Sericin Enhances Cryopreserved Sperm Quality in Chengde Hornless Black Goats by Increasing Glutamine Metabolism

The cryopreservation of Chengde polled goat semen plays a critical role in conserving genetic resources, enhancing the utilization efficiency of superior breeding bucks, and advancing artificial insemination techniques. However, spermatozoa are vulnerable to oxidative stress during the freezing process, which can significantly compromise sperm motility. In this study, pooled ejaculates from multiple bucks were divided into six groups, including a control group cryopreserved with conventional extender and five treatment groups supplemented with sericin at concentrations of 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% (w/v). The results demonstrated that supplementation of the semen cryoprotectant with 0.6% sericin significantly improved post-thaw sperm viability to 65.25% in Chengde hornless goats, while concurrently reducing both the sperm abnormality rate (p < 0.05) and intracellular ROS levels (p < 0.05). Integrated TMT proteomics and LC/MS metabolomics further compared the 0.6% sericin group with the frozen control group and identified 162 differentially expressed proteins and 109 differential metabolites between the sericin supplementation and frozen control groups. Functional analysis revealed the significant enrichment of differential metabolites, such as glutamine, in the alanine, aspartate, and glutamate metabolism pathway, concomitant with the marked upregulation of antioxidant proteins including LRP8, GSTM3, and SIRT2. Thus, 0.6% sericin enhances cryotolerance primarily by improving sperm viability, reducing oxidative damage, and sustaining energy metabolism. These findings indicate that sericin enhances cryotolerance by reducing oxidative damage and supporting metabolic function, providing preliminary molecular insights for improving goat semen cryopreservation.