George Caldow is a vet working with the Scottish Agricultural College who has studied Johne's disease for most of his working life.

Scotland is ahead of the game on this one and introduced a voluntary testing programme in 1998 for Scottish beef and dairy farmers.

It was particularly popular with pedigree breeders and beef farmers, with a lower uptake among dairy farmers.There are now just under 3,000 herds participating in the programme.

Research

Caldow pointed out that through the programme, there were 54 infected herds that were testing before 2004 and 35 (65%) of these have gained Johne's risk one status, which is the lowest level risk a herd can have.

Herds are classified on a risk status of one to five, with risk level one having had three annual clear tests for Johne's disease.

Risk level five is where there is no testing taking place and no health plan on the farm. Caldow presented research showing the losses in a beef herd infected with Johne's can be significant. In a Scottish trial, cows with high antibody results produced calves with a weaning weight of 21.5kg less than the negative cows in the herd. Cows classified as moderate to high shedders produced calves with a weaning weight 58.5kg less than negative cows in the herd.

What is Johne's disease?

It’s an infectious intestinal disease caused by Mycobacterium pvium subspecies paratuberculosis (MAP). It affects ruminants (cattle and sheep) predominantly and young animals are more susceptible to infection.

Disease transmission is via ingesting infected faecal material, colctrum/milk, in utero or via semen. It’s quite a complicated disease with a prolonged incubation period.

How can I test?

Animals can be blood-tested for antibodies to the disease or faecal-sampled to determine whether shedding is taking place.

It’s important that the Johne's test takes place at least six months from the annual TB test as this can distort results.

The advice is to cull any animals that have a positive test and if antibody-positive cows are kept, it’s important that they are not bred and culled as soon as possible.

Animal Health Ireland has produced a very helpful booklet to help Irish farms deal with Johne's disease. See the booklet here: www.animalhealthireland.ie/?page_id=333

High-risk areas

The following are high-risk areas in terms of bringing Johne's on to your farm (AHI):

1 Introduced animals: Even animals that appear healthy may carry the disease without displaying any symptoms. To control this risk, the number of herds from which animals are introduced should be minimised and ideally they should only be from low-risk ones.

2 Biological materials: Colostrum is the main risk here. As calving has passed on many farms, it is not of immediate concern. However, all colostrum used should be handled hygienically and come from Johne’s-free cows.

3 Slurry: As the bacteria responsible for Johne’s disease can be passed through dung, slurry is of major concern. Imported slurry can increase the risks of disease entering a herd and its application to pastures where young stock are grazing should be avoided.

4 Farm workers: Workers who have visited a number of farms can carry infected material back. Cleaning areas should be provided on farms to wash both hands and footwear.

5 Vehicles: Infective material carried on the tyres of machinery and tractors poses a similar risk as farm workers. Especially where machinery has been involved in slurry spreading elsewhere, tyres should be cleaned before entering the farm.

6 Farm visitors: As summer holidays are taken by many, visitors to farms may become more common. If they have visited other farms they may be carrying infective material.

7 Returning animals: Animals can be exposed to risks off-farm when they leave for shows and marts or contract-rearing units. All off-farm areas should have good biosecurity practices and all equipment used for transport should be cleaned on return.

8 Equipment: During this busy period on many farms, it may be necessary to borrow equipment from neighbours and friends. While this should be avoided where possible, should it occur, all equipment must be well-maintained and thoroughly cleaned before and after use.

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How can Johne's disease be controlled?

Iodine deficiency: usually associated with stillbirth and perinatal weak calf