Diet for Horses with Tying-Up: Feeding Considerations for Muscle Disorders

Tying-up is a common name for exertional rhabdomyolysis, a painful muscle disorder that can happen after exercise. In horses, it is not one single disease. Common underlying causes include polysaccharide storage myopathy (PSSM) and recurrent exertional rhabdomyolysis (RER), and the best feeding plan depends on which problem your vet suspects. That is why diet changes should be made with your vet, especially if your horse has repeated episodes, dark urine, severe stiffness, or poor performance.

For many horses with PSSM, the goal is to reduce starch and sugar so muscles are not pushed to store even more glycogen. Merck Veterinary Manual recommends feeding forage at about 1.5% to 2% of body weight and limiting starch to less than 10% of daily digestible energy, often by cutting back grain and using fat or specially formulated low-starch feeds when extra calories are needed. A 1,100-pound horse often needs roughly 16.5 to 22 pounds of forage daily, though the exact amount depends on body condition, workload, and hay quality.

For horses with RER, the feeding target is a little different. These horses often benefit from a high-fat, low-starch program, with hay still forming the base of the diet. Merck notes that concentrates for RER are often selected to provide 20% or less of daily digestible energy as nonstructural carbohydrate and 20% to 25% of digestible energy as fat. In practical terms, that usually means avoiding large grain meals, feeding consistent turnout and exercise, and choosing a commercial low-starch performance feed instead of sweet feed or straight cereal grains.

Not every horse with tying-up needs a lot of added oil. If your horse is an easy keeper, the bigger issue may be starch restriction and calorie control, not adding more energy. Hay testing, body condition scoring, and a review of all treats, supplements, and pasture access can make a big difference. Your vet may also want bloodwork, muscle enzymes, genetic testing for PSSM1, or a muscle biopsy in some cases before recommending a long-term plan.

There is no one safe amount of grain, fat, or sugar for every horse with tying-up. The safer approach is to build the diet around forage first, then add only what your horse truly needs for weight and work. A common starting point is 1.5% to 2% of body weight per day in forage on a dry-matter basis. For a 1,100-pound horse, that is usually about 16.5 to 22 pounds of hay or equivalent forage daily. Horses that are overweight, insulin dysregulated, or also at risk for laminitis may need a more tightly controlled plan from your vet.

If your horse has PSSM, many vets aim to keep starch very low, often under 10% of daily digestible energy. That usually means avoiding sweet feed, corn, oats, and large grain meals. If extra calories are needed, your vet may suggest a ration balancer, a low-starch pelleted feed, or carefully measured fat sources such as vegetable oil or stabilized rice bran. For RER, some horses need a specialized low-starch performance feed because plain oil alone may not provide enough calories for horses in harder work.

Treats count too. Apples, carrots, molasses-based snacks, and many commercial treats can add more sugar than pet parents realize when fed repeatedly through the day. Small amounts may fit some horses, but frequent sugary treats are not ideal for a horse with a muscle disorder linked to carbohydrate handling. Low-sugar options like a few hay pellets, low-NSC treats, or a small amount of appropriate forage are often easier to fit into the plan.

A practical monthly cost range for feeding changes is often $60 to $180 for a ration balancer or low-starch concentrate, with hay costs separate. Hay analysis commonly runs about $30 to $80, and a nutrition consult is often $100 to $300 depending on the service and whether forage analysis is included. Ask your vet which changes matter most first, so you can focus your budget where it helps the most.

See your vet immediately if your horse seems painful after exercise, is reluctant to move, is sweating heavily, or has dark brown or coffee-colored urine. These can be signs of active muscle damage. Some horses look tucked up, breathe fast, act anxious, or develop hard, painful muscles over the hindquarters and back. Others show milder warning signs first, such as repeated stiffness after light work, poor willingness to go forward, or unexplained drops in performance.

Diet-related trouble is not always dramatic. A horse may start tying-up more often after a switch to a sweeter feed, more grain, less turnout, or an inconsistent exercise schedule. Weight gain on a high-fat ration can also become a problem, especially in easy keepers. If your horse is getting heavier, more excitable, or having recurrent episodes despite a "low-starch" label, it is worth reviewing the full ration, hay, pasture, and treats with your vet.

Call your vet sooner rather than later if your horse has recurrent stiffness, muscle trembling, exercise intolerance, or episodes after rest days. Those patterns can fit chronic disorders such as PSSM or RER. Your vet may recommend checking CK and AST muscle enzymes, reviewing the exercise plan, and adjusting the diet in a more targeted way.

Emergency signs include inability to walk normally, collapse, severe pain, dehydration, or urine discoloration. Do not force exercise in a horse that may be tying-up. Stop work, keep the horse calm, offer water unless your vet says otherwise, and contact your vet right away.

If your horse is prone to tying-up, safer alternatives usually start with tested grass hay or other low-NSC forage, fed consistently and in enough quantity to support gut health. Instead of sweet feed or large grain meals, many horses do better on a ration balancer or a commercial low-starch, higher-fat feed chosen with your vet. This can help meet vitamin and mineral needs without overloading the diet with starch.

For horses that need more calories, options may include stabilized rice bran, vegetable oil, or a specialized low-starch performance concentrate. These choices are often more useful than adding oats or corn. Horses with suspected myofibrillar myopathy (MFM) may need a somewhat different approach, with moderate nonstructural carbohydrate, moderate fat, and somewhat higher protein, so it is important not to copy another horse’s plan without a diagnosis.

For treats, consider plain hay pellets, low-sugar commercial horse treats, or very small amounts of approved produce if your vet says they fit the ration. Keep all treats modest and consistent. A horse that gets many "healthy" snacks through the day can still end up with too much sugar overall.

Management alternatives matter too. More turnout, regular daily exercise, avoiding long rest periods followed by hard work, and reducing stress can be just as important as feed selection. If budget is a concern, ask your vet which step is most valuable first. Often, the most helpful conservative changes are removing high-starch grain, testing hay, balancing the minerals, and keeping the routine steady.