Extended in vitro maturation enhances bovine oocyte developmental competence
image: By culturing bovine slow-maturing oocytes for 28 hours, blastocyst formation was found to improve.
Credit: Osaka Metropolitan University
To identify the optimal in vitro maturation (IVM) duration for bovine oocytes with different nuclear maturation speeds (NMS), an Osaka Metropolitan University-led research team assessed how varying IVM durations affect developmental competence and embryo quality in oocytes with fast- or slow-predicted NMS classified via machine learning. Developmental competence was evaluated through cleavage rates, first cleavage timing and patterns, and blastocyst formation under individual culture. Embryo quality was assessed via differential staining of inner cell mass and trophectoderm and expression analysis of quality-related genes in formed blastocysts.
For oocytes with slow-predicted NMS, extending IVM to 28 hours increased cleavage rates and accelerated first cleavage timing. The lower blastocyst formation rates of oocytes with slow-predicted NMS matured for 24 hours improved when IVM reached 28 hours, becoming comparable to fast-predicted NMS oocytes. However, extended IVM decreased expression of pluripotency-related genes regardless of predicted NMS.
In conclusion, extending IVM duration to 28 hours improved developmental competence of slow-predicted NMS oocytes, highlighting the importance of fertilization timing relative to nuclear maturation completion, though it reduced expression of key pluripotency genes. Individualized IVM protocols based on predicted NMS can enhance bovine embryo production efficiency.
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