EFFECTS OF CULTURING BOVINE OOCYTES EITHER SINGLY OR IN GROUPS ON DEVELOPMENT TO BLASTOCYSTS

In vitro maturation, fertilization and culture (IVM/IVF/IVC) of cattle oocytes from individual cows requires adapting existing culture proto cols so that small numbers of oocytes can be cultured. The culture of single oocytes is desirable for correlating the relationship between f ollicular properties with oocyte developmental competence or for facil itating ovum pick-up procedures. In Experiment 1 we compared group and single culture under cell-free conditions on embryo development; sign ificantly higher (P<0.001) rates of cleavage (66.4 vs 47.6%) and blast ocyst formation (7.5 vs 0.5%) were observed in the group cultured oocy tes. In Experiment 2 we compared group and single oocyte co-culture wi th granulosa cells. Although there was no effect of oocyte number on t he percentage cleaving (73.1 vs 66.6%), there were significantly highe r blastocyst yields (37.4 vs 10.1%) and blastocyst cell numbers (91.6 vs 66.2) in group-cultured oocytes. In Experiment 3 we examined the ef fect of group size (1, 5, 10, 20 and 40 oocytes) in a co-culture syste m using granulosa cell monolayers. The results show a difference in cl eavage rates between the single cultured oocytes (66.8%) and each grou p of cultured oocytes, with the highest cleavage rate (81.5%) obtained in the 20-oocyte group. The blastocyst yield from both cleaved and to tal oocytes showed that group culture of 20 or 40 oocytes resulted in the highest number of blastocysts (32.5%), with smaller group sizes yi elding significantly (P<0.05) fen,er blastocysts. In Experiment 4 we e xamined the effects of co-culture on the development of single vs grou p-cultured oocytes. The results showed no significant difference (P>0. 05) in the cleavage rate between single and group culture systems. No blastocysts were formed with single oocytes cultured without monolayer s, while the blastocyst formation rate for those co-cultured with gran ulosa cells was 12.4%. Blastocyst formation was significantly higher ( P<0.006) in group co-culture on monolayers (14.2 vs 8.5%). These data indicate that oocytes cultured in groups are developmentally more comp etent and suggest that for optimum development oocytes need some undef ined paracrine activity that is absent from the culture medium in addi tion to coculture with granulosa cells, which enhances development to the blastocyst stage of both group and singly cultured oocytes. (C) 19 97 by Elsevier Science Inc.