# Extended In Vitro Maturation Enhances Oocyte Developmental Competence but Alters Gene Expression in Bovine Embryos Derived From Oocytes With Slow‐Predicted Nuclear Maturation Speed

## TL;DR

Extending in vitro maturation improves the development of slow-maturing bovine oocytes but changes gene expression in embryos.

## Contribution

Noninvasive machine learning predicts nuclear maturation speed to optimize in vitro maturation duration for bovine embryos.

## Key findings

- Extending IVM to 28 h improved cleavage rates and first cleavage timing in slow-predicted NMS oocytes.
- Extended IVM increased blastocyst formation rates in slow-predicted NMS oocytes to match fast-predicted NMS oocytes.
- Prolonged IVM reduced expression of pluripotency-related genes like NANOG and OCT4 in all embryos.

## Abstract

To identify the optimal in vitro maturation (IVM) duration for bovine oocytes with different nuclear maturation speeds (NMS), this study assessed how varying IVM durations (24, 28, and 32 h) 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 h increased cleavage rates and accelerated first cleavage timing (p < 0.01). The lower blastocyst formation rates of oocytes with slow‐predicted NMS matured for 24 h improved when IVM reached 28 h, becoming comparable to fast‐predicted NMS oocytes. However, extended IVM decreased expression of pluripotency‐related genes (e.g., NANOG and OCT4; p < 0.01) regardless of predicted NMS. In conclusion, extending IVM duration to 28 h 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.

Noninvasive machine learning‐based prediction of nuclear maturation speed (NMS) enables precision optimization of in vitro maturation duration for efficient bovine embryo production. Extending maturation from 24 to 28 h improves cleavage and developmental competence of slow‐predicted NMS oocytes but alters key pluripotency‐related gene expression patterns in formed embryos.