Polioencephalomalacia (PEM) in a Brahman calf

Livestock disease investigation case report

A two-week-old female Brahman calf in the Darwin region was observed to be dehydrated, listless and easily caught. The calf exhibited a flaccid drooping head and ataxia and the next day was convulsing with opisthotonos (body arches backwards with head and legs in hyperextension) and was euthanized. The cow showed no abnormal signs. Gross necropsy revealed no significant findings. Histopathology on various brain sections showed severe polioencephalomalacia and there was a colitis with predominance of bacteria in the intestine.

Polioencephalomalacia is a poorly understood condition that has a myriad of possible causes, including water deprivation (salt toxicity), mercury intoxication, lead intoxication, hypoglycaemia, treatment with the coccidiostat amprolium, sulphur toxicity and thiamine deficiency. Thiamine deficiency is the most commonly recognised cause in ruminants and, in older weaned animals, is often related to a sudden change in diet with associated change in intestinal flora to thiaminase-producing bacteria.

The cause of the polioencephalomalacia in this young calf was not obvious, with the only possible indication being the colitis and associated colonic proliferation of bacteria suggesting there may have been a problem with normal intestinal flora, allowing proliferation of potentially thiaminase-producing bacteria. The case was isolated, with other calves in the herd remaining normal.