Hi Debbie,
Shampooing them about every 2-3 months is probably good unless they really
need it for some reason.  What I have found is that their fur, like our
hair, tends to "absorb" odor.  By washing their bedding on a weekly basis,
and not keeping a dirty litterbox in their cage it will go a long way
toward keeping them smelling pleasant.  Their natural oils are very
pleasant smelling, so usually unless they have gotten into something
smelly or really messy they usually do better with minimal bathing.
 
Give them a hug for me!
Karla
Daisy, and our "angel" Meep
[Posted in FML issue 3617]