The effect of stage of maturation of the germinal vesicle of porcine oocytes at the time of in vitro maturation on subsequent developmental competence was examined. A large variation exists in the germinal vesicle morphology of oocytes at the time of collection of cumulus-oocyte complexes (COCs) and after culture in the absence of dibutyryl cAMP (dbcAMP) for 20 h. However, the morphology of the germinal vesicle was synchronized to a specific stage after culture in the presence of 1 mM dbcAMP for 20 h. There was no difference in germinal vesicle breakdown rate (total mean, 75.0 +/- 5.4%) or in maturation rate (total mean, 82.1 +/- 2.1 %) at 28 and 44 h of culture, respectively. However, differences in meiotic progress of oocytes were observed (p < 0.05) at 36 h of culture when COCs were exposed to dbcAMP for the first 20 h of maturation, as compared to controls. The incidence of embryos that developed to the blastocyst stage after in vitro fertilization was higher (p < 0.05) when COCs were exposed to dbcAMP (21.5 +/- 2.5%) as compared to controls (9.2 +/- 1.6%). After transfer of experimental embryos to four recipient gilts, the three pregnant recipients delivered 19 live piglets. These results indicate that exposure of COCs to dbcAMP for the first 20 h of culture for maturation increases the homogeneity of oocyte nuclear maturation and improves the efficiency of in vitro production of swine embryos.
