How equine botulism differs from similar ailments

Equine botulism is a progressive neuromuscular disease that quickly leads to paralysis. It typically causes death via respiratory failure when not treated soon after the onset of clinical signs. The disease happens due to a toxin produced by the spore-forming bacteria Clostridium botulinum. The most common type of toxin produced is type B, which accounts for 85% of cases in the U.S.

C. botulinum is mostly found in the soil, which can lead to it contaminating feed, especially in the eastern half of the country. Feed contaminated with animal carcasses, or that hasn’t been properly dried, processed or stored, is most at risk.

Initial symptoms

Symptoms can show up 12 hours post-intoxication and are usually observed within 24 hours. Initially, horses will display dysphagia, or difficulty in swallowing. They’ll eat more slowly, and foals will leak milk from the mouth while suckling. Horses will also demonstrate poor muscle tone, particularly noticeable in the eyelids, tongue and tail. Their muscles may tremor, and as the condition progresses, they may be unable to stand, showing many of the same symptoms as colic. Despite similar early symptoms, however, colic and botulism are two very different illnesses.

A real-world example

In an article for The Horse, veterinarian and professor Amy Johnson breaks down the case of a five-year-old Thoroughbred that was diagnosed with equine botulism after displaying colic-like symptoms.

“She was trembling, sweating, looking very distressed and wanting to lie down,” Johnson said. “Her heart rate was high, 60–80 beats per minute, and she didn’t have very good gastrointestinal sounds when we listened to her.”

The horse showed no signs of fever but struggled to swallow the stomach tube given to her. Two other factors rang the botulism alarm bell: When the horse laid down, her sweating and shaking stopped, as she was no longer straining her failing muscles; and typical painkillers used for colic didn’t seem to help, because the horse was experiencing weakness, not pain.

Once these symptoms were noted, Johnson conducted a tongue stress test and a grain test to distinguish the horse’s condition, equine botulism, from other possible ailments.

(You can read the full details of the case at


A vaccine against equine botulism, BotVax® B, inoculates against the disease in three doses, each one month apart, and then once a year. It’s the only U.S. Department of Agriculture-approved C. botulinum type B toxoid licensed for preventing equine botulism in healthy horses.

Johnson also suggests knowing the geographical origin and the harvest practices used for your hay. Because C. botulinum is an anaerobic bacteria, it doesn’t need air to survive, making it easy to thrive in large round bales. Mold also thrives in these conditions, so discard hay that looks or smells moldy.

Johnson also advises keeping areas around feeders clean and free of mud and water, watching out for small animal carcasses in the hay, and avoiding the use of fermented feeds such as haylage and silage.

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