Housing and welfare in laboratory rats: effects of cage stocking density and behavioural predictors of welfare

Using male and female Alderley Park (Wistar-derived) rats housed in single- sex groups in standard laboratory cages, we looked at the effect of group s ize (one, three, five or eight) on competitive behaviour and time budgeting (initial and longer term), changes in their serum testosterone (males), co rticosterone and antibody concentrations, and organ pathology at age 16 wee ks, together with the interrelationships between behavioural measures and p athophysiological indices of social stress. Group size had only limited lon g-term effects on overall time budgeting and did not affect pathophysiologi cal responses, although there were highly significant differences between i ndividuals in replicate cage groups. Pathophysiology within both sexes show ed strong and highly specific correlations with a small subset of behaviour s suggesting frustrated attempts to escape from cages, including chewing th e cage bars. Escape-related behaviour also correlated strongly with one com ponent of competitive behaviour, Aggressive Grooming within both sexes, alt hough Aggressive Grooming correlated with pathophysiological responses only among males. Females generally showed greater escape-related behaviour ass ociated with greater signs of pathophysiology regardless of the level of ag gression shown between cagemates. Major differences in intercorrelated beha vioural and pathophysiological responses between replicate groups implied t hat the individual composition of groups rather than their size had the gre ater impact on the welfare of the rats, especially among females. This may be consistent with adaptive sex differences in their competitive reproducti ve strategies. The frequency of apparent escape-related behaviours and Aggr essive Grooming, particularly when rats are first introduced into their cag e groups, may provide a simple assessment of the welfare implications of pa rticular cage groupings. (C) 1999 The Association for the Study of Animal B ehaviour.