Dispelling the myths around Johne’s (Feb 22)

There are still many myths surrounding Johne’s disease and how to tackle it. NMR vet Karen Bond answers some key questions to correct a few of the most common misconceptions


TEXT KAREN WRIGHT



Q. What are the key misconceptions about Johne’s disease?


A. There’s quite a range, from producers who still think that because they don’t see clinical Johne’s they don’t have it, through to differing beliefs about colostrum pasteurisation and everything in between.


Q. Is it possible for a herd to be 100% Johne’s free?


A. Even CHECS-accredited herds are not classed as ‘Johne’s free’ but as Johne’s Risk Level 1 (low risk). Due to the nature of the disease we can never say a herd is 100% free of the disease, although herds regularly testing with no positive cows are certainly in a better position.


Q. Explain the nature of the disease a bit more.


A. Animals become infected at a young age, often as newborn calves, through muck or milk from infected adults. The bacteria causing Johne’s, known as MAP, then hides away inside the calf, often for many years, waiting until it can multiply and be shed to infect others. This shedding is triggered by a challenge to the animal’s immune system, usually caused by stress (calving, poor nutrition, group change) or another disease (such as mastitis or lameness) leading to infected muck and milk; and so the cycle starts again. This means herds can have many cows infected with Johne’s, but nothing is known about it as they don’t show any outward signs. This is what allows Johne’s to take hold in unmonitored herds.


Routine milk screening for MAP will pick up infected cows. Not all infected cows will have detectable antibodies at each screening test, but a routine quarterly screen of all cows is a practical and accurate way of building a picture of infected cows, which is fundamental in an effective and accurate control programme.


Q. Many vets will say they’ve never seen a clinically infected Johne’s cow.


A. That’s right, even more so during the past 10 years. This is because producers are typically strict on culling cows for health and fertility issues and most Johne’s cows will display a high SCC, lameness or poor milk yield before they show clinical signs of Johne’s. Their culling reason may, for example, be high SCC when the underlying reason is Johne’s.


Producers who are screening and identifying Johne’s-infected cows can manage them appropriately, particularly at and around calving. In most cases these cows will be culled before any clinical signs are seen, meaning the producer can sell them as a higher value cull, rather than a dead loss with clinical disease.


Cows infected with Johne’s won’t show any clinical signs until they are older, but they are still a risk as they may well be shedding MAP and infecting calves. Johne’s can be the silent assassin in a herd if we are not careful.


When a clinically infected Johne’s cow is seen, it’s an extremely sick animal. And this is the tip of the iceberg. For every clinically infected cow seen it is likely between 15 and 20 other animals are already infected.


Q. All Red Tractor-assured herds (98% in the UK) should be Johne’s testing as part of their Johne’s Management Plan. That sounds like impressive progress.


A. It is. This level of testing is great, but the real issue is whether they’re doing appropriate testing. And, unfortunately, that’s where the news is less positive. Some herds are still carrying out just 30 cow targeted screens even though they know they have the disease. This is not appropriate testing, and it is doing nothing to help them actually manage the disease. If you want to manage Johne’s you have to leave the 30 cow screens behind and move to more intensive testing. If there is Johne’s in the herd, producers need to know every cow that’s infected and use that information to manage them. UK producers have access to Johne’s screening services, such as NMR’s quarterly whole herd testing scheme HerdWise. This provides simple, cost-effective whole-herd testing using milk recording samples.


Producers using this testing know the status of each cow and can put preventative measures in place to stop disease spread within the herd, particularly to newborn calves. No new stock should be brought into the herd without seeing rock-solid Johne’s screening records.


Q. The Average Test Value and Progress Tracker are now published on the Johne’s screening service reports offered by the main milk recording organisations. Will this improved transparency on infection levels, within and between herds, help to educate producers and drive control plans?


A. That’s the hope. Once producers get to grips with how this works and can see how herds can progress it will hopefully act as an encouragement to others that it can be done. It also allows producers to see how their herd compares to others. The progress tracker takes it a step further for herds using HerdWise, as it allows them to see what parts of their management are successful and which need to be improved with a simple-to-use tool.


Q. As a judge of Gold Cup herds in the qualifying round, how much attention did you place on Johne’s control?


A. For me, as a vet, it is all about cow health and welfare when I look at judging herds. If they have happy, healthy cows then they will have a good profitable business. Johne’s is obviously a big part of that, alongside the other endemic diseases like BVD, mastitis and lameness.


Karen Bond is a member of the Action Johne’s technical group and will be speaking at a series of processor-led producer meetings during the next six months.



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