An economic model for on-farm decision support of management to prevent infectious disease introduction into dairy farms.

A more-closed farming system can be a good starting point for eradication of infectious diseases from within a herd. The economic implications of a more-closed farming system will not always be obvious to farmers. The management decisions are related to different parts of the farm and are farm-specific. To support these decisions, a model was developed of the economic consequences of a more-closed system (a simple static and deterministic design was used). The risk factors in the model were based solely on bovine herpesvirus type 1 (BHV1) but losses due to introduction of BVDV, L. hardjo, and S. dublin were added to the model. The model was verified and partly validated and a sensitivity analysis was done. The cost to one 55-cow dairy farm that refrained from purchasing cattle, provided protective clothing to professional visitors and a temporary employee, and built and maintained a double fence around 6 ha of land to prevent over-the-fence contacts was Dfl. 4495 over 5 years. The probability of disease introduction was decreased by 74%. The prevented losses for disease introduction amounted to Dfl. 7033 over 5 years (net benefits of Dfl. 2538 over 5 years).A more-closed system would be still beneficial when a sanitary barrier was used instead of just protective clothing, when the probability of introduction of infectious diseases was decreased, and when odds ratios in the model were replaced by more-conservative relative risks. The benefits became negative when a farm had to build and maintain a double fence around 12 ha instead of 6 ha, when the probability of introduction of all diseases was decreased by 50%, and when the estimations were based solely on BHV1.