Actavia 0 Yangngam, Yotsapon Chapanya, Suttiwat Vongpralub, Thevin Boonkum, Wuttigrai Chankitisakul, Vibuntita 2021 2021-1-29 13-20 Silk sericin plays a protective role in a variety of mammalian cells during cryopreservation. This study aimed to determine the effects of sericin supplementation to a freezing extender on sperm quality and lipid peroxidation in dairy bull sperm cryopreservation. Each semen sample of five Holstein-Friesian crossbred bulls was divided into four aliquots and diluted in a tris-egg yolk extender supplemented with different concentrations of sericin [0%, 0.25%, 0.5%, and 1.0% (wt/vol)]. Sperm motility (CASA), viability, acrosome integrity, mitochondrial membrane potential (fluorescent staining) and lipid peroxidation (malondialdehyde - MDA test) were analysed. The results show that the 0.25% and 0.5% sericin groups had the highest total sperm motility (P < 0.05). Sperm viability, acrosome integrity, and mitochondrial function were higher in the group supplemented with 0.25% sericin compared to the control and 1.0% (P < 0.05). Sericin supplementation with 0.25% and 0.5% significantly decreased MDA concentrations compared with the control (P < 0.05). In conclusion, supplementation of the semen freezing extender with sericin at the concentration of 0.25% significantly improved the post-thaw semen quality and reduced lipid peroxidation in Holstein-Friesian crossbred bulls. 1 66