Effect of Hypotaurine in Fertilization Medium on Fertilization of In Vitro Matured Bovine Oocytes and Their Subsequent Development

In Experimental 1, when in vitro matured (IVM) bovine oocytes were inseminated with frozen-thawed spermatozoa in in-vitro fertilization (IVF) medium (BO solution containing 5 μg/ml heparin) (Control) and IVF medium supplemented with 5 mM caffeine (Caf) or 10 mM hypotaurine (HT) for 1, 3 and 5 h, significantly higher percentages of oocytes were penetrated in Caf and HT groups than Control group after 3 h of insemination. Then the rates showed no difference between groups after 5 h of insemination. However, a significantly lower percentage of monospermic oocytes was obtained in Caf group than Control and HT groups. In Experimental 2, IVM oocytes were inseminated with spermatozoa in IVF medium supplememted with 0, 1, 5 and 10 mM HT, and then co-cultured with cumulus cells in TCM 199 with 5% calf serum. There was no difference in the ability of spermatozoa to penetrate oocytes between groups but significantly higher rates of fusion of male and female pro nuclei in monospermic oocytes were obtained in the medium supplemented with 10 mM HT than no addition.The addition of HT in IVF medium significantly improved percentages of embryos developed to the stage of blastocyst. In Experimental 3, IVM oocytes were inseminated in IVF medium supplemented with 10 mM HT or 5 mM Caf and then co-cultured as described in Exp.2. significantly higher percentages of monospermic oocytes and embryos developed to the stage of blastocyst were obtained with HT groups than Caf group. In monospermic oocytes significantly higher rates of fusion of male and female pro nuclei were obtained in HT group than Caf group. These results indicate that addition of HT in the ferti lization medium promotes monospermic fertilization compared with Caf and shortens the duration of insemination needed for spermatozoa to penetrate oocytes resulting in higher percentages of IVM/IVF oocytes develop to the stage of blastocyst than those of no addition.