Modelling of expected prevalences for a paratuberculosis control programmein a dairy herd

A modelling approach to calculate the success of a paratuberculosis control programme in dairy herds is presented. The essential parameters of the mod el are the prevalence at the beginning of the programme, diagnostic sensiti vity and specificity of the tests used, discipline in culling test-positive animals, turnover in the herd, percentage of replacement with own stock an d paratuberculosis prevalence in animals bought into the herd from outside, and a general hygiene-based factor. Diagnostic measures and time schedule used in the modelling approach are given by the paratuberculosis-control-pr ogramme of the local board for infectious disease control in food animals i n the state of Lower Saxony. It was found by the model-calculations that in case of a high initial prevalence the anticipated six-year duration of the control programme is justified in order to ensure a lasting improvement of herd health. If hygienic measures are strictly obeyed and all test positiv e animals are culled a clear reduction on paratuberculosis prevalence can b e achieved within the first year. According to the model in the second and third year the prevalence will increase again despite ongoing diagnostic me asures in order to decrease again continuously with the beginning of the fo urth year. Given an initial prevalence of 10%, 20% or 30% the prevalence af ter six years is calculated to be at 3%, 5% or 8% when all measures are fol lowed as given in the control programme. The presented programme seems to b e appropriate to predict prevalence development in paratuberculosis infecte d dairy herds if the herds are managed according to the guidelines of the " Tierseuchenkasse Niedersachsen", the local board for infectious disease con trol in food animals in the state of Lower Saxony, Germany. It becomes appa rent that within six years a high decrease of the prevalence in the herds, but not a complete eradication of disease can be achieved by consistently c omplying with the rules given in these guidelines.