Equine Botulism Vaccine

Why Should Horses Be Vaccinated? | Botulism | Vaccination Against Botulism

Equine Vaccination Recommendations

  • Many serious equine diseases, such as botulism, can be prevented through vaccination.
  • Equine vaccinations are typically administered in the spring and the fall; however, vaccination against botulism can be given at any time during the year because the organism is in the soil.
  • Remember to maintain accurate records of your horse's vaccination history.
  • Vaccine recommendations are based on an individual horse's geographic location, usage (e.g., show horse, broodmare, trail horse), likely travel plans, management, and age.

Why Should Horses Be Vaccinated?

Many diseases in horses can be serious and even life threatening. They can be expensive to treat and may require significant recovery periods, during which the horse cannot be shown, transported, bred, or ridden. Vaccination is a relatively inexpensive and effective way of helping protect equine health. Thankfully, effective vaccines are available for many serious infectious diseases, such as botulism. On many farms, vaccines are typically administered seasonally, in the spring and the fall. However, vaccination against botulism can be given at any time during the year because the organism is in the soil; therefore, horses can be exposed year-round.

The decision of whether to vaccinate a horse against botulism depends on the animal's individual risk factors, such as geographic location, likely travel or competition plans, potential for exposure to other horses (boarding stable versus backyard barn), age, breeding status, and overall health. Consult your veterinarian about which vaccines are appropriate for your horse.


Botulism is caused by the bacterium Clostridium botulinum. This bacterium can be present in soil as spores, especially in certain areas of the United States (e.g., the mid-Atlantic states), and can be found in areas without sunlight and oxygen. The spores can germinate into active bacteria that produce a neurotoxin (a poison that affects the brain and nervous system) called botulinum toxin. Horses are extremely sensitive to this organism's toxin and its spores; they may be exposed by eating food (e.g., hay, grain, treats) contaminated with the toxin or the spores themselves or through contamination of wounds with soil that contains spores. This infection can occur at any time of year. The disease is not contagious, but outbreaks may occur if horses eat contaminated hay or grain; for example, round bales may become contaminated with botulism spores and can cause many horses on the farm to develop botulism at once. [One of the common ways of feed sources becoming contaminated with botulism spores is through dead animal carcasses decomposing in the feed source.] [The previous sentence does not appear on Vetlearn] Signs of infection can include difficulty chewing/swallowing and progressive weakness, culminating in recumbency (inability to stand) and death.

Botulism is diagnosed with a thorough physical examination and blood and/or fecal tests. Horses with severe infection often require intensive care to survive, and treatment such as administration of antitoxin is expensive. Additional treatment may include antibiotics to help prevent/treat pneumonia (due to inhalation of secretions from lack of proper swallowing) and supportive care, including intravenous fluids and feeding the horse through a tube a few times per day. Horses that are severely affected are likely to develop severe problems such as paralysis and inability to breathe, leading to death.

Vaccination Against Botulism

Vaccination helps prevent botulism and requires an initial series of three vaccines followed by an annual booster. Foals at high risk in an area where infection risk is high can be vaccinated as early as 2 weeks of age, so contact your veterinarian regarding a vaccination schedule for foals. Once you have given the initial series, it is vital to vaccinate your horse at the same time every year so that no more than 12 months pass between vaccinations. If the vaccination lapses for even a few months, horses can develop this preventable disease.

It is important to remember that vaccination is a medical procedure. Consult your veterinarian in order to determine which vaccines are appropriate based on the disease risk analysis for individual horses.