Botulism
Learn what the condition is, how it may be detected early, how it is treated or managed, and which breeds or species are linked to it.
Condition snapshot
A concise guide to the condition’s pattern, detection, management and urgency.
Emergency presentation is possibleProgressive weakness, dysphagia, recumbency or breathing difficulty requires emergency veterinary care.
This snapshot is a general guide, not a diagnosis or treatment plan. New, severe or worsening signs require veterinary assessment.
About the condition
Botulism is a rapidly progressive flaccid paralysis caused by neurotoxin from Clostridium botulinum. Adult horses most often ingest preformed toxin in spoiled forage, silage, haylage or feed contaminated by a decomposing animal carcass. Less commonly, bacteria produce toxin in a wound. Very young foals can develop toxicoinfectious botulism, or shaker foal syndrome, when organisms multiply in the intestine.
The toxin prevents acetylcholine release at neuromuscular junctions, so muscles cannot contract normally even though sensation is generally retained. Early signs include reduced tongue and tail tone, slow chewing, difficulty swallowing, weak eyelid movement, dilated pupils and a short, stiff or trembling gait. Weakness progresses symmetrically to recumbency. Aspiration, inability to clear respiratory secretions and paralysis of breathing muscles cause many deaths. Foals may tremble, tire after standing for only a few minutes and develop constipation before collapse.
Botulism produces weakness, in contrast with the rigid stimulus-sensitive spasms of tetanus. It does not usually spread directly between horses, but multiple animals can be poisoned by the same contaminated feed. Removing the suspected batch is therefore urgent even before laboratory confirmation.
Detecting toxin is difficult and negative testing is common, so diagnosis often rests on characteristic neuromuscular findings, exposure history and exclusion of other causes. Prognosis depends on toxin dose, speed of progression and whether the horse can remain standing and breathe. Recovery is possible because nerves can form new functional endings, but severely affected horses need weeks of intensive support and recumbent adults have a poor outlook.
Botulinum neurotoxin prevents acetylcholine release at neuromuscular junctions, causing flaccid rather than rigid paralysis. Horses may acquire toxin from spoiled forage or carcass-contaminated feed, ingest spores that germinate in wounds, or develop toxicoinfectious disease as foals. Weak tongue tone, dysphagia and recumbency can progress while sensation and awareness remain intact.
Screening & Early Detection
When botulism is suspected, all horses sharing the forage or feed source should stop receiving it immediately. The batch, wrapping, storage conditions and any carcass contamination are documented, and representative samples are retained safely for veterinary or regulatory testing rather than discarded indiscriminately. Other exposed horses are watched closely for swallowing change, weak tongue retraction, tremor and reduced tail tone.
Veterinary examination evaluates cranial nerves, tongue strength, eyelid movement, gait, spinal reflexes, sensation and respiratory function. Endoscopy can identify pharyngeal weakness or aspiration. Blood gas measurement and thoracic imaging help assess respiratory compromise and pneumonia. Feed, serum and gastrointestinal contents may be tested for toxin, while organism culture is more relevant to toxicoinfectious foals or wound botulism. A negative toxin result does not exclude the disease.
Differentials include equine motor neuron disease, tick paralysis in relevant regions, organophosphate toxicity, severe electrolyte disturbance, spinal disease and other causes of dysphagia. A cluster linked to one feed strongly supports intoxication. Because antitoxin is most useful before extensive toxin binding, diagnostic uncertainty should not create an avoidable treatment delay.
Treatment & Management
Botulinum antitoxin neutralises circulating toxin but cannot reverse toxin already bound at nerve endings. It should therefore be given as early as possible when clinical suspicion is strong, using a product covering the likely toxin type and under veterinary supervision. Suspect feed is withdrawn, any infected wound is debrided and toxicoinfectious foals receive appropriate additional therapy.
Supportive nursing determines survival. The horse needs quiet deep bedding, frequent repositioning, eye and skin care, bladder and manure monitoring, and protection from aspiration. Swallowing is assessed before anything is given by mouth; intravenous fluids and enteral or parenteral nutrition may be required. Oxygen, airway suction or mechanical ventilation is considered where available. Antimicrobials treat aspiration pneumonia or wound infection, not toxin already absorbed, and drugs that further impair neuromuscular transmission are avoided.
Recumbent adult horses are difficult to support safely and may develop pressure injury, muscle damage and respiratory failure. Slings can help selected patients but require continuous skilled supervision. Recovery takes weeks as neuromuscular transmission returns. Prevention relies on high-quality correctly stored forage, rejecting spoiled or carcass-contaminated feed and regional vaccination where a licensed toxoid matches the local risk. Other horses exposed to the same source need veterinary assessment even if currently normal.
Breeds or species affected
Akhal-Teke
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Anglo-Arabian
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Arabian
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Barb
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Caspian
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Kathiawari
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Marwari
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Shagya Arabian
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Thoroughbred
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American Quarter Horse
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American Paint Horse
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Appaloosa
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Australian Stock Horse
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Brumby
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Waler
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Morgan
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Standardbred
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American Saddlebred
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Tennessee Walking Horse
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Missouri Fox Trotter
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Rocky Mountain Horse
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Peruvian Paso
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Criollo
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Mustang
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Canadian Horse
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Andalusian
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Lusitano
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Lipizzaner
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Friesian
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Dutch Warmblood
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Hanoverian
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Holsteiner
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Oldenburg
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Westphalian
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Trakehner
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Selle Français
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Belgian Warmblood
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Danish Warmblood
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Swedish Warmblood
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Swiss Warmblood
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Australian Warmblood
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Irish Sport Horse
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Cleveland Bay
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Württemberger
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Zangersheide
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Knabstrupper
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Orlov Trotter
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Camargue
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Icelandic Horse
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Pony of the Americas
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Quarter Pony
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Miniature Horse
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Clydesdale
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Shire
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Percheron
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Belgian Draft
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Suffolk Punch
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American Cream Draft
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Ardennes
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Breton
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Boulonnais
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Comtois
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Dutch Draft
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North Swedish Horse
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Norwegian Fjord
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Haflinger
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Gypsy Cob
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Irish Draught
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Welsh Pony and Cob
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Connemara Pony
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New Forest Pony
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Dartmoor Pony
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Exmoor Pony
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Shetland Pony
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Highland Pony
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Fell Pony
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Dales Pony
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Australian Pony
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Finnhorse
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Black Forest Horse
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