Bovine Embryo Development after in vitro Oocyte Maturation in Culture Medium Supplemented with Taurine or Glycine

Abstract

This study was carried out to investigate the effect of taurine and glycine added to the in vitro maturation medium (IVM) of bovine oocytes, evidenced by the subsequent embryonic development. Follicles were aspirated and oocytes having at least 3 to 4 layers of cumulus cells and homogeneous cytoplasm were washed in TCM 199, plus sodium bicarbonate, sodium pyruvate, penicillin, PVA and HEPES. Groups of 15 to 25 oocytes were matured in TCM 199, supplemented with FSH, LH and FCS, in presence of taurine or glycine, according to the experimental design. In experiment 1, taurine was added to the IVM medium at concentrations of 0 mM, 1 mM, 10 mM and 100 mM. Glycine (experiment 2) was used at concentrations of 0.67 mM, 10 mM and 100 mM. TALP medium was used for Percoll gradient and in vitro fertilization; after a 20 h co-incubation period, cumulus cells were removed, and the presumptive zygotes were transferred to m-SOF medium. The oocytes and embryos were cultured at 39^oC in a humid atmosphere of 5% CO₂. At 72 and 120 h post-insemination (h pi), m-SOF medium was added to the drops. The oocytes that cleaved, and reached morula/blastocyst (M/B), blastocyst/expanded blastocyst (B/EB), expanded blastocyst/hatched blastocyst (EB/HB) stages were recorded at 72, 144, 168, and 192 h pi, respectively. Results were analyzed by ANOVA and Bonferroni t-test, with P<0.05 taken as significant. There were no significant differences among treatment groups (experiment 1) for fertilization, M/B, B/EB and EB/HB rates, with values varying from 88.9 to 93.0%, 42.8 to 51.4%, 33.6 to 41.7% and 23.2 to 30.6%, respectively. In experiment 2, no difference was observed among groups with regard to the fertilization rates (90.3 to 97.0%). However, more (P<0.05) M/B and B/EB were produced in presence of glycine at concentrations of 0.67 (49.3 e 33.3%, respectively) and 10 mM (54.5 e 44.7%) than 100 mM (25.4 e 19.2%), whereas higher percentages (P<0.05) of EB/HB were observed for group 10 mM (36.7%) than for 100 mM (16.2%), with similar results as compared to control (29.9%). In conclusion, under these experimental conditions, the addition of either taurine or glycine to the IVM of bovine oocytes did not have beneficial influence on the embryonic development, as evidenced by the similar rates of embryo production.