Quite a charming report here with mouse information that's news to me:
Although medical science’s favourite critters relish temperatures of a little over 30°C, laboratories routinely keep them at five or ten degrees below that. This is not in order to torture the beasts but, rather, because when kept warm they are unmanageably aggressive. The downside is that they have to eat more than they otherwise would, in order to keep their bodies warm. That changes their physiology. And that in turn alters the way they metabolise drugs, with possibly confusing results.
The report then notes a study suggesting that labs don't have to increase temperatures to get them responding better to drugs; they just have to provide them with paper with which to build nests.