The Johne's Disease (JD) Tracker application 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. Herein, we use milk ELISA data from 154 regularly testing herds to review the temporal trends in JD parameters from 2013 to 2022.

Since 2015, JD Tracker parameters have improved in these herds, most notably average test value (ATV) and within-herd prevalence (%Pos30). Trends in driver parameters suggest that farmers are progressively less likely to serve repeat test-positive (J5) cows and are more readily removing them. The data also reveal that the burden of JD is disproportionately greater in herds with higher ATV. In 2022, the 25% of herds with the highest ATVs accounted for 42% of positive tests and 42% of repeat ELISA positive (J5) cows.

Retrospectively, it is not possible to identify with certainty factors that directly contributed to the trends in JD Tracker parameters, but it is notable that the introduction of the NJMP was coincidental with the improving JD situation. As far as we know, 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 application of the JD Tracker at national scale to enable more comprehensive industry-level monitoring of JD within GB dairy farms.

More information on the JD Tracker: https://panlivestock.com/johnes-disease-tracker/

Published paper: https://www.sciencedirect.com/science/article/pii/S0167587724002034?via%3Dihub