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Kazim R Chohan1 , Alan G Hunter1 *
Department of Animal Science, University of Minnesota, Saint Paul, MN. 1
Our objective was to compare the stages of germinal vesicle (GV) and subsequent meiotic development of fetal and adult cow oocytes relative to follicle size before and after in vitro maturation (IVM). Follicles were dissected from ovaries of 7.5 mo to term fetuses and adult cows at slaughter. Isolated follicles were classified according to size (<2, 2-3, 3-4, 4-6mm in diameter) and cumulus oocyte complexes (COCs) were harvested by puncturing the follicles. Cumulus cells were removed and denuded oocytes were measured, fixed, stained and evaluated for nuclear morphology under fluorescent microscopy. COCs were also matured for 24h in Medium 199 and evaluated as above for nuclear morphology. Data were analyzed by ANOVA and/or chi square. Fetal oocytes from <2mm follicles were smaller (P<0.05) in diameter than fetal oocytes from >2mm follicles and cow oocytes from all follicle size groups. The majority of the fetal oocytes (P<0.05) from <2mm follicles were at GV stage I (40.0%) or II (47.1%). Fetal oocytes from 4-6 mm follicles were at GV stage IV (30.1%) and V (53.4%). This was similar to that of cow oocytes from <2-6mm follicles (P>0.05). Poor maturation to metaphase-II (M-II) was observed for fetal oocytes from <4mm follicles (7.5 to 46.9%) compared to fetal oocytes from 4-6 mm follicles (68.9%:P<0.05). Fetal oocytes from 4-6 mm follicles showed similar (P>0.05) percent maturation to M-II (68.9%) as that of cow oocytes from <2mm or 2-3mm follicles (57.6 & 70.6%). More cow oocytes reached M-II (P<0.05) from 3-4mm (84.3%) and 4-6mm (85.9%) follicles than from <2mm-3mm follicles. In conclusion, successful maturation to M-II for both fetal and cow oocytes depends on their stage of GV development before IVM. Fetal oocytes show poorer maturation rates to M-II than cow oocytes.
This abstract is being presented on Monday, August 2 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.