Vet Warning: Phenylbutazone and Fatal Injuries in Racehorses 2025 🏇💊⚠️

By Dr Duncan Houston, BVSc

Phenylbutazone—commonly known as bute—is a widely used anti-inflammatory drug in the horse racing industry. While it helps manage pain, recent research shows it may also contribute to a higher risk of fatal musculoskeletal injuries in Thoroughbred racehorses. 🧬💉

In this 2025 vet safety alert, Dr Duncan Houston explores the risks of bute use prior to racing, what recent studies reveal, and why pain masking in performance horses must be approached with extreme caution. ⚠️🐎

1. What Is Phenylbutazone? 💊

Phenylbutazone is a non-steroidal anti-inflammatory drug (NSAID) used to relieve pain, inflammation, and lameness in horses. It’s especially common in the racing and performance horse world. ✅

It works by:

• 🧠 Reducing inflammatory mediators like prostaglandins
• 💥 Masking discomfort from chronic injuries
• 🐎 Allowing horses to compete without obvious signs of pain

However, by dulling pain, bute may allow horses to exert themselves beyond their safe limits, leading to more severe injuries. ❌

2. Is Bute Legal in Racing? ⚖️

In the United States, bute is allowed in regulated amounts, but:

• ⏳ The last dose must be administered at least 48 hours before the race
• 💉 Only a trace amount is permitted in post-race drug testing

Regulations vary by jurisdiction, but many argue this is not enough to protect horses from injury risk. 🚨

3. Key Study Findings from Argentina 🧪📉

A large-scale study published in the AVMA Journal evaluated nearly 300,000 Thoroughbred race starts in Argentina. Results showed:

• 🏇 Horses given bute before racing were twice as likely to suffer fatal musculoskeletal injuries
• 🔍 Most deaths were due to racing injuries that required euthanasia—not the drug itself

The findings suggest bute masks pain and enables overexertion, making horses more vulnerable to catastrophic breakdowns. 💥

4. Why Are Horses Given Bute Before Races? 🤔

Common reasons include:

• 🐴 Managing chronic soreness in older racehorses
• 📉 Hiding mild lameness that might disqualify a horse
• 🏁 Attempting to maintain performance in horses at risk

Unfortunately, this approach may delay diagnosis of serious injury—until it’s too late. ⏳💀

5. Age and Injury Risk 🔄

The study’s authors point out that horses given bute are often:

• 🧓 Older with pre-existing injuries or joint degeneration
• ⚠️ Lame or sore and being pushed to race anyway

This makes masking pain even more dangerous—because these horses are already at higher risk. 🧠

6. Alternatives and Best Practices ✅

Instead of masking pain, prioritize:

• 🧪 Full lameness evaluations and diagnostics
• 🌿 Rest, rehab, and conditioning between races
• 🔁 Honest performance tracking and injury reporting

For veterinarians and trainers:

• 🩺 Avoid routine pre-race bute “just in case”
• 🧠 Use bute for recovery—not for racing

7. Summary Table: Phenylbutazone Use & Risk 📋⚠️

8. Final Thoughts from Dr Duncan Houston 💬

Bute is not the enemy—but using it to send a sore horse into competition is. The data is clear: masking pain with bute can double the risk of a fatal outcome. It’s time to prioritize soundness over speed and ethics over short-term wins. 🧠🐴🏁

Need help reviewing your racehorse care strategy or treatment protocol? Visit AskAVet.com or download the Ask A Vet app 📲 for honest, expert advice on equine medications, race prep, and performance care.

— Dr Duncan Houston, BVSc