A horse can lose normal sensation or movement if disease affects either its central nervous system or its peripheral nervous system (see Parts of the Nervous System in Horses). Common signs of nervous system disorders in horses include behavior changes, seizures, tremors, pain, numbness, poor coordination, weakness, and paralysis (inability to move) in one or more legs. If your horse has a nervous system disorder, the signs you see in your horse depend on where the nerve damage is and how severe it is.
Spinal Cord Disorders
Damage to the spinal cord can decrease feeling and movement below the point of injury.
Mild injury can cause clumsy movement and mild weakness.
Moderate injury can cause more obvious weakness.
Severe injury can cause possible paralysis and loss of feeling.
Brain Disorders
How a brain disorder affects a horse depends on the area of the brain involved.
Brainstem injury can cause loss of balance, weakness, exaggerated reflexes, severe dullness, or coma.
Cerebellum injury often causes tremors, poor coordination of the head and legs, and balance problems.
Cerebrum injury can cause seizures, blindness, circling or pacing, coma or stupor, loss of smell, or failure to recognize familiar people.
Some nerve damage is not obvious until 24–48 hours after an injury, often because of swelling or bleeding. True “stroke” from blocked arteries is uncommon in horses.
Causes of Nervous System Disorders
Nervous system disorders can result from birth defects, infections, inflammation, toxins (poisons), body-chemistry (metabolic) problems, poor nutrition, degenerative disease, or cancer.
Many birth defects (congenital problems) show up at or soon after birth. Some inherited diseases slowly damage nerve cells in the first year of life. Others—like some seizure disorders—might not produce symptoms until the horse is 2–3 years old.
Infections can be caused by viruses, bacteria, parasites, or other germs.
Toxins (poisons) that can harm the nervous system include some pesticides and sedative drugs. Certain diseases and toxins—such as botulism, tetanus, some tick-related problems, and some snake venoms—can also cause paralysis.
