Effect of culture methods on cumulus and oocyte morphology and meiotic competence of bovine oocytes from early antral follicles

Abstract. The objective of the present study was to establish a culture system that would maintain the three-dimensional structure of bovine early antral follicles (EAF) or isolated cumulus-oocyte-granulosa complexes (COCGs) and increase the resulting portion of COCs with normal morphology for subsequent IVM. The morphological quality and meiotic competence of oocytes originating from early antral bovine ovarian follicles (0.2 to 0.7 mm and 0.4 to 0.7 mm diameter) were evaluated following culture in vitro for 14 and 7 d, respectively, and subsequent in vitro maturation. Growth culture modifications included culture in the well of the well (WOW) system; a microdroplet of collagen gel (2 x 5 μl vs. 2 x 400 μl; standard system) and culture of EAF in hanging drops of medium (inverted system). Significantly higher (P<0.01) proportions of COCs with normal morphology (60.4%) were obtained from COCGs compared to EAF (4.8%) grown in the WOW system. Embedding of COCGs in microdrops of collagen gel significantly increased proportion of COCs with normal morphology (63.2%) compared to those embedded in standard volume gels (35.3%). Recovery rate of COCs with normal morphology from cultured EAF was improved both by using microdrops of gel (44%) and by culture in the inverted system (39.3%) over that found for the standard system (8.5%).