What does it mean when a horse foams at the mouth?

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What does it mean when a horse foams at the mouth?
A horse's mouth can be prone to irritation and excess salivation. (Digital Vision./Digital Vision/Getty Images)

Foaming at the mouth is a symptom most often associated with rabies in animals including dogs, cattle and horses. However, there are several causes of excess salivation in horses, many of which are much less serious and much easier to treat. The best way to assess the health of a horse is to look for several associated symptoms (rather than just one) that may indicate a virus or infection and have it examined by a trained veterinarian.


The rabies virus can cause horses and other animals to salivate excessively, producing a thick foam around the mouth. However, the foaming usually emerges in the latter stages of the rabies virus. Clear indications, such as the horse appearing sensitive to being touched and demonstrating anxious, agitated behaviour, are likely to be apparent before the animal foams at the mouth. The “dumb” form of rabies, however, may not have any anxious symptoms and cause an animal to be lethargic and immobile for prolonged periods. Rabies can be contagious, so protective gloves are worn by veterinarians when examining a horse.

Vesicular stomatitis

Vesicular stomatitis is caused by a rhabdovirus and typically affects cows, horses and pigs. The virus causes vesicles on the tongue, lips and mouth lining to swell up, producing painful ulcers. This may make a horse refuse to eat to protect itself from the pain and can also lead to excess drooling and foaming around the mouth. Other symptoms of vesicular stomatitis include a necrotic odor on the animal’s breath, a raised temperature and indications of lethargy or depression. The diseases can be confirmed through veterinarian blood tests and the ulcers typically heal within eight or nine weeks.

Environmental irritants

Some horses foam at the mouth due to chemical and mechanical irritants in their living environment. For instance, a horse may lick or chew on a leg bandage treated with medical compounds which can agitate the regions of the mouth and cause excessive salivation. Certain plants, including marigolds and buttercups, contain chemicals that can irritate the oral regions and lead to foaming. Foaming caused by these irritants is usually accompanied by other symptoms such as ulceration, blood haemooraghes around the mouth and ulcers. The condition can usually be cured simply by keeping the animal away from the source of the irritant.

The “slobbers”

The slobbers is a colloquial term used to describe a perfectly healthy horse, which produces large amounts of foamy saliva. Such horses do not display any abnormal behaviours and continue to take food and water. The excess saliva usually occurs in the Spring or Autumn months, when wet, humid weather is commonplace. The problem can also be exacerbated by the presence of red clover in rural areas. This variety of clover is prone to infection by the Rhizoctonia leguminicola fungus, causing it to produce slaframine, which can lead to weight loss, diarrhea and excess salivation in horses. Actropine can be successful in alleviating these symptoms but the problems typically resolve anyway if the animal is kept away from the clover for two or three days.

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