Botulism in horses – rare and deadly!


Botulism is RARE in horses – but it does happen. Botulism is rare, deadly, and it does have a vaccine. ​​​​​​​But how do you know if your horse needs to be vaccinated, or if he’s at risk of botulism?


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botulism bacteria under the microscope

These microscopic jerks can kill your horse. Easily.


What is botulism?


  • It’s a bacteria – Clostridium Botulinum. You may recognize Clostridium Tetani, which causes tetanus. This particular botulism bacteria has the ability to produce 7 different toxins – aptly named A to G.


  • The toxic spores live in areas with no oxygen, some moisture, and a specific pH.


  • While we think botulism mostly lives in decaying animal matter, it’s really more likely to be found in decaying vegetation.


  • It’s the B version to be really worried about – it’s the most toxic to horses. The B strain of C. Botulinum is commonly found in the North East US and Appalachia, but it could be anywhere.


  • Type C of the toxin is usually found in association with decaying animals and bird droppings, which is a great reason to keep birds out of barns.


  • You also have Type A of the botulism family of bacteria, which likes to live in the Northwest US, but is typically not a problem with horses.


gray horse getting vaccinated in the neck

Prevent with vaccines. Treat with antitoxin if possible.


What happens if your horse is infected with botulism?


  • Well – the botulism toxin will interfere with your horse’s neurological system by not letting the muscles respond to the nerves.


  • You will likely see problems eating, swallowing, moving ears, blinking. Your horse might also lose function in his tail, and in some cases, your horse must lay down because of paralysis.


  • The amount of toxin influences how sick he becomes. Some horses have mild cases, other horses die within days from the lungs and heart-stopping as the pulmonary and cardiac muscles are paralyzed.


  • The signs of botulism also mimic those of rabies, EEE, WEE (more on those here) and other neurological diseases.


There is an antitoxin that can be administered.


  • It will help with the spread of the toxin, but it can’t repair damage already done to the nerves.


  • Very often in a horse that is down, there is nothing more to do. There is also a test to detect the botulism toxin, but it can take up to 10 days, in which case it is likely too late.


vet holding a horse tail for neurological exam

Your vet will need to do a neurological exam.


Any time your horse has neurological signs, call the vet. Immediate intervention is key.


  • So how does your horse end up with botulism toxicity? Well, it’s everywhere in the soil – but remember that it really enjoys anaerobic and wet conditions, which means hay is a common location.


  • Round hay bales are recipes for botulism salad. Round bales often rest on the ground, are rained on, and can be a very tempting hotel for C. Botulinum.


  • There’s also the risk that an animal has died in the haymaking process, but that’s typically Type C.


  • You can also find risky amounts of botulism in hay bales that are improperly stored, hay that is thrown on the ground, and haylage or silage for cows. DUDE don’t feed this to your horse ever.


  • Hay tossed on wet/damp/muddy creates that moist environment that C. Botulinum loves. Also, remember about grass clippings! (More on that here!)



round hay bales in hay field


Botulism may find its way into a wound that scabs over quickly.


  • Punctures are notorious for doing this, and the depth of the wound has that anaerobic factor. Even a tiny wound can be trouble, which is why clipping, cleaning, and a quick photo to your vet is a good idea. For any size wound.


The horse world is very lucky that there are vaccines for C. Botulinum, types A and B.


  • Depending on the type of vaccine, your horse might need an initial series and yearly boosters. These are a must for the horse that eats from a round bale or has hay tossed into a paddock. Using deep trough-like feeders for outside feedings is best.


  • If you have a broodmare, in some parts of the country she should be vaccinated. Foals can develop (and die from) botulism-related Shaker Foal Syndrome. A broodmare properly vaccinated can pass along necessary antibodies.


Again – botulism is rare in horses, but it’s also deadly. If your horse has any risk factors, talk to your vet about vaccinations against botulism.


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