Vitrification of bovine embryos by OPS and modified straw method

Recent studies have indicated a correlation between the increasing prevalence of embryo transfer and the rising number of IVP cattle embryos worldwide. The cryopreservation of embryos has emerged as a pivotal aspect contributing to the widespread adoption of embryo transfer techniques. In the domain of cryopreservation techniques, vitrification emerges as a leading method for IVP bovine embryos. There is a need for cost-effective and easily applicable vitrification methods with high success rates. The objective of this study was to assess the efficacy of a vitrification technique that can be utilised in field settings without the requirement for sophisticated laboratory facilities. The efficacy of the developed modified straw (MP) was evaluated in comparison with OPS and a non-vitrified control group. Quality oocytes obtained from slaughterhouse ovaries were subjected to IVM, IVF and IVC procedures. In the study, 25 embryos were used for each of the OPS, MP and Control groups. The vitrification groups were subjected to the process of vitrification, then thawed and loaded into culture, while the Control group was cultured without vitrification. The vitrification solution of OPS group was TCM199 medium containing 20% FBS (v/v), 16.5% EG (v/v), 16.5% DMSO (v/v) and 0.5 M sucrose, while the vitrification solution of MP group was TCM199 medium containing 20% FBS (v/v), 15% EG (v/v), 15% DMSO (v/v) and 0.5 M sucrose. Thawing process was the same in all vitrification groups and was performed in a single step at 38.5°C in 0.25 ml straws. TCM199 medium containing 20% FBS (v/v) and 0.2 M sucrose was used as thawing solution. After thawing, there was no difference between the 0 h (64% and 72%) and 24 h (92% and 100%) re-expansion rates in OPS and MP groups, respectively (P˃0.05). Post-thawing development rates were found at 24th (60% and 76%) and 48th hours (68% and 76%) in OPS and MP groups, respectively (P˃0.05). In the study, hatching/hatched rate was determined at 24th (28%, 48% and 40%) and 48th hours (36%, 60% and 52%) in OPS, MP and Control groups, respectively (P˃0.05). Despite the MP device demonstrating superior hatching outcomes in comparison to the OPS, the statistical significance of this discrepancy could not be substantiated, owing to the limited number of embryos utilised in the study. In future studies, more comprehensive studies should be conducted regarding the success of this technique using a higher number of embryos. Furthermore, the transfer of embryos following vitrification, in conjunction with the subsequent evaluation of pregnancy rates, will provide a more accurate assessment of the technique's efficacy. Given the greater complexity of the MP technique in comparison with OPS, it is recommended that its utilisation be reserved for those with a proven level of manual dexterity. The widespread adoption of vitrification techniques in the field is contingent upon the development of a successful method that does not necessitate complex procedures.