Shivers in Horses: Newest Facts and FindingsBy Kentucky Equine Research Staff · January 8, 2018
Cold weather may be affecting many horses and owners in the Northern Hemisphere, but ambient temperature has absolutely no impact on whether or not a horse has shivers, despite its bone-chilling name. While widely recognized in certain breeds of horses over the past several centuries, until recently little was known about the cause of this neuromuscular disease or, more importantly, what to do about it.
“The equine community knows more about shivers than it did even 10 years ago, thanks in large part to research efforts, and can finally begin to make progress in terms of treatment,” shared Kathleen Crandell, Ph.D., a nutritionist who has dealt with her fair share of shivers cases during her career with Kentucky Equine Research (KER).
By definition, shivers is a chronic, slowly progressive neuromuscular condition characterized by quivering of the hind limbs and tail during backward movement. Most horses show no signs of shivers at the walk or trot. Affected horses often show hyperflexion or hyperextension of one or both hind limbs when asked to back, though. With hyperflexion, the horse raises one hind limb up and away from the body in a spastic, trembling motion for several seconds or longer. With hyperextension, the horse places the hind feet further back than normal when moving backwards. The stifle and hock joints become hyperextended, held rigid and spastic. Trembling of the muscles of the hindquarter may also occur, especially in advanced cases.
Shivers appears to be caused by a defect in a region of the brain called the cerebellum that controls muscular activity. Based on the most up-to-date details, the cerebellum of horses with shivers lacks an “off switch,” causing certain muscles to be active at all times.
Here’s what else you need to know about shivers:
- Diagnosing shivers can be relatively easy based on distinct telltale signs described above. In the early stages of disease, however, the signs can be subtle and intermittent, making diagnosis difficult until the disease is well established. Collaborate with a veterinarian to achieve a definitive diagnosis.
- Most horses do not begin showing signs of shivers before the age of five years, though some show signs as younger horses.
- Geldings are more likely to be diagnosed with shivers than mares.
- Tall horses, especially those over 16.2 hands, are also more susceptible than shorter horses; ponies and Miniature Horses are, if ever, rarely affected.
- Researchers suspect a genetic component, considering shivers most commonly occurs in draft horses, Warmbloods, and occasionally light breeds, such as Quarter Horses and Thoroughbreds.
- Shivers can be similar to other musculoskeletal and neuromuscular disorders, especially during the early stages of the disease. A veterinary examination should rule out stringhalt, upward fixation of the patella, equine motor neuron disease, and even equine protozoal myeloencephalitis (EPM). Do not confuse shivers with polysaccharide storage myopathy (PSSM), and appreciate that certain horses can actually suffer from both conditions concurrently.
- There is no cure or definitive treatment for shivers. While some horses can continue to compete or perform athletically, others require retirement or even humane euthanasia.
“Vitamin E plays an important role in neuromuscular conditions. Experts recommend having shivers horses have adequate levels of vitamin E. If not, supplementing with products such as Nano•E is recommended,” suggested Crandell. “A single 5,000 IU dose of natural-source, water-soluble vitamin E, like Nano•E, doubles serum vitamin E levels within 12 hours of supplementation.”
Do you have additional questions on shivers and vitamin E? Ask a KER nutrition advisor today.