Short communication: rat's demand for group size.

Social isolation compromises the welfare of rats. However, it is not clear how many rats should be housed together under laboratory conditions. Pair housing, sometimes recommended over group housing, may help avoid aggression and disease transmission. Female rats, however, showed the highest average demand for a group size of 6 (versus 1, 2, 4, and 12) when stocking density was maintained at 20 cm2/rat. This finding contributes to work suggesting that rats should be group housed. This article shows that further studies are required into the actual risks of disease and injury associated with group versus pair housing.