Horses shake their heads for various reasons, but some horses shake their heads so much they cannot be ridden and these horses may have headshaking syndrome. That is a condition in which the horse shakes or flips the head uncontrollably without any apparent stimulus or reason. Dr. John Madigan from the University of California Davis indicates that the syndrome has been reported worldwide and it is believed by many to be related to abnormal function of the trigeminal nerve. The trigeminal nerve provides sensory function to the horse's facial area. It is believed pain from this nerve causes burning, tingling, itching or electric-like sensations on the horse's face, which causes the horse to shake or flip the head. This has been proven in a number of horses by blocking or numbing the nerve and noting a decrease or elimination of headshaking while the nerve is blocked.

Because the nerve block works, a surgical procedure of cutting the nerve should be successful in eliminating headshaking but it is only effective in about 30% of the horses, and some actually have more headshaking after the surgery. One group of horses is called photic headshakers as they only shake their heads when out in bright sunlight. Exercise is another factor that affects headshaking as 50% of headshakers only do so when exercised. If your horse is diagnosed with headshaking, an exam is important to rule out any medical problems such as dental disease or sinus infection. Possible treatments for headshaking include nose masks and covers, magnesium supplementation, melatonin supplementation, cyproheptadine treatment, or various combinations of all these.