In the Netherlands, a feasible control program is desired for paratuberculosis. The basis for control is biosecurity. The purpose of this study was to determine the effect of bio security on the sero-status of dairy herds.Blood samples were taken with a 3-year interval from cows originating from 1,022 dairy herds and tested for antibodies against Mycobacterium avium subspecies paratuberculosis (Map). The herds participated in a voluntary control program in which their management was assessed on a yearly basis during the study period. Eight factors related to calf-management and purchase of cattle were tested in two logistic-regression models, one each for the sero-status at the start of the study and sero-status after 3 years as the dependent variables. Backward elimination was used to exclude non-significant management factors from saturated models.Larger herds were more likely to be infected than smaller herds. No other management factors were found to be related to the sero-status of the herds at the start and at the end of the study. The sero-status at the end of the study was strongly related to the serostatus at the start. Only purchase of cattle during the study from herds with an unknown status of paratuberculosis was associated with a positive sero-status at the end of the study.A period of 3 years was too short to evaluate the results of calf rearing management during the study on the sero-status of a herd. Purchase of cattle is a risk factor for introducing Map in a herd. The on-going increase in herd size can lead to an increase in herd level sero-prevalence.