Colcemid‐treatment of heifer oocytes enhances nuclear transfer embryonic development,establishment of pregnancy and development to term

Four experiments were designed to examine the effects of colcemid, a microtubule assembly inhibitor, on the development of bovine nuclear transfer (NT) embryos in vitro and in vivo. Recipient oocytes matured at different times were exposed to colcemid. Approximately 80–93% of the exposed oocytes, with or without the first polar body (PB1), developed obvious membrane projections. In Experiment 1, oocytes matured for either 14–15 or 16–17 hr, treated with colcemid and used as recipient cytoplasm for NT resulted in over 40% blastocyst development. In Experiment 2, oocytes matured for 16–17 hr were treated with either 0.2 or 0.4 µg/ml colcemid for 2–3 or 5–6 hr, respectively. The percentages of blastocyst development (39–42%) were not statistically different among the different colcemid treatment groups, but were both higher (P < 0.05) than the control group (30%). Colcemid concentrations and length of colcemid treatment of oocytes did not affect their ability to support NT embryo development to the blastocyst and hatched blastocyst stages. Results from Experiment 3 indicate that semi‐defined medium increases morula and blastocyst development of NT embryos derived fromcolcemid‐treated oocytes under 5% CO₂ in air atmosphere. In addition, cell numbers of blastocysts in colcemid‐treated groups were numerically higher than the control groups. After embryo transfer, higher (P < 0.05) pregnant rates were obtained from the colcemid‐treated group than the nontreated group. Five of 40 recipients (12.5%) which received embryos from colcemid‐treated oocytes delivered healthy calves, significantly higher than those recipients (3.3%) that received embryos derived from nontreated oocytes. Mol. Reprod. Dev. 76: 620–628, 2009. © 2009 Wiley‐Liss, Inc.