Sericin Ameliorates the Capacitation State and Chromatin Integrity of Frozen-Thawed Stallion Spermatozoa by Reducing Oxidative Stress

In the process of sperm cryopreservation, apart from cryoinjury, the production of Reactive Oxygen Species (ROS) can adversely affect the integrity of chromatin and cellular membranes. Addition of natural antioxidants to freezing me-dium is an approach to reduce the destructive effects of ROS on sperm. In this study, during 60 min of cooling process, the ejaculates of five stallions were diluted in the following media: INRA 82 medium as Control (C), INRA 82 medium supplemented with 0.25% Sericin (S), INRA 82 medium supplemented with 1.5 mM Glutathione (G), and INRA 82 medium supplemented with 0.25% Sericin+1.5 mM Glutathione (S+G). In the frozen/thawed sericin supplemented group, while the integrity of DNA and the activity of catalase and Glutathione Peroxidase (GPx) were increased, the lipid peroxidation and midpieceab normality decreased, compared with other groups (p<0.05). The proportions of sperms with abnormal head in group S and the sperm with distal droplet in G and S+G groups decreased, compared with group C (p<0.05). In CTC assay, the percentage of capacitated spermatozoa in treatment groups was lower than control (p<0.01). In conclusion, the presence of sericin in freezing medium of stallion semen could improve sperm DNA integrity and its resistance to ROS and lipid peroxidation.