Your farm takes the brunt of this nasty behavior issue. There are 2 things that come to mind when I hear this term: Boredom and Nutrition. Horses in the wild tend to chew not only to wear down their ever-erupting teeth, but also to replace vitamins and minerals they may be lacking. By examining the diet of the horse you may be able to pinpoint where a deficiency exists. Looking into the amount of fiber and quality of forage your horse is ingesting may aid as a remedy for this behavior. The second reason is boredom. Horses who spend great lengths of time in confines will often entertain themselves – usually in obnoxious ways such as cribbing. Horses are animals which need mental stimulation to keep them honest. Usually this is in the form of work, turn-out, or some type of ground work where attention and respect are expected. If the horse is not receiving the stimulation needed to satisfy his/her mental needs cribbing becomes an instant remedy. By increasing turnout, or offering time outside of the stall in some fashion, the mental confines change interrupting the mental staleness. Although both of these approaches to the issue may be a bit time consuming they may give a great look into the real issue.