Size and number of corpora lutea and serum progesterone concentrations when administering two doses of eCG in an estrous synchronization treatment regimen for dairy cattle
Introduction
Progesterone produced by corpus luteum (CL) is essential for establishing uterine embryo receptivity (Graham and Clarke, 1997; Forde et al., 2009), growth regulation and elongation of conceptus (Garrett et al., 1988; Spencer et al., 2004; Carter et al., 2008) and production of optimal quantities of interferon-tau (Kerbler et al., 1997; Rizos et al., 2012; Lonergan and Sánchez, 2020). When there are relatively lesser progesterone concentrations between Days 3 and 8 post-ovulation, there are smaller embryos on Day 16 post-ovulation, which in turn can negatively affect production of interferon-tau (Mann and Lamming, 2001). In contrast, increased progesterone concentrations in the first week post-ovulation enhanced production of interferon-tau (Mann and Lamming, 1999).
There were inconsistent results when there were fertility assessments following exogenous progesterone supplementation beyond day 6 after AI (Walton et al., 1990; Rajamahendran and Sianangama, 1992; Wiltbank et al., 2014; Couto et al., 2019; Steichen and Larson, 2019). The period of greatest importance for progesterone actions in supporting embryonic growth and elongation is between Day 3–7 subsequent to when natural mating or artificial insemination (AI) occurs (O’Hara et al., 2014a). Exogenous progesterone supplementation during the first few days after ovulation, however, could induce a premature luteolysis (Ginther, 1970; Niasari-Naslaji et al., 2012; O'Hara et al., 2014a; Randi et al., 2016; Parr et al., 2017; Martins et al., 2018). In the present study, it was hypothesized that if there was an earlier increase in endogenous progesterone production after natural mating or AI this could have a positive effect on fertility. Consequently, if there were ovulations from co-dominant follicles, this could be a method of choice to increase progesterone production, particularly in recipient females during embryo transfer programs. The administration of eCG (500 IU) 2 days after GnRH injection, concurrent with the emergence of the follicular wave, could induce follicle co-dominancy and ovulations from these co-dominant follicles (Hosseini et al., 2018). In the present study, this strategy was used to induce ovulations from co-dominant follicles. The objective of the present study, therefore. was to induce ovulations from co-dominant follicles following eCG administration at the time of follicle wave emergence after imposing an estrous synchronization treatment regimen in cattle.
Section snippets
Materials and methods
The procedures used in this study were approved by the Animal Ethics Committee of the Faculty of the Veterinary Medicine, University of Tehran, Tehran, Iran (LAT890/15.02.2018).
Results
In Experiment I, the growth pattern of co-dominant follicles of heifers treated with eCG compared to heifers in control group are depicted in Fig. 2. In Experiments I and II, all females had emergence of new follicular wave on Day 2 (two days after GnRH administration). At the time of CIDR removal (Day 8), most eCG-treated heifers (Exp. I: 8/9) and cows (Exp. II, eCG-2: 5/6) had co-dominant follicles compared to those in the control group (Exp. I: 1/7, Table 1; Exp. II: 1/7; Table 2; P < 0.05).
Discussion
The objective of this study was to investigate the possibility of ovulations from co-dominant follicles with one or two eCG administrations following synchronization of the timing of follicle wave emergence among females using GnRH. Results from the three experiments supported the hypothesis that eCG administration at the time of follicle emergence could induce follicular co-dominancy in dairy heifers and cows, which is consistent with results from previous studies (Martinez et al., 2014;
Conclusion
In conclusion, when there was imposing of the 8day CIDR treatment regimen (Day 0 = Day of CIDR insertion), during which heifers/cows were administered GnRH on Day 0 followed by two injections of eCG (500 IU, I.M) 4 days apart, by administering the first dose of eCG at the time of follicle wave emergence (Day 2), it is possible to induce co-dominant follicle development that results in multiple ovulations and consequently greater progesterone concentrations during the ensuing luteal phase of the
Author contribution statement
Niasari-Naslaji and Vojgani developed the hypothesis and the design of experiment. Mahdavi Roshan and Nikjou performed experiments and wrote the first draft of manuscript. Niasari-Naslaji analyzed data and revised the manuscript.
Declaration of Competing Interest
The authors of this manuscript have no competing interests to disclose.
Acknowledgements
The Deputy for Research, University of Tehran funded this research.
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