Exertional Rhabdomyolysis (Tying Up) in Horses
In January, we had a scare with my son. After getting the flu (which he quickly recovered from), he developed rhabdomyolysis and ended up in the hospital for two days. I was, of course, familiar with rhabdomyolysis because it happens in horses, but I’d never realized it could be a complication from influenza in people. Fortunately, we caught it in time and he made a complete recovery.
I’ve personally never had a horse experience rhabdomyolysis, aka “tying up”, but I remember seeing it happen at a weekend trail ride when I was a kid. I thought I’d dig into this topic a little further, though, and share what I’ve learned with you.
Rhabdomyolysis appears to have several different underlying causes, which I’ll get into in a bit. But for informational purposes here are the main and categories and sub-categories of the condition (taken from this article):
- Exertional rhabdomyolysis (ER)
- Sporadic rhabdomyolysis
- Chronic rhabdomyolysis
- Recurrent exertional rhabdomyolysis (RER)
- Polysaccharide storage myopathy (PSSM)
- Non-exercise associated rhabdomyolysis
- Inflammatory myopathy
- Nutritional myopathy
- Toxic myopathy
- Traumatic rhabdomyolysis
For this blog post, I’ll mainly be focusing on the different forms of Exertional Rhabdomyolysis (ER).
Causes of ER
As shown above, ER can be subdivided into two forms: sporadic and chronic. Horses that experience a single episode or infrequent episodes of ER are classified as having sporadic ER, whereas horses that have repeated episodes of ER are classified as having chronic ER.
Sporadic ER appears to have several causes including:
- muscle trauma;
- dietary/ electrolyte imbalances (especially high-NSC diets, insufficient selenium and vitamin E, or electrolyte imbalances).
Overexertion can occur when horses are exercised more intensely than their level of conditioning (such as the horse I saw at the weekend trail ride) and is more common after a layoff period. Sporadic ER might also be more common on hot, humid days due to high body temperatures and increased sweating.
Likewise, chronic ER can be further subdivided into two categories: Recurrent Exertional Rhabdomyolysis (RER) and Polysaccharide Storage Myopathy (which I won’t delve into here).
RER is believed to be caused by an abnormality in the regulation of muscle contraction and relaxation and may be triggered by excitement. This form of rhabdomyolysis is most common in Standardbreds and Thoroughbreds, and interestingly enough, RER occurs most commonly after low-intensity exercise.
Symptoms of ER
ER usually isn’t hard to miss as the horse will be very uncomfortable and may even be reluctant to move. The most common signs include:
- Firm, painful muscles over the loin and croup muscles (lower back and rear) along the top line, as well as the gluteal muscles;
- Excessive sweating;
- Quick, shallow breathing;
- Rapid heart rate;
- Muscle tremors.
ER episodes can range from mild to quite severe, with the more severe episodes possibly leading to muscle necrosis and/or renal failure. Therefore, it’s important to get your veterinarian involved with any case of ER.
If you suspect your horse is tying up, immediately stop any exercise and call your veterinarian. While you’re waiting, offer your horse water and don’t force him to move. You can also gently massage the back and hindquarter muscles if your horse will tolerate that. If you need to transport the horse to a veterinary hospital, walk him slowly to the trailer, stopping for breaks as needed. Add deep bedding in the trailer in case the horse needs to lie down during transport.
Your vet will take a blood sample in order to determine the extent of the muscle damage, and two different muscle proteins are usually measured: creatine kinase (CK) and aspartate transaminase (AST).
Depending on the severity of the episode, ER is typically treated by relieving muscle pain and restoring electrolyte balance. Your veterinarian may use tranquilizers to calm the horse, non-steroidal anti-inflammatories (NSAIDS), muscle relaxers, and IV fluids.
After immediate treatment, stall or paddock rest is generally recommended with some hand walking for the first few days after the episode. Horses with mild episodes can likely return to gradual work after a few days, but horses who have suffered more severe episodes may need additional time off. Once horses are back in training, it’s recommended they get daily exercise with a prolonged warm up period, as CK levels can actually increase on days off.
For horses prone to RER, stress management is important. Allowing these horses to live as naturally as possible with companion horses is beneficial (as it is for all horses!) Ensure that your horse is getting enough salt, as well. Other supplements which may be helpful include sodium bicarbonate, B vitamins, branched-chain amino acids, and dimethylglycine.
Consider putting horses with RER on a high-fat, low-starch diet and when conditions are hot and humid, electrolyte supplementation may be needed.
Massage, stretching, and acupressure for muscle relaxation may be beneficial for horses with RER as well.
Exertional Rhabdomyolysis (study)