38 VITRIFICATION OF BOS TAURUS INDICUS AND BOS TAURUS INDICUS×BOS TAURUS TAURUS EMBRYOS PRODUCED IN THE PRESENCE OR ABSENCE OF FETAL CALF SERUM

In vitro-produced Bos taurus indicus (zebu) and Bos taurus indicus × Bos taurus taurus (cross-bred) embryos behave differently when vitrified. The present experiment aimed to examine the effect of vitrification on embryos produced in the presence or absence of FCS. Cumulus-oocyte complexes (COC) were matured in TCM-199 and fertilized in human tubal fluid medium with frozen Nelore bull semen. On Day 1 (Day 0 = IVF), presumptive zygotes were cultured with SOFaa + BSA in the presence of FCS (Group 2.5%) or in the absence of FCS (Group 0%) until Day 7. The cleavage was analysed on Day 3 and the blastocyst rate on Day 7. Blastocysts were vitrified and, after warming (Campos-Chillòn et al. 2006) the viability was evaluated. Data were analysed with ANOVA, using the general linear model (GLM) of SAS (SAS Inst Inc., Cary, NC, USA). Sources of variation in the model included FCS concentration and first-order interactions; all factors were considered fixed effects. The arcsine transformation (√y/100) was applied to percentage data. If the ANOVA was significant, means were separated using the Tukey test. There was no difference in cleavage (for zebu embryos: Group 0%: 87.2 ± 6.8; Group 2.5%: 87.4 ± 9.5; for cross-bred embryos: Group 0%: 79.6 ± 11.9; Group 2.5%: 73.1 ± 13.7; P > 0.05). On the other hand, zebu embryos cultured in the presence of FCS reached blastocysts at a higher rate than cross-bred embryos in the absence of FCS (for zebu embryos: Group 0%: 33.3 ± 12.4ab; Group 2.5%: 46.8 ± 13.2a; for cross-bred embryos: Group 0%: 21.8 ± 8.3b; Group 2.5%: 33.6 ± 10.1ab; P < 0.05). After vitrification and warming, no significant differences in re-expansion rate (zebu embryos: Group 0%: 82.7 ± 13.1; Group 2.5%: 75.0 ± 9.8; cross-bred embryos: Group 0%: 93.7 ± 8.8; Group 2.5%: 84.1 ± 11.3; P > 0.05) and cell number per embryo (zebu embryos: Group 0%: 65.1 ± 34.7; Group 2.5%: 42.6 ± 17.2; cross-bred embryos: Group 0%: 64.3 ± 44.2; Group 2.5%: 52.0 ± 31.5; P > 0.05) between species groups and within species were seen. However for zebu embryos, Group 0% showed a lower damaged cell rate than Group 2.5%. The same effect was not observed in the cross-bred embryos (zebu embryos: Group 0%: 20.3 ± 22.7c; Group 2.5%: 63.3 ± 27.0d; cross-bred embryos: Group 0%: 25.4 ± 24.3cd; Group 2.5%: 45.8 ± 34.6cd; P < 0.05). The addition of 2.5% FCS had a higher deleterious effect on zebu embryos than cross-bred (zebu × taurine) embryos after vitrification. These results also reinforce the species differences observed between zebu and cross-bred, as they behaved differently in relation to the addition of FCS in the culture medium and in relation to their cryopreservation sensitivity. Supported by FAPESP 10/50410-2.