"Doc, you've got to get here quickly. My horse is foaming at the mouth, and I think it might be rabies!" This is a fairly
typical call, usually in the early spring after a stretch of wet weather. With further questioning, you discover that the
affected horse is acting relatively normal but that a large amount of watery saliva is constantly dripping from its mouth,
creating puddles in the barn aisle and anxiety in its owner (Photo 1).
Photo 1: Horse owners and barn managers can't help but notice the often impressive pool of saliva produced by horses affected
with various gingival diseases or plant toxicoses. (Photos courtesy of Dr. Marcella)
Stomatitis, or irritation or ulceration of the mouth, is a fairly common event in horses given the aggressive and indiscriminant
grazing nature of some horses and their exposure to many plants, shrubs and weeds in their environment. Excessive salivation
is a primary sign of stomatitis, along with a reluctance to graze or eat and a decrease in performance related to avoiding
The causes of equine stomatitis and salivation can vary from mild and self-limiting to severe or even fatal in the case of
rabies. As the spring approaches, and we once again enter "slobbers" season, it is a good time to review the causes of excessive
salivation in horses so that serious conditions are promptly addressed and not-so-serious ones do not create undue panic.
Be sure to first rule out common causes of excessive salivation in horses such as foreign bodies (sticks stuck in the mouth),
choke (obstruction of the esophagus) and dental abnormalities.
Rabies, caused by a rhabdovirus, can make an affected animal salivate and produce often thick, ropey saliva, but these unfortunate
individuals are also typically showing more severe or advanced neurologic signs such as anxiety, irritability, sensitivity
to being touched, other odd behaviors and incoordination or ataxia. The clinical signs of rabies progress quickly, and by
the time drooling is observed, the condition is not likely to be confused with other diseases.
However, horses can manifest the "dumb" form of rabies commonly seen in cattle. These horses are lethargic and depressed,
and their salivation may be interpreted as a case of choke. Most cases of rabies exposure in veterinarians or horse owners
involve this type of presentation, and caution should always be used when investigating cases of excessive salivation in horses.
Practitioners and anyone examining the mouths of these horses are encouraged to always wear gloves, and contamination of wounds
on the hands and arms should be avoided.
This serious condition affecting horses, cattle and pigs is also caused by a rhabdovirus. Vesicular stomatitis is characterized
by fluid-filled vesicles on the tongue, mouth lining, nose and lips that rupture to produce ulcerated lesions. These horses
may be unwilling to eat normally and will salivate or drool. Their breath will generally have a slight to more severe necrotic
odor because of the nature of the ulcerated tissue in their mouths. They may have mildly elevated temperatures and appear
clinically depressed. This disease can become systemic, and ulcerated areas may appear on the udder, sheath or coronary band,
making these animals lame as well.
To rule out the possibility that the lesions are caused by other conditions such as sunburn or irritating feeds, blood testing
is required. The ulcers usually heal in two weeks to two months. Until that time, the horse is infective and can spread the
disease. Vesicular stomatitis is a reportable disease. For all suspected cases, veterinarians must contact state and federal
animal health authorities. When a case of vesicular stomatitis is confirmed, the state veterinarian's office will quarantine
the affected farm or ranch.