Beware of B1 deficiency

David Oertly, Veterinarian
With mating now well underway and most calves weaned and being prepped for grazing, it is important to keep an eye out for the insidious but potentially fatal condition called polioencephalomalacia, cerebrocortical necrosis, or simply polio, vitamin B1 deficiency. Note that this is completely different to vitamin B12 deficiency or supplementation!

B1 deficiency most commonly affects young cattle from weaning to one year old, although we sporadically see rising 2 year-old heifers and milking cows also affected. Spring and summer to early autumn are the most common times of year for this condition to develop.

Affected stock present as though they have just been watching a recent US Presidential candidates' debate, showing any of the following clinical signs: headaches, confusion, disorientation, irritability, a tendency to need to sit or lie down and even head-pressing. If animals are able to walk, they are often ataxic or unable to walk straight. Appetites are depressed, and abnormal eye movements or even convulsions can develop. If treatment is not administered promptly, brain damage can become irreversible, leading to death within days.

The condition often affects several yearlings within a mob simultaneously, and numbers of animals can develop symptoms over several weeks within a group. Cases in older heifers or adult cows tend to be more sporadic and limited to individual animals. The clinical signs can be confused for metabolic disorders, plant poisonings, lead or selenium poisoning, blue-green algae toxicosis, Listeria, meningitis or even water deprivation.

The condition can best be diagnosed based on a thorough clinical examination and response to prompt administration of thiamine (Duoject). Initial treatment is best given intravenously, followed by daily intramuscular injections (for 3-5 days). It can also be beneficial moving young stock off the pasture they have been on and providing more fibre in their diet (e.g. hay or bailage). The prevalence of B1 deficiency is highly variable from year to year but it is still unclear why some years are worse than others. It is postulated that environmental conditions favour gut bacteria which break down thiamine rather than the thiamine producing bacteria that usually dominate the rumen. The production of thiamine in the healthy rumen usually provides the animal with all the thiamine required.

brain fluorescence caused by B1 deficiency

brain fluorescence caused by B1 deficiency
A post mortem diagnosis of thiamine deficiency can be readily and cheaply made by examination of the brain under ultraviolet light. This can be done in-clinic using a 'Woods Lamp' (also used for diagnosing ringworm on small animals). A definitive diagnosis is essential to be able to effectively treat and even prevent further B1 deficiency. Sometimes treatment of a whole group of yearlings with thiamine is warranted.

If you are concerned about thiamine deficiency in your stock, or suspect you have lost stock due to this, talk with your vet about diagnosis and treatment options. It will take a headache off your mind!


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