Effect of two Different Permitting and Combination of Cryoprotectants on Cattle Oocytes Maturation Rate Following Brilliant Cresyl Blue Exposure

The objectives of this study were to elucidate the toxicity of Dimethyl sulfoxide (DMSO), Ethylene glycol (EG), and the combination of both permitting cryoprotectants (CPAs) to cattle oocytes and the effectiveness of Brilliant cresyl blue (BCB) on immature oocytes pre-selection. Cattle ovaries were collected from the local slaughterhouse and transported within 2 hours of slaughter. The oocytes were exposed to 26 mM BCB solution. The other oocytes were not exposed to BCB solution or CPA. Oocytes were classified as BCB positive (+) or BCB negative (−). Oocytes were either exposed to DMSO, EG, or DMSO + EG at different CPA concentrations as follows: toxicity test 1 (TT1) was 0, 5, 10, 15, and 20%, followed by exposure to TT2 as follows: 10, 20, 30 and 40%. The oocytes were then in vitro matured as per treatment groups. After maturation, oocyte polar body extrusion was evaluated. Treatment means were compared using the Fisher-protected t-test least significant difference. The DMSO treatment group: The oocytes with polar body extrusion were 55.1% (positive control, no BCB and no CPA exposure), 55.0% (control, CPA exposure no BCB), 22.7% [BCB− with CPA toxicity test (DMSO 5 + 10%)], 21.8% [BCB− with CPA toxicity test (DMSO 10 + 20%)] and 7.3% [BCB− with CPA toxicity test (DMSO 20 + 40%)]. The BCB + groups (DMSO 5 + 10 and DMSO 10 + 20%) had more oocytes with polar body extrusion (67.0 and 66.9%, respectively; P>0.05). The EG treatment group: There was a drastic decline of oocytes with polar body extrusion as EG CPA concentration increased (P<0.05). The BCB+ groups (EG 5 + 10 and EG 10 + 20%) had significantly more oocytes with polar body extrusion (68.9 and 51.9%). The DMSO + EG treatment group: There was a decline in oocytes polar body extrusion recorded, as the DMSO + EG CPAs concentrations were increased (P<0.05). The BCB+ groups (DMSO 5 + EG 5% and DMSO 10 + EG 10%) recorded numerically highest number of oocytes with polar body extrusion (55.1 and 55.8%) as compared to positive control (51.1%), respectively (P>0.05). In conclusion, a decline in oocyte polar body extrusion was recorded, as the DMSO, EG, and DMSO + EG concentrations were increased. The BCB can be used to identify developmentally competent oocytes.