We designed a study about usage of hCG instead of GnRH. Our pregnancy rates (PR) were very low compared with GnRH.
In my opinion, hCG instead of GnRH in Cosynch induces ovulation without maturation and our early artificial insemination decrease PR.
Is this hypothesis true or false? Can you share your ideas or experience about this issue?
It depends on circumstances, experimental design of study or the other factors... For example, according to a study, although HCG induces more luteal tissue and higher ovulation rate, the ovulated follicular size is smaller than GnRH treated cows. Also according to some studies there are no significantly difference between CR in replacemet of the last GnRH injection with hCG.
This is a complex problem and not all studies have shown detrimental effects. GnRH induces a release of LH that is that is relatively short-lived, but hCG has a much longer half-life and its effect is spread over a longer period -- often causing more than one ovulation to occur. The dose is also critical and it seems that many investigators uses doses that are relatively higher than needed. This can lead to effects that are longer than desired. Giving hCG may also alter the CL's responsiveness to PGF, so luteolysis may occur earlier in cows induced to ovulate with hCG.
https://www.researchgate.net/publication/264789606_Synchronization_of_ovulation_in_suckling_beef_cows_with_hCG_or_estradiol_cypionate_for_timed_artificial_insemination
Conference Paper Synchronization of ovulation in suckling beef cows with hCG ...
Hi Antonio,
Firstly thank you for your link,
I have recently checked out your abstract about usage of hCG in estrus synchronization.
I have found some differences between your experiment and our study. We similarly used P4 ear implant (3mg P4, Creastar)(implanted at the time of first GnRH and removed at the time of PGF/Day7) we carried out AI and hCG injection, 56h following PGF inection. We checked follicular diameter at the time of AI. We found that pregnancy rates(PR) were higer in cows with large preovulatoric follicules in hCG compared with GnRH. There was no any difference in GnRH according to follicular size and PRs. Nevertheless, overall PRs was statistically lower in hCG compared with GnRH. In your study, you used also 25 IU FSH/LH (Pluset) at the time of removal of PRID in your study. Maybe FSH/LH administration increased follicular devolopment and diameter. So at the time of hCG injection there were alot of cows with large preovulatoric follicules because of FSH/LH administration. Moreover You used estradiol bezoat the begining of administration of PRID. We can not use estradiol benzoat or cypionate in Turkey, because of forbidden of estradiol usage in livestocks.
I think an other important difference was the time of artificial insemination (timed artificial insemination TAI). You carried out TAI day 10 following withdrawn of PRID. It is paradoxical with our study findings because we found that large follicule gives response to hCG administration, we obtained alot of PR in cows with large preovulatoric follicle.
Please check out our study about hCG usage in Cosynch. I want to continue the discussion.
I want to discuss possible reasons why hCG administration in Cosynch decreased overall PRs and why the PRs was higher in cows with large follicules in hCG group.
Thank you again,
Umut
Article Efficacy of hCG and GnRH with Respect to Follicular Size and...
I agree with Dr Britt. It may also happen that used doses of hCG may induce follicle luteinization without ovulation...
Hi Rita,
I also agree with Prof. Britt. It is possible to induce luteinization without ovulation in high doses of hCG but we administered only 1500 IU hCG in our study (in link), it was not high dose for hCG. Also, hCG may have been alternating response of CL to PGF and in this way early regration of CL may have occurred in our study and caused embryonic lost. Maybe the doses of hCG was lower than that needed for ovulation. And I think hCG may induce ovulation without oocyte maturation in cosynch protocol. In our study, the gap is we did check out only follicular diameters before artificial insemination and we did not follow the ovulation and development CL and also regretions of CLs during luteal phase in cosynch protocol.
Article Efficacy of hCG and GnRH with Respect to Follicular Size and...
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