Morphological characterization and conservation of bovine spermatogenic cells by refrigeration at 4 °C and freezing using different cryoprotective molecules

The objectives of this study were study a practical method to characterize bovine spermatogenic cells and test the efficiency cells conservation by refrigeration at 4 °C and cryopreservation in different solutions using two cooling curves. Cellular identification was performing by analysis of shape, size and morphology, associated with nucleus positioning and nuclear-cytoplasm ratio (NCR). Cellular samples were kept at 4 °C for a period of 96 h in refrigeration solution and every 24 h plasma membrane and DNA integrity were evaluated. Cryopreservation of cells was carried out using solutions containing 10% Dimethyl sulfoxide, 5% Dimethylformamide, 7% Glycerol and 7% Ethylene glycol, using a controlled and non-controlled cooling curve. Results of cellular characterization demonstrated that spermatocytes II presented a cylindrical shape, NCR of 1:1.5 and diameter ranging from 14.5 to 17.5 μm. Round spermatids presented diameter ranging from 7.6 to 13.4 μm, acrosomal cap and NCR of 1:2. Elongation and elongated spermatids showed to marked divergence in shape. There was a daily significant loss of viability of cooled cells until third day of storage, however they presented 72.77 ± 5.16% viability after 4 days of storage at 4 °C. There was no difference among the cryoprotectant solutions and cooling curves. In conclusion we demonstrated that association of microscopes and staining was a practical method to identify bovine spermatogenic cells. Furthermore, refrigeration at 4 °C is an important strategy to preserve over 70% of viable cells after 4 days and cryopreservation, regardless of cryoprotectant solution or cooling curve used, can maintain over 50% of cells viable.