Developmental kinetics of in vitro produced bovine embryos: the effect of sex, glucose and exposure to time-lapse environment.

In this study, a simple time-lapse video recording system was used to compare developmental kinetics of female and male bovine embryos produced in vitro. Following embryo sex determination, the timing of each cleavage up to the 4-cell stage was compared between the sexes from the videotapes after culture in the presence and absence of glucose. In the second experiment, the consequences of exposure to a time-lapse video recording (TL) environment were studied by culturing embryos further until day 7 in an incubator, followed by collection and sex determination of morulae and blastocysts. In the absence of glucose, female embryos cleaved earlier than male ones. In the presence of glucose, however, male embryos cleaved earlier than female ones. There was no difference in the number of morulae/blastocysts in the absence of glucose, but in the presence of glucose more male than female embryos reached the morula and blastocyst stage. Exposure to the TL environment itself also had a sex-related effect, being more detrimental to male than female embryos. The difference in the number of functional X chromosomes between the sexes during early preimplantation development could explain these findings. In females, an increased capacity for oxygen radical detoxification through the pentose phosphate pathway could result in a reduced cleavage rate. Furthermore, glucose may influence the expression of enzymes located on the X chromosome. According to these results, a simple time-lapse video recording system is suitable for investigating embryo developmental kinetics and perhaps for the selection of embryos with the greatest developmental potential.