The Effect of a Mixture of Amino Acids and Endogenous Lipids on in vitro Oocyte Maturation of Cows

Understanding the effects of amino acid (AA) and endogenous lipid (EL) metabolism during in vitro oocyte maturation is important; however, most studies use undefined routine maturation media supplemented with glucose or an oxidative agent. The present study was conducted in two phases, with each phase consisting of two stages, and aimed to use supplemented AA (a mix of the 20 amino acids and glutamine) or EL (triacylglycerols) as unique oxidative substrates for oocytes during in vitro maturation (IVM) to understand the oocyte requirements during maturation. Cumulus-oocyte complexes (COCs) obtained from slaughtered Aberdeen Angus cows were matured in five groups to evaluate AA utilization and in the other five groups to evaluate EL utilization. The COCs were incubated in a defined medium either without oxidative substrates (negative control) or supplemented with AA, AA and salicylate as deamination inhibitor, AA and glucose (Glc), and Glc alone (positive control) to evaluate AA catabolism. To assess EL utilization, COCs were cultured with L-carnitine (β-oxidation activator), etomoxir (β-oxidation inhibitor), L-carnitine with Glc, Glc alone (positive control), and without oxidative substrates (negative control). Nuclear maturation, ammonia production, and oocyte lipid content were evaluated after maturation. Cleavage and blastocyst rates were assessed at 48 hours and seven days after fertilization. The results indicated that oocytes matured in media with AA and Glc (51% and 52%, respectively) or AA with salicylate (38%) had higher nuclear maturation rates than the control group (11.76 %), and a synergistic effect was observed in the group supplemented with AA and Glc (70 %). When AA was added to the maturation media as a unique oxidative substrate, ammonia production increased, while embryo development was observed only in the AA and Glc-supplemented group. Media with Glc (68 %) or L-carnitine with Glc (61%) increased the nuclear maturation. A higher lipid content was observed with Glc. Glc (63%) and L-carnitine with Glc (57.9%) increased cleavage rates compared with the other groups, but no group reached the blastocyst stage. Catabolism of AA, EL, or Glc alone served as an oxidative substrate and sustained bovine oocyte nuclear maturation, but they were insufficient to induce oocyte developmental competence.