🐴 Tying Up in Quarter Horses and Other Breeds: Diagnosing & Managing PSSM in 2025 🧬💪

By Dr Duncan Houston BVSc

Many horse owners are familiar with the term “tying up”, but what may come as a surprise is that this condition has multiple forms—and not all are caused by overwork. In 2025, we now recognize three distinct types of tying up, each with different causes, symptoms, and treatments. Understanding which type your horse may have is the key to successful prevention and performance recovery. 🧠🐎

💥 What Is Tying Up?

Tying up refers to a syndrome of muscle cramping, stiffness, and pain in horses, usually during or after exercise. Signs may include:

• 🔥 Muscle stiffness or spasms (especially in the hind limbs)
• 💧 Excessive sweating
• 💓 Elevated respiratory and heart rate
• 🚷 Reluctance to move or shifting hindlimb lameness
• 🧪 Dark-colored urine in severe cases (myoglobinuria)

But tying up isn’t always a one-time event. Some horses suffer from recurrent or genetically-linked forms of the condition. 🧬

⚠️ Type 1: Exertional or Sporadic Tying Up

This form of tying up is usually seen in horses that:

• 🏃 Are over-exercised without proper conditioning
• 🌡️ Overheat or become dehydrated
• ⚖️ Have electrolyte imbalances

It typically occurs in unfit horses asked to perform too much, too soon—especially in hot weather. Once identified and managed, this form usually does not recur unless similar conditions are repeated. ⛱️

🔁 Type 2: Recurrent Tying Up (RER)

This form is most often seen in:

• 🏇 Thoroughbreds
• 🚴 Standardbreds

Recurrent exertional rhabdomyolysis (RER) is a genetic condition involving abnormal calcium regulation inside muscle cells, making them contract erratically. Symptoms appear during or after exercise, especially in highly strung or fit horses. 🧬

RER management includes:

• 🧘 Consistent routines and low-stress environments
• 🍽️ High-fat, low-starch diets
• 📆 Regular, non-strenuous exercise

🧬 Type 3: PSSM (Polysaccharide Storage Myopathy)

PSSM is most common in:

• 🐴 Quarter Horses
• 🚜 Draft breeds
• 🎩 Warmbloods and other heavy-muscled breeds

This genetic muscle disorder involves a defect in how glycogen is stored in muscle cells. Horses with PSSM overaccumulate unusable glycogen, leading to energy depletion and muscle damage during exertion. 🧠

🔬 Diagnosing PSSM

There are two types:

• 🧪 PSSM1: Detectable via a hair or blood genetic test
• 🧫 PSSM2: Requires a muscle biopsy for confirmation

Some horses may test negative on genetic screens but still suffer from PSSM-like symptoms, which makes proper diagnosis essential. 🎯

🍽️ Managing PSSM Through Diet

The good news? Most horses with PSSM can be managed successfully with diet and exercise adjustments. Key recommendations include:

✅ Feed High-Fat, Low-Starch Diets

• 🥩 Use rice bran, flaxseed, or stabilized fat supplements
• 🌾 Avoid oats, sweet feed, or other high-NSC grains
• 🥦 Base the diet on forage and add ration balancers if needed

✅ Consistent Exercise Routine

• 🏃 Light daily turnout or riding prevents glycogen buildup
• 🚫 Avoid stall rest when possible

✅ Electrolyte and Vitamin Supplementation

• 🧠 Vitamin E and selenium may support muscle function
• 💧 Electrolytes can help reduce heat-related episodes

🧠 Why Accurate Diagnosis Matters

Each form of tying up requires a unique approach. Treating a Quarter Horse with PSSM like a Thoroughbred with RER can worsen symptoms. That’s why testing is so valuable—it provides a roadmap for diet, management, and exercise planning. 🗺️

📲 Ask A Vet for Genetic Guidance

If your horse has tied up or shown exercise-related muscle stiffness, visit AskAVet.com or use the Ask A Vet App to get personalized advice. 📱🧠

Dr Duncan Houston and the team can help order genetic tests, review results, and develop a diet and management plan tailored to your horse’s unique needs. 💬🐴

🏁 Final Thoughts

In 2025, we now know that tying up isn’t just one condition—it’s a collection of disorders with different causes. The key is diagnosis. With the right tests and a well-balanced diet, most horses can return to full work—even those with PSSM or RER. 🧬💪

Want help managing tying up? Visit AskAVet.com and take the guesswork out of muscle health 🐎🧠