Follicular cells affect the fertilizability and developmental competency of bovine oocytes in vitro

Abstract

The present study examined the time-dependent effects of follicular cells on the fertilizability of oocytes and their subsequent development to blastocysts. The percentages of oocytes reaching the metaphase-II stage of maturation rose from 51·3% after 16 h of culture to 86·2% at 28 h (cumulus-intact oocytes; CIO) and, for the same time points, from 65·4% to 83·3% (corona-enclosed oocytes; CO) and 54·3% to 88·9% (denuded oocytes; DO), respectively. When DO were cultured for more than 24 h before insemination, fertilization rates were significantly lower compared with CIO and CO. The maximum rates of development to blastocysts were observed when the oocytes were cultured for 24 h in the CIO group (22·1%), 20 h in the CO group (19· 7%) and 18 h in the DO group (9·2%), respectively. These results suggest that (i) the presence of cumulus cells or corona cells during maturation is not necessary for nuclear maturation of oocytes; (ii) the attachment of corona cells to the oocytes during maturation is important for the further development to the blastocyst stage, and (iii) the presence of attached cumulus and/or corona cells during maturation in vitro extends the maturation period required for further development to the blastocyst stage.