Exploration of Slow Freezing Effects on Bovine in Vitro Embryos
The study aims to explore the development of embryos formed by oocytes of different quality levels and their adaptability to slow freezing at different stages of development,and evaluate their development effects after freezing,thereby improving embryo utilization,reducing resource waste and reducing costs.In this test,197 donor cows were collected through the Ovum Pick-Up tech-nique,and a total of 3681 Cumulus oocyte complexes(COCs)were obtained,of which an average of 18.69 COCs were obtained per cow.Subsequently,these COCs were divided into 4 levels based on the appearance quality identification standards of oocytes.Then,relevant operations such as in vitro maturation,in vitro fertilization,and in vitro culture were carried out on different levels of COCs to evaluate the effect of slow freezing of embryos in vitro.The results showed that:The cleavage rate and blastocyst rate of grade 1 oocytes were significantly greater than those of other grades(P＜0.05).The development rates of blastocysts and expanded blastocysts formed by grade 1 oocytes were significantly greater than those of early blastocysts(P＜0.05).There was no significant difference in the embryo development rate of grade 2 oocytes at three developmental stages(P＞0.05),but the early blastocyst development rate was significantly higher than that of other grades(P＜0.05).The thawed embryo development rate of grade 3 and grade 4 oocytes was significantly lower than that of the other two grades(P＜0.05).The developmental rates of blastocysts and expanded blastocysts were significantly greater than those of early blastocysts(P＜0.05),but there was no significant difference between blastocysts and expanded blastocysts(P＞0.05).It can be seen that the selection of 1～3 grade oocytes for cultivation can improve the overall cleavage rate and blastocyst rate,and the selection of expanded blastocysts for freezing can improve the development rate of slow-freezing embryos.
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