Reproductive performance in a dairy herd is determined by how rapidly the reproductive management program turns nonpregnant cows into pregnant cows. When designing or evaluating a reproductive management program, the following 2 questions need to be addressed: (1) How and when are cows submitted for first artificial insemination (AI)? (2) How and when are nonpregnant cows identified and re-inseminated? The strategies and technologies implemented to address these 2 questions vary from farm to farm and form the foundation of the reproductive management program that determines the 21-d pregnancy rate. A variety of management strategies can be implemented to achieve excellent reproductive performance on dairy farms. Two factors under management control that determine the 21-d pregnancy rate are the AI service rate ( ability to inseminate nonpregnant cows, thereby giving them a chance to conceive) and the resulting fertility of inseminated cows measured by the pregnancies per AI (P/AI) at a given time after AI (the proportion of inseminated cows that actually conceive). Thus, one or both of these factors must be increased to cause a concurrent increase in the 21-d pregnancy rate. Current reproductive technologies now allow dairy managers to affect both the AI service rate and P/AI to timed AI (TAI), thereby increasing the 21-d pregnancy rate.

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