I agree with Liz(nootka). Although I do suspect that lack of mental stimulation may be a factor in true cribbing, I think it is a great oversimplification to suggest that it is due'merely' to being stalled. That said-- I definitely do NOT like, and never have liked, to keep horses 'up' in stalls unless absolutely necessary. My 'at-the-barn' horses, too, are VERY seldom confined to their(roomy-12' square)stalls; they do spend most of their time in roomy runs, as there is very scant and seldom-available grazing opportunity here. I have a miniature gelding, born and raised here, who is a confirmed cribber(sucks wind.) I have tried the Weaver collar, and it does prevent him from cribbing, if adjusted properly(meaning very snug), but also tends to rub him after awhile- I seldom if ever put it on him. He has never had any health issues-never. I HAVE spent some time setting his living area up to minimize his opportunities to crib successfully-closeweave wire lines the panel fencing of his run, his feeder is a shallow trough, which isn't heavy enough not to just 'move' if he tries to crib on it, etc. He still cribs, but not very efficiently. Other than having worn his upper incisors off a bit at an angle, before I managed to limit his access, he shows no ill effects, and enjoys very good health. In college, I got a little 'catty' QH gelding, who'd been trained for cutting, that I trained for and was very successful running barrels and poles on-he was a cribber, and it never affected him in any manner, healthwise.
It is my belief that cribbing usually bothers the owner more than the horse. I also do not think horses are likely to "learn" it from other horses; I do believe that there are horses whose personalities/dispositions predispose them to begin to crib--especially horses who are 'busy', that is, are always 'looking for' something to do. One thing I did in the years since the aforementioned miniature gelding, now 10 years old, was raised, was to provide LOTS of variety of 'toys' within the enclosure of young stock, especially those who seemed to have that 'busy' personality. I hung a length of thick cotton rope from the fence, I put in Jolly balls, flexible rubber tubs, plastic corn oil jugs with a few rocks inside, etc., etc.-fed as much hay as I could safely provide- and also made an effort to give even more arena turnout time. I do believe that this effort to provide more of these kinds of possibilities *MIGHT* help keep a horse with a susceptible personality from starting to crib-it is certainly true that one does not 'cure' a confirmed cribber.
Wood chewing(which is NOT cribbing, by definition) is largely a result of how most modern horses live, and, I believe, is mostly from boredom. Wood is more or less 'edible'; horses are 'made' to want to eat most of the hours in a day, and,especially under confinement, are likely to seek to satisfy the urge to 'graze'...I have one little gelding who is a food hound, yet does not bother two wooden posts within his enclosure, whereas all the others would happily gnaw down any unprotected wood(of which there is virtually none here, for that very reason!)--go figure! I presume that EVERY horse is apt to be a wood chewer, and have built accordingly. I wouldn't necessarily 'go looking' for a cribber, but am not at ALL concerned about 'having one on the place', as I think in most cases it just isn't that big an issue.There will always be the occasional horse so obcessive that it would rather crib than eat, and that would be a problem, but otherswise, I'm just not that concerned about it. I believe it *MIGHT* be helpful to set up a horse's living quarters to minimize its opportunity to crib 'effieciently', but wouldn't 'worry about it', otherwise.