Med. Weter. 81 (6), 273-277, 2025
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| MAGDALENA PROFASKA, ALEKSANDRA LASOŃ-KUBAREK, MATEUSZ KUBAREK |
| Cryopreservation of mare’s embryos obtained in vivo. |
| Cryopreservation of equine embryos eliminates the need to have a herd of recipient mares and to synchronize the donor and recipient mares. It also makes it possible to store embryos for long periods of time and transport them across international borders. The extracorporeal fertilization of equine oocytes by the intracytoplasmic sperm injection (ICSI) method, together with the procedure of live oocyte collection (Ovum Pick Up, OPU), has revolutionized the possibilities of transplanting frozen embryos. However, the high costs of OPU + ICSI and the large range of expected results in the form of ultimate, cultured and frozen embryos suitable for transplantation (34) stimulate the current intensive search for increasingly effective methods of cryopreservation of embryos obtained not in the laboratory, but washed out after mare mating/insemination. The aim of this paper is to describe the methods of cryopreservation of equine embryos collected in vivo. There are two main methods of cryopreservation of equine embryos collected in vivo: slow freezing and vitrification (ultrafast freezing). Compared to the slow freezing of embryos, vitrification is a cheaper, simpler and faster procedure that does not require specialist freezing equipment, and, moreover, can be performed in the field, which is why it has found wider application in clinical practice. The main obstacle to cryopreservation of embryos in the field and obtaining an acceptable pregnancy rate after their transplantation (> 55%) is the need to obtain an embryo whose size does not exceed 300 μm, i.e. in the early stage of development (from morula to early blastocyst) between 144 and 168 hours after ovulation (3, 14, 35). Another factor that impacts the effectiveness of embryo cryopreservation is the presence of the embryonic capsule – an acellular glycoprotein envelope that is produced after the embryo descends from the oviduct into the mare’s uterus along with the formation of a blastocyst (5, 17). It has been shown that vitrification of punctured mare blastocysts smaller than 550 μm allows pregnancy to be achieved after thawing and transfer rate > 75%, regardless of whether the blastocyst fluid has been aspirated. In the case of embryos with a diameter of more than 550 μm, aspiration of the blastocyst fluid is necessary for effective vitrification (45). |
| Key words: Cryopreservation embryos, vitrification, mare |