Many of us consider muscle pain to be normal after a long ride — but what about our horses? Do they feel thesame muscle soreness we do? How do they display this discomfort, and how can it be treated?


A variety of problems can contribute to muscle pain in horses.

  • Primary muscle soreness will usually present itself quite dramatically. Symptoms can include muscle stiffness, sweating, reluctance to move, violent tremors, tucked-up abdomen, or even collapse. Primary muscle problems are often due to an improper function of muscle metabolism, sometimes linked to a genetic component.
  • Secondary muscle pain can stem from improperly-fitting equipment, foot soreness or arthritis. Symptoms can be seen in behavioral changes such as a reluctance to go forward, bucking, tail swishing, and changes in overall demeanor. As a start, observe and differentiate between primary and secondary muscle problems.


Primary muscle soreness can be due to a muscle condition such as Polysaccharide Storage Myopathy (PSSM) Type 1 or 2, or Equine Hyperkalemic Periodic Paralysis (HYPP).

PSSM has been documented in over 20 breeds in the last couple of years. It occurs when there is an improper buildup of excess glycogen (the stored version of sugar) in the muscles. Signs of PSSM Type 1 or 2 include muscle stiffness, sweating, reluctance to move, tremors, and a tucked-up abdomen. These symptoms usually occur ten to 20 minutes into a ride. A blood test by your veterinarian will usually reveal an elevated CK level, and a muscle biopsy will show excess glycogen storage. A genetic test is also available using hair roots and blood. PSSM2 affects horses in the same manner, but these horses will not test positive for the gene found in PSSM1. Muscle biopsy is still the most effective way to diagnose both PSSM1 and 2.

HYPP is caused by a genetic defect seen in relatives of Impressive, the quarter horse sire. Excessive potassium levels or stress can cause a dysfunction within sodium channels in the muscle, causing dramatic tremors, weakness or even collapse. Unlike PSSM, these symptoms do not come after exercise but can manifest while the horse is at rest, during transport or a stressful event. Genetic testing is available and treatment includes dietary reduction of potassium, routine turnout, and possible drugs to stabilize potassium and glucose levels.


While secondary muscle pain is more common than primary, it can be frustrating to diagnose its exact cause (see sidebar below). The multitude of contributing factors include, but are not limited to: poor fitness, dietary deficiencies, improper saddle fit, shoeing problems, or altered movement due to joint pain. This type of pain usually presents as a mild reluctance to go forward; behavioral changes under saddle, such as bucking, spooking or excessive tail swishing; or behavioral changes while being groomed or shod. Keeping this in mind, you can often address and correct some of these problems prior to a veterinarian visit.


Treatment for PSSM is mainly environment-based, involving strict dietary changes, including high fat low starch feeds; exercise routines; turnout; and ration balancer supplements containing high levels of vitamin E. With proper management, a return to work is seen in over 75% of horses diagnosed with PSSM1 or 2.

Treating secondary muscle pain includes finding the source of the problem and alleviating it. This can be followed by spinal manipulation/chiropractic, acupuncture, massage or muscle relaxants. Once the problem has been identified, treatment is critical to reduce pain and prevent its return. Non-invasive options like spinal manipulation/chiropractic and acupuncture will allow your horse to move through his normal range of motion again, and open pathways that allow for healing. Muscle relaxants can be used in combination with these therapies to break the pain cycle in the horse. Remember, these treatments are used to heal and maintain a healthy horse, but will not fix the problem if there is still an underlying issue that needs to be addressed.

Whether he’s suffering from primary or secondary muscle soreness, every horse has a different pain tolerance and can display discomfort in a variety of ways. Listen to what your horse is telling you. Notice his behavioral changes and get to the root of the problem.

Dr. Jennifer McDonald is an equine veterinarian at The Equine Clinic at OakenCroft. She graduated from The Royal Veterinary College in London, England and is certified in both spinal manipulation and acupuncture. Dr. Jen specializes in lameness and sport horse medicine.