I am not an expert, and I bet some vets will write in with the same
response.
 
An antigen is not the same thing as an allergen, the later of which causes
and allergy.  An allergen is distinct in that is is not an infective agent,
i.e. a parasitic bacteria, but something in the environment that the body
THINKS is an infective agent.  The allergic response is very similar to a
response to an infection, because the body thinks it must send out immune
defenses for something innocuous, in my case, cat hair.
 
Antigens INCLUDE allergens, but also include anything else that causes an
appropriate immune response in the body, such as bacteria, viruses, etc.
When the vet report says "undetermined antigen," that may or may not be an
allergen.  It is possible that an allergen in your ferrets diet/environment
is causing the ulcers, but I think it is just as likely that an infection
(bacterial?) is causing the problem.  Dr. Williams has some great info in
the ferret FAQ at Ferret Central, esp.  about ulcers and the heliobacter
bacteria.
 
And if it is an infection, antibiotics along with a soothing and coating
medicine (I've used carafate) should help.
 
Good luck.
 
Lori,
Squeegy, "I had ulcers from ECE and boy does that medicine taste AWFUL."
Hoover, "My stomach is like a rock.  I never caught ECE."
 
P.S.  Esp. to Melissa L. and Lynn M.
Thank you again for your kind words and advice.  I am happy to report
that Squeegy is well recovered form, 2-mo. ECE-triggered illness.  His
weight is good, his dookie is normal (not even seedy), and his spirit is
as bright as ever.  His brothers are happy to have the old Squeegy back.
[Posted in FML issue 1803]