🩺 Polysaccharide Storage Myopathy (PSSM) in Horses: A Vet’s 2025 Guide | Dr Duncan Houston BVSc

Meta description: ⚡️ A deep 2025 veterinary guide by Dr Duncan Houston on PSSM in horses: types, signs, testing, dietary/exercise management, and Ask A Vet support.

1. 🧠 What Is PSSM?

Polysaccharide Storage Myopathy (PSSM) is a metabolic muscle disorder where glycogen and abnormal polysaccharides accumulate in muscle fibers, causing painful episodes of “tying-up” or exertional rhabdomyolysis (muscle breakdown) :contentReference[oaicite:3]{index=3}.

2. 🧬 Types of PSSM

• PSSM Type 1: Caused by a mutation in the GYS1 gene (glycogen synthase); autosomal dominant; tested via genetic screening :contentReference[oaicite:4]{index=4}.
• PSSM Type 2: Lacks GYS1 mutation; diagnosed via muscle biopsy. Etiology unknown; affects warmbloods, draft crosses :contentReference[oaicite:5]{index=5}.

3. ⚡ Prevalence & At-Risk Breeds

PSSM1 is common in Quarter Horses, Paints, Appaloosas (~6–28%) and draft breeds. PSSM2 is seen in warmbloods and sport breeds :contentReference[oaicite:6]{index=6}.

4. 🔍 Clinical Signs to Know

• Muscle stiffness, reluctance to move, shifting lameness, sweaty or firm muscles :contentReference[oaicite:7]{index=7}.
• Muscle tremors, pain on palpation, pawing, sweating, dark urine (myoglobinuria), muscle wasting :contentReference[oaicite:8]{index=8}.
• Occurs during/after exercise; milder signs in Type 2 but variable :contentReference[oaicite:9]{index=9}.

5. 🩺 Diagnosis & Testing

• Genetic testing for Type 1 using hair or blood sample :contentReference[oaicite:10]{index=10}.
• Muscle biopsy with PAS staining for glycogen/polysaccharide inclusion (especially Type 2) :contentReference[oaicite:11]{index=11}.
• Clinical history and symptoms are also critical.

6. 🩹 Treatment & Management

There is no cure—but effective management allows most horses to live performance lives:

• Diet: Low non‑structural carbohydrate (<12%), high fat (>15–20% DE), high fiber diet :contentReference[oaicite:12]{index=12}.
• Fat supplements: Rice bran, vegetable oils boost fat energy :contentReference[oaicite:13]{index=13}.
• Forage: Grass hay low in sugar/starch; beet pulp for calories :contentReference[oaicite:14]{index=14}.
• Exercise: Daily consistent work prevents glycogen buildup. Gradually introduce fitness :contentReference[oaicite:15]{index=15}.
• Nutritional balance: Ensure quality protein, vitamin E, selenium, magnesium support muscle function :contentReference[oaicite:16]{index=16}.
• Medication: NSAIDs, muscle relaxants, sedatives during flare-ups :contentReference[oaicite:17]{index=17}.

7. 🎯 Long-Term Prognosis

About 90% of horses managed well (diet + exercise) remain flare-up free; half improve with diet alone :contentReference[oaicite:18]{index=18}. Flare‑ups return quickly if management lapses.

8. 🛡️ Prevention Strategies

• Genetic screening: Avoid breeding Type 1 carriers.
• Early diagnosis: Test young horses with symptoms.
• Nutrition: Maintain low‑NSC diet throughout life.
• Consistent exercise: Prevent glycogen accumulation.
• Monitor weight/metabolic status: Watch insulin sensitivity and EMS risk :contentReference[oaicite:19]{index=19}.

9. 💬 Ask A Vet Support

• 📸 Send videos or reports of tying-up signs for triage.
• 📋 Receive personalized diet (NSC/fat ratios) and exercise plans.
• 📆 Set reminders for testing, feeding, and fitness check-ins.
• 🎓 Join webinars by Dr Houston on “Living with PSSM,” dietary tweaks, and flare-up response.

10. ❓ FAQs

What triggers a flare-up?

Lay‑up, high‑starch meals, abrupt exercise changes, stall rest, illness or metabolic imbalance can trigger symptoms :contentReference[oaicite:20]{index=20}.

Can a PSSM horse compete?

Yes—many perform at eventing, dressage, or show; management adherence is key.

Is PSSM transmissible?

Type 1 is genetic (dominant). Type 2 unknown. Non‑infectious.

Is forage-only enough?

Often yes for small/maintenance horses—but fat supplements help for working horses :contentReference[oaicite:21]{index=21}.

Can diet alone control it?

Yes, in ~50% cases. Adding exercise improves control in ~90% :contentReference[oaicite:22]{index=22}.

11. ✅ Final Takeaway

• PSSM is a lifelong metabolic disorder—manageable, not curable.
• Low‑starch, high‑fat diet and daily work are essential.
• Genetic testing and muscle biopsy confirm diagnosis.
• Continuous care prevents flare-ups and supports performance longevity.
• Ask A Vet provides live support for test planning, diet/exercise regimes, and flare-up emergencies 💙

🐾 Notice Muscle Stiffness or Tying-Up?

Send samples and history via Ask A Vet. As Dr Duncan Houston, I’ll help determine if it’s PSSM, guide testing, design nutrition and conditioning plans, and assist during flare-ups—keeping your horse healthy, sound, and thriving. 🐎⚡️