MUSCLE DISEASE
Exertional Rhabdomyolysis
Several myopathies cause exertional rhabdomyolysis (ER) or tying-up symptoms with elevated CK and AST enzymes.
These include recurrent exertional rhabdomyolysis (RER), which occurs most often in Thoroughbred and Standardbred racehorses with high digestible energy (DE) requirements as well as Arabian endurance horses that exhibit tying-up symptoms at the outset of a race as well as the glycogen storage diseases type 1 polysaccharide storage myopathy (PSSM1) and type 2 PSSM in Quarter Horses with ER (PSSM2-ER).
The figure above provides an approach to managing horses with myopathies that result in ER, or those with sporadic ER episodes.
Horses that have moderate to high caloric requirements should be fed a reduced-NSC, high-fat concentrate, such as RE-LEVE®.
RE-LEVE Veterinarian-recommended feed formulated for horses requiring a low-starch diet. Studies have shown that replacing traditional grain-based diets with RE-LEVE resulted in significant improvement in horses with RER and PSSM.
RE-LEVE is fully fortified to provide the appropriate levels of the vitamins and minerals necessary for optimal performance. RE-LEVE® features natural-source vitamin E, a powerful antioxidant more bioavailable than synthetic sources, to ensure horses receive the maximum benefit.
Horses that are overweight or have low caloric requirements should either be provided with a balancer pellet, such as All-Phase, as their concentrate feed, or if fed below the recommended intake rate of RE-LEVE, be provided with a supplemental source of nutrients, such as Micro-Max.
All of these horses will benefit from antioxidant supplementation, particularly vitamin E, and selenium, if low.
Nano-E® Nanodispersed, liquid natural-source vitamin E supplement. Nano-E provides a highly bioavailable natural (d-α-tocopherol), water-soluble source of vitamin E to horses through a unique delivery system. We recommend providing 1,000-3,000 IU of vitamin E per day. Greater antioxidant protection may be timed before competition or stressful events.
Nano-Q10™ Antioxidant for horses in training. Coenzyme Q10 is a powerful antioxidant that improves aerobic energy generation while protecting against exercise-induced muscle damage. Nano-Q10 is a rapidly absorbed source of coenzyme Q10 that is three times more bioavailable than the powdered crystalline form.
EO-3™ Omega-3 supplement. EO-3 is a rich source of the long-chain omega-3 fatty acids DHA and EPA, compounds found to optimize the well-being of all horses, regardless of age or use. Choose EO-3 to balance fatty acids, benefiting joint health as well as immune, respiratory, and reproductive function.
Myofibrillar Myopathy in Warmblood Horses (MFM-WB)
A subset of horses that may have originally been diagnosed with PSSM2 has now been reclassified as a myofibrillar myopathy due to muscle biopsies showing normal glycogen concentrations, myofibrillar disarray, and desmin aggregates. This exertional myopathy does not typically result in full episodes of tying up or elevated CK concentrations post-exercise. Rather, it is typically characterized by exercise intolerance that may also be accompanied by muscle atrophy.
Onset of symptoms typical occurs in horses aged eight years or more, and muscle biopsy results may yield false negatives in younger horses as desmin aggregates may not have had time to accumulate.
Unlike dietary management of horses with RER, PPSM1 or PSSM2-ER, the rationale for whether a low-NSC diet is indicated for warmblood horses affected by MFM, is dependent on the individual's muscle biopsy findings. In addition, because oxidative stress is highly involved, it is very important to both provide antioxidants and their precursors and to reduce oxidative stress, such as from high fat diets. When no glycogen accumulation is observed, concentrates for horses with MFM diagnosed by a muscle biopsy or young horses suspected of being affected by MFM (for whom other causes of exercise intolerance have been ruled out) should include a generous concentration of high-quality protein (12-14%) with moderate NSC (20-30%) and fat (4-6%) content.
This is quite similar to the typical diet of warmbloods in Europe, and may explain why symptoms often present after horses are imported to the U.S. and their diets changed to the U.S. custom of feeding low-NSC, higher fat diets to warmbloods. Concentrates for horses whose muscle biopsies do display glycogen accumulation should have NSC at or below 20%.
Horses with MFM often display topline muscle atrophy, muscle soreness, and have altered gene expression affecting mitochondrial energy generation and resulting in degradation of key cysteine-based antioxidants in their muscle, leaving them susceptible to greater muscle damage. Therefore, we recommend supplementation of high-quality protein rich in specific amino acids, especially N-acetylcysteine to support muscle regeneration as well as the addition of coenzyme Q10 to the diet due to its role in mitochondrial energy generation and antioxidant activity.
MFM Pellet™ Muscle recovery and repair. MFM Pellet contains several important amino acids, including cysteine, a key component in many antioxidants. Also included in MFM Pellet are the branched-chain amino acids (BCAA) leucine, isoleucine, and valine, all three of which are essential amino acids that must be obtained from the diet. Use MFM Pellet to increase the amount of key amino acids and high-quality protein to protect the muscle from oxidative stress and rebuild damaged muscle fibers.
Nano-Q10™ Antioxidant for horses in training. Coenzyme Q10 is a powerful antioxidant that improves aerobic energy generation while protecting against exercise-induced muscle damage. Nano-Q10 is a rapidly absorbed source of coenzyme Q10 that is three times more bioavailable than the powdered crystalline form.
Reference: Pagan, J.D., and S.J. Valberg. 2025. The role of nutrition in managing muscle disorders. Veterinary Clinics of North America: Equine Practice. In press.
