Effect of Hormone-treatment Duration in <i>in vitro </i>Maturation of Immature Oocytes on Pig Cloning Efficiency

This study aims to analyze the influence of hormone-treatment duration in <i>in vitro </i>maturation of porcine immature oocytes on the pig cloning efficiency. Although there were no significant differences in the maturation rate of immature oocytes and cleavage rate of somatic cell nuclear transfer embryos according to the hormone-treatment period (22, 27, 32, 37 and 42 h), the blastocyst rates of somatic cell nuclear transfer embryos derived from oocytes cultivated for 22, 27 and 32 h (19.0%, 21.5% and 22.4%, respectively) were significantly (<I>P</I><0.05) higher than those for 37 and 42 h (13.2% and 12.4%, respectively). In particular, there were significant (<I>P</I><0.05) increase in the hatching blastocyst rates of 27 and 32 h cultivated groups (13.7% and 16.5%, respectively) compared to 22, 37, 42h cultivated groups (8.2%, 5.6% and 6.7%, respectively). Moreover, the cloning efficiency and the delivery rates of normal lives of 27 (1.4% and 1.2%, respectively) and 32h (1.5% and 1.3%, respectively) cultivated groups were significantly (<I>P</I><0.05) higher than those of 22h cultivated group (0.9% and 0.6%, respectively). To sum up, this study shows that the increase of hormone-treatment duration in<i> in vitro</i> maturation of porcine immature oocytes to a certain extent has a positive impact on the cloning efficiency.