Three-dimensional morphology of bovine blastocysts hatched against lipopolysaccharide exposure in vitro

Embryo transfer in cattle is globally becoming more ubiquitous, but the pregnancy rate is lower than that of artificial insemination. The uterus contains its own bacteria, and concentrations of lipopolysaccharides (LPS) from gram-negative bacteria are higher in uteri affected by endometritis than in healthy uteri and they suppress embryogenesis. The purpose of this study was to investigate the morphological characteristics of bovine embryos with a higher viability and implantability, by analyzing the morphology of bovine blastocysts that successfully hatched under challenge of LPS, using an optical coherence tomography (OCT) system. Developing embryos produced by in vitro fertilization that had reached the blastocyst stage on Day 7 were three-dimensionally scanned using an OCT system, then were continued to culture with or without LPS until Day 9, when the presence or absence of hatching was determined. The OCT-captured three-dimensional images were used to quantify 20 different metrics, including inner cell mass (ICM), trophectoderm, blastocoel, and total embryo volume; each of the parameters was compared between the hatched and unhatched embryos. Under the LPS challenge, hatched embryos had higher ICM thickness and volume, and lower trophectoderm thickness than unhatched embryos. Furthermore, hatched embryos under LPS challenge had higher ICM thickness and ICM volume than hatched embryos without LPS challenge. The present results suggest the possibility that ICM thickness and ICM volume calculated by OCT system could be indices for good quality bovine embryos.