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Action Johne’s: preventing disease by managing risk

With milk producers needing an approved Johne’s disease control strategy, it is important to understand the risks of this disease

01 June 2020, at 8:25am
FIGURE (1) Approximately 1,200 individuals in the UK are Accredited Johne’s Veterinary Advisors
FIGURE (1) Approximately 1,200 individuals in the UK are Accredited Johne’s Veterinary Advisors

Milk producers are asked to submit a Johne’s disease control strategy to their milk buyer and this is cer-tified by their vet. Not just any vet but one who is a BCVA Accredited Johne’s Veterinary Advisor (BAJVA; Figure 1). Some 1,200 individuals have completed the online training and correctly answered the test. This is no easy achievement for those who have developed the strategies and the pro-gramme. One of the big issues is that the farmer and his vet need to have a real understanding of risk with this disease. A dramatic statement that “80 percent compliance is 100 percent failure” has eased into the veterinary psyche.

Working with dairy farmers to reduce the risk of Johne’s disease requires an element of missionary zeal. Both the farmer and the vet need faith and perseverance because the benefits will not be realised for years to come. Detailed work now to prevent MAP (Mycobacterium avium subspecies paratuberculosis) coming into a herd and spreading within a herd will yield benefits as the calf grows into a heifer and then a productive cow. The work now intends to raise productivity in individuals and the herd for three, four, five, six and seven years hence. Also, turn that aware-ness around and adopt awareness that the incidence of the disease now reflects management weaknesses or strengths that took place historically.

The 15th International Association for Paratuberculosis Colloquium 2020 was due to take place in Dublin in June, but is now arranged for 6 to 9 April 2021. Pete Orpin has published widely, together with Dick Sibley, on developing a national and practice Johne’s control programme. Pete has been preparing a paper for the meeting that brings together the efforts and understanding of veterinary surgeons, farmers and milk buyers in the UK. It is likely to become essential reading for all involved. Many members of BCVA and those collaborating with My Healthy Herd have already contributed to the knowledge base and there is much to be further understood and appreciated. Hopefully there will be an opportunity for discussion later this year so that UK vets are able to benefit from the lessons learned. Work with Joh-ne’s disease is not standing still and the meetings attended by veterinary surgeons as the BAJVA programme was being run out will have fresh awareness now, to be applied moving onwards.

The clinical issues with Johne’s disease appear to be well understood. The bacteria causes thickening of the intestinal wall which leads to inhibition of the absorption of nutrients, with a range of outcomes from poor productive performance to loss of weight, scour and a bullet. There is no national incidence data but various assessments have indicated that certainly half, and maybe three quarters, of dairy herds are infected. What is more accurately identified are the herds at risk. An awareness of risk indicates that over half of the herds do not have adequate biosecurity and biocontainment. Protecting the herds with a low or nil level of infection is a primary aim of the veterinary activity. Assessing risk has moved on a long way from a simple discussion with the farmer. There are tools available online and there is increasing awareness of the value of the My Healthy Herd approach. This is a commercial assessment tool but also a hand-holding exercise to enable veterinary surgeons to offer fact-based advice to their clients and to continue to monitor progress.

Testing plays a part, but the indications are that relying on a test and cull policy does not control the disease entering the herd and does not prevent the organism from circulating within the herd. The milk samples that are taken for milk quality assessment and farmer payment can be ELISA tested for the presence of MAP, with a warning that groups of cows need to be carefully selected to reflect the true incidence of disease. This is an area requiring detailed awareness and the National Milk Laboratory is able to select samples as required. One of the difficulties is the interference with detecting MAP if the herd is being tested for bTB and the MAP sample needs to be taken more than 42 days after the bTB test. For herds being tested for bTB every 60 days, this provides a narrow window and requires detailed attention by vet and farmer.

There are complexities for the farmer in the management of MAP contaminated dung. An infected cow is understood to have peaks and troughs of shedding the organism. The idea that identifying super shedders and culling them will lead to control does not fit the technical awareness. The farmer and his vet need to consider that if there is disease within the herd then any cows may shed the organism at any time. All cows at all times are therefore considered a risk to calves. The whole programme has been described as the need to prevent “dung in mouth”. Infected faeces contaminate the teats, the calf suckles and three years later the impacts start to be realised. Examples of improvements include a detailed awareness of colostrum management, infection within the calving areas and spreading of slurry.

The risk of introducing infection with bought-in cattle has to be addressed and a strict protocol developed. Fortunately the need for dairy herds to buy in replacements is diminished by the use of sexed semen and importing embryos. The Cattle Health Certification Standards (CHECS) allows breeding bulls to be purchased from certified low-risk herds with a long-term testing history of negative test results. The current testing regimes do not enable herds to be classified as JD free.

Participation in the National Johne’s Management Plan is now a mandatory part of the Red Tractor Scheme. Veterinary certification for herds will need to be completed by October 2020 and one of six strategies is to be overseen by the vet. Roughly half of the participating herds in 2019 chose to improve the farm management by breaking the cycle of transmission from cow to calf coupled with strategic testing. Improving the farm management, combined with culling test positives, is suitable for low prevalence herds and was adopted by 30 percent of the farmers. Herds with no evidence of disease and adopting biosecurity protect and monitor, involving a robust security protocol with surveillance testing, account for 10 percent. Breeding to a terminal sire with no herd replacements, improved herd management without testing and adopting firebreak vaccination that does not prevent infection accounts for the remaining 10 percent of herds. As the 2020 participation data is assessed the figures are expected to change.

The milk buyers are a major mover for change. There are concerns relating to the potential human health risks from MAP and this has helped to drive the adoption of the National Johne’s Management Plan in the UK. This is an important time for veterinary surgeons to interact with their dairy farmer clients and continue to develop the on-farm management of risk from disease. There is a major difference between the farmer agreeing to adopt a protocol, actually carrying out the plan and then realising the benefits. Meetings between farmers unsure about the whole topic and farmers who have successfully adopted disease control are very enlightening. All good vibes as the UK Animal Health Pathway is further developed, with the intention of supporting high animal welfare, to increase productivity and profitability and lead to a reduction in greenhouse gas emissions.