Effect of B-mercaptoethanol on the viability of IVM/IVF/IVC bovine embryos during long-distance transportation in plastic straws

Experiments were conducted to assess the effect of beta-mercaptoethanol (beta-ME) on the quality and viability of bovine blastocysts derived from in-vitro culture (IVC) of in-vitro matured and fertilized (TVM-IVF) oocytes during their transport between 2 distant places. Follicular oocytes were collected from ovaries obtained at a slaughterhouse and were cultured for 20 to 21 h in modified TCM-199. The IVM oocytes were fertilized in vitro with frozen-thawed spermatozoa. Fertilized oocytes were cultured for 7 d, and embryos that developed to the blastocyst stage were used for the experiments. The blastocysts, packed in straws with transportation medium that consisted of modified TCM-199 with HEPES equilibrated in air and supplemented with 20 % calf serum and 0, 10, 50, 100 or 150 microM beta-ME, were transported at 37 degrees C from Tokyo to Sapporo by air (18.3 h). The quality of blastocysts was assessed and ranked as excellent (A), good (B), fair (C) or poor (D) after transportation. The percentages of blastocysts ranked as A or B were significantly higher (P < 0.05) when the embryos were transported in beta-ME supplemented medium (80 to 100%) than when transported without beta-ME (54 %). Blastocysts ranked as A or B after transportation in medium with or without 150 microM beta-ME were nonsurgically transferred to synchronous recipients; 60 d after embryo transfer, 21/36 and 19/35 cows, respectively, were diagnosed as pregnant by palpation per rectum. These results indicate that beta-ME maintains the quality of bovine blastocysts in plastic straws for several hours without control of CO2 and that the concentration of beta-ME used in this experiment is not detrimental to the blastocysts.