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Feeding Horses
Medical Index
First Posted: July 21, 2008
Updated: Feb 9, 2014

Botulism in Horses

by Debora Johnson

Update: Botulism in Horses: An Update
Diagnosing and Managing Tetanus and Botulism in Horses (An excellent article)
Diseases that can be caused from dietary origin
Botulism (Merck Vet Manual)

A bacteria, Clostridium botulonum causes botulism in horses. Tetanus is caused by a bacteria that is closely related. It is called Clostridium tetani. The botulism bacterium is found in the soil. The toxins produced by C. Botulinum is one of the most potent poisons known to man. Horses are particularly sensitive to botulinum toxin; untreated foals can suffer up to 90 percent mortality. Mortality is also high in untreated adults.


You may notice some of the following:
  • Unable to swallow food
  • Unable to drink water
  • Saliva drips from lips
  • Grain falls out of mouth
  • Loss of coordination
  • Ataxia
  • Muscle tremors
  • Depression
  • Protruding tongue
  • Dilated pupils
  • Constipation
  • Colic
  • Shortness of Breath
  • Spasms and/or seizures
  • Inability to stand

These symptoms mimic other horse diseases such as rabies, equine protozoal mylitis (EPM) tetanus, and tying-up (Azorturia), however, the horse's decline is rapid. The more the toxin the faster the decline. Botulism is considered one of the most deadly poisons known to man.

Shaker foal syndrome is a term used to describe botulism in foals.


Bad hay and silage that has been stored improperly can become contaminated. Decomposition of rodents, birds, and other carcasses in baled hay are often blamed. Large round bales of hay put a horse at greater risk for botulism.


An antitoxin can be given but it is very expensive.


Botulism may be prevented through vaccination with BotVax B.

For More Information:

Beat Botulism
Botulism in Horses/University of KY Extension Service
Botulism in Horses and Haylage
Type A botulism in horses in the United States: Review of the past ten years (1998-2008)

Feeding Horses
Medical Index