A change in diet is a risk of disease

A change in diet is a risk of disease

Any change in diet, especially from a poor, grass blade to a good, fresh pasture, can increase the risk of polioencephalomalacia (PEM).

PEM is a disease that affects the nervous system of ruminants and is caused by low levels of vitamin B1 (also known as thiamin).

Thiamine is required to maintain normal fluid balance in body tissues.

Thiamine deficiency leads to fluid balance dysfunction leading to cell swelling in the brain and subsequent cell death.

Long-term storage of thiamine in the body is not possible, which means that cattle are dependent on the daily production of this vitamin by bacteria in the rumen. In healthy cattle, the daily thiamine requirement is usually balanced by the daily thiamine production.

Most commonly, PEM occurs when there is an overproduction of enzymes called thiaminases that break down and inactive thiamine, leading to an overall deficiency.

These thiaminases can come directly from bacterial overgrowth in the rumen or indirectly from plant sources. PEM is also associated with high sulfur content in water or feed.

PEM marks

In grazing animals, PEM occurs predominantly in well-nourished, gentle, young animals between 6 and 18 months of age, although adults may rarely be affected.

In Australia, PEM commonly occurs in calves weaned in early summer. It is usually sporadic, affecting only a few animals in a herd, although occasional outbreaks may occur.

In feedlot cattle, the disease is associated with a high-carbohydrate, low-fiber diet that leads to rumen acidosis and overproduction of thiaminase-producing bacteria.

Symptoms of the disease usually develop suddenly within 12 to 48 hours after a change in diet.

Blindness, depression, staggering, restlessness, frothy saliva and pressure on the head are common. In some cases, affected animals may simply be found dead.

If untreated, neurological symptoms progress to twitching, muscle tremors, collapse with extended head and neck, seizures, and eventually death.

Diagnosis and treatment

Your veterinarian should be consulted with any suspicion of PEM. There are other diseases that can cause similar symptoms, and a full veterinary clinical examination is necessary to rule out these conditions.

The history and clinical signs alone may be enough to start treatment, but in some cases your vet may want to take samples from affected animals to help with a definitive diagnosis.

Other diseases to consider include lead poisoning, salt/water toxicity, listeriosis, vitamin A deficiency, and bacterial meningitis.

Treatment with vitamin B1 should be started as soon as possible, and the response to treatment is often diagnostic of PEM. Repeat treatments may be required.

If treated quickly in the early stages of the disease, animals may respond within six hours of treatment.

Animals affected in the later stages of the disease may partially respond and suffer permanent symptoms such as blindness. Severely affected animals should be euthanized.

Always consult your veterinarian if your cattle shows neurological signs of disease. Further testing, including post-mortem sampling, may be required to reach a diagnosis.

Dr Gemma Chuck works for Apiam Animal Health in the dairy operations team where she writes technical service programs for farmers and vets.

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