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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.
Herds are classified on a risk status of 1-5 with risk level 1 having had three annual clear tests for Johne’s disease. Risk level 5 is where there is no testing taking place and no health plan on the farm.
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There are now just under 3,000 herds participating in the programme and many Scottish pedigree breeders will only buy animals from risk level 1 herds.
Caldow said 54 infected herds were identified under the programme before 2004 and 35 (65%) of these have gained Johne’s risk level 1 status. He 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 lower 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?
Johne’s is 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. It is transmitted by the ingestion of infected faecal material, colostrum/milk, inutera or via semen. It is 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 sampling can be used to determine whether shedding is taking place. It is 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 is important that they are not bred and culled as soon as possible.
Animal Health Ireland has produced a very helpful booklet to help Irish farmers deal with Johne’s disease (www.ifj.ie/ahijohnes).
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. Pre-movement testing is advised to be carried out.
2 Biological materials
Colostrum is the main risk. Be very careful where you source it from. All colostrum used on the farm 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/vets
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. Vets pose a high risk and all visitors should be asked to scrub down and foot dip before entering the farm.
5 Vehicles
Infective material carried on the tyres of machinery and tractors pose a similar risk to farm workers. Especially where machinery has been involved in slurry spreading elsewhere, tyres should be cleaned before entering the farm.
6 Farm visitors
Make sure all visitors have clean footwear before entering calf pens or calving areas. Similar to farm workers, 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 calving, 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
In January 2017, before calving began, a case of Johne’s disease was detected on Tullamore Farm. The cow in question, a second-calver, was slaughtered and the rest of the herd was blood-sampled. This showed up three antibody-positive cows. Antibody-positive cows don’t shed the virus. However, they pose a risk as they could start shedding at any time. They were monitored closely and the three cows in question were not put in calf in 2017 and culled. The herd was tested in July 2018 and one cow tested inconclusive. This animal will be monitored closely and culled as soon as possible. All animals that are now purchased on to the farm are pretested for Johne’s disease. Particular attention is also paid to hygiene at calving time. If needed, colostrum is provided by a local dairy farm that has tested clear of Johne’s.
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