We rescue and rehab a lot of horses and quite a few of them have foundered.
This horse is one of my favourites, he is a well into his 20s, connemara and you could not get a bigger clown.
He had spent a lifetime with terrible laminitis verging on founder before coming to us in 2010. Previously he could barely walk and certainly didn't bounce around.
Since we completely changed his diet - he is in fields of long DRY grass NO CLOVER and he is barefoot (his hooves are terrific thanks to great quality mineral supplements), we have not had any problems. We keep a close eye on all our horses of course, and if the weather changes and the grass flushes green, we know to get Danny off the paddock (we have a dirt track where they live on hay)until the intense growth is past.
Anyhow, this is him being an idiot with my equally 'aged' stock horse Persil, over summer last year - must get some more this year!
What I mean to say is it is all about management, but if the diet is well managed and the horses are BAREFOOT, there should be no problem.
Also make sure they get plenty of salt added to the feed especially in spring and autumn!!! (This balances the potassium overload present in green growing grass!)