These days—fortunately—few horses die of botulism and tetanus. One reason why is the availability of two types of products: toxoids, which prevent disease, and antitoxins, which treat it.

Toxoids stimulate the production of antibodies

A toxoid is a modified bacterial toxin that has been treated, typically with formaldehyde or heat, to remove its damaging properties while maintaining its ability to stimulate an immune response. The botulism toxoid vaccine, for instance, stimulates a horse’s immune system to produce antibodies to the toxins released by Clostridium botulinum spores. The antibodies then neutralize the toxins, preventing disease.  

The tetanus vaccine is also a toxoid product. So are vaccines that protect people against pertussis and diphtheria. For optimal protection, horses receive annual boosters after completing the initial vaccine series.

Antitoxin contains antibodies derived from immunized animals

Unlike toxoids, which stimulate the production of protective antibodies,  antitoxin contains preformed antibodies derived from immunized animals. Antitoxins are used therapeutically rather than preventively. If a horse develops botulism, for example, he receives botulism antitoxin to neutralize toxins already in the bloodstream. Likewise a horse with tetanus is treated with a tetanus antitoxin.

An antitoxin can prevent further damage, thus slowing or halting the progression of disease. But it cannot reverse the damage that toxins have already done. Horses treated with antitoxin are also provided supportive care.

In addition to botulism and tetanus, antitoxin products are available for treating snake bites in horses. As with any treatment, antitoxin therapy has risks as well as benefits. Your veterinarian will make a diagnosis before prescribing an antitoxin.