Fresh warning over ‘hidden disease’ in dairy herds

PROGRESS is being made in controlling what vets call a “major hidden disease” in cattle, but there is an acceptance among researchers and scientists that eliminating Johne’s disease is far over the horizon.

With almost half the Scottish dairy herds believed to be infected with Johne’s, or paratuberculosis, the Scottish Funding Council last year set up a three-year project under the Paraban title to tackle the wasting disease.

The project involves nine farms – eight in Scotland and one in Cumbria – and combines the expertise of research workers, veterinarians and scientists. It also has the backing of organisations such as Quality Meat Scotland and the National Farmers Union of Scotland.

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Speaking in Brechin, Graeme Richardson, of the Thrums veterinary practice, said that for every cow showing the clinical signs of wasting and diarrhoea another ten or more in the herd could be infected and not present symptoms.

The problem is that even if the cattle are not showing any outward signs and even if they are not being diagnosed with the disease because the diagnostic test is not 100 per cent foolproof, they can still lose performance. He quoted a figure of just under £1,000 potential annual loss of milk production in a cow carrying the disease and said a loss of fertility was another big problem in affected herds.

Transmission of the bug is usually by calves being infected by dirty bedding, but it can also be from infected mother’s milk, or from ingesting the bug on infected land.

Adult cows can also transfer the disease, although it is most likely transmitted early in life, thereafter living sub-clinically for years before moving to full-blown cases. Once ingested, the bacteria live in the small intestine, causing the intestinal wall to thicken and lose its ability to absorb nutrients.

Richardson said a strict on-farm regime involving the separation of infected stock, regular testing and high levels of cleanliness had dramatically helped to reduce infection levels at the Milne’s dairy farm at East Pitfortthie, Brechin. Although vaccines are available to help control Johne’s, he is not keen on using them as they can mask symptoms and make it harder to identify the disease.

Rabbits and sheep have also been implicated in the spread of the disease, but SRUC epidemiologist Selene Huntley said the risk of transmission from those animals was low compared with the potential spread between cattle.

Meanwhile, Rubert Hough of the James Hutton Institute, Aberdeen, said the bugs tended to live in acidic soils with high levels of iron and with a high water table.

Liming was, therefore, a good way of counteracting this menace but he said there was no practical or economically viable method of eliminating the bug from infected soils.