It could be the result of boredom. This is normally seen when horses are stalled for long periods of time or when they do not have adequate grazing available in paddocks. However, it is more likely due to a lack of fiber intake, which reduces the scratch effect in the horse’s hindgut. The horse’s gastrointestinal (GI) tract contains a microbial population located in the cecum of the large intestines. The microbes, bacteria, protozoa, and fungi produce an enzyme cellulase that digests fiber. In normal feeding situations, the enzyme consumes higher quality (immature forage) fiber that causes increased microbial activity in the cecum and digestion. However, if a low amount of fiber reaches the cecum, the microbes are less active, and gut motility decreases throughout the horse’s GI tract. The horses will attempt to consume additional fiber (wood, hair, and sometimes dirt) to restore normal GI tract motility. Feeding at 1.5% to 1.75% of body weight with a long-stem fiber, such as alfalfa, other legumes, and certain grasses, will normally prevent wood chewing. Finer stem forages, such as coastal bermudagrass, may have to be fed at higher intake levels to eliminate wood chewing.