Glad things are improving, and hope you can find a way to get him to eat the proper food. Nutrical can be misused, can lessen their appetite and cause rebound hypoglycemia, and should be balanced with protein when it is used. Have you tried giving him finely diced boiled chicken breast? I've never met a dog that would refuse that.
This old thread is very educational:
http://www.yorkietalk.com/forums/yor...ly-dosage.html
FYI, last I heard the protocol for fasting before bile acid testing was changed, and fasting is not necessary. Again I reference a thread discussing it:
http://www.yorkietalk.com/forums/sic...-required.html
By the way, thank you YorkieTalk members who have taught me almost everything I know about Yorkies health, and who are always there to help.