Pronounced inter-gilt variability in the secretory activity of day 11 porcine embryos

Early porcine embryos undergo rapid growth and extensive physiological remodeling during the peri-implantation period. Despite the importance of this developmental window for establishment of pregnancy, the degree of biological variation among embryos and animals during this stage remains poorly characterized. The objective of this study was to evaluate secretory activity of porcine embryos on gestational day (GD) 11 and to determine the relative contribution of embryonic sex compared with inter-animal variability. Gilts (n = 3) were euthanized and hysterectomized on GD 11, embryos were recovered, individually cultured for 24 h, and subsequently sexed by polymerase chain reaction. Concentrations of estradiol and interleukin-1β (IL1B) in spent culture media were quantified by ELISA, and the expression of interleukin-1β2 (IL1B2) mRNA was assessed by quantitative PCR. Differences in estradiol and IL1B concentrations in media (p ≤ 0.0001), as well as in the embryonic expression of IL1B2 mRNA (p ≤ 0.0001) were observed among gilts. In contrast, there was no effect of embryonic sex on estradiol or IL1B concentrations in media, or embryonic IL1B2 mRNA expression (p > 0.10) in the current dataset. These results demonstrate substantial inter-animal variation in secretory activity of GD11 porcine embryos. The magnitude of this variability exceeded any detectable effect of embryonic sex and highlights the dynamic and heterogeneous nature of early embryo development in pigs. Consideration of this biological variation should be of high importance when designing and interpreting studies investigating early conceptus physiology.