Thanks for your reply. Where would I get custom-made minerals? I had thought of that, but the thought of having to find every separate mineral my horse needed to balance the hay ration and mixing it was just way too time-consuming. I had managed to get magnesium, selenium, and Vitamin E, but having to get phosphorus, chromium, and other things in order to balance the minerals correctly seemed a recipe for a nightmare, as well as expensive. That's why I was so glad to find at least one or two supplements that seemed to have just about everything for the IR/Cushings horse. If my hay analysis then indicated I needed more magnesium or other mineral, I could buy that separately and add it in.

But it sounds like you have found an easier way to do the custom mix (and with the extreme cost of these supplements, I would be glad to hear it!)