🩺 Exertional Rhabdomyolysis in Horses: A Vet’s 2025 Guide | Dr Duncan Houston BVSc

Meta description: 🐎 A vet’s 2025 guide by Dr Duncan Houston on equine ER—causes, signs, emergency care, genetic types, rehab & prevention, with Ask A Vet support.

1. 🧠 What Is Exertional Rhabdomyolysis (ER)?

Exertional Rhabdomyolysis (ER), often called “tying-up,” is a muscle condition in horses where muscle cells break down during or after exercise. This leads to muscle stiffness, pain, and potential kidney damage if not treated quickly. It’s most common in athletic horses under physical or metabolic stress.

2. 📍 ER Types: Sporadic vs Chronic

ER falls into two main categories:

• Sporadic ER: Occurs occasionally due to overexertion, dehydration, or poor conditioning.
• Chronic ER: Linked to inherited metabolic issues like:
• PSSM (Polysaccharide Storage Myopathy): Common in Quarter Horses, Warmbloods, Drafts.
• RER (Recurrent Exertional Rhabdomyolysis): Seen in nervous Thoroughbreds, Arabians, and Standardbreds.

3. 🧬 What Causes ER?

The root of ER is energy metabolism disruption. Muscles can’t properly store or access energy during exercise, leading to cell breakdown. Common triggers include:

• Sudden intense exercise without adequate conditioning
• Electrolyte imbalances or dehydration
• High-carb diets with low fat/fiber
• Excitement or stress before exercise (especially RER)
• Genetic mutations (e.g., GYS1 in PSSM1)

4. ⚠️ Clinical Signs of ER

Signs can be subtle or severe. Key indicators include:

• 🧍 Reluctance to move, shortened stride, stiff gait
• 🥵 Excessive sweating, elevated heart and respiratory rate
• 🔴 Pain or firm muscles, especially in the hindquarters
• 🧪 Dark red or brown urine—indicates myoglobin from muscle breakdown
• 🛑 Horse may stop, freeze, or refuse to walk post-exercise

5. 🩺 How I Diagnose ER as a Vet

Diagnosis combines clinical signs with diagnostic testing:

• Physical exam: Assess muscle tension, vitals, gait
• Blood tests: Elevated creatine kinase (CK), aspartate aminotransferase (AST)
• Urine sample: Red or coffee-colored urine confirms myoglobinuria
• Genetic testing: For chronic ER (PSSM1, PSSM2, RER)

6. 🚨 Immediate Treatment for ER Episodes

If I’m called to a horse mid-episode, here’s how I act:

• 📍 Stop exercise immediately! Keep the horse calm and still
• 💧 Fluids: IV fluids prevent kidney damage and rehydrate
• 💊 NSAIDs: Banamine or phenylbutazone for inflammation and pain
• 🧘‍♂️ Muscle relaxants: Methocarbamol or dantrolene for severe cramping
• 🧪 Urine and blood monitoring: To assess severity and kidney health

7. 📆 Long-Term Management of Chronic ER

Managing chronic ER like PSSM or RER involves three key pillars:

7.1 🍽️ Nutrition

• Low starch, high fat diets (e.g., beet pulp, rice bran, flaxseed)
• Vitamin E, selenium, magnesium support muscle health
• Avoid grain spikes and sugars—stick to consistent routines

7.2 🏋️ Exercise Regimen

• Daily low-stress work (lunging, hand-walking)
• Avoid days off—muscles regress quickly
• Warm-up slowly, avoid high-speed gallops

7.3 🛠️ Environmental & Handling Support

• Reduce stress—calm turnout, routine handling
• Keep horses in familiar environments
• Blanketing in cold weather to prevent chill-induced spasms

8. 🧬 Genetic Testing & Breeding Advice

For PSSM1 and RER, genetic testing identifies risks. I advise:

• Test horses showing recurrent signs—early planning is key
• Avoid breeding affected horses where inheritance is strong

9. 📉 Complications & Prognosis

• 🔴 Myoglobinuria may lead to acute kidney injury
• 🟡 Recurrent damage causes scar tissue, poor performance
• 🟢 With proper care, many horses return to light riding or even performance

10. 🛡️ Prevention Tips

• 📅 Keep a consistent routine—avoid unplanned breaks
• 💧 Ensure hydration before/after work (with electrolytes)
• 🧬 Screen breeding stock for PSSM1, RER where relevant
• 🥗 Provide appropriate forage and avoid sugar spikes
• 🏃 Ease into exercise—especially after rest or illness

11. 💬 Ask A Vet to Stay on Track

Use Ask A Vet to:

• 📸 Share videos for gait assessment during stiffness episodes
• 📋 Get diet reviews & exercise programs tailored to ER types
• 📈 Monitor CK/AST trends with ongoing logs and vet input
• 🎓 Attend webinars with Dr Duncan Houston on ER management

Ongoing support matters—and Ask A Vet ensures you’re never managing this alone.

12. ❓ FAQs

How fast do CK levels rise in ER?

CK elevates within 2–6 hours post-episode; AST rises more slowly and stays longer.

Can I ride a horse with chronic ER?

Yes—with vet-guided management, many do low-level riding. Sudden work increases must be avoided.

What supplements help?

Vitamin E, magnesium, selenium, and oil-based fat sources like flax or canola are common in ER diets.

Is PSSM curable?

No, but symptoms are manageable through diet, exercise, and stress reduction.

13. ✅ Final Takeaway

• ER is a muscle disorder triggered by stress, diet, or inherited metabolism issues
• Prompt diagnosis and early fluid support are essential
• Genetic testing helps differentiate chronic ER types
• Diet, turnout, exercise, and routine build long-term success
• Ask A Vet offers around-the-clock help for planning, flare-ups, and recovery

🐾 Need Help Managing ER?

Whether it’s a one-off “tying-up” episode or a chronic condition, Ask A Vet and I are here to guide your horse toward safer training, better health, and happier movement. 💙