Polio encephalomalacia occurs when an animal lacks enough thiamine (vitamin B1), an essential nutrient for normal body metabolism.
In healthy ruminants — cattle, sheep and goats — thiamine is produced naturally in the rumen, the first stomach, where microbes aid in breaking down food.
However, if this microbial community is disturbed, thiamine levels can become dangerously low.
Any condition that disrupts the balance of rumen microbes can lead to thiamine deficiency. This includes grain poisoning, low-fibre diets, or an excess of sulphur in feed.
The disease most commonly affects well-grown calves or lambs aged between six and 12 months old, but it can affect animals of any age or sex.
Things to look out for
The earliest signs can be subtle — animals may seem lethargic, lose their appetite, or wander away from the herd.
They may bump into objects, appear blind, or stand motionless — sometimes with their heads drooped, at other times gazing fixedly at the sky.
As the condition worsens, affected animals may experience convulsions, collapse with their head arched backward, and ultimately slip into a coma.
Without treatment, death often occurs within two to three days.
But not every case is the same. Some animals are found dead without warning, while others show only mild symptoms and recover on their own.
Treatment and prevention
If caught early, the condition may potentially be reversed with an injection of thiamine, which is available without a prescription from veterinarians.
Farmers are also advised to support the rest of the herd by offering high-fibre feed, which promotes a healthy rumen environment and consistent thiamine production.
Unfortunately, once blindness or paralysis occurs, the brain damage is often irreversible. In such cases, humane euthanasia is usually the only option.
Farmers are encouraged to seek advice from their local veterinarian. In Victoria, advice is also available from Agriculture Victoria veterinary or animal health officers, and in NSW, through Local Land Services.
Dr Jeff Cave is a senior veterinary officer with Agriculture Victoria.
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