COMPARATIVE ANALYSIS OF POST-THAW DEVELOPMENTAL DYNAMICS IN IN VITRO-FERTILIZED AND CONVENTIONALLY PRODUCED BOVINE EMBRYOS

Abstract

In Vitro Fertilization (IVF) enables progressive cattle producers to reach genetic, reproductive, and financial goals; however, cryopreservation of IVF embryos, while vital to the industry, remains a challenge. In this study, short-term (48 h) post-thaw in vitro culture was used to evaluate the developmental potential of IVF (n = 83) and in vivo–derived (IVD; n = 76) embryos, cryopreserved in 1.5 M ethylene glycol (EG). Embryos were thawed for 5 s in air and 27ºC water bath for 30 s, rinsed in commercially available holding media, and placed individually into commercially available in vitro culture media (5 µL drops; 5% CO₂, 5% O₂, and 90% N₂, 100% humidity) and evaluated for grade and stage (IETS standards) at thaw, 24, and 48 h (compared with repeated ANOVA within group and ANOVA between groups during 4 replicates; SAS Software Version 9.4). IVF embryos developed (P<0.05) from thaw to 24h (6.5±0.06 to 6.8±0.07) and from 24 to 48h (6.8±0.07 to 7.4±0.10) as did the IVD embryos (thaw to 24h = 4.4±0.06 to 6.0±0.13; 24 to 48h = 6.0±0.13 to 7.1±0.14; IETS standards). Although development at 48h was similar between the IVF embryos and IVD embryos, the IVF embryos were cryopreserved at a more (P<0.05) advanced stage (6.5±0.06) compared to IVD embryos (4.4±0.06). IVD embryos advanced further (P<0.05) during culture (2.7±0.14) compared to IVF embryos (1.0±0.10).  The IVD embryos were of higher (P<0.05) quality (IETS standards) at 48h compared to IVF embryos (1.7±0.10 vs 2.2±0.13).  These data indicated that IVF embryos did not tolerate the freeze/thaw cycle as well as IVD embryos. Embryo quality at thaw for both groups was acceptable; however, some embryos did not advance during the culture period suggesting developmental arrest. These data suggested that culturing IVF (and perhaps IVD) embryos for an additional 24-48 h post-thaw provided an additional selection mechanism and may provide higher quality embryos to be used for embryo transfer.  The embryos in this study were collected during commercial embryo transfer activity and donated to the Texas Tech University School of Veterinary Medicine (TTU-SVM) and were from a variety of Holstein donor matings, which is a limitation of this study.  Further research is warranted to evaluate the cryosurvivability associated with IVF and IVD embryos.