Horses smack their lips for several distinct reasons, ranging from a normal stress-release reflex to signs of discomfort or social signaling. The most common cause is a natural physiological response that happens when a horse shifts from a tense state to a relaxed one, essentially resolving the dry mouth that builds up during stress. But context matters: a foal smacking its lips around an older horse means something very different than an adult horse doing it repeatedly while grazing on clover.
The Stress-Release Response
When a horse feels threatened, confused, or pressured, its nervous system kicks into fight-or-flight mode. One side effect: the body suppresses salivation, leaving the mouth dry. Once the stressful moment passes and the horse’s nervous system shifts back into a calm, “rest and digest” state, saliva production resumes. The licking, chewing, and lip-smacking you see is largely the horse’s response to moisture returning to a dry mouth.
A 2018 study at the Norwegian University of Life Sciences observed nearly 200 horses, including feral populations, and confirmed this pattern. Researchers found that the chewing behavior consistently appeared after tense situations resolved, not during them. This challenges a popular belief in horse training circles that licking and chewing means a horse is “processing what it learned.” While the horse may have learned something, the physical behavior itself is more of a physiological reset than a sign of deep thought. In fact, some trainers now view frequent licking and chewing during training as a signal that the horse found the session stressful enough to trigger a noticeable relief response.
You might also notice lip smacking when your energy changes around a horse. If you approach a task with high intensity and then become calmer, the horse picks up on that shift and often responds with licking and chewing as its own tension drops.
Foal “Champing” as a Social Signal
Young horses have their own version of lip smacking called champing (sometimes called snapping). A foal will rapidly open and close its mouth, often exposing its teeth, in a rhythmic, exaggerated motion that looks distinctly different from adult lip movements. This behavior is most commonly described as a submissive or appeasement gesture, and it typically appears when the foal feels uncertain around an older horse.
Foals champ most often toward stallions or dominant herd members, though they sometimes do it toward their own mothers, particularly during tense moments like when a stallion is interacting with the dam. Bottle-raised foals sometimes direct the behavior toward humans, likely because they’ve imprinted on people as their social group. Whether champing is a deliberate visual signal to defuse potential aggression or simply a self-soothing displacement behavior remains an open question, but it serves the foal well either way. It tends to disappear as the horse matures and establishes its place in the social hierarchy.
The Flehmen Response
Sometimes what looks like lip smacking is actually the beginning or tail end of the flehmen response, that dramatic curling of the upper lip that makes a horse look like it’s laughing. This behavior channels scent molecules into the vomeronasal organ, a specialized sensory structure connected to the nasal passages and mouth. Once scent chemicals reach this organ, signals travel to the brain and can trigger various physiological or behavioral reactions.
Horses flehmen most often after sniffing another horse’s urine or feces, but they sometimes do it in response to smells their owners can’t even detect. Stallions frequently display it around mares. The lip curling and associated mouth movements beforehand, including smacking or licking, are part of the horse actively sampling its chemical environment. It’s not a sign of disgust, even though it resembles the face humans make at bad smells. It’s closer to the opposite: the horse is trying to gather more information.
Slobbers From Infected Clover
If your horse is smacking its lips excessively while grazing or shortly after, and you notice heavy drooling, the culprit may be a fungus-infected pasture. Red clover can harbor a fungal pathogen called Rhizoctonia leguminicola, which produces a compound that causes livestock to salivate profusely. The condition is commonly known as “slobbers syndrome,” and it can lead to dehydration if the horse continues eating affected forage.
The excessive saliva production naturally triggers constant lip smacking, chewing, and drooling. Look for dark spots on clover leaves in your pasture, which signal the fungal infection. The problem resolves once the horse is removed from the contaminated forage, but persistent cases or signs of dehydration warrant attention. Infected hay can cause the same issue, so the problem isn’t limited to fresh pasture.
Dental Problems and Mouth Pain
Horses’ teeth grow continuously throughout their lives, and the natural grinding motion of chewing creates sharp enamel points on the cheek teeth. These points can lacerate the inside of the cheeks and tongue, causing ongoing mouth discomfort that shows up as unusual oral behaviors. A horse dealing with dental pain may smack its lips, fuss with a bit, toss its head, or chew in exaggerated ways that seem out of context.
Other dental issues, including broken teeth, abscesses, or misaligned bite surfaces, can produce similar behaviors. If lip smacking is new, persistent, and not clearly tied to a situational trigger like stress relief or grazing, dental discomfort is worth investigating. Most horses benefit from routine dental maintenance every one to two years, during which sharp points are filed smooth in a process called floating.
Gastric Ulcers and Digestive Discomfort
Equine gastric ulcer syndrome is remarkably common, affecting a large percentage of performance horses and even many leisure horses. Proposed signs include teeth grinding (bruxism), the flehmen response performed without an obvious scent trigger, poor appetite, weight loss, and behavioral changes. While lip smacking isn’t listed as a standalone diagnostic sign, the related oral behaviors, particularly teeth grinding and unexplained flehmen, often overlap with what owners describe as lip smacking.
A horse that repeatedly smacks or grinds while eating, or that curls its lip after meals with no apparent scent stimulus, may be responding to gastric discomfort. This is especially worth considering if the behavior appears alongside other signs like a dull coat, reduced appetite, or sensitivity when the girth is tightened. Ulcers are treatable, and catching them early makes management much simpler.
How to Read the Context
The key to interpreting lip smacking is timing. A horse that smacks its lips once after you release pressure during training is showing a normal relaxation response. A foal doing it around older horses is being socially appropriate. A horse that does it constantly on pasture, especially with heavy drooling, points to a dietary or toxin issue. And a horse that smacks or grinds its teeth repeatedly without clear triggers, particularly around feeding time, may be dealing with pain in the mouth or gut.
Pay attention to what was happening in the seconds before the behavior started. A single episode after a tense moment is routine. A pattern that shows up in the same context repeatedly, or that comes with other changes in behavior or condition, tells you something more specific about what your horse is experiencing.