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The introduction of more specialised and productive dairy breeds into commercial herds in recent decades has caused a gradual loss of interest in dual-purpose cattle breeds, such as the Flamenga. Because of its importance to biodiversity, the high risk of loss of this small Brazilian herd, located in one geographic region in Southern Brazil, justifies the need for and efforts in genetic conservation of the Flamenga breed. The ovum pickup (OPU) procedure is a potential tool for such conservation purposes. Thus, the aim of this study was to evaluate the oocyte and embryo yield potential of the Flamenga breed, as compared with Holstein control counterparts, after in vivo oocyte retrieval followed by in vitro embryo production (IVP). Four Flamenga and 4 Holstein multiparous milking cows from the same herd were subjected to weekly ultrasound-guided OPU sections for 10 consecutive weeks. The number of visible follicles per ovary per female was recorded before the aspiration of ≥3-mm follicles. Retrieved cumulus–oocyte complexes (COC) were morphologically graded according to the method of (Leibfried and First 1979 J. Anim. Sci. 48, 76–86), and viable COC (Grades I, II, and III) from both breeds and from slaughterhouse ovaries (IVP controls) were used for the IVP of embryos, based on our established procedures (Vieira et al. 2002 Cryobiology 45, 91–94). Frozen semen from the same Flamenga breed bull was used in all groups. Quantitative (visible and aspirated follicles, collected COC), and qualitative (COC recovery efficiency, cleavage and blastocyst rates) data were compared between breeds and IVP controls (when pertinent) by Student’s t-test and chi-square test, respectively, for P

Exposing bovine embryos and porcine oocytes to hydrostatic pressure has been shown to increase cryosurvival, possibly by a resulting expression of stress tolerance proteins. This study aimed to evaluate the effect of the negative pressure stress condition (a 5-min-long embryo exposure to a negative pressure) and the interval between vacuum exposure and vitrification (40 min or 2 h) on survival of bovine in vitro-produced (IVP) embryos. The negative pressure was achieved with the same apparatus used previously for the cryopreservation of embryos (Nitrocooler; Mezzalira et al. 2009 Reprod. Fert. Dev. (1) 134), in which a negative pressure (vacuum) is applied to liquid nitrogen to increase the cooling rate through the slush phenomenon, except that in this study, the vacuum was applied to the chamber without liquid nitrogen, at room temperature. Grades 1 and 2 bovine IVP expanded blastocysts were allocated to 1 of 5 experimental groups: embryos in vitro-cultured as fresh (control) or after vitrification (Vitri); and embryos subjected to the negative pressure for 5 min and then in vitro-cultured as fresh (NP-fresh) or after vitrification performed 40 min (NP-Vitri-40 min) or 2 h (NP-Vitri-2h) following the vacuum exposure. Embryos were vitrified in pulled glass micropipettes in a solution with 20% ethylene glycol + 20% dimethylsulfoxide + 20% fetal bovine serum and rewarmed in decreasing sucrose concentrations (Mezzalira et al. 1999 Acta Scientiae Veterinariae 27 262-262). In vitro culture was carried out in all treatments for 72 h for the assessment of re-expansion and hatching rates (Table 1), which were analyzed by the chi-square test, for P < 0.05. No differences in re-expansion rates were observed between groups. However, the vitrification of embryos after 2 h of exposure to a 5-min-long negative pressure (NP-Vitri-2h) improved embryo survival expressed by a higher hatching rate than for embryos vitrified without vacuum exposure (Vitri) or after 40 min following the 5-min-long exposure to vacuum. In addition, hatching rates in group NP-Vitri-2h were similar to those for fresh embryos (control and NP-fresh). Our results indicated that a short exposure of embryos to a negative pressure can improve cryotolerance following vitrification, which is dependent on the time interval between NP exposure and cryopreservation. Bovine IVP embryos should be allowed to recover for at least 2 h after NP exposure before the increase in cryotolerance is achieved. Table 1.Effect of negative pressure on re-expansion and hatching rates of fresh and vitrified