Early cooperative research efforts contributed to the use of Lutalyse as an estrus synchronization tool. Recently, rigorous studies have examined control of folliculogenesis with the goal of better regulating estrus synchronization, timed insemination, superovulation procedures and treatment of ovarian cysts. Work from several laboratories including our own has demonstrated that a single dominant follicle regulates the growth of other, smaller follicles on both ovaries. This allowed us to develop creative procedures utilizing GnRH analogues to regulate the growth of the dominant follicle. As a result, we have developed unique and multiple approaches to improve reproductive management. Optimal success in estrus synchronization depends on synchronizing both the corpus luteum and follicular growth.

With this concept, procedures were developed using hCG and GnRH analogues to improve the degree of synchrony for estrus synchronization, the implementation of timed insemination by inducing ovulation as part of the protocol and fertility after insemination. One such example is use of the GnRH analogue, Buserelin, that can regulate follicle dynamics through its actions on LH and FSH release and subsequent ovulation or luteinization of large follicles and recruitment of a new pool of growing follicles. Injection of Buserelin induces LH release and thereby re-programs follicle development in the ovary much like a spontaneous LH surge at the onset of estrus. Large follicles undergo either ovulation or luteinization and a new pool of follicles is recruited from which a single follicle is selected and expresses dominance. The new dominant follicle can become the ovulatory follicle following PGF_2α injection 7 days after injection of Buserelin. This system is the basis for a new system of estrus synchronization that synchronizes both follicle development and CL regression. It is currently known in the industry as "Select Synch". Indeed, it programs follicular development to avoid the presence of large dominant follicles that are sustained on the ovary for long periods of time in lactating dairy cows. This system has been applied to both heifers and lactating dairy cows and has also been utilized as an experimental model to examine various experimental treatments on follicular development. This system of estrus synchronization currently is being implemented in the management of lactating dairy cows as part of a programmed insemination program.

The system has been extended both by our laboratory and Dr. Milo Wiltbank at the University of Wisconsin with an additional injection of GnRH at 48 h post-injection of PGF_2α and AI is conducted 15 h later before ovulation. It is important to realize that this new system is a system for ovulation synchronization rather than estrus synchronization. Moreover, use of this system offers tremendous opportunities for further penetration of artificial insemination into breeding systems of dairy and beef animals because the need for estrus detection, which is time-consuming and often inefficient, is eliminated. Furthermore, use of dynamic modeling indicates that application of this reproductive management system increases net revenue for the dairy producer far beyond the costs of the drugs.