Mice in a particular experiment tend to be housed in the same room or same rack, with enough circulation in the room to hopefully assure a homogeneous temperatu

Mice in a particular experiment tend to be housed in the same room or same rack, with enough circulation in the room to hopefully assure a homogeneous temperature in the room. Therefore, the control animals were likely right next to treatment animals. In this way, one could reasonably say that variations between the groups is not due to the way they were housed. Many other things that are controlled in housing include their feed, bedding, access to water, number of animals in a cage, etc.