Polioencephalomalacia

Polioencephalomalacia (PEM) literally means softening of the cerebrocortical grey matter distributed in a laminar (layered) pattern. It is also called cerebrocortical necrosis (CCN), laminar cortical necrosis or cortical necrosis. PEM is a sporadic disease caused by the overconsumption of simple carbohydrates, and the underconsumption of fiber; it occurs in cattle, sheep and goats, and was first seen in the 19th century when ruminants were fed the byproducts of sugar refining. Today PEM is most commonly seen in cattle at 6–18 months of age when fed concentrate rations. Sheep are usually affected at 2–7 months of age.