My mare had a colic operation 2 years ago, she stayed in the hospital for ten days and she was fed with mash and hay. When she came back home she was on a liquid diet and continued in that for months
I would ask your vet. That would be the safest option, every horse is differant!
My horse was in the hospital in intensive care for 2 weeks, after a week he was eating wet hay and when we got him home he went staight on to dry hay (rationned)