The effect of exogenous progesterone on the quality of in vitro produced bovine embryos

Abstract

Maternal genetics can be advanced with the implementation of in vitro fertilization (IVF) in the beef and dairy industries. The efficiency of IVF-derived pregnancies is impacted by oocyte and embryo quality. An experiment was conducted in 2 replicates over a 2-year period to determine the effect of exogenous progesterone on the quality of IVF-produced embryos. In Year-1, mature beef cows were randomly assigned to either GnRH+CIDR (n=5) or GnRH-Only (n=5). All cows received GnRH (100ug) at day -7 and follicle stimulating hormone (FSH) on days -5, -4, -3 and -2. Cows in the GnRH+CIDR treatment received exogenous progesterone (Eazi-Breed CIDR®) on day -7 through day -1 while cows in the GnRH-Only group received only GnRH on day -7. Ovum pickup (OPU) via ultrasonography was conducted on day -1. Oocytes were collected via ovum pickup (OPU) on day -1 and matured for 24-hours prior to IVF. Embryos were cultured for 7 days post-fertilization in Year-1 and 6 days in Year-2. Embryos were stained on day 8 in Year-1 and day 7 in Year-2. Embryo quality was determined by cell count. In Year-2 blood samples were obtained on day -6, -3, and -1 to measure progesterone levels. Data were analyzed using the GLIMMIX procedure of SAS v.9.4 (Cary, NC), with cow as the experimental unit. In Year-1 and Year-2, cows that did not produce embryos that were viable at time of staining were excluded. In Year-1 there was no significant difference (p=0.4229) in cell number per embryo between GnRH+CIDR (n=4) and GnRH-Only (n=4) treatments. GnRH+CIDR cows had an average of 61.1 +/- 10.8 cells per embryo, while GnRH-Only cows average of 74 +/- 10.8 cells per embryo. In Year-2, there was a tendency (p=0.0507) embryos from GnRH+CIDR cows (n=3) to have increase in cells. The GnRH+CIDR treatment resulted in an average of 61.1 +/- 4.4 cells per embryo while the GnRH-Only treatment averaged 39.3 +/- 5.3 cells per embryo. Progesterone levels for Treatment GnRH+CIDR (n=5) were 6.8, 6.5, 2.8 ng/ml on days -6, -3, and -1, respectively. For GnRH-Only, progesterone levels were 7.7, 9.4, 6.9 ng/ml for days -6, -3, and -1 respectively. This study did not find an effect of exogenous progesterone on embryo production, although the high variability and few animals was most likely a factor.