engleski

Follicle size effect on oocyte recovery and developmental competence of oocytes retrieved from slaughterhouse ovaries or by ovum pick up

The aim of this research was to investigate the effect of follicle size on oocyte recovery and developmental competence of oocytes recovered from slaughterhouse ovaries (SO) and those recovered in vivo by Ovum Pick Up (OPU). Immature cumulus-oocyte-complexes (COCs) were obtained by aspirating follicles ≤ 5 mm or > 5 mm from the ovaries of cows, either at slaughter or using OPU. OPU (Pie Medical, the Netherlands) was performed in 17 donor cows synchronized with PGF2 and stimulated with pFSH, twice a day during two days (Folltropin®, Bioniche). Total of 4 OPU sessions were performed on each cow. The number of aspirated follicles, retrieved oocytes and oocyte recovery rate were recorded. Recovered oocytes were morphologically classified into four quality categories. COCs of grade 1 and 2 were matured in TCM199 with FCS, FSH/LH and cysteamine, fertilized with frozen/thawed semen prepared on gradient of BoviPure™ and subsequently cultured for 9 days in SOFaaBSA. The number of cleaved embryos was recorded at 24, 27, 30, 33, 36 and 48 hpi. Embryo yield was recorded on day 5, 6, 7, 8 and 9. Data were analized by Chi-square test. In donor cows significantly more oocytes were retreived from follicles > 5 mm, with higher recovery rate comparing to follicles ≤ 5 mm. On contrary, more oocytes were obtained from follicles ≤ 5 mm of slaughtered cows (Table 1). There were no significant differences between oocyte quality, with highest proportion of grade 1 and 2 oocytes in both SO and OPU, regardless to follicle size. Kinetics of early cleavage shown that significantly more oocytes from follicles > 5 mm, either from SO or OPU, cleaved in significantly higher proportion 30 hpi (74.03% SO ; 83.80% OPU) compared to follicles ≤ 5 mm (61.22% SO ; 74.26% OPU). Overall cleavage rate 48 hpi and embryo yield on day 5, 6, 7, 8 and 9 was also significantly higher when oocytes originate from follicles > 5 mm (Table 1). Table 1. Effect of follicle size and oocyte origin on oocyte recovery and embryo production Oocyte origin Follicle size (mm) Aspirated follicles Retreived oocytes Recovery rate (%) Cleaved (%) Day 5 (M) Day 6 (MBL) Day 7/8 (MBL) Day 9 (HBL) OPU (n=17) ≤5 (n=216) 4.21 ± 0.53a 2.42 ± 0.31a 54.0a 82, 2a 15.8 a 30.7a 41.6a 12.9a >5 (n=319) 6.27 ± 0.60b 3.59 ± 0.48b 58.3b 89, 4b 28.9b 42.9b 47.9b 26.1b SO (n=173) ≤5 (n=1692) 19.37 ± 1.59c 12.87 ± 1.06c 69.8c 78, 3c 11.2c 16.1c 20.2c 7.5c >5 (n=501) 5.74±0.71d 3.87±0.47d 69.8c 86, 1d 19.9d 31.8d 36.1d 15.9d Values with different superscript within columns are significantly different, P <0.05 The results demonstrate that the oocytes recovered after OPU are more competent to develop to the blastocyst stage than those derived from SO. The majority of oocytes collected from SO originated from small follicle, which have impared developmental competence confirmed by lower cleavage and embryo production rate compared to large follicles.

bovine; oocyte; follicle size; developmental competence

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