Association between sex and the developmental morphokinetics of in vitro derived bovine embryos.

Fertilization with sex-sorted semen is the most used approach to increase the proportion of female calves in dairy farms; however, it is commonly characterized by a lower pregnancy rate. We provide new insights into embryo developmental morphokinetics following fertilization with sorted semen. We also examined whether morphokinetic parameters are sex specific and can be used to select embryos with a desired sex. The first experiment included in vitro fertilization with X- and Y-sorted or unsorted semen. Embryos were developed in a time-lapse system and their developmental morphokinetics was recorded; blastocysts were collected for DNA-PCR and their sex was determined by TSPY and BOV97M expression. In the second experiment, fertilization was performed with unsorted semen and the embryo sex was predicted by the differential kinetic parameters that were found in the first experiment. The proportion of embryos that developed to blastocysts was higher in the unsorted vs. the sex-sorted group; embryos in this group also had diverse morphokinetics. Moreover, male and female embryos displayed different developmental kinetics. The prediction rate for male embryos was relatively low (~ 59-67%), indicating a limited accuracy of sex predication based on the kinetic data. A larger-scale study with a higher number of embryos might clarify this point.