Petra,
There are some things that could cause male ferrets, neutered young, to start
showing male intact behavior suddenly.
The most common cause of this in my experience are adrenal tumors that are
releasing hormones.  The ferrets I've seen with these symptoms usually don't
have hairloss until late in the disease process (if you look closely you may
see hair thinning between the shoulder blades oron the rear feet).  There is
now a new (and expensive) blood test to diagnose adrenal tumors in ferrets.
Other potential causes include retained testicles (one or two testicles that
never came down into the scrotum, and are still in the abdomen).  To diagnose
this we generally have to do exploratory surgery.  Once the testicles are
removed the symptoms will subside.
Changes like this could also be behavioral, but in my experience this is not
very common.
Since both ferrets are showing these behavioral changes at the same time one
could have one of the problems I discussed and the other is copying the
behavior or they both could have concurrent problems or it could be
behavioral.
To tell if it is purely a behavioral problem you would probably have to
seperate them and introduce them to other ferrets and see if the behavior
persists.
 
Dr Weiss
301-299-4142
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[Posted in FML issue 1194]