Three out of four draft horses on a property in New York (NY) were found acutely down in lateral recumbency on December 17, 2025. All three recumbent horses were afebrile, dysphagic with decreased tongue tone, and exhibited uncoordinated limb movement. All three recumbent horses were euthanized. The fourth horse was standing but depressed with decreased gut sounds and rapidly progressed to recumbency over the following 24 hours, after which he was euthanized. The horses were fed round bales only and lived in a barren pasture. The top differential was botulism toxicity associated with the consumption of round bales containing pre-formed Clostridium botulinum toxin. The attending veterinarian contacted the Veterinary Support Services veterinarian at the Animal Health Diagnostic Center (AHDC) and after a phone consultation, serum and feces were collected from all four horses, and stomach contents and liver were collected from one of the euthanized horses. Samples were submitted to the NY Department of Health Wadsworth Center. Fecal samples on all horses were positive for Clostridium botulinum type B by real-time PCR and two of the fecal samples were positive for Botulinum neurotoxin type by MALDI TOF MS, indicating presence of active toxin.

Clostridium botulinum is a gram-positive rod-shaped anaerobic spore forming bacterium that can persist in the environment.¹ There are 7 toxins (A through G)² and C. botulinum type B is found in the eastern US,¹ in improperly stored hay and animal feed that favors an anaerobic environment. C. botulinum type C is associated with animal carcasses and occurs when an animal accidentally gets baled up in the hay when the hay is harvested.³ Horses are highly susceptible to very small doses of Clostridium botulinum. It causes neurologic disease presenting with flaccid paralysis. An inability to swallow is a prominent clinical sign in affected horses. This was a classic presentation of an equine outbreak due to feeding of round bales. There is a USDA approved vaccine called Neogen®Vet BotVax® B⁴ available for C. botulinum type B. A nearby horse farm feeding the same round bales vaccinated their herd after this diagnosis. C. botulinum neurotoxins are classified as select agents by the CDC and USDA⁵ and detection in animal samples requires notification to the CDC and confirmation of destruction of any remaining samples in a diagnostic laboratory.

References

1. Johnson A. AAEP Infectious Disease Guidelines: Botulism. Accessed December 30, 2025.
2. WHO. Botulism. Accessed December 30, 2025.
3. Press release - FDA confirms Clostridium Botulinum type C was found in alfalfa hay cubes tied to the death of multiple horses in Louisiana. Louisiana Department of Agriculture and Forestry. Accessed January 2, 2026.
4. Neogen®Vet BotVax® B | Animal Care. Available online. Accessed December 30, 2025.
5. Select Agents and Toxins List | Federal Select Agent Program. 2025. Accessed December 30, 2025.