engleski

SELECTION OF IMMATURE BOVINE OOCYTES AS THE PRELIMINARY PHASE OF IN VITRO FERTILISATION

Ten Holstein-breed cows, 3 to 7 years old, with an unknown reproductive history were selected from a feedlot and underwent gynaecological examination in order to determine the stage of the oestrus cycle and to choose possible donors of immature oocytes for in vitro maturation and fertilisation.Two cows, in which ovarian atrophy and cysts were diagnosed, were excluded from the research.After the slaughter of the remaining 8 cows, immature oocytes were aspirated from follicels sized more than 2mm.Phase of the oestrus cycle was determined for each individual cow, based on vaginal, rectal and ultrasound exeminations and on a morphological evaluation of pairs of ovaries and corpus luteum mass.Follicles were classified by size into four categories.Follicles determined by rectal and ultrasound examinations were compared with those identified by macroscopic assessment.Number and category of aspirated oocytes were sorted according to the phase of the oestrus cycle.Immature bovine oocytes were morphologically evaluated under a stereomicroscope(magnification x50, x100, x210).They were then classified into three categories:(1)oocytes surrounded by compact multi-layers of follicle cells and even, granulated ooplasm ; (2)oocytes with partial cumulus present, or enclosed by 1-2 layers of compact cumulus cells and granules clumped or unevenly distributed in ooplasm, and(3) oocytes partially surrounded with less compact expanded cellular investment and"nude" oocytes with degenerated, vacuolated or fragmented ooplasm.The authors concluded that morphological evaluation of the layer of follicular cells surrounding immature oocytes and their ooplasm could be used as a criterion for selection of immature oocytes suitable for in vitro maturation and fertilisation.Additionally, ultrasound examination of the ovaries prior to aspiration is a simple and non-invasive method for the selection of potential donors of immature bovine oocytes.

cow; follicle; immature oocyte; aspiration

nije evidentirano