Individually Cultured Bovine Zygotes Successfully Develop to the Blastocyst Stage in an Extremely Confined Environment

Abstract

The possibility of detecting the developmental competence of individually cultured embryos through analysis of spent media is a major current trend in an ART setting. However, individual embryo culture is detrimental compared with high-density group culture due to the reduced concentration of putative embryotropins. The main aim of this study was to identify an individual culture system that is not detrimental over high-density group culture in the bovine model. Blastocyst rates and competence were investigated in a conventional (GC) group, semi-confined group (MG), and individual culture (MS) in a commercial microwell device. Main findings showed that: (1) individual embryos can be continuously cultured for 7 days in ~70 nL microwells (MS) without detrimental effects compared with the GC and MG; (2) MS and MG blastocysts had a reduced number of TUNEL-positive cells compared to GC blastocysts; (3) though blastocyst mean cell numbers, mitochondrial activity, and lipid content were not different among the three culture conditions, MS blastocysts had a higher frequency of small-sized lipid droplets and a reduced mean droplet diameter compared with GC and MG blastocysts. Overall, findings open the way to optimize the development and competence of single embryos in an ART setting.

In Vitro Culture of Mammalian Embryos: Is There Room for Improvement?

“…The beneficial effects of confinement in culture systems that avoid the harmful exchanges between oil and medium in reduced volumes microdrops was also elegantly shown by Thouas et al (2003) [148] which cultured two mouse embryos in 1 µL glass capillaries achieving blastocyst cell numbers similar to those observed in high-density group culture with 20 zygotes in 10 µL drops under oil. Recently, Travaglione et al (2024) showed that extreme confinement of individually cultured bovine embryos in ~70 nl microwells improved blastocyst rates compared to both conventional group culture (50 embryos/ 500 µL) and semi-confined group culture in microwell chambers (16 embryos/60 µL) [149]. Other studies showed that the spacing among embryos in high-density group cultures is critical.…”