Gastric ulcers are not a well-established direct cause of headshaking in horses, but there is a plausible indirect connection through gut health, pain signaling, and nerve sensitivity. The vast majority of headshaking cases in horses are classified as trigeminal-mediated headshaking, a form of neuropathic facial pain. However, digestive discomfort from ulcers can contribute to behavioral changes, and emerging research suggests the gut may influence the nerve pathways involved in headshaking more than previously thought.
What Headshaking Actually Looks Like
Headshaking in horses is predominantly vertical, often with sharp, violent flicking motions. Horses frequently show signs of nasal irritation, as if a bee flew up their nose, and may rub their muzzle on their legs or on the ground. Symptoms are typically worst during exercise, though some horses are affected at rest too. About 60% of headshaking horses show seasonal patterns, with signs peaking in spring and summer.
In a large owner survey, 93% of owners described their headshaking horse as otherwise “good and reliable,” and only 10% of horses showed signs exclusively when ridden. Changing bits, saddles, and trainers had no effect on the behavior in most cases, which helps rule out tack fit or training as the primary issue.
The Most Common Cause: Trigeminal Nerve Pain
Most headshaking horses have what veterinarians now call trigeminal-mediated headshaking (TMHS). The trigeminal nerve runs through the face and is responsible for sensation in the muzzle, eyes, and forehead. In affected horses, this nerve fires inappropriately, sending pain signals without any external trigger. It’s similar to trigeminal neuralgia in humans, a condition sometimes described as one of the most painful known.
This neuropathic pain is the explanation behind most cases that used to be labeled “idiopathic” or unexplained. Light, wind, exercise, and warmth can all lower the threshold for triggering these misfiring nerves, which explains the seasonal pattern many owners notice.
How Ulcers Could Play a Role
Equine gastric ulcer syndrome (EGUS) causes a range of behavioral changes. Around 32% of horses with squamous gastric disease and 33% with glandular gastric disease present with documented behavioral changes. Girthiness (flinching or pinning ears when the girth is tightened) is one of the most recognized signs, present in 25 to 31% of ulcer cases. Other common signs include poor appetite, weight loss, irritability under saddle, and reluctance to work.
Headshaking is not listed among the primary behavioral signs of gastric ulcers. However, the connection between gut health and nerve pain is more complex than a simple checklist suggests. Research published in Veterinary Medicine and Science found that gut bacteria influence chronic pain, visceral pain, neuropathic pain, and even headache through several pathways. These include modulation of nerve roots in the spinal cord and neuroinflammation of both the peripheral and central nervous systems. In other words, an unhealthy gut can change how the entire nervous system processes pain signals.
Diet also plays a role. Dietary components influence blood pH and levels of ionized calcium and magnesium, both of which are essential for normal nerve transmission. Horses on high-grain, low-forage diets (the same diets that predispose to ulcers) may experience shifts in these electrolytes that make nerves more excitable. A study of headshaking triggers found that high grass diets, lucerne hay, and clover hay were all reported by owners as making symptoms worse.
Gut Bacteria and Nerve Sensitivity
Researchers have specifically studied the cecal (hindgut) microbiota of horses with trigeminal-mediated headshaking. The premise is straightforward: if gut bacteria can modulate neuropathic pain in other species, they may influence the trigeminal nerve misfiring that drives headshaking. The gut-brain axis, the communication network between the digestive tract and the nervous system, is an active area of investigation in equine medicine.
This doesn’t mean ulcers directly cause headshaking. But it does mean that a horse with gastric ulcers, disrupted gut bacteria, and altered electrolyte balance may have a lower threshold for trigeminal nerve pain. If your horse has both ulcers and headshaking, treating the ulcers could potentially reduce the severity of headshaking even if it doesn’t eliminate it entirely.
Other Causes Worth Ruling Out
Before focusing on ulcers, it’s worth knowing the full list of conditions that can trigger headshaking. Some are uncommon but treatable:
- Ear mites or middle ear inflammation
- Dental problems, particularly infections around tooth roots
- Sinus infections
- Guttural pouch disease (fungal infections in the air-filled pouches near the throat)
- Eye conditions
- Cervical (neck) injuries
- Poorly fitted tack, though this is a less common cause than many owners assume
- Flies or insects on the face
A thorough veterinary workup typically includes an oral exam, endoscopy of the upper airway and guttural pouches, and sometimes nerve blocks to confirm trigeminal involvement. Gastroscopy to check for ulcers is a reasonable addition, especially if your horse shows other signs of digestive discomfort alongside the headshaking.
What to Watch For in Your Horse
If you suspect ulcers are contributing to your horse’s headshaking, look for overlapping signs. A horse with ulcers will often show poor body condition, a dull coat, reluctance to eat grain, sensitivity around the girth area, or a sour attitude under saddle. These signs alongside headshaking would strengthen the case for a gastric workup.
Pay attention to timing. Trigeminal-mediated headshaking tends to worsen with exercise, sunlight, and warm weather. Ulcer-related discomfort often worsens around feeding times or when the stomach is empty. If your horse’s headshaking seems unrelated to light or season and instead correlates with feeding schedules or dietary changes, digestive pain becomes a more plausible contributor.
Also note whether the headshaking is truly vertical flicking (characteristic of trigeminal pain) or more of a general tossing, turning, or shaking that looks like generalized discomfort. Horses in visceral pain from ulcers are more likely to show restlessness, flank-watching, or pawing alongside any head movements, rather than the sharp nasal-irritation flicks seen in classic trigeminal headshaking.