Management Of Equine Shivers

Shivers is a chronic, slowly progressive, neuromuscular condition, characterised by hyperflexion or hyperextension of the hindlimbs when backing up, muscle tremors in the hindquarters, and muscle atrophy as the condition progresses. Recent research has revealed that Shivers is caused by damage to the Purkinje cells which are located in the cerebellar cortex of the brain, in the outer layers of the cerebellum (Valberg et al., 2015)​. The cerebellum plays a fundamental role in balance and movement. The underlying mechanisms behind the damage to the cells are currently unknown.

The severity of clinical signs for the disorder can be highly variable and often difficult to detect in the early stages. If your horse exhibits muscle quivering, difficulty in backing up, discomfort while being shod on hind hooves, or other signs of Shivers, have your horse evaluated by your veterinarian. Currently there is no diagnostic test for Shivers, and instead diagnosis is based on the characteristic gait pattern during backward walking that is absent during trotting and only apparent in advanced cases in <20% of strides. No causal link has been identified between Shivers and PSSM. However, horses can suffer with both disorders concurrently, so it may be worth conducting a muscle biopsy to rule out PSSM. There are a range of other disorders that a veterinarian will have to rule out when diagnosing Shivers, including Stringhalt, Upward Fixation of the Patella, Fibrotic Myopathy, Equine Motor Neuron Disease, Equine Protozoal Myeloencephalitis, and Stiff-Horse Syndrome.

Geldings are three times more likely to be diagnosed with Shivers than mares, and horses over 16.3hh are more susceptible. The syndrome affects several breeds, including draft horses, Warmbloods and occasionally lighter breeds, including Quarter Horses, and Thoroughbreds. In ponies, Shivers is considered uncommon to rare. Because Shivers is breed related, there may be a genetic predisposition for the disorder. In some countries, it is recommended that stallions with this disorder not be used for breeding purposes. Currently, there is no specific genetic pattern identified and there is no genetic test.

At this time, there is no cure or effective treatment for Shivers, however management methods have been proposed from owner reports. Clinical signs have been said to improve with turn out and consistent exercise but can also regress during times of stress. Muscle disorders such as PSSM are managed through a low starch, high fat ration. However, when Warmblood or Warmblood-cross horses with Shivers were fed grass hay and their grain ration was replaced with a high fat supplement, clinical signs did not improve. These dietary recommendations were combined with a gradually increasing daily exercise program and maximal turnout. Starch intake should be controlled for horses prone to anxious or stressy behaviours, as a high starch intake can exacerbate these behaviours and worsen clinical signs of Shivers. Feeding the recommended rate of a ration balancer or fully fortified feed alongside forage is vital, to ensure all essential nutrient requirements are met.

Horses with possible Shivers need to have a complete veterinary evaluation. A thorough lameness exam should rule out abnormalities in the hooves, bones, joints, and tendons that may cause the horse to show signs similar to Shivers. The exam should involve backing horses up and lifting the hindlimbs in a flexed position. Your veterinarian will be able to confirm the diagnosis, rule out other possibilities and recommend appropriate treatment and management.