Disease Reference: Botulism

The causes, treatment, and prevention of botulism in horses.


Horses are more sensitive to botulism than any other domesticated animal species. The bacterium that causes this disease is ubiquitous in nature, especially in soil.

Horse with a round bale of hay

Causes and Symptoms of Botulism

Botulism occurs when toxins produced by the bacterium Clostridium botulinum enter a horse’s body via a wound or, more commonly, through contaminated feed and water. The bacterium can be harbored in moldy feed; it can also grow on animal carcasses. Botulism infection is sometimes associated with hay fed in roundbales if a rodent carcass, for example, ends up in the hay during the baling process.

Symptoms, Treatment and Prevention

Botulism can cause weakness, paralysis and death in horses. While an antitoxin exists for horses affected by the disease, it’s costly and many die despite treatment.

A vaccine to prevent botulism is also available; the American Association of Equine Practitioners (AAEP) recommends vaccination only in endemic areas, with special recommendations for foals.

For more information, visit www.aaep.org.

Further Reading
What’s Lurking in Your Hay?


  1. I lost my loved 7 year old Fox Trotter gelding to botulism several years ago. It took him less than one day from just not looking okay to dead. The vet could do NOTHING for him except to spare him the last throes… The horror of it is still with me. By the time this is diagnosed, it is already too late… It was and is a mystery as it did NOT come from his hay or feed. That it was botulism was confirmed by his brain tissue. My other horse who was in the adjacent pen never showed any symptoms.


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