Why did my horse start grinding its teeth?

Teeth grinding in horses — the audible grinding or crunching of the teeth distinct from the normal sounds of chewing — should always be taken seriously as a potential indicator of physical discomfort rather than dismissed as a habit or a nervous quirk. Its appearance as a new behavior in a horse that was not previously grinding is most commonly a signal that something physical is causing genuine discomfort and that an investigation is warranted. Gastric ulcers are the most commonly identified physical cause of teeth grinding in horses, and the association between the two is well established. Any horse presenting with new-onset teeth grinding should have gastric ulcers high on the differential list regardless of the horse's management situation or apparent overall health. Ulcers cause a burning acidic pain that worsens when the stomach is empty and that many horses express through behaviors including teeth grinding, girthiness, reluctance to work, and poor performance. A veterinary examination including gastroscopy is the only definitive way to diagnose ulcers. Dental pain is the second major physical cause. Sharp points, hooks, uneven wear, loose teeth, or other dental abnormalities that cause pain when the horse closes his jaw can produce grinding as the horse attempts to avoid the painful contact or shift his jaw to a more comfortable position. A thorough dental examination by a veterinarian or qualified equine dental technician, including examination of the back teeth not visible without proper instrumentation, is the appropriate evaluation when dental pain is suspected. Pain elsewhere in the body can also produce teeth grinding as a general stress response to discomfort — back pain, joint pain, and other sources of chronic discomfort can manifest as teeth grinding in horses that express pain through oral behaviors. If gastric ulcers and dental pain have been ruled out and the grinding persists, a broader physical examination is the appropriate next step. Anxiety and psychological stress can produce teeth grinding in some horses without an underlying physical cause, but this should be a diagnosis of exclusion arrived at after physical causes have been investigated rather than an assumption made because the horse appears otherwise healthy.