I've used echinacea with ferrets.  It should not be given when the immune
system is hyperactive.  It also should only be given for a maximun of 2
weeks then off for at least a week.  Vitamin C is also a very good immune
system booster though if given too much it can cause diarrhea in humans
and ferrets so start with a small amount.  Ester C is easier on tummies
and liquid is easier to dose.
 
For colds, Sambucol works well.
 
I've found a very reasonably priced site that has a very large selection
of natural therapies -
www.vitamin-resource.com
 
Hugs to all. tle
Troy Lynn Eckart
Ferret Family Services
http://www-personal.ksu.edu/~sprite/ffs.html
http://www.geocities.com/Petsburgh/Haven/5481/
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[Posted in FML issue 3531]