Polioencephalomalacia (PEM) in cattle is a neurological emergency caused by thiamine deficiency or sulphur toxicity, producing brain swelling and blindness that is reversible if treated promptly but fatal if delayed.
Polioencephalomalacia causes severe neurological suffering — affected cattle experience blindness, disorientation, and seizure activity that must be deeply distressing for a prey animal that relies on vision for safety. The opisthotonus posture — head pulled back over the spine in severe cases — indicates profound central nervous system dysfunction. Yet this condition is uniquely reversible: thiamine injected promptly can produce dramatic recovery from animals that appeared moribund. The welfare imperative is speed of treatment — every hour of untreated cerebral oedema increases the risk of permanent brain damage. Stockperson recognition of early neurological signs and immediate veterinary contact is the primary welfare intervention.