We assessed the value of sleep behaviour as a novel measure of stress in group-housed animals. We observed, non-invasively, sleep behaviour in 144 group-housed rats, and related it to other physiological and physical indicators of stress and welfare. Sleep frequency and duration correlated
negatively with adrenal weight, and positively with bodyweight gain, and final bodyweight. Thus, low frequencies of sleep behaviour and low sleep duration correlate with some indicators of elevated physiological and physical stress, raising the possibility that sleep behaviour may provide
an under-utilised, but potentially important, non-invasive indicator of stress and welfare for animals in groups.