Grass Founder

I just found out that my boarding stable has been offering my horse a complimentary turn out service while I am at work all day. They started turning the horses out on very lush pasture for up to 12 hours a day. He has been turned out a few days in a row now with a LOT of grazing time. At the barn I used to keep him at, he never got any grass, only hay. He's a 16 hand TB, healthy weight with no history of founder. But, like any worried horse mom I kind of freaked out when I found out he's been grazing so much while I am at work. What are the chances he can founder? What should I look for? Thanks!

How nice of them......Yes it's highly possible for horse's to founder from just throwing them out on rich grass. Keep a close eye and I would be checking for a digital pulse daily.

Hope you've had a stern word with the people at the barn. I would be looking for other accommodations myself .

Yes, definitely have a word with them.

They told me that they thought it would be nice for the horses to get out, but they never notified me before hand. I found out from another boarder that they do this every year, and they use the grass as a replacement for hay to save on hay. This is not okay IMO.

Is there anything I can do? What should I look for? I don't know the signs of founder, besides lameness. Does it come on immediately, or could it show up a few days/weeks later? He seems fine to me right now. Do you think he's in the clear, or should I do something? Worried....

Acute laminitis generally shows up about 72 hours after the initial cause. Lots of walking exercise in the interim is the best thing to do to ward off the worst of the pain, as walking will help the horse metabolize what's going to cause the problem. If you are pretty sure he's in for a bad bout, have him trimmed BEFORE the pain sets in, as ANY excess wall will work against him when the inflammation hits.
Signs include noticeable heat in the hooves, BOUNDING pulse, and stance where the horse puts all his weight on his hind legs and is reluctant to walk or walks as if on eggshells.
Cold therapy can help minimize damage, don't make him move during this time (the acute pain stage lasts about 72 more hours). Let him lay down if he wants, and only give him hay to eat. Some people like to give Bute or something for pain, but in this case, the pain keeps him from doing more damage to his hooves, so letting him ride it out may actually prevent more suffering in the long haul, but that's for you to decide. If he has shoes, pull them now! Keep him quiet until the acute phase has passed. Once he's comfortable in a couple of days, start handwalking him and letting him exercise in a dry lot. Don't make sharp turns (that tears up the damaged lamina). May need a trim in a couple more weeks. Build up to more exercise and keep him on short trim schedule (every 2-4 weeks instead of the usual 6-8 )
If in a few days he shows no lameness or heat, he probably made it through alright, but I'd sure be upset that they just tossed my horse out like that, when they should KNOW BETTER!!