Johne's disease: ongoing challenges
Johne's disease (JD) in cattle is a significant global animal health challenge. Johne's disease is chronic, affecting the gastrointestinal tract of cattle and other ruminants and is caused by the bacteria Mycobacterium avium ssp. Paratuberculosis. Many countries have introduced schemes and programmes to try and control the spread of JD, including the UK. Despite efforts to control it, JD remains consistently ranked by UK producers as the top disease negatively affecting productivity, indicating that schemes are not perceived to have fully solved the problem. Building on a global systematic review of the literature on barriers and solutions for JD control on-farm, the authors of this paper by Morrison et al (2024) (10.1016/j.prevetmed.2024.106295) conducted an empirical study with over 400 farmers and 150 veterinary professionals across the UK. The study used workshops and semistructured interviews to understand better the challenges dairy farmers and veterinarians face in implementing on-farm JD management schemes to identify solutions. The study found that four main challenges are faced in the on-farm control of Johne's:
These findings have relevance for the control of JD in the UK and other countries, including for regions with voluntary and compulsory control programmes.
Johne's disease over 10 years
Despite the challenges outlined above, effective management of cattle infected with JD is crucial to minimising transmission and within-herd prevalence. Within GB, the voluntary National Johne's Management Plan (NJMP) requires farmers and a certified vet to conduct a risk assessment to determine the herd risk, examine the herd JD status and formulate a management plan. Individual milk ELISA tests for JD antibodies are widely used to monitor infection. The JD Tracker application, available on the dairy data management software InterHerd+ and other websites, is being used by farmers and veterinarians to facilitate the practical use of milk ELISA data to aid JD-related management decisions. The JD Tracker application uses a herd's milk ELISA data to calculate a collection of ‘JD parameters’ that are indicative of the current JD status of the herd alongside contemporary and retrospective drivers linked to transmission and maintenance of infection. In a study by Taylor et al (2024) (https://doi.org/10.1016/j.prevetmed.2024.106317) milk ELISA data from 154 regularly testing herds is used to review the temporal trends in JD parameters from 2013 to 2022. Progress is being made despite the many challenges; since 2015, JD Tracker parameters have improved in these herds, most notably average test value (ATV) and within-herd prevalence. Trends in driver parameters suggest that farmers are progressively less likely to serve repeat testpositive cows and are more readily removing them. The data also reveal that the burden of JD is disproportionately greater in herds with ahigher ATV. In 2022, the 25% of herds with the highest ATVs accounted for 42% of positive tests and 42% of repeat ELISA-positive cows. Retrospectively, it is not possible to identify with certainty factors that directly contributed to the trends in JD parameters, but it is notable that the introduction of the NJMP coincided with the improving JD situation. In 2019, participation in the NJMP or an equivalent scheme became mandatory for dairy farms to be compliant with the food and farms standards assurance scheme Red Tractor, with the result that JD management plans are now completed by 95% of UK dairy farms. The authors state that to their knowledge the UK is unique in its development of a tool (the JD Tracker), which adds utility to milk ELISA data using specifically designed JD parameters. Anticipated further work includes the development of a national database of JD testing herds and the application of the JD Tracker at a national scale to enable more comprehensive industry-level monitoring of JD within GB dairy farms.
Changes to CHECS
Those familiar with Johne's control programmes should note that from 1 October 2024 CHECS (formerly known as Cattle Health Certification Standards) is introducing an additional level of JD Risk-Level Certification RL1*. The new Risk Level 1* will be awarded to RL1 herds, which have a negative blood test for JD. Risk Level 1 herds containing animals that have a blood positive test for Johne's, that are subsequently faecal negative, will not qualify for RL1* status. Risk Level 1* status will also be accompanied by the number of consecutive years in brackets that the herd has held the RL1* status. So, for a herd that has had no animal testing blood positive for four years, its classification will be RL1*(4 years). Further information can be found by visiting: https://checs.co.uk/2024/09/23/new-risk-level-to-aid-in-johnes-disease-control/.