There are multiple types of uroliths.  They arise for different reasons.
Yes, there are also ones caused by too much vegetable matter and also
affect the urine pH differently.  In fact, those struvite stones have
been the more common form of stones in ferrets.  Here's are some articles
on them:
http://www.vin.com/VINDBPub/SearchPB/Proceedings/PR05000/PR00299.htm
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?
cmd=Retrieve&db=PubMed&list_uids=3451569&dopt=Abstract
 
Now, cystine stones are increasing found in testing labs.  The rate
change is intriguing and while the postulation seems quite clear it
always pays to do the actual research to get a handle on a problem.
When that can be done for an emerging problem before it has a chance to
become common so much the better because that is the best way to help.
 
That help explain it?  I didn't realize there was more than one type of
urolith in ferrets, either, till we wound up with two having them.  What
a way to learn!  It's late again so rather than read or even skim some
resources for you I'm going to pull up some by a recognized expert even
if the animal type is wrong because the general info will be there.
 
Here's something on Cystine stones:
http://w3.vet.upenn.edu/research/centers/penngen/research/
cystinuria_update.html
and here are struvite stones and on calcium stones for you:
http://www.vin.com/VINDBPub/SearchPB/Proceedings/PR05000/PR00125.htm
Here are photos of a range of kidney stone types including a struvite
one from a ferret (Notice the large range of types and each is going
to have it's one way of forming in whatever gets it.):
http://www.herringlab.com/photos/
 
Anyway, you can see why it is so essential that the stones themselves be
analyzed.  Different approaches are needed to prevent a repetition of
each type.  What works for one stone type is not going to be the right
corrective measure for some other types, in fact, when it comes to
adjusting urine pH some stone types happen more with alkaline urine and
others happen more with acidic urine so if the urine pH is manipulated
without knowing what type of stone is present but the guess is wrong...
(Moral: also test urine pH when stones occur!)
 
USDA list of renal and urinary pubs on ferrets (including Dr. Dutton's
cystine stone article):
http://www.nal.usda.gov/awic/pubs/ferrets/renal.htm
 
The new study on cystine stones (cystine uroliths) in ferrets is being
coordinated by
Dr. Michelle Hawkins VMD DABVP (Avian) who your vets can reached at:
2108 Tupper Hall, University of CA, Davis, CA 95616
1-530-752-1363 (phone)
[log in to unmask]
 
Please, let your ferret vets know about this new study and give them
that contact information in case they run into a ferret or are treating
a ferret or ferrets who have or have had cystine urolith problems.
 
--Sukie, not a vet and learning about all sorts of things as I go along
(even Bubba Ho-Tep)
http://www.vin.com/VINDBPub/SearchPB/Proceedings/PR05000/PR00298.htm
http://www.vetsoftware.com/acvc2002-hess2.htm
http://www.bubbahotep.com/
http://www.retrofuture.com/
http://www.eweek.com/article2/0,1759,1749948,00.asp?kc=EWRSS03119TX1K0000594
http://www.apple.com/macmini/design.html and
http://www.apple.com/ipodshuffle/
http://www.betterhumans.com/News/news.aspx?articleID=2005-01-11-3
[Posted in FML issue 4756]