This thesis is an investigation of the reproductive performance of dairy herds managed using automated activity monitoring systems for heat detection (AHD) in comparison to herds using timed artificial insemination programs (TAI). Two approaches were taken: a randomized clinical trial and a retrospective cross-sectional study. In the field trial, pregnancy risk (PR) was not different between the AHD (14.6%) and TAI program (15.9%). Overall, time to pregnancy, time to 1st service and time to 2nd service were not different between breeding programs. In the observational study, annual herd-summary reproductive performance in farms using AHD and TAI were not different. Finally, a retrospective analysis in herds that were using AHD for more than one year compared the years before and after adoption of the system. A significant increase of PR and insemination risk was found. In conclusion, AHD systems had comparable reproductive performance to TAI-based programs. / Ontario Ministry of Agriculture, Food and Rural Affairs. Gencor and SCR Engineers Ltd.