Embryo development of prepubertal goat oocytes fertilised by intracytoplasmic sperm injection (ICSI) according to oocyte diameter

The aim of this study was to evaluate embryo development of prepubertal goat oocytes fertilised by ICSI according to their diameter. Three experiments were carried out to achieve this objective. In all experiments, oocytes were matured in TCM199 supplemented with hormones, cysteamine and serum for 27 h at 38.5 °C. In Experiment 1, we studied the nuclear stage of goat zygotes produced by conventional ICSI and IVF using 20 nM ionomycin plus 10 μM heparin as sperm treatment. A group of Sham-injected oocytes was used as control. Results showed differences in the percentage of 2 PN (zygotes with male and female pronuclei) between ICSI, IVF and Sham (40.9, 26.6 and 3.0%, respectively; P < 0.05). In Experiment 2, we evaluated the embryo development of prepubertal goat oocytes produced by ICSI and IVF after 192 h of culture in SOF medium. The percentage of morulae plus blastocysts obtained was higher in the ICSI than in the IVF group (13.4 and 5.1%, respectively; P < 0.05). In Experiment 3, IVM-oocytes were classified in four groups depending on their diameter (Group A: <110 μm; Group B: 110–125 μm; Group C: 125–135 μm; Group D: >135 μm), fertilised by ICSI and cultured for 192 h. Results showed a positive correlation between oocyte diameter and embryo development (morulae + blastocysts: Group A: 0%; Group B: 6.2%; Group C: 46.4% and Group D: 33.3%).In conclusion, sperm treatment with ionomycin plus heparin using the conventional ICSI protocol improved fertilisation rates in comparison to IVF. Oocytes smaller than 125 μm were unable to develop up to blastocyst stage.