141 BOVINE EMBRYO CULTURE IN THE MODIFIED WELL OF THE WELL SYSTEM INCREASES BLASTOCYST RATE BUT LOWERS BLASTOCYST QUALITY

Abstract

Individual culture of cattle embryos in serum-containing medium has a detrimental effect on blastocyst development. As we previously demonstrated, this effect is not caused by the individual culture itself but by some component present in serum (Heras et al. AETE Proc. 2012). The high blastocyst rates achieved with group culture in serum-containing medium can be explained by the neutralizing effect of the produced autocrine factors. Autocrine factors produced by individually cultured embryos cannot neutralize the detrimental component due to its low amount and their diffusion in the high culture volume. Using a modified well of the well (mWOW; Vajta et al. 2000 Mol. Rep. Dev.), where embryos are singly cultured in a small well, the effect of the autocrine factors produced by individual embryos can be maximized. We hypothesized that the use of mWOW for individual embryo culture in serum-containing medium, can maximize the neutralizing effect of the autocrine factors, increasing both blastocyst rate and quality. Bovine oocytes (n = 1143, 3 replicates) were matured in TCM-199 with 20% fetal bovine serum (FBS). Presumptive zygotes were cultured in groups (Gr; 25 embryos/50-µL drops), individually (Ind; 20-µL drops), or in mWOW (20-µL drops) in SOFaa with 5% FBS. Blastocyst evaluation occurred 7 and 8 days post-insemination (dpi). Hatching rate is the proportion of hatching/hatched blastocysts out of total 8-dpi blastocysts. Blastocysts were collected at 8 dpi for differential apoptotic staining, evaluating total cell number (TCN), inner cell mass (ICM) ratio, and apoptosis (ACR; Wydooghe et al. 2011 Anal. Biol.). Developmental data were analyzed using binary logistic regression; data concerning blastocyst quality were analyzed using linear mixed model analysis. Since ACR was not normally distributed, a logarithmic transformation was performed. Differences at P < 0.05 were considered significant. Regarding blastocyst development, all groups were significantly different both at 7 dpi (Gr 33.9%, Ind 10.7%, mWOW 19.6%) and at 8 dpi (Gr 37.3%, Ind 14.0%, mWOW 29.1%). Hatching rates were significantly higher in Gr (27.9%) compared to Ind (4.0%) and mWOW (4.1%). Concerning blastocyst quality, TCN was significantly higher (P < 0.001) in Gr (233.23 ± 8.39), no differences between Ind (143.77 ± 6.32) and mWOW (125.11 ± 4.30) were observed. No differences in ICM ratio were observed (Gr 0.41 ± 0.01, Ind 0.30 ± 0.02, mWOW 0.37 ± 0.02). ACR was significantly different between all groups (Gr 0.03 ± 0.002, Ind 0.04 ± 0.003, mWOW 0.08 ± 0.005). In conclusion, the mWOW had a positive effect on blastocyst quantity, increasing blastocyst rates compared to individual culture, but still lower than in group culture. Surprisingly, mWOW had a negative effect on blastocyst quality, producing the highest ACR and the lowest TCN. This negative effect can be caused by toxic products arising from the manufacture (although the wells were rigorously flushed), or by the longer manipulation time needed. This work was funded by FWO G.0210.09N and IWT g111438.