Re: IR Mare
Eleanor Kellon, VMD
There are a lot of issues to sort through here and I hope you can get a formal history up soon because that will help.
In the meantime, at her age I would always be suspicious of a potential component of PPID in poor IR control, regardless of the ACTH (which I assume came from Cornell???).
As you seem to already realize, there are multiple areas where her diet could be tightened up. There's really no getting around that.
It is well documented that dexamethasone induces insulin resistance in all species, including horses. Even topical dex can do this. It is also well documented that elevated insulin will cause laminitis. What hasn't been done experimentally, and I'm sure won't, is to deliberately give dexamethasone to IR horses to see if they are more likely to develop laminitis than non-IR horses on dex. The closest thing to this is many observations of laminitis after dex suppression tests or injection of arthritic joints. There is also enough of a problem that manufacturers are required to put a warning on their package inserts. It's really several cuts above an isolated anecdote.
Instead of dexamethasone you could consider trying her on clenbuterol or albuterol which are actually beneficial for IR. Another option is Lung EQ:
Search results for: 'lung eq' - Uckele Health & Nutrition
Eleanor in PA