Social play in juvenile mice is a sensitive indicator of welfare and early life experience, with deprivation of play opportunities causing lasting behavioral and neurological changes.
Social play is not a trivial luxury for juvenile mice but a developmental necessity with lasting consequences when denied. Mice isolated during the juvenile period show impaired social recognition, increased anxiety, altered stress hormone responses, and reduced play behavior even after being housed with others. These are not minor behavioral differences but fundamental alterations in the neural and behavioral systems shaped by early social experience. Laboratory mice housed individually from weaning, which is standard practice in many facilities, are denied the developmental experiences that shape normal social competence. The welfare cost of this deprivation persists throughout the animal life and undermines both welfare and scientific validity in studies of social and stress behavior.