Vaccination is the only way to provide protection against tetanus. A potentially deadly disease, tetanus occurs when a wound becomes infected with the bacterial spores, Clostridium tetani. Once inside a horse’s body, the spores germinate and produce a poison that affects muscles: Horses with tetanus become stiff and rigid; they may fall and be unable to rise. Paralysis of the breathing muscles can lead to death. A tetanus antitoxin exists, but it’s expensive and often unsuccessful. The American Association of Equine Practitioners recommends an annual tetanus vaccination, with special recommendations for foals.