Eficiência de formulações de cultivo embrionário elaboradas para melhorar a criotolerância e a competência em estabelecer a gestação de embriões bovinos produzidos in vitro

Abstract

The success of cryopreservation of embryos produced in vitro (IVP) shows itself to be the key point for commercial expansion. However, successful cryopreservation of in vitro-produced embryos is a fundamental requirement for the expansion of the IVP industry.The present study aims to evaluate the efficiency of different formulations of FBS-free culture media supplemented with medium A or B on cryotolerance, and the establishment of pregnancy. In a first experiment, oocytes from slaughterhouse ovaries were matured and fertilized and then the presumptive zygotes were cultured in vitro and randomly distributed into three groups: i) Control (C): modified synthetic oviduct fluid (mSOF) culture medium supplemented with 5 mg/mL BSA and 2.5% fetal calf serum; ii) Medium A (MA): serum-free altered mSOF medium A; and iii) Medium B (MB): serum-free altered mSOF medium B. The use of MA and MB media improved the embryo viability to cryopreservation without affecting the production of blastocysts. Blastocysts from the MB group had the highest (P <0.05) hatching rate (26%) in relation to the other groups (P <0.05); and the highest percentage of MB transferable embryos (92.1%, 187/203) compared to control group [85.8% (175/204)]. This result can be explained by the lipid and transcriptional profile of the embryos. The lipid profile of IVP embryos of the MB group was similar to that of embryos produced in vivo. Furthermore, the morphometry of the cytoplasmic lipid droplets seems to have conferred less fragility to the vitrification. The MA and MB media showed downregulated lipid metabolism genes in relation to the control, indicating a better embryo quality. In addition, the MB group demonstrated the upregulation of the Lumican gene (LUM), with an important function in the structure of the plasma membrane. The sum of these findings led us to investigate the conception rate of embryos from the MB medium. The conception rates, at 45 days, resulting from the transfer of MB medium-derived blastocysts (49.2%) was similar (P>0.05) to that for control-derived embryos (47.9%). Therefore, the novel MB culture medium favors cryotolerance without impairing pregnancy rate in a large-scale in vitro bovine embryo production program. We believe that this finding can be explained by the embryonic lipids and transcriptional profile.