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Learn About Botulism Poisoning


Botulism Poisoning:

We usually think of botulism as something that only affects people. The most common source for botulism poisoning in people is food. Botulism poisoning, although rare, is deadly. And for horses the source is food as well. There are some fodders that can be risky to feed horses and for this reason they should probably be avoided. The key to having any hope of recovery is a speedy diagnoses and treatment.

Other Names for Botulism Poisoning:

Clostridium Botulinum, C. Botulinum

Causes of Botulism Poisoning:

The spores in Clostridium Botulinum, the bacteria responsible for botulism poisoning live in soil throughout our continent. From the soil, botulism spores can be in wet or spoiling feed or it can be in the feed from rotting animal carcasses. As hay is cut and baled, it’s not unusual for small animals like chipmunks, mice and voles, birds, rabbits and snakes to get baled into the bales. Haylage, baylage, or silage provides the ideal anaerobic conditions that botulism thrives in and for that reason these feeds are not recommended for horses. The botulism bacteria can enter the horse’s body either by being ingested or it can enter through an open wound. EGUS can make a horse more susceptible to botulism.

One type of botulism affects foals up to eight months old particularly. Sometimes it strikes so quickly that the foal dies before treatment can begin.


Botulism is a neurotoxin—the toxins block the nerve messages to the muscles. The botulism grows in the horse’s intestinal tract where it produces toxins. These toxins then spread through the horse’s nervous system and if left untreated, paralysis will set in quickly. Horses that are suffering from botulism will have problems swallowing, have trembling, muscle weakness and  the inability stand, shuffling and unsteady gaits, drooping tail and eyelids, lolling tongue and drooling, swelling of head and face, and paralysis of the respiratory muscles leading to death. Symptoms can appear as quickly as a few hours after ingesting the bacteria or spores. Death can occur within twenty-four to seventy-two hours. Foals may show signs of frequent urination and constipation.


Botulism is very difficult to treat in horses because they are very susceptible to the bacteria’s toxin. Your veterinarian will need to diagnose the problem very quickly. This can be complicated because the symptoms can be similar to several other diseases. Treatment of your horse will start with an anti-toxin and must begin promptly, within hours of the initial symptoms. Treatment can be very costly, and the outcome is not certain. Fluids and other supportive therapies may be used as well. While it is possible for a horse to recover, the majority of horses that get botulism need to be euthanized or will succumb to respiratory failure. There is a better chance of recovery if treatment begins while the horse can still stand, but again, there are no guarantees.


Some horse owners may be familiar with feeding their horses silage or haylage. However, the way these feeds are baled and stored makes them the ideal growing medium for botulism. If bales are plastic wrapped, or if they are stored in a silo, they will be kept in the perfect anaerobic conditions of heat and moisture for botulism to grow. If you feel you must feed your horses these types of fodders, talk to your veterinarian about vaccination.

Many people feel the risk of botulism is too great and choose not to feed silage or haylage. Discard any bales that contain dead animals and check water buckets and troughs for drowning victims and take measures to prevent these accidental drownings. Wet and spoiled hay should be discarded.

In some areas, botulism vaccine is recommended for foals to prevent Shaker Foal Syndrome. Because there are variations in the types of botulism, the vaccine will not protect a horse 100%. Vaccinating mares in foal is felt to help protect young foals.


Hayes, M. Horace, and Peter D. Rossdale. Veterinary notes for horse owners: an illustrated manual of horse medicine and surgery. 17th ed. New York: Prentice Hall Press, 1987. Print. "The Merck Veterinary Manual." The Merck Veterinary Manual. N.p., n.d. Web. 9 Feb. 2012. .

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