Effects of bovine ova density and culture supplements on cleavage and blastocyst development rates of in vitro embryos

An optimized in vitro culture system is important to maximize bovine blastocyst development. Four experiments were conducted to explore manipulation of culture environments and investigate the benefits of culturing embryos in groups. Follicles were aspirated from abattoir-derived ovaries and selected oocytes were matured, fertilized, vortexed, and randomly placed in culture groups. Experiment 1 evaluated the effects of ova culture density on blastocyst development among embryos cultured individually or in groups of 5, 10, 20, or 50 embryos. Experiment 2 evaluated the effects of conditioned media from previous replicates on embryo development of the current culture. In Experiment 3, cleaved embryos were grouped together after being in culture for 24 hours. Lastly, in Experiment 4, grouped embryos were placed in 10 μl culture drops to evaluate the effect of high density/low media volume on development. Cleavage and blastocyst rates analyzed via Chi-square indicated that although cleavage rates were similar among culture groups (and experiments), blastocyst development was lower (p < 0.05) in 1 embryo culture group compared to other groups. When conditioned culture media from previous replicates were added to original culture media, blastocyst development was similar among original and conditioned culture groups of 20 and 50 embryos. When cleaved embryos were amalgamated and cultured, blastocyst development was higher (p < 0.05) in culture groups of 10 than 1 cleaved embryo groups but similar to controls for both culture groups. When embryos were cultured in 10 μl drops, embryos cultured in groups of 5 had lower development to blastocysts compared to groups of 2, 10, 25, and control. In conclusion, these data indicated an apparent ‘helper effect’ expressed in culture environments of groups, and this effect apparently occurred after cleavage but before blastocyst development. Direct or indirect role(s) that additional cells have on in vitro culture and the mechanism of this helper effect requires further investigation.