On the basis of a subjective evaluation of ultrastructural morphology, it was suggested that bovine embryos produced in serum-free culture medium have morphology comparable with that of embryos produced in vivo. In contrast, based on morphometric analysis in the present study, the ultrastructure of embryos produced in serum-free culture (mSOF) was not comparable to that of embryos produced in vivo. These discordant conclusions may have resulted from differences in methods used for embryo production or for the evaluation of embryo ultrastructure.
Agreement among evaluators is reduced when determinating stage of development of compact morulae produced in vitro. Furthermore, pregnancy rates following transfer of compact morulae produced in vitro were lower than those obtained after transfer of compact morulae produced in vivo. Data presented in this study may provide some insights into the basis for the difficulties found when evaluating bovine compact morulae produced in vitro. Ultrastructural alterations resulting from in vitro culture could influence the assessment of both stage of development and quality grade of compact morulae. This, in turn, could have direct implications in resulting pregnancy rates.
In summary, on the basis of data in the present study, bovine embryos produced by in vitro methods were not comparable at an ultrastructural level to those produced in vivo. Overall, in vitro culture resulted in compact morulae with an increased amount of lipid and a decreased density of mature mitochondria. Compact morulae cultured entirely in serum-supplemented medium (IVPS) had the greatest degree of morphological deviation, with decreases in the densities of both mature and total mitochondria, an increased density of vacuoles, and an increased cytoplasmic-to-nucle-ar ratio.