During oogenesis, immature oocytes are arrested at the prophase of the first meiotic division until the resumption of meiosis after a luteinising hormone (LH) surge. Oocytes are the largest mammalian cells and store large amounts of lipid droplets and mitochondria to generate sufficient adenosine triphosphate (ATP). Oocytes develop in the form of cumulus cell oocyte complexes (COCs); cumulus cells rely on glycolysis for energy production and provide metabolites such as pyruvate to oocytes [1,2]. Oocytes have low glycolytic activity due to low phosphofructokinase (PFK) activity [3] and rely on oxidative phosphorylation (OXPHOS) in the mitochondria. Furthermore, oocytes accumulate lipid droplets consisting of triglycerides and cholesterol in the cytoplasm, which are used for energy production via beta-oxidation [4].

The follicular fluid (FF) is the sole environment for oocyte maturation and contains many types of energy substrates, such as glucose, pyruvate, lactate, lipids, amino acids and fatty acids. In vitro oocyte maturation (IVM) is the initial step in embryo production. Notably, a medium for IVM, which contains glucose, pyruvate, lactate and amino acids, has been developed to mimic in vivo conditions [5]. However, the efficacy of the current medium has not been established because of the low developmental competency of in vitro-matured oocytes [6].

Acetic acid, a short-chain fatty acid, is a key substrate present at a concentration of 0.05–0.20 mmol/L in human blood [7] and at 0.15 mmol/L in pig blood [8]. Further, the acetic acid level in the FF of pigs is 0.3–1.5 mmol/L [9]. However, despite its high concentration in the blood and FF, the role of acetic acid in oocyte maturation has not been evaluated.

In this study, we examined the effects of supplementing porcine IVM media with acetic acid on oocyte maturation and subsequent embryonic development. The metabolic background underlying these effects was explored using RNA-sequencing (RNA-seq) and protein expression assays.