Im so sorry to hear of your plight--we bought a rundown house w land that we are fixing up--it has a gorgeous yard that wraps around under enormous sugar maples that i envisioned my beloved old mare would enjoy grazing under when she retired. Well, she was diagnosed IR two years ago and will never be able to eat grass. She is, however, perfectly content in her drylot, out moseying around 24/7, still has a nice tree to stand under. The kicker? The young horse i bought as her replacement is also IR. He also is very happy in his drylot and "grazes" on the Ontario Dehy Timothy Balance hay cubes that the barn staff painstakingly scatter around his paddock each day. Horses dont need grass to be happy. Both of mine are very sound & healthy (even my 21yo mare) thanks to the recomendations given here. Both love going out on trail rides and the old mare still loves nothing more than a jumper show or hunter pace. As long as they get exercise and daily attention from you, they will be fine w/o grass. What horses crave even more than grass is companionship.
You'll get through this. It will be tough, yes, but so are horses' spirits. As long as you keep looking forward, so will your mare. I had a terrible autumn with my mare last year but pulled through and shes sounder than shes ever been. You can do it.
Others will chime in soon with more detailed advice but dont despair about the grass--horses can & do live just fine w/o it. Its more in *our* heads to feel sorrow when horses are denied access. They quickly forget with good hay avail, creative toys(Nose It balls) & other enrichment, and lots of love & attention from you.
You'll get through this. Many have!
Kerry in NY
Pinky 21yo IR/PPID
Tofurky 8yo IR