To achieve a timely first-service conception rate, dairymen must have an efficient method of heat detection. It is difficult to precisely control time to first service based on spontaneous expression and detection of estrous behavior on a herd basis. The most efficient way to reduce days open would be to reduce the number of missed heats and increase the rate of submission of animals for insemination. Effective estrus synchronization is one approach of scheduling animals for insemination and to reduce days open.