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Cryopreservation is not a routine procedure for the storage of equine embryos. Regardless of the method of cryopreservation, its efficiency in the transplantation of frozen embryos is relatively low. The success of freezing depends on the phase of embryo development, the type and concentration of the cryoprotectant and the freezing method. Equine embryos can be successfully cryopreserved by using conventional, slow-cooling methods or by vitrification, when embryos do not exceed 250 µm in diameter. In bigger equine embryos, changes in tolerance to cryopreservation are observed. These failures may result from the glycoprotein capsule, which appears in later stages of embryo development. New methods of vitrifying embryos in a reduced volume of fluid (2-10 µl) enable embryos to pass quickly through the critical stage of rapid temperature changes and make it possible to lower the concentration of cryoprotectants in the vitrification mixture. Vitrification is a rapid procedure that requires limited equipment and time. Further research is needed to increase the survival of equine embryos after slow-freezing or vitrification.
Despite intensive research to develop an effective cryopreservation method, the use of frozen boar semen is very limited in practice and accounts for less than 1% of all inseminations. Boar spermatozoa are more sensitive to freezing compared to the sperm of other farm animals. The semen preservation procedure largely disturbs the endogenous antioxidant system, which is counteracted by some antioxidant extender components. Another issue in the improvement of boar semen cryopreservation technique is the introduction into the extender of the components that protect sperm plasma membranes against cryogenic damage. Research was conducted at the Department of Animal Reproduction Biotechnology of the National Research Institute of Animal Production to modify the composition of freezing extender by supplementing it with a mixture of vegetable protein and/or soybean lecithin (Pp) as well as antioxidants L- glutathione, butylated hydroxytoluene (BHT), and catalase. This study, involving 54 ejaculates, showed that following the freezingthawing procedure, the highest percentage of progressively motile sperm and the highest percentage of live sperm and sperm with high mitochondrial potential were observed for the extender supplemented with BHT. The lowest percentage of apoptotic spermatozoa was identified in the extender supplemented with vegetable proteins and soybean lecithin (Pp) (0.0005 g/ml). Statistically significant differences (P<0.05) were found for the percentage of individual sperm subpopulations between different extender variants. The present study shows that cryopreservation procedure does not induce DNA fragmentation in boar spermatozoa.
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