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SALIVATION INDUCING PLANTS
Excessive salivation or slobbering characterized by frothing or drooling of saliva is generally an indication of traumatic, chemical, or infectious injury to the mouth, or obstruction to the esophagus (choke) that prevents the swallowing of saliva and food. In addition to trauma from sharp points on teeth, poorly fitting or inappropriately used bits, or infectious diseases such as the virus induced vesicular stomatitis, that causes blister-like lesions of the mouth, as well as a variety of grasses and other plants, may cause trauma to the mucous membranes of the mouth resulting in excessive salivation. Plants with thorns, bristles, stinging hairs, or sharp awns can produce a variety of lesions ranging from reddening of the mucous membranes to deep granulating ulcers on the tongue and gums. Blister-like lesions around the lips, nose, eyes, and anus may also occur in horses bedded on wood shavings containing bitterwood (Quassia simarouba), a tree indigenous to Central and South America, where it is harvested for lumber. Similar blisters occur on the hands and face of people who prune these trees. Affected horses recover completely from the vesicular dermatitis once they are removed from the bitterwood-containing shavings.
Grasses such as foxtail barley (Hordeum jubatum) bristle grass (Setaria spp.) and wheat or rye awns can become embedded in the mucous membranes of the cheeks, tongue, and gums, causing painful ulcers, excessive salivation, and difficulty in eating. The grass awns are often not visible in the ulcers, as they are covered by a layer of granulation tissue. A wide variety of plants have the potential to cause irritation and trauma to the mouth of horses if they are present in hay or are abundant in the pasture. Occasionally these plants can cause trauma to the skin; sometimes potentially serious injury to the eyes may result from bristles of burdock (Arctium spp.) and other plants that become lodged in the tissues around the eyes or cornea.
Eating the following plants may also cause excessive salivation: (1) laurel (Kalmia spp.), (2) azalea (Rhododendron spp.), (3) buttercup (Ranunculus spp.), (4) poison hemlock (Conium maculatum), (5) water hemlock (Cicuta spp.), (6) death camas (Zigadenus spp.), (7) yellow star thistle (Centaurea solstitialis, (8) Russian knapweed (C. repens), or tremetol-containing plants such as (9) white snakeroot (Eupatorium rugosum), (10) Crofton weed (E. adenophorum), (11) Jimmyweed or rayless goldenrod (Haplopappus spp.), and (12) Burrow weed (H. tenuisectus). However, colic is the major clinical effect of the first three of these plants. Sudden death is the major clinical effect of the next three plants (numbers 4, 5 and 6), and neurologic-disease resulting in an inability to take in or chew feed (numbers 7 and 8) and muscular trembling (numbers 9 to 12) are the major clinical effects of the last six plants.
Profuse salivation as the only major clinical sign occurs in horses and other livestock eating clover or alfalfa pasture or hay that is infected with the fungus Rhizoctonia leguminicola. The factor responsible has been identified as slaframine, a mycotoxin produced most commonly by this mold on red clover (Trifolium pratense), but may also occur on other common legumes, including alfalfa, white clover, alsike clover, lupines, cow pea, and kudzu. Slaframine is chemically similar to the toxin swainsonine produced by locoweeds (Astragalus and Oxytropis spp.). Under wet or humid conditions, the slaframine producing mold grows on the leaves, producing black or brown spotting. After eating infected legumes for several days, horses begin to salivate excessively, lose weight, and may have excessive tearing or lacrimation, diarrhea, and frequent urination. Pregnant mares may abort if they continue to consume the infected clover. Recovery occurs rapidly once horses are removed from the infected forage. Problem pastures can be grazed if they are mowed, the affected hay is removed, and the regrowth has no brown or black spotting on the leaves.
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