Ultrastructural morphometry of bovine blastocysts produced in vivo or in vitro

The objective of this study was to compare the ultrastructure of bovine bla stocysts produced in vivo or in vitro by using morphometric analysis. Blast ocysts produced in vivo (multiple ovulations, MO) were obtained from supero vulated Holstein cows. For blastocysts produced in vitro, cumulus-oocyte co mplexes aspirated from ovaries of Holstein cows were matured and fertilized in vitro. At 20 h postinsemination (hpi), zygotes were distributed into on e of three culture media: 1) IVPS tin vitro produced with serum): TCM-199 10% estrous cow serum (ECS); 2) IVPSR tin vitro produced with serum restri ction): TCM-199 + 1% BSA until 72 hpi, followed by TCM-199 + 10% ECS from 7 2 to 168 hpi; and 3) mSOF (modified synthetic oviductal fluid): mSOF + 0.6% BSA. At 168 hpi, six or seven grade 1 blastocysts from each of the four tr eatments (MO, IVPS, IVPSR, and mSOF) were fixed and prepared for transmissi on electron microscopy. Random micrographs of each blastocyst were used to determine the volume density of cellular components. Overall, as blastocyst s progressed in development, the volume densities of cytoplasm and intercel lular space decreased (P < 0.05) and the volume densities of mature mitocho ndria, nuclei, blastocoele, and apoptotic bodies increased (P < 0.05). Acro ss treatments, the proportional volumes of nuclei and inclusion bodies were increased in inner cell mass cells compared with trophectoderm cells for m id- and expanded blastocysts. For blastocysts produced in vitro, the volume density of mitochondria was decreased (P < 0.05) as compared with that of blastocysts produced in vivo. The proportional volume of vacuoles was incre ased (P < 0.05) in blastocysts from the mSOF treatment as compared with bla stocysts produced in vivo. For mid- and expanded blastocysts from all three in vitro treatments, the volume density of lipid increased (P < 0.05) and the volume density of nuclei decreased (P < 0.05) compared with those of bl astocysts produced in vivo. In conclusion, blastocysts produced in vitro po ssessed deviations in volume densities of organelles associated with cellul ar metabolism as well as deviations associated with altered embryonic diffe rentiation. However, the specific nature of these deviations varied with th e type of culture conditions used for in vitro embryo production.