Horses drool because salivation is a core part of how they digest food, but excessive or sudden drooling usually points to something specific: a fungus on clover, a dental problem, a plant irritant, or occasionally a serious illness. A healthy mature horse produces 35 to 40 liters (9 to 11 gallons) of saliva every single day, so some amount of drool is completely normal. The key is knowing when drooling crosses the line from routine to concerning.
Normal Saliva Production in Horses
Horses don’t produce saliva constantly the way some animals do. Their salivary glands activate in response to chewing, and the volume depends on what they’re eating. A mouthful of dry hay triggers significantly more saliva than a mouthful of moisture-rich grass, because the saliva needs to soften and lubricate the feed for swallowing. This is why you might notice more drool when a horse eats hay compared to fresh pasture.
That saliva serves a second critical purpose beyond lubrication: it buffers stomach acid. Horse stomachs produce acid continuously, even when empty, and the bicarbonate in saliva helps neutralize it. A horse that spends long stretches chewing forage throughout the day produces a steady flow of this natural antacid, which is one reason continuous access to hay or pasture is so important for gut health. Seeing some saliva around the mouth during or after meals is perfectly normal and expected.
Clover Slobbers: The Most Common Cause
If your horse is suddenly drooling heavily and grazing on pasture that contains red or white clover, the likely culprit is a condition literally called “slobbers.” It’s caused by slaframine, a toxin produced by the fungus Rhizoctonia leguminicola, which grows on clover plants. The fungus creates dark patches on the clover leaves (called blackpatch disease), and when horses eat the affected plants, slaframine stimulates the salivary glands into overdrive.
Slobbers looks dramatic. Horses may produce long ropes of saliva that drip continuously from the mouth. It’s alarming the first time you see it, but the condition itself is generally not dangerous as long as the horse stays hydrated. The real risk is dehydration from the sheer volume of fluid loss. Removing the horse from the clover pasture typically resolves the drooling within 24 to 48 hours. The fungus tends to be worse in warm, humid conditions, so slobbers peaks in late spring and summer.
Dental Problems
Horses’ teeth grow continuously throughout their lives, and uneven wear creates sharp enamel points and hooks that can lacerate the inside of the cheeks and tongue. When this happens, a horse may drool because chewing becomes painful or because the mouth tissue is inflamed and irritated. You might also notice the horse dropping partially chewed food from its mouth, a behavior called quidding.
Other dental issues that trigger excessive salivation include broken or lost teeth, infected teeth and gums, periodontal disease, retained baby teeth, and uncomfortable wolf teeth. Additional warning signs to watch for alongside drooling: foul mouth odor, facial or nasal swelling, traces of blood in the mouth, undigested feed in manure, head tilting, resistance to the bridle, or a noticeable drop in body condition. Most dental problems are caught and corrected during routine dental exams, which is why regular floating (filing of sharp edges) is a standard part of horse care.
Toxic Plants That Irritate the Mouth
Several common pasture weeds cause drooling by directly irritating the tissues of the mouth and throat. Buttercups are one of the most widespread offenders. The plants contain compounds that inflame the oral tissues on contact, triggering excessive salivation along with potential colic and diarrhea. Horsenettle is another culprit, causing salivation along with muscle tremors, weakness, and gastrointestinal upset.
Unlike clover slobbers, which is caused by a fungus rather than the plant itself, these toxic plants cause a direct chemical irritation. If you notice drooling along with signs of pain, digestive distress, or behavioral changes, checking the pasture for known irritants is a practical first step. Horses typically avoid bitter or irritating plants when better forage is available, so overgrazed pastures with limited grass pose a higher risk.
Choke: A Blockage in the Esophagus
Equine choke is not the same as choking in humans. The horse can still breathe because the blockage is in the esophagus, not the airway, but it cannot swallow. Food and saliva back up and often come out through the nostrils as a green, frothy discharge. This nasal discharge is actually the most recognizable sign of choke, and it’s distinct from simple drooling.
Other signs include excessive salivation, coughing, gulping, difficulty swallowing, sweating, restlessness, and stretching the head and neck forward. Choke commonly happens when a horse eats dry feed too quickly or doesn’t chew adequately, and it can also occur with beet pulp that wasn’t properly soaked. Most cases resolve on their own or with veterinary assistance, but a prolonged blockage can damage the esophageal lining, so prompt attention matters.
Vesicular Stomatitis
Vesicular stomatitis is a viral disease that causes painful blisters inside the mouth, and excessive drooling or frothing is often the very first visible sign. The blisters develop on the inner surfaces of the lips, gums, tongue, and sometimes around the nose, ears, or where the hoof meets the skin (the coronary band). Clinical signs appear 2 to 8 days after exposure.
As the blisters swell and rupture, they cause significant mouth pain. Affected horses often refuse to eat or drink, leading to weight loss. Fever may develop before or at the same time the lesions first appear, and if lesions form near the hooves, lameness can follow. Vesicular stomatitis is a reportable disease in the United States, meaning cases must be reported to state and federal animal health authorities. It’s spread by insect vectors and direct contact, so an affected horse is typically quarantined to prevent spread to other livestock.
Rabies
Rabies is rare in horses but fatal once symptoms appear, and drooling is one of the hallmark signs. The paralytic form of rabies, which is the more common presentation in horses, involves progressive paralysis of the throat and jaw muscles. This creates a combination of excess salivation and an inability to swallow, so saliva pools and drips from the mouth. A drooping lower jaw is a characteristic feature.
Rabies should be on the radar any time a horse shows sudden, unexplained drooling alongside neurological changes such as unusual behavior, unsteadiness, difficulty swallowing, or progressive weakness. Horses are typically exposed through the bite of an infected wild animal, most often raccoons, skunks, bats, or foxes depending on the region. Vaccination is the primary form of prevention.
How to Tell What’s Causing the Drool
Context narrows it down quickly in most cases. A horse that’s grazing clover pasture and drooling heavily but acting otherwise normal almost certainly has slobbers. Drooling that appears during or after meals, especially with quidding or weight loss, points toward dental issues. Green discharge from the nostrils after eating suggests choke. And drooling accompanied by visible blisters, fever, lameness, or neurological changes warrants immediate veterinary attention.
The timeline matters too. Slobbers and choke develop acutely, within hours. Dental problems tend to build gradually over weeks or months. Vesicular stomatitis follows a distinct pattern of fever, then blisters, then ruptured sores over the course of about a week. Paying attention to what else is happening alongside the drooling, and how quickly it started, gives you the clearest picture of whether you’re dealing with something routine or something that needs urgent care.