An outbreak of paralysis in finisher pigs in South Africa after ingestion of feed containing 54,581 mg/kg
of selenium is described. The main and entirely consistent lesion was bilaterally symmetrical focal
poliomalacia of the ventral horns of the spinal cord, which was most severe and consistent in the lumbar
intumescence. Acute and subacute lesions were characterized by malacia with large numbers of
gitter cells. The main features of chronic lesions were loss of neurons and gliosis. Focal degeneration
and necrosis of the myocardium and skeletal muscles were also consistent, but there were fewer specific
changes. Endothelial swelling, mild fibrinoid degeneration and perivascular leukocytic infiltration
were present in the acute stage. Dermatitis, coronitis and hoof sloughing, usually present in more chronic
cases of intoxication, were not a feature of the present outbreak, although alopecia and crusting were
evident on the backs of a few pigs several weeks after the episode of intoxication.
Serum- and tissue-selenium levels were elevated in the early stages after intoxication. Serum levels
were nearly normal in chronic cases two months after the episode, while liver and kidney levels were
still higher than normal. Higher levels were found in liver, kidney and serum than in muscle, with the
highest levels in the kidney. Less than 20% of affected pigs recovered sufficiently to be marketed.
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