Effect Of Presynchronization With GnRH 7 Days Prior To Resynchronization With CO-Synch On Pregnancy Wastage In Lactating Dairy Cows

Abstract

Increased secretion of prostaglandin F2α (PGF) between d 30 and 36 of pregnancy causes luteal regression and embryonic loss. In addition, administration of gonadotropin releasing hormone (GnRH) or human chorionic gonadotropin (hCG) has been held responsible for early embryonic death when administered at pregnancy diagnosis between 29 and 42 days after insemination. The objective of this study was to determine the effect of GnRH administration at 28±3 d after artificial insemination (AI), 7 d prior to the initiation of resynchronization with CO-Synch, on pregnancy wastage rate (late embryonic and early fetal loss rate; PWR) for the previous insemination. All parity (2.38±1.45; range 1-10) lactating Holstein cows (n=1417) from a dairy farm in Washington state were enrolled. Cows that were not detected in estrus by 28±3 d (Day -7) after AI were assigned to receive either GnRH (100 μg, im; n=693) or no GnRH (control; n=724). Cows not detected in estrus during 7 d following GnRH administration were presented for pregnancy diagnosis (35±3 d after AI, Day 0) and non-pregnant cows were submitted for resynchronization with CO-Synch protocol for subsequent timed AI. The cows that were not pregnant to resynchronization were resubmitted for CO-Synch resynchronization with presynch-GnRH for a second time or to other breeding protocols. Cows were examined for pregnancy at 35 d after AI and pregnant cows were submitted to determine pregnancy status for a second time approximately at 60 d after AI. The overall PWR was 13.9% (142/1044). The PWR for GnRH and control groups was 14.8% (75/506) and 12.5% (67/538), respectively (P=0.27). In conclusion, the GnRH treatment 7 d prior to initiation of resynchronization with CO-Synch, when administered at 28±3 d after a previous breeding, did not increase pregnancy wastage compared to controls.