Equine Tying Up Syndrome

RER is typically diagnosed in racing breed horses such as Thoroughbreds and Standardbreds. It affects females more often than males, and the condition tends to occur in young racehorses in training. Trainers typically describe affected horses as nervous or high strung.

“Acute signs can be very similar to sporadic tying up,” says Uehlinger. “So again, your horse may look like it’s colicky — it’s sweaty, it’s reluctant to move.”

However, tying up episodes due to RER are not usually associated with overtly exerting events — such as racing — but may occur during light training.    

Horses with PSSM or RER can also experience milder episodes that may present as lameness, back pain, an inability to engage the hind end, or poor performance. 

Unlike sporadic tying up, episodes of muscle cramping associated with PSSM or RER can occur after short periods of light exercise, trailering, or pasture turnout. These episodes are recurrent. In all cases, an acute episode of tying up is considered a veterinary emergency.

If your horse ties up repeatedly, Uehlinger recommends talking to your veterinarian about investigating the condition’s underlying cause. As a starting point, your veterinarian may conduct an exercise test by collecting an initial blood sample before lightly exercising your horse for 15 minutes. A second blood sample will be collected about four to six hours after exercising.

“If a horse has a tendency to tie up, we can demonstrate substances that are being released from the damaged muscle in the blood [samples],” says Uehlinger. Specifically, veterinarians measure muscle enzymes that are being released into the horse’s blood. 

Once your veterinarian has established that your horse has a tendency to tie up, further diagnostics can help identify which condition is affecting your horse. Since a genetic abnormality has been identified for Type 1 PSSM, a genetic test can be run on a hair or blood sample. For Type 2 PSSM and RER, a muscle biopsy is necessary to make a definitive diagnosis. 

“Unfortunately, we cannot heal these horses of PSSM or RER,” says Uehlinger. “The predisposition to tie up will always be present and we have to implement lifelong management strategies to prevent these episodes.”

There are two key components to managing affected horses: diet and exercise. Horses diagnosed with PSSM or RER benefit from a diet that is low in sugars as they are not able to properly use sugar for energy in their muscles. The primary energy source in their diet should be in the form of fat and fibre.

The basis of the diet should be hay — ideally a good quality grass hay like timothy or brome. Horse owners can provide additional energy through vegetable oil or feeds that are specifically formulated with a high fat and fibre content.

Uehlinger also recommends that affected horses receive daily exercise. The exercise doesn’t need to be strenuous, but it does need to be consistent. This routine is important to maintain energy metabolism in the muscle. If you are unable to ride every day, daily turnout can help keep your horse moving. The most important thing is to try and avoid lay-ups and stall rest.