Wobbler Syndrome in Horses

Wobbler Syndrome refers to a number of disease states in the horse. The most common is termed cervical vertebral malformation (CVM) and is characterized by malformation or compression of the spinal cord which leads to spasticity, ataxia, and incoordination. These symptoms are caused by damage to or compression on the spinal cord.

Cervical vertebral instability (CVI) and cervical static stenosis (CSS) are the two distinct types of CVM. CVI causes dynamic spinal cord compression. It typically affects horses from 4-12 months of age. CSS typically affects horses between 12-36 months of age and is characterized by a closing of the cervical canal causing compression on the spinal cord. The compression, malformation or lesions of CVM usually occur between the third and fifth cervical vertebrae. The miniature horse is the only breed that has escaped diagnosis of the wobbler syndrome. The Thoroughbred, Quarter Horse, and Morgan are the most commonly affected breeds.

Causes

The exact cause of the wobbler syndrome in horses is unknown. It is believed that the syndrome is caused by several factors: (1) genetic predisposition, (2) nutritional imbalances, (3) rapid growth, (4) physical trauma, or (5) a combination of these. Researchers have suggested that the wobbler syndrome is related to neck length, implying the longer the neck, the more likely the horse is to develop the syndrome. Surveys have shown that males with wobbler syndrome out-number females three to one. The reason for this sex difference is not fully understood. However, the difference may result from the influence of estrogen and testosterone on rate of growth or on the development of orthopedic disease. The breeding of two wobbler parents does not always increase the incidence of the syndrome in the offspring. However, other metabolic bone disorders such as osteochondrosis, physitis, and contracted tendons are more common in the offspring of wobbler parents. Nutritional imbalances and physical trauma are two causes that are the easiest to control.

Nutritional imbalances can be avoided by feeding a balanced ration that meets the nutrient requirements for the particular class of horse being fed. For more information on feeding, consult the nutrition series ASC 111-115. Physical trauma usually results from injury, particularly when a young horse is tied up for the first time or when a horse is cast in a stall.

Clinical Signs

Malformation most commonly occurs between the 3- 4, 4-5, and 5-6 cervical vertebrae, depending on the type of CVM. Lesions occur most frequently at C3-4 and C4-5 for CVI and compression at C5-6 and C6-7 for CSS. However, malformation, lesions, and compression have been reported on other cervical vertebrae.

These malformed or compressed vertebrae press against the spinal cord and interfere with messages being sent by the brain. Therefore, the interference with normal nerve transmission from the brain to the legs leads to noticeable incoordination (ataxia). Ataxia is usually seen in the hind quarters. As the condition persists, weight loss and weakness may be noticeable. Clinical signs may appear suddenly or gradually, following known or suspected trauma, and may increase in severity until death. However, death from the wobbler syndrome is unusual. The horse may show periods of slight improvement, but will never completely recover, if aggressive treatment is not performed.