The aim of our study was to examine the effects of cow's body condition score (BCS; scale 1–5) and season on the quality of bovine in vitro produced embryos. The proportion of good quality oocytes (Q1 and Q2) was higher (P < 0.05) in the BCS 2 (57.60%) and BCS 3 (60.90%) groups compared with the BCS 1 (43.60%) group. There were no statistical differences in embryo cleavage and blastocyst rate among the BCS groups. The highest total cell number (TCN, DAPI stain) of blastocysts (P < 0.05), recorded in BCS 1 (122.27 ± 6.90) in comparison with BCS 2 (101.8 ± 3.60) or BCS 3 (105.44 ± 3.70) groups, was related to higher dead cell (DCI, TUNEL) index in this group (7.07%) when compared with BCS 2 (6.54%) or BCS 3 (6.06%), respectively. The yield of good quality oocytes during spring was lower (P < 0.05) compared with the summer season. There were significant differences (P < 0.05) in maturation and cleavage rates between autumn and summer (73.42%, 76.2% vs. 85.0%, 41.8%, respectively). The highest (P < 0.01) blastocyst rate was noted during spring and summer months. Significant difference (P < 0.05) in the TCN among spring (99.38 ± 3.90), autumn (110.1 ± 4.58) or summer (108.96 ± 3.52) was observed. The highest proportion of embryos with the best (grade I) actin cytoskeleton (phalloidin–TRITC) quality was noted during the summer months. Our results indicate that body condition affects the initial quality of oocytes, but does not affect embryo cleavage, blastocyst rate and actin quality. This finding may suggest that development in vitro can mask the influence of BCS. The season affects yield and quality of blastocysts in the way that the autumn period is more favorable for embryo development.

The selection of competent oocytes for in vitro maturation is still a major problem during bovine in vitro embryo production. Markers for in vitro cytoplasmic maturation, based on the organization of cortical granule and mitochondria, are lacking. We examined the pre-selection of immature bovine oocytes by brilliant cresyl blue stain (BCB test) based on glucose-6-phosphate dehydrogenase (G6PDH) activity during oocyte development. Oocytes were recovered from ovarian follicles exposed to 26 μM BCB stain and classified according to the aspect of their cytoplasm: BCB+ (oocytes with blue cytoplasm) and BCB− (unstained cytoplasm) and then in vitro matured into a conventional in vitro maturation (IVM) medium and standard procedure. In Experiment 1, nuclear maturation was determined by polar body identification, while cytoplasmic maturation was based on cortical granule (CG) migration (peripheral) and mitochondria distribution (central). Evidence of polar body, cortical granule migration and of centrally located mitochondria was significantly (p < 0.05) higher in BCB+ oocytes than in BCB− (polar body present: 65% vs 20%; peripheral CG: 72% vs. 14%; and central mitochondria: 85% vs. 19%, respectively). In Experiment 2, the efficiency pre-selection of bovine oocytes by BCB on embryo development in vitro was assessed. Cleavage rates were similar (75%) among control, BCB+ and BCB− groups, while blastocyst rates on D7 were (p < 0.05) higher (35%) in BCB+ vs BCB− (10%) or control (28%). We showed that the BCB test is efficient to identify competent immature bovine oocytes to undergo synchronous nuclear and cytoplasmic in vitro maturation thus yielding higher in vitro embryo development to blastocyst stage.