Comparison of a Concentrated Soy-Lecithin-Based Formulation and a Conventional Egg-Yolk-Based Formulation for Liquid Storage of Bull Semen at 0 °C: Effects on Sperm Quality, Antioxidant Capacity, and Fertility

Semen diluents are crucial for the effective utilization of male germplasm resources and for enhancing the efficiency of artificial insemination (AI). However, reports on the in vitro low-temperature preservation of semen are still limited. This study comprised three separate experiments. Experiment 1 (semen storage): An ex vivo experiment using one ejaculate from each of five bulls, split into two aliquots per ejaculate, stored at 0 °C for 15 days, with repeated assessments of sperm quality (n = 5 biological replicates). Experiment 2 (IVF): An in vitro fertilization study using slaughterhouse-derived oocytes fertilized with day-15 stored semen from Experiment 1, conducted in five independent sessions (n = 5 sessions). Experiment 3 (AI): A non-randomized interventional field study involving 400 synchronized cows at China Hualing Ranch, allocated upon detection of estrus to receive either treatment or control semen (n = 400 cows). The primary outcome for Experiment 1 was total motility at day 15; for Experiment 2, blastocyst formation rate per oocyte; for Experiment 3, pregnancy rate at day 50 post-AI among all allocated cows. These findings suggest that the treatment formulation may offer advantages for liquid storage of bull semen at 0 °C.