The symptoms of blowing through the nostrils (snorting), rubbing the nose muzzle and face, flipping or shaking the head up and down or side to side or rotational, can be associated with ear mites, eye problems, nasal and ocular mucous membrane, irritation from allergens or irritants, sinus cavity irritation or infection, dental problems including tooth roots residing in the sinus cavity, and the head shaking syndrome.
Idiopathic head shaking, which includes flipping the head and others of the above listed symptoms, occurs in the absence of tack and rider. This syndrome can be associated with photic (light) stimulus. The trigeminal nerve giving rise to other facial nerves has been shown to have a heightened firing potential. This trigger is compared to photic stimulated sneezing in people. The headshaking symptoms are commonly experienced on a seasonal basis as the days lengthen. Some of these horses have been found seeking shade for relief. Insect controls may or may not help.
According to the John Madigan, Stephanie Bell study reported at the 1997 AAEP meeting, they found a majority of the cases have a seasonal component.
Some of the tools bringing relief include nose nets, which can cause panic and local skin irritation, face masks blocking UV radiation, which can be associated with reduced vision and stumbling, and magnesium supplementation which can be overdosed while more readily absorbed with high forage diets.
According to a study by John Madigan, Kirstie Pickles and others, reported at the 2014 AAEP meeting, the trigeminal nerve giving rise to the facial nerve has a decreased threshold for firing in these horses. However, no structural abnormalities of the nerve have been detected. In the 1997 and 2014 studies, cyproheptadine is a pharmacologic tool used with significant success. Cyproheptadine is an antihistamine, seratonergic blocking agent, and anticholinergic.
Possible adverse side effects associated with cyproheptadine’s use include lethargy, drowsiness, incoordination and colic. Other pharmacologic tools include melatonin. A 5pm daily dose beginning before the days lengthen in spring may be keeping the horse’s biologic clock in winter, thus a significant portion of these horses will not shed their winter coats properly. Additionally, melatonin use can negatively influence sex steroid (hormone) production.
Some horses have responded favorably to melatonin use by diminished headshaking apart from the prior to spring protocol. The scientists in this study theorize that melatonin’s effect on pain modulation reducing it through multiple mechanisms. A double blind study of pulsed high dose dexamethasone (corticosteroid) therapy showed no effect on idiopathic headshaking. However, the report given in 2014 revealed some benefit associated with corticosteroid administration. Long term and high dose corticosteroid use has potential negative side effects associated with immune system suppression and laminitis.
The 2014 study reported the best results associated with the use of magnesium and melatonin together. Magnesium decreases the reactivity of the nerves, consequently, reducing the reactivity of the trigeminal nerve.
Veterinarians can aid in the diagnosis of idiopathic head shaking by helping to eliminate other factors causing similar symptoms. The care giver’s use of recordkeeping for tracking symptoms and variables surrounding their expression can be very helpful to the veterinarian applying diagnostic tools. Remember to avoid fans on their face and grazing in tall grasses.