🩺 Blister Beetle Poisoning in Horses: A Vet’s 2025 Guide | Dr Duncan Houston BVSc

Meta description: ⚠️ Dr Duncan Houston’s 2025 guide on blister beetle poisoning (cantharidin toxicosis) in horses—signs, diagnosis, emergency care, prevention & Ask A Vet support.

1. 🧠 What Is Blister Beetle Poisoning?

Also known as cantharidin toxicosis, this occurs when horses ingest blister beetles—usually in alfalfa hay. These insects release cantharidin, a potent vesicant causing internal damage that can be fatal even in small doses :contentReference[oaicite:2]{index=2}.

2. ⏱️ Rapid Onset & Risk Dose

Clinical signs often begin within 3–12 hours after exposure :contentReference[oaicite:3]{index=3}. As little as 5 g of dried beetles (around five beetles) can be lethal to a 1,000 lb horse, and death can occur in 3–18 hours without intervention :contentReference[oaicite:4]{index=4}.

3. 🩺 Clinical Presentation

• Colic signs: Pawing, rolling, abdominal discomfort :contentReference[oaicite:5]{index=5}.
• Oral/gastro-mucosal lesions: Blisters, drooling, water submersion for relief :contentReference[oaicite:6]{index=6}.
• Urinary issues: Frequent, painful urination; blood in urine :contentReference[oaicite:7]{index=7}.
• Muscle stiffness: Rigid gait, reluctance to move :contentReference[oaicite:8]{index=8}.
• Fever, depression, tachycardia :contentReference[oaicite:9]{index=9}.
• Secondary ulcers: Gastric or intestinal ulceration common :contentReference[oaicite:10]{index=10}.
• Electrolyte imbalance: Hypocalcemia, hypomagnesemia, elevated PCV :contentReference[oaicite:11]{index=11}.

4. 🔍 Diagnostic Steps

• History & forage inspection: Alfalfa, especially late-cut or crimped :contentReference[oaicite:12]{index=12}.
• Physical exam & labs: CBC, biochemistry, urinalysis–checking electrolytes and renal function :contentReference[oaicite:13]{index=13}.
• Cantharidin assay: Urine or gastric content testing confirms exposure :contentReference[oaicite:14]{index=14}.

5. 🏥 Emergency Treatment

Cantharidin is rapidly absorbed—no direct antidote exists. Treatment focuses on aggressive supportive care :contentReference[oaicite:15]{index=15}.

• Remove forage: Discontinue suspect feed immediately.
• IV fluids: Restore volume, flush kidneys, correct electrolytes (especially calcium, magnesium) :contentReference[oaicite:16]{index=16}.
• Activated charcoal: Early administration absorbs residual toxin :contentReference[oaicite:17]{index=17}.
• Pain management: NSAIDs (post-rehydration) or opioids if needed :contentReference[oaicite:18]{index=18}.
• Ulcer therapy: Omeprazole, sucralfate per protocols :contentReference[oaicite:19]{index=19}.
• Antibiotics: Prevent secondary infections in ulcerated areas :contentReference[oaicite:20]{index=20}.
• Electrolyte & mineral supplements: Calcium, magnesium continued as needed :contentReference[oaicite:21]{index=21}.
• Diet transition: Introduce palatable, digestible feeds until recovery (~7–10 days) :contentReference[oaicite:22]{index=22}.

Prognosis: Guarded—survival more likely if treated within 72 hours :contentReference[oaicite:23]{index=23}.

6. 🛡️ Prevention Strategies

• Avoid high-risk hay: Use first-cut alfalfa harvested before bloom or after frost; avoid crimped hay :contentReference[oaicite:24]{index=24}.
• Field scouting: Remove or treat blister beetle-infested fields :contentReference[oaicite:25]{index=25}.
• Source wisely: Buy hay from trusted suppliers with controlled practices :contentReference[oaicite:26]{index=26}.
• Education: Train farm staff to recognise beetles and forage risks :contentReference[oaicite:27]{index=27}.
• Safe packing: Harvest alfalfa with equipment that allows beetles to escape before baling :contentReference[oaicite:28]{index=28}.

7. 🤝 Ask A Vet Support

We provide:

• 📸 Remote hay inspection advice and risk assessment.
• 📋 Customized hydration and ulcer management plans.
• 📆 Treatment and recovery checklists.
• 🎓 Webinars: “Farm-Proofing Hay,” “Cantharidin: Internal Shielding,” and Emergency protocols.

8. ❓ FAQs

Can small amounts cause illness?

Yes—even a few beetles can trigger colic or ulcer pathology :contentReference[oaicite:29]{index=29}.

Is all alfalfa risky?

No—first-cut, pre-bloom hay reduces risk; avoid crimped or late-season cutting :contentReference[oaicite:30]{index=30}.

Any long-term effects?

Horses can fully recover, but risk of repeat exposure and ongoing ulcer care remains.

Can humans be poisoned?

Yes—blister beetle toxins can cause severe skin blisters or systemic illness if contacted or ingested :contentReference[oaicite:31]{index=31}.

9. ✅ Final Takeaway

Blister beetle poisoning is a **veterinary emergency**. Early recognition, aggressive supportive care, ulcer therapy—and strong prevention—are essential for survival and recovery. As Dr Duncan Houston, I encourage proactive hay management, early vet involvement, and Ask A Vet’s expert support to keep your horse safe in 2025 and beyond.