Abstract
Very small follicles (<3.0mm diameter) are over-represented on the surface of ovaries of non-cycling pigs, and the oocytes collected from these follicles generally have reduced developmental competence invitro. This study examined the effect of follicle size on the nuclear maturation (n=608), the potential of parthenogenetic activation (n=243) and the cyclic AMP (cAMP) content of pre-pubertal porcine oocytes (n=480). In addition, the influence of follicle size on steroid hormone synthesis was analysed. Cumulus oocyte complexes (COCs) flushed from small (2.5-4.0mm) or large (4.5-6.0mm) ovarian follicles were cultured for 0, 28 and 46h. After 46h of IVM, a greater proportion of oocytes from 4.5- to 6.0-mm follicles reach metaphase II (MII) compared with those from follicles with 2.5-4.0mm of diameter (96.1 vs 77.0%, respectively; p<0.001). Parthenogenetic activation of oocytes from large follicles produced higher developmental rates than oocytes from large follicles (p<0.05). At 28h, the IVM medium with oocytes from large follicles contained significantly more 17ß-oestradiol (E2 ) than the medium with oocytes from small follicles (5.55 vs 3.45ng/ml, respectively; p<0.05) and at 46h, the medium with oocytes from small follicles contained significantly more progesterone (P4 ) than the medium with oocytes from large follicles (276.7 vs 108.2ng/ml, respectively, p<0.05). Porcine oocytes from large follicles have higher nuclear and cytoplasmic maturation capacities, but the differences did not appear to be cAMP-mediated. Our findings also suggest that COCs from small follicles undergo more intensive luteinization than COCs from large follicles. The results show that oocytes from follicles with a diameter greater than 4.0mm are more suitable for invitro studies.
Published Version
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