Frank wrote:
I forgot to mention...Dr. Eleanor Kellon is the expert on Cushings and IR http://www.drkellon.com/consultations.html , and there is a "Cushing's and Insulin Resistance Group" on Yahoo that you can join for information and support.

THIS THIS THIS THIS THIS!!!!

Get in touch with Dr. Kellon or join that list.  They'll step you through all of it.  I'd say at least 90% of vets don't know how to deal with metabolic issues just like they really aren't trained in nutrition. 

My mare isn't IR nor does she have metabilic issues currently.  BUT she is an easy keeper so I manage her as if she were IR but with treats, lol.  She wears a muzzle, gets grass pellets and ration balancer only and does fine. 

Good luck.  SEriously though, go with Dr. Kellon.  She's the best there is and most of the people on the Equine Cushings yahoo list are quick to help.