Treating Horse Muscle Trembling

horse muscles trembling

If your horse experiences occasional muscle trembling, he will likely need nothing more than rest and dry hay while waiting for a professional veterinary evaluation. In contrast, chronic cases may require muscle relaxers to offer relief. The condition is often worse during hot, humid weather conditions when horses sweat excessively to help dissipate body heat. The excessive sweating can cause dehydration and loss of important electrolytes such as Sodium (Na), Potassium (K), Chlorine (Cl), Magnesium (Mg), and Calcium (Ca) from the extracellular fluid.

A specific muscle disorder known as “shivers” affects the hind legs of horses and can be quite severe in some cases. It is characterized by spasmodic hyperflexion of the hind limb that appears to be involuntary. The affected limb is raised up and away from the body with the toe held in the air for several seconds or minutes during an episode of shivering, followed by rapid extension to bring the foot to the ground. Horses experiencing a shivering episode will often refuse to back up and will not permit their hind feet to be picked up for grooming or farrier work.

The condition is thought to be caused by damage to a part of the cerebellum called Purkinje cells, which control movement of the hind limbs. This damage has been linked to a defect in a specific protein that regulates the sodium channels in these nerve cells. The faulty protein causes the muscles to become overexcited and contract more readily than normal. The condition is more common in geldings than mares, and it tends to progress over the course of the horse’s life. It is not contagious, but it may be passed on genetically through breeding.

Affected horses are usually a few years old when symptoms appear and it is more common in males than females. Horses that are over 16.3 hands tall are also more susceptible to the condition. The cause of the disorder is unknown, but a genetic component seems to be involved as horses with the disorder are more likely to have ancestors that also showed signs of shivering.

Many athletic horses that have shivering will continue to perform at a high level, but their ability to perform slow, learned movements such as backing up or executing a halt is significantly impaired. These slow, learned movements are regulated by different circuits in the cerebellum than the spinal circuits that control the faster, natural gaits such as the walk and trot.

A differential diagnosis of shivers must be made by ruling out other conditions that affect hind limb movement, such as stringhalt and EPM. Affected horses are often resistant to having their hind feet picked up for grooming or farrier work, and some will even buck when stalled. Those horses are more likely to be diagnosed with an underlying orthopedic issue and not shivering.