"Doc – Does summer bring on horse problems that may not be seen during the rest of the year??"
© A.J. Neumann, D.V.M.
published in The Draft Horse Journal, Autumn 2004

Let’s look into four common problems of the horse which I see occurring in late spring and summer.

EXCESSIVE SALIVATION

“White Clover Slobbers” – Mare slobbers about one pint to one quart of saliva at a time. She has been on a white clover pasture for about 30 days.

Close up of white clover in the pasture. Notice the brown to black spots on the clover leaves. This is the fungus which causes the problem of the excess salivation of the mare.

Let’s take the first one and call it “excessive salivation” or “slobbering.” When this condition occurs the animal is frothing or drooling a large amount of saliva. This generally will be the result of a chemical, traumatic or infectious injury to the mouth. It could also be a symptom of “choke” in which the esophagus is plugged and the animal cannot swallow. Factors causing the trauma may be a poor fitting bit, points on the molars or the ingestion of thorns and bristles, which have injured the mucous membrane of the mouth. Infectious diseases such as vesicular stomatitis and rabies will also cause the affected animal to slobber. All of these causes for excessive salivation must be checked out in making a diagnosis.

If profuse salivation is the only clinical sign or symptom and the horse, mule or donkey is on pasture look to see how much clover or alfalfa is available for consumption. Common legumes such as alfalfa, red clover, white clover, alsike clover, lupines, cow peas and kudzu can be infected with the fungus Rhizoctonia leguminicola which produces an indolizidine alkaloid mycotoxin known as slaframine. This mycotoxin is occasionally found in red clover and alfalfa hay.

During hot, humid and wet seasons white clover grows abundantly in many pastures. The mold grows on the small leaves, producing black or brown spots on them, which can easily be seen. Horses love white clover and after eating the infected plant for several days they begin to slobber a large amount of saliva. They may “run at the eye,” have diarrhea, lose weight and their mucous membranes may turn slightly yellow. One noticeable symptom is frequent urination with the urine being yellow in color. Pregnant mares, eating much infected clover, may abort.

Overall the most pronounced symptom is the excessive drooling of pints or quarts of saliva at a given time.

Horses so affected will recover quickly in three or four days if removed from the clover pasture. They can be returned to the pasture after it has been mowed, the infected hay removed and destroyed and the new forage does not show the brown or black spots on the leaves.

As a boy growing up among horses and horse people I heard this often called “the white clover slobbers.” By the way, it will also affect cattle and sheep.

You would be very surprised to find this condition is often misdiagnosed. The pictures I show you here illustrate a case I had in July 2004. One vet thought it was her teeth; another thought it might be vesicular stomatitis. The mare was pastured on a two-acre area just covered with white clover due to abundant rainfall and the ideal weather to produce the growth of the forage.

FOXTAIL TRAUMA

Now let’s look at a second condition we often see in the summer and it may carry over into the winter. I call it “foxtail trauma.”

This condition occurs when a pasture becomes overgrazed or the normal forage grasses do not grow due to drought. It also occurs when the owner of the livestock becomes desperate for hay and he mows oat or wheat stubble fields and puts up the clippings for hay.

Cattle will generally eat any type or kind of forage. Horses and mules are more selective, however, they will eat almost anything when faced with a lean table. Towards the end of the summer some animals find themselves forced to eat foxtail barley, bristle grass and wheat or rye stalks containing their awns. If they are then fed poor hay containing a large amount of foxtail barley, the problem worsens.

These animals will exhibit excessive salivation and drooling. They will have difficulty in eating and begin to lose weight. An examination of the mouth, tongue and cheeks will reveal a large number of ulcers present in the mucous membranes. The ulcers will be especially prominent at the gum line near the teeth. The animal will probably have very bad breath. You will not see the barbs or awns, as they are deep in the tissue.

Treatment of this condition is simple. Remove the horses from the pasture or hay being fed and feed them coarse stemmed alfalfa roughage mixed with good quality grass hay. The act of chewing the coarse stemmed roughage will remove the barbs and the ulcers will soon heal. It will not take long and the animals will be back on course.

PHOTOSENSITIVITY OR “DEW POISONING”

A third common disease or condition of the horse and mule which is seen primarily in the summer is known as “photosensitivity.”

This condition occurs in horses which are grazing clover, especially alsike clover, in wet and humid weather. It does not have to rain but will occur simply in dew laden clover pastures. The affected horses will develop a photosensitivity and hepatitis known as Trifoliosis. Horses and sheep grazing on kleingrass in hot humid weather will also succumb to the same condition.

Horses grazing on clover pastures will develop an acute photosensatization involving the white areas of the muzzle, lips, nose and the areas of the feet between the bulbs of the heel. These areas of dermatitis will blister and peel. The condition is commonly referred to as “dew poisoning” because of the location of the dermatitis and its contact with the dew and clover in the pasture. Some of these horses will have yellow mucous membranes and when blood is drawn and tested will have high serum elevations in liver enzyme tests. Sometimes these horses may show liver degeneration and enlargement of the organ.

Occasionally some of these affected horses will show a good amount of swelling in the knee, hock and pastern joints.

In my experience these afflicted horses will recover if removed from the pasture. I apply olive oil, to which I have added some dexamethazone, to the photosensitized area of the nose, muzzle and the rear areas of the feet. It is best to keep the horse out of the sun for a week or so. For those animals which have swollen joints, I put them on anti-histamines and dexamethazone for several days. They respond to the treatment very well.

I have included pictures of a young roan filly which illustrate the “dew poisoning” condition. You will notice the areas of photosensitization and the swollen joints. She fully recovered in about a week. Horses may graze the same pasture without problems when growing and weather conditions become drier.

SUMMER SORE

The so-called “summer sore” is the fourth disease or condition, which plagues the horse population especially in the summertime.

There are three species of stomach worms that invade the equine’s stomach. Since house and stable flies act as intermediate hosts for these parasites and the larvae the flies carry often invade wounds and abrasions on the horse, one can readily see this becomes a seasonal problem. Through the action of these flies, wounds, especially those that are left unattended, may be infected with untold numbers of the microscopic larvae. With the larvae present in the tissue more so-called “scar tissue” is formed due to the irritation in the area. These summer sores can expand into non-healing ugly appearing masses of connective or scar tissue.

In addition, due to the flies’ activities, larvae will invade the eyes and the conjunctiva causing a chronic infection of the area called conjunctivitis.

With the advent of the drug ivermectin, it became possible to control the stomach worm adults as well as the larvae in the tissues of the horse, as the drug will destroy the larvae regardless of where they reside in the host animal.

The treatment of summer sores today is relatively simple. If there is a large mass of infected tissue at the wound site, it should be surgically removed. The area then should be treated daily with a good wound medicine containing among other things, ivermectin.

I have injected small amounts of ivermectin into these wounds with apparently excellent results as well as using the topical wound treatment.

It is also important to treat the animal orally every month for several times with the proper dose of a worming product containing the drug ivermectin.

There are probably more conditions of the equine, which are summer related, but I believe the four I have discussed are the most common and several of them may challenge a person’s diagnostic ability when he or she first encounters them.