Some problems with the nervous system in horses are "congenital," meaning they are present at birth. Some congenital defects (birth defects) are inherited, whereas others might be linked to environmental factors during the mare's pregnancy, such as exposure to toxic plants, nutrition problems, or infections. In many cases, the cause is unknown. Foals are born with a fairly mature nervous system, so problems might be noticed early.
The following congenital disorders are grouped by the main area affected: cerebrum, cerebellum, or spinal cord.
Congenital Disorders of the Cerebrum
Juvenile epilepsy is characterized by seizures, which can lead to injury or blindness. It occurs in young foals—especially Arabians—up to about 12 months old. Some foals improve without treatment, but antiseizure medicine is often recommended for the first 1–3 months of life.
Narcolepsy is characterized by sudden episodes of extreme sleepiness or sudden collapse with muscle weakness. It occurs in several horse breeds, especially Shetland ponies. Horses with narcolepsy are usually conscious during episodes and otherwise healthy.
Congenital Disorders of the Cerebellum
Cerebellar problems in horses often cause tremors and poor coordination in the head and legs.
Cerebellar hypoplasia is a condition in which the cerebellum doesn't fully develop. Tremors are common and usually do not worsen with age. Some affected horses also have hydrocephalus (too much cerebrospinal fluid around the brain, causing the head to look enlarged).
Cerebellar abiotrophy happens when cells of the cerebellum begin to die after birth. It is inherited and occurs mostly in Arabian foals. Signs can begin from birth to age 9 months, and they get worse over time. Signs of cerebellar abiotrophy include tremors, poor control of movement, exaggerated front-leg action, and a wide stance.
Congenital Disorders of the Spinal Cord
Neuraxonal dystrophy is an inherited spinal cord disorder in Morgan horses (and occasionally Haflinger horses). Symptoms often appear at 6–12 months old and include weakness and stiff, awkward, uncoordinated movement. It may be the same condition as equine degenerative myeloencephalopathy.
Equine degenerative myeloencephalopathy has been linked to low vitamin E levels in the dam and in the foal after birth, and could also have an inherited component in some breeds. In horses with this disorder, nerve pathways between the spine and cerebellum slowly fail, leading to progressive incoordination and sometimes paralysis (inability to move) in all four legs, starting as early as 7 months.
Cervical vertebral stenotic myelopathy ("wobbler syndrome") is a disorder in which neck-bone changes or injuries compress the spinal cord. This usually happens between the ages of 6 months and 3 years and might involve genetics plus rapid growth in young horses. Thoroughbreds, Tennessee Walking Horses, and warmblood breeds are at higher risk, and males develop the disorder more than females. Wobbler syndrome is diagnosed using x-rays and sometimes more advanced imaging studies. Surgery might be needed to stabilize the horse's neck, and the outcome of surgery varies.
Occipitoatlantoaxial malformation involves abnormal bones at the top of the neck. It is an inherited disorder in Arabian foals and can also occur in miniature horses. Signs of this malformation include worsening incoordination, partial paralysis (inability to move) in all four legs, and standing with an extended neck. Some foals are weak at birth, whereas others develop signs later. This disorder is diagnosed using x-rays.
For More Information
Also see professional content regarding congenital and inherited anomalies of the nervous system.
