Effects of fusion-activation interval and embryo aggregation on in vitro and in vivo development of bovine cloned embryos.

Nuclear reprogramming in somatic cell cloning is one of the key factors for proper development, with variations in the protocol appearing to improve cloning efficiency. This study aimed to determine the effects of two fusion-activation intervals and the aggregation of bovine cloned embryos on subsequent in vitro and in vivo development. Zygotes produced by handmade cloning were exposed to two fusion-activation intervals (2 h or 4 h), and then cultured in microwells either individually (1 × 100%) or after aggregation of two structures (2 × 100%). Zona-intact oocytes and zona-free oocytes and hemi-oocytes were used as parthenote controls under the same fusion-activation intervals. Day-7 cloned blastocysts were transferred to synchronous recipients. Cleavage (Day 2), blastocyst (Day 7) and pregnancy (Day 30) rates were compared by the χ2 test (P < .05). Extending fusion-activation interval from 2 to 4 h reduced cleavage (91.0 vs. 74.4%) but not blastocyst (34.8 vs. 42.0%) rates. On a microwell basis, cloned embryo aggregation (2 × 100%) increased cleavage (91.5% vs. 74.4%) and blastocyst (46.0% vs. 31.3%) rates compared to controls (1 × 100%), but did not improve the overall embryo production efficiency on Day 7 (23.0% vs. 31.3%), on a per reconstructed embryo basis, respectively. Treatments had no effects on in vitro developmental kinetics, embryo quality, and in vivo development. In summary, the fusion-activation interval and/or the aggregation of cloned bovine embryos did not affect cloning efficiency based on the in vitro development to the blastocyst stage and on pregnancy outcome.