After reading the question Have any animals that have been studied onboard the ISS come back alive?, my first thought was this: what about the ones that don't live?
It would seem that this wouldn't be an uncommon occurrence at least at first - humans don't do very well in microgravity, and animals even more so.
Obviously, one wouldn't want deceased animals floating around the station. Are these unlucky critters sent back with normal trash, or in a different way?