What is headshaking or incense burning in horses?

Headshaking, or “incense-shaking,” is a highly debilitating condition that significantly hinders riding and can even strain the rider-horse relationship. Difficult to diagnose, this disorder requires thorough evaluation and specialized care to help the horse regain a good quality of life and harmony with its rider.

How can you recognize headshaking?

Description of headshaking

The phenomenon of headshaking in horses gets its name from the head movements that resemble the motion of a censer. While it may resemble the stereotypical behaviors frequently observed in stalls, headshaking differs in its intensity and duration, which do not subside during training sessions. In fact, it is often more pronounced when the horse is active and increases with the intensity of the effort exerted.

These violent movements, which may appear suddenly or gradually, occur in a vertical, horizontal, or rotational plane. They appear to be triggered by facial pain (similar to facial neuralgia in humans) when exposed to bright light or tactile stimuli such as air passing over the nostrils, rain, or wind.

Whether constant or intermittent, these repetitive movements are associated with signs of nasal discomfort such as sneezing, snorting, snuffling, nasal discharge, and rubbing the muzzle against objects in the environment or against the forelegs. The horse appears anxious, and some horses may even go so far as to self-mutilate or stop eating altogether because the condition is so debilitating. In these situations, riding becomes impossible because the horse’s behavior can be dangerous.

The Different Levels of the Census

The first symptoms of headshaking generally appear in horses between the ages of 6 and 10, usually in the spring or summer.

Depending on their severity, symptoms are classified into 5 grades:

• Grade 1: Symptoms are mild and intermittent. The horse can be ridden.
• Grade 2: Symptoms are moderate and occur in specific situations. The horse can be ridden, though with difficulty.
• Grade 3: The symptoms are more severe, and the horse is difficult to control during breeding.
• Grade 4: The symptoms are so severe that the horse can no longer be ridden.
• Grade 5: The symptoms are severe, and the horse's behavior makes it dangerous.

Generally, clinical signs worsen over time, negatively affecting the animal’s quality of life. In 60% of affected horses, these signs appear in the spring and summer, as sunny days can cause symptoms to worsen in certain horses known as photosensitive snuffers.

What causes headshaking?

At present, there is no clearly identified cause of headshaking, although the hypothesis of trigeminal nerve hypersensitivity is the one most widely supported by veterinarians. More specifically, there appear to be two types of headshaking based on their etiology:

• Trigeminal-mediated facial paralysis, formerly known as idiopathic facial paralysis: This is the most common form of facial paralysis resulting from inflammation of the trigeminal nerve, which causes neuralgia. Photosensitive facial paralysis is widely represented in this group. The trigeminal nerve is one of the horse’s 12 cranial nerves. It divides into three branches (mandibular, maxillary, and ophthalmic) and provides sensation to the face as well as motor function to the masticatory muscles. Hormonal and dietary factors are also thought to play a role in trigeminal-mediated salivation.
• Structural involvement resulting from an identified condition that causes visible tissue damage. This damage may affect, for example, the teeth, eyes, respiratory system, or the musculoskeletal system.

How do you diagnose laminitis in horses?

Diagnosing headshaking in horses remains very complex. It relies primarily on exclusion criteria—that is, ruling out various possible causes before concluding that the horse is actually suffering from headshaking. As a result, it can take a long time to reach a diagnosis. In particular, the veterinarian will look for:

