A key question in the management of group-housed captive animals is how long can an individual be removed from a social group and still be reintroduced with minimal social upheaval. In order to answer this question we require a knowledge of how long cage-mates, following a specified period of group-housing, can remember one another after separation. This issue was investigated in laboratory rats (Rattus norvegicus). Rats were group-housed for 18 days before being housed individually. One hour, 48 hr, and 96 hr after separation, they were exposed simultaneously to odour cues originating from unfamiliar rats and from former cage-mates. The rats spent significantly more time investigating the unfamiliar odour 1 hr and 48 hr, but not 96 hr, after separation, suggesting that, after 18 days of group-housing, juvenile rats remember former cage-mates for between 48 and 96 hr. The implications of this result for animal welfare are discussed.
