Dynamic Changes in Meiotic Progression and Improvement of Developmental Competence of Pig Oocytes in Vitro by Follicle-Stimulating

The effects of FSH, LH, and epidermal growth factor (EGF) on the dynamics of nuclear maturation and subsequent embryo development were examined in pig oocytes cultured either con-ventionally or after preincubation with cycloheximide (CHX). In conventional culture, FSH or EGF significantly increased the rate of attainment of metaphase II (MII) for both gilt (50.0 % 6 4.2% and 54.8 % 6 4.3%, respectively; control, 5.8 % 6 1.8%; P, 0.001) and sow (87.6 % 6 3.4 % and 78.8 % 6 3.9%, respec-tively; control, 7.8 % 6 2.5%; P, 0.001) oocytes. Gilt oocytes treated with both FSH and EGF showed an additive response (93.7 % 6 2.1%). Treatment with LH had no effect. Preincuba-tion with CHX caused the majority (84–100%) of both gilt and sow oocytes to undergo germinal vesicle breakdown. Compared to those treated with LH and/or EGF (both.80%), fewer FSH-treated oocytes reached metaphase I (43.8 % 6 5.3%, P, 0.001) by 14 h and MII (48.4 % 6 5.9%, P, 0.001) by 24 h, although the majority (71%) did mature to MII by 36 h after removal of CHX. After in vitro fertilization, higher proportions of both CHX-pretreated and untreated, FSH-exposed oocytes cleaved (71.3 % 6 2.9 % and 75.3 % 6 3.1%, respectively) com-pared with those not treated with FSH (37.7 % 6 3.0 % and 43.0 % 6 2.9%, respectively; P, 0.001). Pretreatment with CHX significantly increased blastocyst yield for both FSH-treat-ed (32.8 % 6 2.0 % and 10.3 % 6 1.5%, respectively; P, 0.001) and untreated (16.7 % 6 1.5 % and 9.4 % 6 1.2%, respectively; P, 0.001) oocytes. Polyspermy rates were unaffected. In con-clusion, pig oocytes meiotically arrested by CHX before matu-ration retain and improve their developmental competence. FSH stimulates nuclear maturation but slows meiotic progression. follicle-stimulating hormone, in vitro fertilization, luteinizing hor-mone, meiosis, oocyte developmen