Dairy cattle breeders regularly use the process of artificial insemination in their herds. Nowadays, the process of visual heat detection has proven to be very time consuming because there is tendency to increase the number of animals in herds. Furthermore, silent estrus is more often observed and sings of estrus are becoming weaker. In order to reduce the need for visual detection of estrus, hormonal protocols are increasingly used, which enable the synchronization of a large number of animals and timed artificial insemination. Most commonly used hormonal protocol that uses GnRH and PGF2α is called Ovsynch. In this protocol, GnRH is applied at any stage of the cycle, followed by PGF2α application seven days after, and another GnRH application two days after the application of second GnRH. Timed artificial insemination is preformed 8-24 hours after the second GnRH application. The disadvantage of this protocol is that animals respond differently to hormonal treatment. Thus, for example, the Ovsynch protocol shows poorer results in heifers and in cows with cycles with three follicular waves. Various modifications of the original Ovsynch protocol are attempted to resolve this problem. For example, the Double Ovsynch protocol was developed, which shows better results in heifers. Another modification is supplementation of Ovsynch protocol with progesterone, which is more commonly used in anestric cows or cows with cystic ovaries. In order to increase the synchronization rate within the herd, presynchronization protocols are used, which, due to their longer duration, synchronize the heard more homogeneously. Resynchronization protocols are used in cows that have not become pregnant after previous insemination. Such protocols allow rapid reinsemination of non-pregnant cows. Furthermore, these hormons are effective in treatment of some fertility-related problems in dairy cows.