Johne's Disease Control in Beef Cattle: Balancing Test-and-Cull Strategies with Economic and Epidemiological Trade-Offs.

Johne's disease (JD) is a chronic infection of cattle that undermines herd productivity and profitability. While test-and-cull programs are commonly proposed for control, their effectiveness and economic feasibility remain uncertain in beef production systems. This study used an updated agent-based model (ABM) to simulate JD transmission in a representative 300-cow Western Canadian beef herd, coupled with a partial budget model to evaluate net present value (NPV) over a 10-year time horizon. Seven diagnostic test-and-cull strategies were compared, varying in test type (ELISA, individual PCR, and pooled PCR), sampling frequency (6, 12, or 24 mo), and risk-based sampling protocols. Results showed that, under baseline assumptions (6% starting prevalence; 1% prevalence in purchased stock), all strategies reduced JD prevalence relative to no testing, and six of seven yielded higher NPVs. Annual individual PCR testing provided the best balance between prevalence reduction and profitability, whereas semi-annual PCR most effectively reduced prevalence but at greater economic cost. Failure to implement control measures resulted in increasing prevalence and long-term economic losses. Sensitivity analyses demonstrated that strategy performance was consistent across variations in market conditions, cost of production, and replacement female management, although profitability declined substantially when JD prevalence in externally sourced stock was high (i.e., 10%). Collectively, these findings indicate that JD can be controlled economically in beef herds, with long-term application of various test-and-cull strategies offering robust options adaptable to management preferences.