Season-specific effects of α-tocopherol supplementation during bovine oocyte in vitro maturation on embryo yield and quality

Elevated temperature-humidity index (THI) levels, common in subtropical summers, can impair bovine oocyte development by increasing reactive oxygen species (ROS) accumulation, leading to oxidative stress and reduced developmental competence. Alpha-tocopherol, a potent antioxidant, has the potential to mitigate these effects by scavenging ROS. However, its seasonal efficacy during bovine oocyte <i>in vitro</i> maturation (IVM) remains underexplored. This study evaluated the impact of 100 µM α-tocopherol supplementation during IVM on oocytes collected in spring (THI: 68.7±3) and summer (THI: 73±3) in Northern Uruguay. Oocytes underwent IVM, fertilization, and embryos were cultured <i>in vitro</i> until day 9 post-fertilization. Blastocysts were assessed for ROS levels, apoptosis, and the abundance of transcripts linked to development and oxidative stress. Results showed a season-specific response to α-tocopherol supplementation. While no significant effects were observed in spring, summer oocytes exhibited increased maturation, cleavage, and blastocyst rates, along with improved blastocyst quality characterized by reduced apoptosis and lower <i>BAX</i> transcript levels. These findings indicate that α-tocopherol supplementation during IVM enhances oocyte developmental competence under heat stress conditions, supporting its potential as a strategy to mitigate oxidative damage and improve bovine embryo production during summer.