At a well managed barn they will do what poppy said, start out at an hour a day for a few days, increase to 2 hours a day for a few days, and so on, it slowly accustoms their digestive system to the grass instead of just tossing them out one day when someone decides the grass is ready, which is what causes founder and colic and a lot of diarrhea. Yes it can be tricky getting horses rounded back up after only an hour or 2 out on grass, but it is best for them. I also wouldn't suggest every other day, to me you'd be delaying his transition and confusing his gut, as well as frustrating him from being in a stall all day one day and out the next.
Have you talked to the new barn manager about how he handles turnout on spring grass? He may already have a plan in place for that, most do, and you can explain your concerns about your horses sensitivity to rich spring grass and his past history of colic, he may even be able to monitor your horse while hes turned out to make sure he doesn't colic during that transition period.
Thanks! They are on the same pasture all year so as it grows in they get used to it right? My old barn would just switch pastures and the one they would go on is really green while the other grows back..
I asked about colic and have they ever had a horse die, he said in the three years he has been there two horses have died but they were both from old age, being 30+ years old, and were part of the therapy program.