engleski

The effect of follicle size on developmental competence of bovine oocytes collected by Ovum pick-up

The objective of this study was to investigate the effect of follicle size on developmental competence of oocytes collected by Ovum pick up (OPU). Immature cumulus-oocyte-complexes (COCs) were obtained by aspirating follicles ≤ 5 mm or > 5 mm. Transvaginal ultrasound guided oocyte collection was performed in 4 Charolais donor cows. Cows were synchronized with PGF2 and stimulated with pFSH, twice a day during two days (Folltropin®, Bioniche). OPU was performed 24 hours after the last FSH injection. Total of 6 OPU sessions were performed on each cow. The number of aspirated follicles, retrieved oocytes and oocyte recovery rate (RR) were recorded. The recovered oocytes were morphologically classified into four (1-4) quality categories. Grade 1 and 2 oocytes were matured, fertilized and subsequently cultured in vitro for 9 days. In order to study the kinetics of early cleavage, the number of cleaved embryos was recorded at 24, 27, 30, 33, 36 and 48 hours post insemination (hpi). Embryo yield was recorded on day 5, 6, 7 and 9 of culture in vitro. Data were analyzed by t- test and Wilcoxon test. There was no difference in recovery rate or quality of oocytes collected from large or small follicles. Oocytes originate from follicles > 5 mm cleaved in significantly higher proportion 24 hpi (p<0.05) which was reflected to higher overall cleavage rate assessed 27, 30, 33, 36 and 48 hpi (p<0.05). The kinetics of cleavage are consistent with subsequent morula development at day 5 where 28% of oocytes collected from follicles > 5 mm reached the morula stage compared to 13, 1% of morulas when oocytes originated from follicles ≤ 5 mm (p<0.05). The blastocyst yield on day 7 was slightly higher when oocytes originate from follicles > 5 mm (48, 1% vs. 40, 2%), although without statistical difference. Hatching rate on Day 9 was significantly higher when oocytes originate from follicles > 5 mm (29, 7% vs. 10, 7%, p<0.01). The results demonstrate that the selection of oocytes from larger follicles could improve the OPU/IVF results.

oocyte; ovum pick-up; follicle size

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