Be sure to catch this taurine discussion
http://www.smartgroups.com/message/viewdiscussion.cfm?gid=1423922
&messageid=4011
 
There are other nutrition discussions there and in the FHL Archives at
http://fhl.sonic-weasel.org/
(See especially ones with the name "Willard" attached.)
and in the FML Archives
http://listserv.cuny.edu/archives/ferret-search.html
and in the Performance Foods (Totally Ferret) site (Find it through
http://www.google.com .)
and other places as links in http://www.ferretcongress.org .
as well as others, I'm sure.
 
You will find that Dr. Tom Willard whose doctorate is in animal nutrition
is very happy to help people to understand the particulars.  He even once
helped us design a special diet for a ferret who could not have
pre-prepared foods due to an unusual health need.
[Posted in FML issue 4124]