Complex sentence: Bumblefoot in rodents is caused by wire and mesh flooring and/or wheels, the only exception is in gerbils which have tougher feet and can safely walk on mesh and wire.
Split into simpler sentences: Bumblefoot in rodents is caused by wire and mesh flooring and/or wheels. The only rodent not affected is the gerbil, which has tougher feet and can safely walk on mesh and wire.