# High Concentrations of Non-Esterified Fatty Acids During Bovine In Vitro Fertilisation Are Detrimental for Spermatozoa Quality and Pre-Implantation Embryo Development

## TL;DR

High levels of fatty acids during bovine in vitro fertilisation harm sperm quality and early embryo development, possibly by affecting both the egg and sperm.

## Contribution

This study reveals the detrimental effects of high non-esterified fatty acids during bovine in vitro fertilisation on both sperm and embryo development.

## Key findings

- High NEFA concentrations reduced fertilisation, cleavage, and blastocyst rates in bovine embryos.
- Sperm exposed to high NEFAs showed increased DNA damage and reduced mitochondrial function.
- High NEFAs delayed the loss of H3K27me3 histone marks in embryos, potentially contributing to developmental issues.

## Abstract

High non-esterified fatty acids (NEFAs) during negative energy balance in dairy cattle can impair reproduction. While their effects on oocyte maturation and preimplantation embryo development are known, their impact during fertilisation is largely unexplored. This study examined the effects of high NEFA exposure exclusively during in vitro fertilisation (IVF). Bovine oocytes were matured in vitro and fertilised under physiological or high NEFA concentrations. High NEFA concentrations decreased fertilisation, cleavage, and blastocyst rates. Reactive oxygen species production in zygotes was not affected, but blastocysts derived from the High-NEFA group had fewer cells. Spermatozoa exposed to high NEFA concentrations exhibited increased plasma membrane and acrosome damage, higher DNA fragmentation, and reduced mitochondrial membrane potential. The expression of H3K27me3, a repressive histone mark normally erased from fertilisation to embryonic genome activation, was higher in 2-cell than in 4-cell embryos on day 2 after IVF, but only in the High-NEFA group. This delayed H3K27me3 loss, along with increased DNA damage, could partially explain the reduced blastocyst formation observed. In conclusion, high NEFA concentrations can impair pre-implantation embryo development during zygote formation, potentially via effects on both the oocyte and spermatozoon. The latter warrants further investigation using an intracytoplasmic sperm injection model.