AUTHOR=Hubner Andrew M. , Peixoto Phillip M. G. , Hillesheim Joshua , Canisso Igor F. , Lima Fabio S. 

TITLE=Effect of GnRH 7 Days Before Presynchronization With Simultaneous PGF2α and GnRH on Reproductive Outcomes in Holstein Dairy Cows

JOURNAL=Frontiers in Veterinary Science

VOLUME=7

YEAR=2020

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2020.574516

DOI=10.3389/fvets.2020.574516

ISSN=2297-1769

ABSTRACT=<p>We evaluated if an additional GnRH injection 7 days before pre-synchronization with simultaneous PGF<sub>2α</sub> and GnRH (PG+G) would improve responses to presynchronization, synchronization, and pregnancy per AI (P/AI). We hypothesized that administering GnRH 7 days before PG+G would increase ovulation and corpus luteum (CL) presence at the PG+G, improve response to OvSynch treatments and P/AI. Holstein cows were blocked by parity and randomly assigned to either a PG+G (Control, <italic>n</italic> = 205); or to GnRH followed 7 days later by PG+G (ExtG, <italic>n</italic> = 201). At enrollment, Control was left untreated, whereas ExtG received GnRH. Seven days after enrollment, Control and ExtG received PG+G followed by OvSynch 7 days later (GnRH, 7 days PGF<sub>2α</sub>, 56 h GnRH, 16 h timed AI). Ovarian dynamics were assessed using ultrasonography in a subset of cows (<italic>n</italic> = 53 for Control; and <italic>n</italic> = 50 for ExtG) at each treatment, except the 2<sup>nd</sup> GnRH of OvSynch. Pregnancy diagnosed at 32- and 67-days post AI. Ovulation at enrollment tended (<italic>P</italic> = 0.06) to be higher for ExtG, but ovulation was not different at PG+G (<italic>P</italic> = 0.41) and first GnRH of the OvSynch (<italic>P</italic> = 0.25). There was a tendency (<italic>P</italic> = 0.08) for ExtG to have larger CL than Control at PGF<sub>2α</sub> of the OvSynch. There were no differences in CL and follicle sizes in any other treatment point assessed. There were no differences (<italic>P</italic> = 0.12) in luteolysis between treatments after PG+G. Overall P/AI was similar between treatments on Day 32 (Control = 33.0% vs. ExtG = 34.6%, <italic>P</italic> = 0.75) and 67 (Control = 31.8% vs. ExtG = 32.5%, <italic>P</italic> = 0.29) post AI. There was a tendency for an interaction between treatment and parity (<italic>P</italic> = 0.09) for P/AI at day 67 post-AI. In multiparous cows, ExtG tended to have greater P/AI than Control, whereas, in primiparous cows Control tended to have greater P/AI than ExtG at day 67 post-AI. In conclusion, the effects of GnRH 7 days before PG+G presynchronization lead to positive and negative tendencies, respectively, in multiparous and primiparous cows for P/AI at day 67 post-AI and needs further investigation.</p>