Selenium toxicity and porcine focal symmetrical poliomyelomalacia: description of a field outbreak and experimental reproduction.

An acute afebrile paretic condition was diagnosed in 18 of 225 feeder pigs between eight to ten weeks of age. Nine pigs died acutely, seven pigs were euthanatized and two appeared to recover. Macroscopic lesions in the ventral horns of the cervical and lumbar/sacral spinal cord enlargements consisted of focal, bilateral, depressed areas. Histopathologically, the lesion consisted of endothelial proliferation, glial cell reaction and microcavitation. Similar lesions were observed in some brain stem motor nuclei. High selenium levels were detected in the pig feed and in pig tissues and blood. Two of five experimental pigs fed a commercial grower ration and supplemented with 52 ppm selenium as sodium selenite developed paresis and paralysis after a 29 day feeding trial. Histopathological lesions of focal symmetrical poliomyelomalacia confined to the cervical and lumbar/sacral spinal cord enlargements, and identical to those in the field cases, were produced. Select brain stem motor nuclei were also affected.