Beware of Botulism!

Botulism is not seen frequently in horses, but some areas are more prone to this deadly disease than others.
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Beware of Botulism
Botulism is difficult to treat, says Wright, although there are antitoxins that can be effective. | Photo: Anne M. Eberhardt/The Horse
Botulism is a silent, deadly killer with several forms. While it is not a common disease across the United States, it can crop up anywhere. Botulism occurs when toxins produced by the bacterium Clostridium botulinum get into the body of an animal or human. There they cause weakness because they block the connection between nerves and muscles. Paralysis often occurs.

Unfortunately, horses are perhaps the most sensitive of domesticated animals to botulism. They and other mammals can contract the disease in three basic ways:

  • By ingesting toxins that are present in forage, also known as forage botulism. This is the form that normally strikes adult horses.
  • By having growth of the agent in the gastrointestinal system, also known as toxicoinfection botulism. This form normally afflicts young horses.
  • By contamination of wounds, which is also known as wound botulism.

The ingestion of pre-formed toxins in forage is the usual route of infection in adult horses. This type of botulism occurs when the horse consumes bits of decayed or decaying forage that sets up an environment for Clostridium botulinum proliferation and toxin release. Bits and pieces of dead animals that wind up in hay bales is another way in which the disease is introduced. Another route can be the consumption of silage or haylage that has been contaminated by the organism.

In cases where toxicoinfection is the route for introduction of the disease, young horses ingest the spores, which then germinate and produce toxins in the gastrointestinal tract. When this occurs, the foals often are afflicted with what is termed shaker foal syndrome, so called because the foal’s muscles will tremor with neurological weakness as he attempts to stand and walk around the stall

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Les Sellnow was a prolific freelance writer based near Riverton, Wyoming. He specialized in articles on equine research, and operated a ranch where he raised horses and livestock. He authored several fiction and nonfiction books, including Understanding Equine Lameness and Understanding The Young Horse. He died in 2023.

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