Botulism Trends & Care in Horses – 2025 Vet Guide 🐴🦠

By Dr Duncan Houston, BVSc

Introduction

Botulism—a serious flaccid paralysis caused by Clostridium botulinum toxins—is increasingly diagnosed in horses. A 2005 report noted growing numbers :contentReference[oaicite:1]{index=1}, and modern data confirm upticks, especially linked to contaminated round-bale hay and improper silage :contentReference[oaicite:2]{index=2}. This updated 2025 guide offers owners vital insight on prevention, recognition, and treatment to protect horses effectively.

Why Botulism Risks Are Rising

• Feeding round bales poses high risk due to potential carcass contamination during baling :contentReference[oaicite:3]{index=3}.
• Feed spoilage—poorly cured haylage or hay ensiled too moist—creates conditions for toxin production :contentReference[oaicite:4]{index=4}.
• Although regional hotspots exist (e.g., “Botulism Belt”), spores are globally widespread—anywhere horses graze or consume feed :contentReference[oaicite:5]{index=5}.

How Horses Contract Botulism

Three main forms occur:

1. Forage poisoning: Eating preformed toxin in contaminated feed (most common in adults) :contentReference[oaicite:6]{index=6}.
2. Wound botulism: Growth of C. botulinum in deep wounds creating anaerobic toxin generation :contentReference[oaicite:7]{index=7}.
3. Shaker foal syndrome: Spore germination in the immature foal gut produces toxin; foals are particularly at risk :contentReference[oaicite:8]{index=8}.

Key Clinical Signs

• Progressive weakness, exercise intolerance, muscle tremors :contentReference[oaicite:9]{index=9}.
• Flaccid paralysis of tongue; difficulty swallowing; “tongue-hanging” test is diagnostic :contentReference[oaicite:10]{index=10}.
• Reduced tail, eyelid tone; drooling; nasal discharge :contentReference[oaicite:11]{index=11}.
• Horses often calm when recumbent—unlike colic horses, which display pain :contentReference[oaicite:12]{index=12}.
• Respiratory paralysis is often fatal if untreated :contentReference[oaicite:13]{index=13}.

Diagnosis Challenges

Tests are slow and insensitive:

• The mouse bioassay (5+ days) yields many false negatives :contentReference[oaicite:14]{index=14}.
• PCR tests are not yet widespread :contentReference[oaicite:15]{index=15}.
• Diagnosis is often clinical—based on signs, feed history, and toxin exposure :contentReference[oaicite:16]{index=16}.

Treatment Strategies

• Antitoxin: Early administration halts progression; systemic antitoxin is essential :contentReference[oaicite:17]{index=17}.
• Supportive care: Stall rest, deep bedding, frequent repositioning, tube feeding, eye lubrication, ventilatory support if needed :contentReference[oaicite:18]{index=18}.
• Antibiotics may be prudent in wound or toxico-infectious cases, but avoid aminoglycosides that worsen neuromuscular blockade :contentReference[oaicite:19]{index=19}.

Survival & Prognosis

• Adult survival ranges from 50–90%, but drops significantly in recumbent cases :contentReference[oaicite:20]{index=20}.
• Foals with supportive intensive care can have survival rates up to ~88% :contentReference[oaicite:21]{index=21}.
• Earlier intervention markedly improves outcomes—delays can be fatal.

Vaccination & Prevention

• Type B toxoid vaccine is highly effective (~95%) and safe for adults, pregnant mares, and foals >2 weeks :contentReference[oaicite:22]{index=22}.
• But it does not protect against types A or C :contentReference[oaicite:23]{index=23}.
• Vaccine protocols include an initial series followed by annual boosters; pregnant mares can confer maternal immunity to foals :contentReference[oaicite:24]{index=24}.

Biosecurity & Feeding Best Practices

• Inspect all hay—discard moldy or discolored bales.
• Avoid round bales or high-moisture silage; use dry hay and store elevated off ground :contentReference[oaicite:25]{index=25}.
• Eliminate decaying vegetation, lawn clippings, and carcasses near feed areas :contentReference[oaicite:26]{index=26}.
• For high-risk regions or feed types, vaccinate accordingly.

Case Study: Round Bale Botulism Outbreak

1. Four horses in one barn fed from a newly purchased round bale developed weakness, drooling, tongue paralysis within 24h.
2. Rapid antitoxin administration in two horses saved them; two others remained recumbent and were euthanized.
3. Hay was tested—mouse bioassay confirmed botulism. Farm switched to square-bale, vaccinated herd, and no further cases occurred.

Conclusion

Botulism is a rising threat in equine care—but understanding risk factors, promptly recognizing early signs, and taking rapid preventive and medical action can dramatically improve outcomes. Vaccination, safe hay management, and awareness during hay season are your best defenses.

If you suspect botulism or want tailored prevention advice, contact Ask A Vet via AskAVet.com or our app 📱 for real-time vet-led guidance from Dr Duncan Houston and our specialized team. 🩺