Many horse owners and riders are familiar with the “lipstick” that often coats the mouth of a horse in work, whether ridden or on the flat. Many people unfamiliar with horses occasionally panic at the sight of a horse foaming at the mouth, thinking it’s most likely a sign of illness, disease, or the result of excessive exertion to the point of cruelty.

Horses may salivate excessively and foam at the mouth simply because it’s a generally relaxed horse that’s been worked correctly, in most cases. Excess salivation or foaming at the mouth can also be caused by the bit, by certain foodstuffs or, in rare and exceptional cases, an underlying medical issue.

It is only by knowing the natural and normal conditions of the horse in question that one would be able to tell whether excess salivation or foam at the mouth is a healthy and regular occurrence and whether or not it’s cause for concern.

This article will take a closer look at why horses tend to foam at the mouth and the rare instances when it could be a sign of trouble.

Causes

The inside of a horse’s mouth, much like the mouth of any other living mammal, is where saliva accumulates to aid digestion. Salivation is caused by pressure placed on the salivary glands that you can find at the rim of the jaw bone and the muscles of the neck.

A horse may excessively salivate if he stretches his neck forwards in an arch while flexing at the poll, which is the point right between his ears. If his poll and jaw are both relaxed, there is the possibility that he may produce a lot of saliva.

Additionally, horses also salivate more if they are chewing softly, moving their tongue, and swallowing — all movements associated with eating and relaxation of the poll and jaw.

Therefore, if a horse is being ridden correctly — stretching forward, accepting the contact from the bit correctly, chewing or mouthing due to relaxation, being relaxed at the poll and jaw, all while being ridden — they will naturally salivate more.

This is why foaming at the mouth in ridden work is generally seen as a positive trait.

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Protein

Unlike other mammals, horses are very unique in the sense that their sweat is incredibly protein-rich. They also sweat through their skin like humans, which is an uncommon trait of mammals in general.

This protein-rich substance in horse sweat is called latherin, and it is found in all equid species, namely, the horse, zebra, donkey, and onager (wild ass). It is very similar to a family of proteins found in the oral cavity of other mammals and also present in the oral cavity of the horse.

Latherin produces a severe reduction in water surface tension at low concentrates, and it can effectively cool down the horse if produced through the skin. However, this rapid reduction in water surface tension is also responsible for a detergent-like activity, which then forms a dense protein layer or foam.

This foamy layer can often be observed on the heaving flanks of an exerted horse, especially where the numnah or saddle would have rubbed against the skin. Additionally, as the protein is also present in the oral cavity, it is very much responsible for the foam that often coats the lips of a working horse (source).

Foraging

Because a horse eats so much roughage in a single day, their salivary glands have adapted to produce up to 10 gallons of saliva per day. Excessive salivation can sometimes occur because of the types of foodstuffs a horse consumes during grazing.

Some plants have barbs that only slide in one direction, which means they easily get embedded in the gums and tongue where they, as foreign matter in the mouth, cause excessive salivation.

Some cooler and wetter climates are also ideal for the spores of the fungus Rhizoctonia leguminicola, also known as “black patch.”

This fungus is especially prevalent on red, white, and alsike clover, as well as alfalfa and stored or dry hay. Rhizoctonia is persistent and contains slaframine, which causes horses to excessively salivate. This affliction is termed “clover slobbers” (source).

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Exercise and Exertion

A horse will most likely only foam at the mouth when in work, whether ridden or on the flat. If a horse is exercised correctly, the foam is actually a desired trait, especially in dressage horses.

If the animal is carrying its own weight, working from behind and arching his neck while relaxing at the poll and jaw, the horse will not be rigid, braced, or stiff and, therefore, due to suppleness, the salivary glands are stimulated and produce more saliva.

The saliva then collects in the mouth and, if a horse is chewing softly, as mentioned earlier, moving their tongue and swallowing, the saliva will foam when it gets into contact with the air.

Concerns

Although there are numerous harmless reasons why a horse may be foaming at the mouth or bit, there are a few rare instances when hypersalivation, drooling, or foaming at the mouth is an indication of an underlying issue or problem.

Generally, excessive salivation is only a problem if the foam isn’t a normal occurrence for the horse in question, has blood in it, or is accompanied by other abnormal behavior.

Poisoning

Poisoning isn’t very common as animals are generally fairly intuitive regarding what they can and cannot eat, but occasionally horses may ingest poison in the form of insecticide, cleaning materials, paint, animal baits, or toxic plants or substances.

Common salivation-inducing poisons include insecticides and Slaframine poisoning from the clover, arugula, and hay fungus Rhizoctonia leguminicola.

If you suspect that your horse has been poisoned, it is important to call your vet immediately. You should identify the type of poison, the source of the poison, and how long ago the horse ingested it if possible. It is best if you can show the vet a sample.

As with many other types of poisoning, you should remove the toxic contents from the stomach using a gastric tube.

The vet should assist you with administering an activated charcoal slurry, followed by a laxative. They will often administer intravenous atropine for salivation, recommending this in severe cases (source).

Mouth Injury

Stomatitis, which is ulceration or irritation in the mouth, is fairly common in horses since they tend to graze so very aggressively and indiscriminately. They are also exposed to many plants, weeds, and shrubs, which may have barbs or spikes that can either get embedded in the oral cavity or cause irritation.

If you do a quick oral examination, you may see redness in some areas, ulceration, and possibly hemorrhaging. If you inspect their feed sources and pasture, you should be able to tell where they picked up the affliction, and an avoidance of the offending material will likely be all that is needed for a cure.

If the ulceration is severe, it is best to contact the vet, and if sharp or broken teeth cause it, the dentist should be called to assist.

Choking

A horse that is excessively salivating may also be choking. Be sure to check the nasal cavity for any discharge and keep a close eye on the animal for signs of wheezing, difficulty breathing, coughing, or actual choking.

Horses can occasionally get sticks or other foreign objects stuck in their throat when grazing, and this obstruction will prevent them from swallowing, causing hypersalivation.

In the case of a foreign body stuck in the throat where you can see and access it, it is generally easily removed if you are careful. If you cannot find the foreign object or if it is so deep that you fear you may push it further in or cause damage when removing it, it is best to call your vet for assistance (source).

Rabies

Rabies in horses is exceptionally uncommon and, unfortunately, in unvaccinated horses, uniformly fatal. The rabies virus does have a reputation for causing its host to foam at the mouth, but more often than not, horses with rabies won’t be salivating to the point of excess.

A horse that has contracted the rabies virus will probably display signs of colic, lameness, incontinence, paralysis, tremors, fever, depression, convulsions, and sensitivity to touch.

They may also refuse to eat or drink and be grinding their teeth. The grinding of teeth is where their saliva may mix with air and cause a foam.

In most positive rabies cases, the affected horse will die within three to five days. The best remedy is to get all horses in your care vaccinated against rabies.

In areas where rabies has been reported, horse owners should also limit exposure by properly disposing of trash, securing food containers, grain, and other feed, and not leaving the items as mentioned earlier outside (source).

Final Thoughts

If a horse is foaming at the mouth, this is generally an indication that the animal is relaxed and exercised properly. It is no cause for concern and generally the result of a protein-rich substance, latherin, present in all horse saliva.

If a horse is drooling, there could be a foreign object stuck in its throat or irritation in the oral cavity. In some cases, horse slobber is caused by a fungus often found on clover and alfalfa and generally not dangerous.

The only truly dangerous reason for hypersalivation is poisoning and, in this case, the foam will be accompanied by other worrying signs.