Evaluation of a test-and-cull strategy to control bovine paratuberculosis based on the detection of Mycobacterium avium ssp. paratuberculosis DNA using the high-throughput Johne's fecal polymerase chain reaction test.

Bovine Johne's disease (BJD) is a chronic, debilitating enteritis caused by Mycobacterium avium ssp. paratuberculosis (MAP), with both animal welfare and economic consequences. The detection of MAP in feces is an important measure of transmission from infectious animals through environmental contamination. Therefore, control programs focused on early removal of infectious animals from a herd, combined with management approaches to reduce exposure of susceptible young animals, have a high likelihood of reducing the disease burden. Quantitative PCR (qPCR) tests to detect MAP in feces enable rapid and sensitive detection of infectious animals. The aim of this study was to evaluate the use of the high-throughput Johne's direct fecal qPCR in a test-and-cull approach to control BJD. Testing was performed annually from 2015 to 2023 on a dairy farm in Victoria, Australia. A total of 7,153 fecal tests were conducted on 1,955 individual Jersey cows. A pooled screening approach was used (5 or 10 animals/pool) with follow-up testing of individual cows. Significant reductions in both the prevalence of fecal shedders (from 9.6% in 2015 to 1.2% in 2023) and mycobacterial shedding levels were achieved, together with elimination of clinical cases. Factors that may improve outcomes using this approach were also identified. This was the first application of this test in a BJD control program in a dairy herd in Australia and demonstrated the potential of the approach to effectively control BJD.