Wood chewing and crib biting (also called cribbing) are common undesirable horse behaviors. These behaviors are usually associated with a problem in the environment. A group of vets from the University of Bristol in England indicated in Equine Vet Journal that in horses at pasture these conditions may be related to a diet low in fiber or other nutrients. Wood chewing was shown to be related to diets consisting of concentrates only as compared to those fed only hay. Wood eating is observed to a lesser extent in horses at pasture but it tends to happen on fences and trees during the spring when the sugar content of the pasture is high and fiber content is low. Also, some believe wood chewing can lead to cribbing, in which the horse grabs a solid object and pulls back with the front teeth while sucking in air; that is sometimes called wind sucking. Cribbing is also associated with low-forage and high-fat diets. Increased fiber intake increases chewing, and the horse chews, the more saliva that is produced. Horses that produce more saliva by being fed more hay have been shown to crib less than horses fed complete pelleted feeds. The increased saliva also increases the pH of the stomach and decreases the chance of stomach ulcers and subsequent colic. Since horses that crib are known to have an increased incidence of colic, this could be part of the reason.
Although these unwanted behaviors are not this simple in many cases, it is obvious that enabling horses to show normal behavior by interacting socially with other horses and increasing their time spent grazing is likely to aid in decreasing wood chewing and cribbing. Decreasing pelleted feed, increasing hay, and allowing the horse out with other horses is a good start.