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Find information on animal health topics, written for the veterinary professional.

Nervous System Disorders and Effects of Injuries in Horses

By William B. Thomas, DVM, MS, DACVIM (Neurology), Professor, Neurology and Neurosurgery, Department of Small Animal Clinical Sciences, University of Tennessee ; Daniela Bedenice, DVM, DACVIM, DACVECC, Assistant Professor, Cummings School of Veterinary Medicine, Tufts University ; Kyle G. Braund, BVSc, MVSc, PhD, FRCVS, DACVIM (Neurology), Director, Veterinary Neurological Consulting Services ; Cheryl L. Chrisman, DVM, MS, EDS, DACVIM (Neurology), Professor of Veterinary Neurology, College of Veterinary Medicine, University of Florida ; Caroline N. Hahn, DVM, MSc, PhD, DECEIM, DECVN, MRCVS, Senior Lecturer in Veterinary Clinical Neuroscience, Royal (Dick) School of Veterinary Studies, University of Edinburgh ; Charles M. Hendrix, DVM, PhD, Professor, Department of Pathobiology, College of Veterinary Medicine, Auburn University ; Maureen T. Long, DVM, PhD, DACVIM, Associate Professor, Department of Infectious Diseases and Pathology, College of Veterinary Medicine, University of Florida ; Robert J. MacKay, BVSc, PhD, Professor, Large Animal Medicine, Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida ; Karen R. Munana, DVM, MS, DACVIM (Neurology), Associate Professor, Department of Clinical Sciences, College of Veterinary Medicine,North Carolina State University ; Charles E. Rupprecht, VMD, MS, PhD, Director, LYSSA LLC ; Josie L. Traub-Dargatz, DVM, MS, DACVIM, Professor of Equine Medicine, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University ; Susan L. White, DVM, MS, DACVIM, Professor of Large Animal Internal Medicine, Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia

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A change in an animal’s ability to sense its environment can be caused by disease in either the central nervous system or the peripheral nervous system. The primary signs of nervous system disorders include behavioral changes, seizures, tremors, pain, numbness, lack of coordination, and weakness or paralysis of one or more legs. The effects of an injury on sensory and motor functions depend on its location and severity.

A spinal cord injury can cause loss of feeling and paralysis below the level of the injury. Mild spinal cord injuries can result in clumsy movement and mild weakness of the limbs. Moderate spinal cord injuries can cause a greater weakness of the limbs. In severe spinal cord injuries, a complete loss of movement (paralysis) and feeling can occur. However, not all spinal cord injuries cause paralysis. For example, injury to the spinal cord in the lower back can result not in limb paralysis but in loss of bladder control.

Brain injuries result in different effects, again depending on which part of the brain is affected. Injuries to the brain stem can cause a loss of balance, weakness of the limbs, hyperactive reflexes, stupor, or coma. Injuries to the cerebellum can result in a lack of coordination of the head and legs, tremors, and a loss of balance. Injuries to the cerebrum can cause complete or partial blindness, loss of the sense of smell, seizures, coma, stupor, pacing or circling behavior, and inability to recognize an owner.

Some injuries to the nervous system can cause damage that is not evident until 24 to 48 hours after the injury occurs. Longterm damage is usually caused by swelling or internal bleeding of the vessels in the brain. Strokes caused by clogged arteries or high blood pressure are rare in animals.

Mechanisms of Disease

In addition to the effects of injuries, nervous system disorders can include birth defects, infections and inflammations, poisoning, metabolic disorders, nutritional deficiencies, degenerative diseases, or cancer.

Most birth defects, often called congenital disorders, are obvious at birth or shortly after. Some genetic diseases cause the neurons to degenerate slowly and irreversibly in the first year of life. In other inherited diseases, such as epilepsy, the animal may not show any signs for 2 to 3 years.

Infections of the nervous system are caused by specific viruses or microorganisms. Other inflammations such as certain types of meningitis can be caused by the body’s own overactive immune system. These are known as autoimmune disorders. Various chemicals can cause a toxic reaction in the nervous system. These include certain pesticides and herbicides, rat poisons, antifreeze, and sedatives. Botulism, tetanus, and tick bites, as well as coral and tiger snake venom, can also affect the nervous system and cause paralysis.

Some metabolic disorders affect the function of the nervous system, including low blood sugar, shortness or loss of breath, liver disease, and kidney failure. Thyroid gland abnormalities can also cause neurologic signs.