Evaluation of activation treatments for blastocyst production and birth of viable calves following bovine intracytoplasmic sperm injection

The objective of this study was to compare the effectiveness of different methods of bovine oocyte activation following intracytoplasmic sperm injection (ICSI) in terms of oocyte cleavage and blastocyst rates, and calf production. Oocytes were harvested, post mortem, from the ovaries of Japanese Black heifers or cows. ICSI was carried out using a piezo-electric actuator. The injected or sham-injected oocytes that were assigned to three activation treatments, each replicated three times, were studied: (1) exposure to 5 μM ionomycin for 5 min (ionomycin); (2) exposure to 5 μM ionomycin for 5 min followed by culture in TCM199 for 3 h and a further 3 h culture in 1.9 mM 6-dimethylaminopurine (DMAP – ionomycin + DMAP); (3) exposure to 7% ethanol in TCM199 for 5 min, 4 h after ICSI (ethanol). One or two blastocysts from the ionomycin + DMAP (8 recipients) and ethanol (17 recipients) oocyte activation treatments were non-surgically transferred into Holsteins for the study of calf production. ghest cleavage and blastocyst production rates were observed in the ionomycin + DMAP treatment (83.9% and 40.1%) by the ICSI. These rates were significantly (P < 0.05) higher than those for the ionomycin oocyte activation treatment (57.6% and 18.2%) but did not differ from the ethanol treatment (75.6% and 29.4%). In the sham-injected, the highest blastocyst production rates were observed for the ionomycin + DMAP and ethanol treatments (10.7% and 11.3%). Pregnancy and birth rates for blastocysts derived from the ethanol oocyte activation treatment (58.8% and 47.4%) were significantly higher (P < 0.05) than those of the ionomycin + DMAP treatment (12.5% and 9.2%). The results showed that post-ICSI oocyte activation with ethanol is more effective than activation with ionomycin alone or with ionomycin + DMAP for the production of viable blastocysts and calves.