in units of two joined, but div ided cages. Units were divided by different types of barrier that allo wed 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. Rel ative to group-housed animals, singly-housed rats showed reduced activ ity and a greater incidence of self-directed behaviours and behaviours apparently related to escape or seeking social information. Pathophys iological evidence was consistent with Baenninger's (1967) suggestion that tail manipulation in singletons is a surrogate social response, b ut was also consistent with an overall increase in self-directed activ ity, reflecting elasticity in time budgeting. Variation in the degree of increase in self-directed activity among singletons and the negativ e correlation between self-directed activity and organ pathology may h ave reflected differences in the ability of individuals to avoid an ac tivity limbo. While reduced corticosterone concentration and organ pat hology compared with grouped rats implied that separation may remove s ocial stress, responses to contact with neighbours, and correlations b etween behaviours and organ pathology suggested that rats may actively seek social interaction. Broad differences in stress responses betwee n single and grouped housing conditions may therefore be an inadequate yardstick to-the animals' welfare. However, exposure to neighbours re duced the aggressiveness of singly-housed males when they were eventua lly introduced into an unfamiliar group, suggesting that a degree of e xposure to neighbours (separation, but not isolation) may have some we lfare benefits for laboratory-housed rats, depending on procedures.