*5.2.3 GnRH-based treatment*

Estrus synchronization and fertility with a combination of GnRH and prostaglandin F2α are good for cyclic females, and this combination may induce cyclicity in cows experiencing postpartum anestrus [20]. The new methods of estrus synchronization more precisely and control the time of ovulation more exactly in order to allow a single, timed insemination without the need for detection of behavioral estrus. Administration of GnRH during the estrous cycle in bovines causes regression or ovulation of the dominant follicle and initiates the emergence of a new wave of follicular growth [20]. Ovsynch, CO-Synch, Select-Synch, and Hybrid-Synch are the four systems for synchronization of estrus with GnRH-PG combinations.

At day 1 GnRH injection is used to program follicle growth in cyclic females and to induce ovulation in anestrous females, and PGF2α on day 8 induces regression of CL that is present to cause a decline in progesterone. Then on days 10–11, the second GnRH is given which induces ovulation of dominant follicles that have been preprogrammed by the first GnRH treatment. The major GnRH programs that do not involve use of the CIDR are described as follows:


In Ovsynch program, an injection of GnRH on day 1, an injection of prostaglandin on day 8, a second injection of GnRH on day 10, and then a timed insemination on day 11 are given [20]. The first GnRH injection alters follicular growth by inducing ovulation of the dominant follicle in the ovaries after the GnRH injection to form a new or additional CL [20]. Thus, estrus usually does not occur until a PGF2α injection regresses the natural CL and the secondary CL which is formed from the follicle induced to ovulate by the first GnRH injection. Based on transrectal ultrasonographic evidence, a new group of follicles appear in the ovaries, within 1–2 days after the first injection of GnRH [38]. From those follicles, a newly developed dominant follicle emerges, matures, and can ovulate after estrus is induced by PGF2α, or it can be induced to ovulate after a second GnRH injection. This GnRH release luteinizing hormone, the natural ovulation-inducing hormone of the estrous cycle. The stage of the estrous cycle when Ovsynch was initiated also affects synchronization and conception rate [38]. Ravi Kumar and Asokan [39] reported higher conception rate in subestrus buffaloes initiating the treatment with Ovsynch during the later stages of estrous cycle, but conception rate was nil in anestrus buffaloes though incidence of cyclicity was observed due to the treatment. Benefits of this program are as follows: there is tight synchronization of estrus, most females respond to the program, and it boosts estrus in non-cycling cows that are at least 30 days postpartum.

In CO-Synch program, an injection of GnRH on day 1, an injection of prostaglandin on day 8, and then a second injection of GnRH with breeding on day 10 are given. The benefits are as follows: there is tight synchronization of estrus, most females respond to the program, and it boosts estrus in non-cycling cows that are at least 30 days postpartum.

The Hybrid-Synch program is applied with an injection of GnRH on day 1, an injection of prostaglandin on day 8, and then estrous detection and breeding from day 8 to 11. Second injection of GnRH was given to the females which were not observed in estrus from day 8 to 11 and were bred on day 11. Hybrid-Synch program has a lower cost and less handling compared with Ovsynch and CO-Synch but more than Select-Synch. The program appears to have the highest conception rates among all GnRH-prostaglandin programs.

### c.Progesterone in combination with GnRH-PG:

Oral administration of MGA to the cows for 14 days is performed, and 10 days after the withdrawal of MGA, GnRH injection was given. PGF2α is given after 7 days of GnRH injection. Patterson et al. [29] reported that 80% of the cows showed estrus within 48–96 hours after PGF2α injection.

#### *5.2.4 CIDR to GnRH-based protocol*

Failure to synchronize cyclic animals appropriately or to induce fertile ovulation potentially in anestrous females can have major effects on the success of a synchronization program. This CIDR to GnRH-based program has the potential to decrease losses in each of these areas. The most common use of this system comprises insertion of the CIDR on day 1 and its withdrawal on day 8. GnRH injection is given on the day of CIDR insertion and CIDR is kept in situ for 7 days. Injection of prostaglandin is given on the day of CIDR withdrawal, and then the second GnRH injection is given after 2 days of prostaglandin injection.

The primary advantage of inclusion of the CIDR in this program is that it guarantees that females will be exposed to progesterone during the period between day 1 and day 8. This progesterone exposure will result in normal (21 days) rather

**143**

**Author details**

Karnal, Haryana, India

Prasanna Pal and Mohammad Rayees Dar\*

provided the original work is properly cited.

\*Address all correspondence to: rayeesr21@gmail.com

Animal Physiology Division, ICAR- National Dairy Research Institute,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Induction and Synchronization of Estrus DOI: http://dx.doi.org/10.5772/intechopen.90769*

estrus and ovulation between days 1 and 9.

*5.2.5 Managemental interference*

than short (10 days) cycles in earlier anestrous cows. Moreover, the withdrawal of a progestin has been demonstrated to induce onset of cycles in some anestrous females; the likelihood of an ovulation is enhanced. A second advantage to inclusion of the CIDR in this program is that the early heats (day 6 to day 9) that are inherent to these systems are prevented. The progesterone released by the CIDR will prevent

In general management has a tremendous role in the reproduction of animals. Proper nutritional management of the herd is essential for successful implementation of several synchronization programs in both cows and heifers. Managemental procedures like timed insemination and calf removal have been reported to be useful for synchronization of estrus and may also be applied in most of the synchronization programs for better results. Usually conception rates on timed insemination are lower than for visual observation. However, this lower conception rate may be counterbalanced by the reduction in management from timed insemination. Suckling frequency of calves causes a hormonal response which inhibits return to estrus, which is evident in beef cows. Short-term calf removal combined with other forms of synchronization increases estrus synchrony and conception rates in cows. Even a 48-hour calf removal alone has been shown to cause synchrony and cyclicity in some cows. This procedure is suitable, but requires better management and good facilities to prevent separated cows and calves from rejoining with each other.
