Subchronic Selenium Toxicosis
Pigs fed a diet supplemented with selenium >20–50 ppm for >3 days develop a subchronic selenium toxicosis characterized by neurologic abnormalities. Animals are initially ataxic and uncoordinated, followed by anterior paresis, then quadriplegia. Even though neurologic impairment is occurring, the pigs continue to eat, which would indicate neurologic damage that is not centrally mediated. The hooves show breaks and impaired growth similar to those seen in cattle. Alopecia may also be seen. In sows, conception rate decreases and the number of stillborn pigs increases. Lesions of subchronic toxicosis include focal symmetric poliomyelomalacia, which is most prominent in the cervical and thoracic spinal cord. Death may result from complications of permanent paralysis. Hoof and hair damage is similar to but in most cases less severe than that seen in chronic selenium toxicosis. Treatment is similar to that for chronic toxicosis, but spinal lesions are usually permanent.