• A purely behavioral disorder such as stereotypies, which are common in horses. These are repetitive movements performed for no apparent reason, which are generally not considered serious given their short duration and low intensity. These stereotypies occur in specific contexts (social isolation, boredom, stress, insufficient forage, etc.). However, unlike headshaking, stereotypical head shaking in horses is characterized by the repetition of a single, identical movement.
• Discomfort or pain in the mouth: this may be due to dental problems (an extra tooth, gum inflammation, tooth decay, etc.), an abnormal jaw structure leading to malocclusion (prognathism or retrognathism), conditions affecting the mucous membranes of the cheek or palate, inflammation caused by the bit, etc.
• Discomfort or pain in the sinuses, such as infectious sinusitis caused by bacteria, fungi, or parasites, equine rhinitis (whether allergic or non-allergic), etc.
• Discomfort or pain in the throat, as in the case of strep throat, an extremely contagious bacterial infection that causes abscesses in the lymph nodes of the throat.
• A condition affecting the pharyngeal pouches (located on either side of the throat), such as mycosis, a very serious fungal infection that causes difficulty swallowing and profuse nosebleeds that can be fatal.
• An ear infection, such as otitis, which can be caused by bacteria or fungi (fungal otitis).
• An eye condition such as allergic conjunctivitis (inflammation of the conjunctiva) or uveitis (inflammation of the internal structures of the eye).

All of these diagnostic possibilities are investigated before considering headshaking, as Ludovic Tanquerel, a veterinarian at the EnvA Equine Hospital, explains in a video. In addition to taking a history of the symptoms and performing a clinical examination, a variety of tests can be conducted: head CT scan, X-rays, endoscopy, etc.

How can headshaking be treated?

Conservative Treatments

Like the diagnosis, the treatment of prancing in horses is complex, relying on a combination of different techniques and medications tailored to the animal’s profile and the severity of the condition. The veterinarian may prescribe specific medications containing sodium cromoglycate, carbamazepine, gonadotropin, or cyproheptadine to relieve the horse’s symptoms.

There are also blends of herbs selected for their calming properties, such as Arbalou Equiexpert’s Headshaking.

He may also prescribe sodium, magnesium, and anti-inflammatory medications. Surgery on the trigeminal nerve may be considered; however, it has a success rate of only 49% 18 months after the procedure. The use of dietary supplements helps reduce symptoms by alleviating the animal’s anxiety and preventing conditions that lead to secondary structural inflammation. These supplements also offer the benefit of relieving pain that may arise from the horse’s repetitive movements.

Neuromodulation

Neuromodulation is a nerve electrostimulation technique that appears to be effective in treating head tremors resulting from trigeminal nerve dysfunction. Véronica L.H. Roberts, a researcher and associate professor at the University of Bristol (United Kingdom), demonstrates in a 2019 study of 168 horses that 53% of the treated horses showed a reduction in headshaking for more than 9 weeks. Dr. Ludovic Tanquerel, mentioned earlier, also uses electrostimulation at the Equine Hospital to treat horses with headshaking.

Performed under light sedation, this technique “fatigues” the trigeminal nerve during sessions lasting several minutes at increasing electrical intensities. The horse then experiences relief for a few days. Repeating these sessions provides the animal with increasing relief and up to a 60% recovery rate after one year. While some horses are permanently cured following this electrostimulation protocol, the majority of horses require a new session each year to maintain trigeminal nerve function.

Wearing a protective mask

Since external stimuli are often triggers for snorting in horses, the use of a protective mask can reduce the frequency of this behavior and help relieve the animal’s discomfort and pain. While a noseband reduces airflow through the nostrils and tactile stimulation, it does not protect the eyes from bright light in photosensitive horses that exhibit this behavior. Using a UV-protective mask with ear and nose covers therefore meets the horse’s need for full head protection.

Whether in the pasture, in the stall, during outdoor work, or on flat ground, the Equidival mask provides 90% protection against UV rays. It also protects against dust, insects, and wind. UV-protective goggles are particularly recommended for training sessions, offering 100% protection. Their tint varies depending on the horse’s needs and the activity being performed. Note that they are permitted in dressage competitions.

If your horse suffers from headshaking, there are ways to help improve its daily well-being. In addition to implementing a specific veterinary treatment plan, using a high-protection face mask and administering dietary supplements can help alleviate your horse’s stress and minimize sources of discomfort. With this relief, your horse will rediscover joy and serenity, fostering a renewed harmony between horse and rider.

Sources:
Incense Use in Horses: Clinical Signs, Prevalence, Pathophysiology
Equine Veterinary Practice No. 219, October 1, 2023
Headshaking in Horses
La Semaine Vétérinaire No. 1743, December 7, 2017