HEPES buffer in ovary-transportation medium influences developmental competence of cattle oocytes
This study was conducted to investigate the effects of ovary transportation in a semi-complex medium containing HEPES at different temperatures on the developmental competence and the quality of in vitro-produced embryos. The cattle ovaries were transported in normal saline (NS), phosphate buffer saline (PBS), K simplex optimization medium (KSOM), Chatot-Ziomek-Bavister medium (CZB) and Charles Rosenkrans medium (CR1) at various temperatures (38 ºC, 25 ºC and 4 ºC). The developmental competence of retrieved cumulus oocyte complexes (COCs) was evaluated by maturation, fertilization, morula and blastocyst formation and numbers of inner cell mass (ICM) and trophectoderm (TE) cells. The COC maturation rate was affected by medium and temperature. It was found that 4 ºC resulted in a higher maturation (81.0 ± 4.75) rate than other transportation temperatures. The CR1 (80.5 ± 6.66) and KSOM (80.2 ± 6.15) gave a better maturation rate than the others. Fertilization rate, which was evaluated by cleavage rate, was not affected by transportation temperature. However, the transporting medium had a significant effect on the fertilization rate. Moreover, CR1 (43.6 ± 4.60), KSOM (43.2 ± 4.86) and CZB (41.1 ± 4.86) media gave higher percentages of cleaved embryos. There was no significant difference in morula and blastocyst formation rate or in ICM and TE cell counts regarding transportation factors. In conclusion, the transport of ovaries in CR1 at 4 ºC is effective for maintaining early developmental competence of cattle oocytes.
Keywords: Cattle embryo, in vitro embryo production, ovary transportation