Botulism and Horses
By Eleanor Blazer

        One of the world's most powerful toxins may be living in your barn or pasture. 

        This toxin, clostridium botulinum, is commonly known as botulism.

        One microgram is lethal, and there are a 1, 000,000 micrograms in a gram.  A dime weighs about a gram, so it doesn't take much.

        Botulism toxicity kills 70% of untreated adult horses.  Nearly 90% of all affected foals will die.

        In adult horses the first sign of botulism toxicity may be dysphagia - difficulty in swallowing.  The affected horse may drop water and feed from the mouth.  He will have an appetite, but be unable to eat or drink.  Other symptoms include weakness, depression, muscle tremors, inability to move or a stiff choppy gait when moving, respiratory stress, dilated pupils, colic or constipation.  The symptoms may progress quickly, or occur over several days.  The amount of toxin ingested affects the severity and progression of the symptoms.

        The symptoms of botulism poisoning can mimic other diseases.  Tetanus, rabies, lead poisoning and equine protozoal encephalomyelitis (EPM) are a few.  The veterinarian should be able to rule out most of these illnesses based on observing the central nervous system, asking about the horse's general health and the events leading up to the onset of the symptoms.

        Horses that are exposed to a large amount of the toxin may be found dead with no previous symptoms.

        An affected foal will have trouble swallowing; milk will run out of the mouth when trying to nurse.  The foal will lay around an abnormal amount of time, with the head resting on the ground.  As time passes the foal will become weaker and develop muscle tremors.  The term "shaker foal syndrome" is a common name for the disease in foals.

        The veterinarian will try to rule out other foal illnesses such as selenium deficiency, polyarthritis, hypoglycemia and septicemia (navel ill).

        Diagnosing botulism may come too late to treat the killer.  It takes time to run the tests and results can be inconclusive.  If a veterinarian suspects botulism, treatment is generally started immediately.

        Treatment can be expensive and time consuming.

        Horses fighting botulism poisoning must have their activity controlled.  Physical movement accelerates the progression of muscle weakness and increases the possibilities of death.  Mineral oil is usually given to aid in the passage of the toxin and help prevent impaction colic.

       The veterinarian may administer an antitoxin, which is very expensive.  The horse cannot be down and the antitoxin must be given early in the progression of the illness to be reasonably successful.

        Protecting the horse from exposure to botulism can be difficult as the botulism is in the soil. Decaying vegetation and animal carcasses give the spores the perfect incubation environment.  The bacterium likes a warm moist medium that is slightly alkaline.

        Improperly fermented haylage or silage, hay not completely dry before baling, dried hay not stored properly, the presence of a dead animal in the feed or dead animal carcasses in the drinking water are all avenues of contamination.  Large round bales of hay are frequently the source of botulism poisonings. The contamination of a wound or umbilical stump can also cause the illness.

        There are currently eight types of c. botulinum identified.  These are types A, B, C1, C2, D, E, F, and G.  Horse owners need only be concerned with A, B and C.  The most prevalent type to affect horses is Type B.

        A vaccine to prevent Type B is available.  Consult your veterinarian.

        Being vigilant and practicing good management can alleviate the exposure risk.  Silage and haylage should not be fed to horses that have not been vaccinated against c. botulinum.  Hay should not be baled unless its moisture content is less than 35 percent.  Hay processing equipment should not be set low to the ground - gathering soil into the bales must be avoided.  Throw out any bales of hay where dead animals are found. Water sources must be kept clean.

        Horse owners must be aware of the dangers that may lurk in the shadows.
        Proper nutrition and management practices can prevent many problems associated with caring for horses.  You can learn how to provide your horse with a better life-style by taking the online course "How to Feed for Maximum Performance" taught by Eleanor Richards Blazer.

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