I do not know what you have done up until this point for your ferrets, but
having had experience with intestinal blockage AND symptoms that looked
like intestinal blockage but weren't I would give you these suggestions.
 
First of all if all three ferrets have had this problem ongoing for a long
period of time I wouldn't rush to surgery.
 
Our Meep has gone through what sounds like blockage symptoms - thinner
stools (sometimes runny), weight loss, etc causing him to lose weight
over time.  Two different vets gave up on ideas and simply placed him on
Amoxicillin (?sp) for 10 days.  Each time, whatever it was went away and
he went back to "normal"
 
Our Daisy on the other hand has a real liking for the taste of rubber and
it is a constant battle with trying to keep her away from such things.
Unfortunately she has had intestinal blockage despite our best efforts.
Symptoms included lethargy, thin to non-existent poops (but she never
experienced diarrhea), and vomiting leading to dehydration.  Regular x-rays
do not show most things that cause a blockage in ferrets, but the barium
x-rays did.  I would certainly go the barium x-ray route with your ferrets
before agreeing to surgery, though if they truly have a blockage that may
be what you'll have to do.
 
A lot of foods can cause diarrhea in ferrets - too much fruit or food that
doesn't quite agree with them.  Take a good look at their treats and see if
you think anything is causing these problems.
 
Also......since you have three experiencing these symptoms, I would start
with the ferret who seems to be the worst.  If the vet gets in there and
finds nothing you know that the other two probably don't have a blockage
either.
 
I know it must be frustrating for you - and wish you the best with them all.
 
Karla
[Posted in FML issue 2925]