I hate to say this, but you may need to consider intestinal lymphoma.
Sounds like you've tried a number of different idea, and so far none
is working. How long has he had the diarrhea for? If its been awhile,
I would consider looking into more aggressive treatment, as his
intestines could be really inflamed and irritated if it has been going
on for awhile now.

I would give the vet who told you the warning about Pred another shot.
She is right, if Pred is used now, it may not work when needed later.

You may want to consider an ultrasound... but make sure it is a really
high quality US machine. Like try at a college or university ferret vet
dept. My boy Gus has intestinal lymphoma, and like you, I had tried
everything. My vet had suggested an exploratory/biopsy surgery, but
I was so hesitant about that. He did the ultrasound, which showed
enlarged lymphnodes, inflamed intestines, and couple of spots on Gus'
spleen, which led my vet to believe we were dealing w/ intestinal
lymphoma, so I went ahead w/ the surgery.

Good thing, as once he was diagnosed positively, unfortunately
lymphoma, he was then started on the proper chemo med. Cleared up his
diarrhea w/in a couple of days.

My vet is an expert-to-the-hilt, and he says that all these probiotics
and whatnot is not needed. If the ferret's poops are off - something
is going on and a biopsy (considering of course you've done all the
non-invasive tests: fecals, etc) is the best way to find out
definitively what you are dealing w/ so the ferret can get proper
treatment.

Good luck w/ Minky.
Andrea

[Posted in FML 6757]