Follicle size and oocyte diameter in relation to developmental competence of buffalo oocytes in vitro

Follicular size, oocyte morphology and diameter were investigated for their possible relationship with in vitro developmental competence of buffalo oocytes. Cumulus oocytes complexes (COCs), aspirated from small (<3 mm), medium (3-8 mm) and large (>8 mm) follicles of normal ovaries and cystic ovarian follicles of abattoir-derived ovaries, were graded for their morphological appearance and were cultured to assess their developmental competence. The influence of cystic follicles on maturational competence of COCs recovered from co-existing follicles of cystic ovaries was studied. The mean diameter of oocytes from follicles of different size were examined, and the influence of oocyte diameter--(i) <126 microm; (ii) 127-144 microm; (iii) 145-162 microm; and (iv) >163 microm--on in vitro maturation, cleavage and embryo yield was studied. Results suggested that increased fertilization, cleavage and embryo development were significantly (P<0.05) higher in COCs aspirated from large follicles, followed by medium and small-sized normal follicles, and the presence of cystic follicles had no significant (P<0.05) effect on the maturation competence of the COCs recovered from co-existing follicles. The mean diameter of the buffalo oocyte obtained from normal ovaries was found to be 146.4 microm and the rate of blastocyst production in vitro was significantly higher (P<0.05) in oocytes with diameters greater than 145 microm. In conclusion, the larger the size of the follicles and oocytes, the greater the developmental competence in vitro of buffalo oocytes.