Polioencephalomalacia is a rather fancy name that describes the changes to the brain that result from a thiamine deficiency. All animals require thiamine for brain function, among other things, but ruminants are unique in that they use the microbes in the rumen to produce thiamine rather than having to rely solely on it being in their diet.


PEM can occur when there is a disruption to the production of thiamine, or a breakdown of the thiamine by chemicals called thiaminases, before it can be absorbed. PEM typically affects well-grown calves about 6-12 months of age but can occur in older animals. Often it will only be the one animal affected, but outbreaks have been reported.


The clinical signs will vary from sudden death to depression and head pressing as if the animals have a headache. Nervous signs do develop with the muscles becoming stiff and the head raised (star gazing) see right. Convulsions and recumbency occur as the disease progresses but even in these latter stages treatment with intravenous thiamine and anti-inflammatories can be very effective. Interestingly, on post mortem the affected areas of the brain glow under UV light.

 The main differentials for this disease are lead poisoning (access to old paint on fences and sheds, old batteries etc.); tetanus (vaccinate!); water deprivation (check your troughs are clean). With prevention being better than cure pasture management for calves becomes rather important. Moving calves more frequently so that their diet becomes more consistent rather than having the stalky to lush change will reduce the risk of PEM as well as improve your heifer growth rates.