Development of golden hamster embryos effectively produced by injection of sperm heads sonicated in Tris‐HCl buffer with EGTA

PURPOSE: To investigate the effects of sperm treatment medium—TCM199 or EGTA in Tris‐HCl buffer (TBS + EGTA)―for sonication of frozen‐thawed hamster spermatozoa in terms of sperm chromosome integrity and development of hamster oocytes injected with the sperm heads (ICSI). METHODS: Frozen‐thawed hamster spermatozoa were separated into heads and tails by sonication in TCM199 or TBS + EGTA. Sperm heads were injected into mouse oocytes to assess hamster sperm chromosomes. We further compared the development of hamster ICSI embryos produced by injecting sonicated sperm heads in TCM199 vs TBS + EGTA. RESULTS: Sperm chromosome integrity was greater following sonication of frozen‐thawed hamster spermatozoa in TBS + EGTA than in TCM199 (89.7% vs 69.0%). Embryonic development was improved following hamster oocyte injection with sperm heads sonicated in TBS + EGTA compared to in TCM199 (8‐cell: 84.1% vs 65.4%; morula: 78.4% vs 43.2%; blastocyst: 42.0% vs 17.3%). Gene expression of zygotic genome activation in 2‐cell embryos was significantly higher with TBS + EGTA than with TCM199. We transferred 43 morulae/blastocysts from the TBS + EGTA group to foster mothers, and 4 (9.3%) developed into live offspring. CONCLUSION: These results showed that the rapid injection of hamster sperm heads separated by sonication in TBS + EGTA effectively produced more ICSI embryos during a short time.