The aim of this study was to evaluate the impact of supplementing Tris-extender with different levels of nano-oleic acid (NOA) on sperm characteristics, and enzyme activity and antioxidant status of post-thawed sperm medium of bull semen. Semen was collected by artificial vagina from 5 Holstein bulls, then pooled, diluted by Tris-egg yolk extender supplemented with NOA at levels of (0, 1, 2, 4 and 6 µL/mL), equilibrated at 5°C for 4h, loaded in straws, and stored in liquid nitrogen, then thawed at 37oC for 30 s for evalua-tion. Supplementing Tris-extender with nano-oleic acid (5 µL) increased (P<0.05) the per-centages of progressive motility and membrane integrity after dilution, progressive motili-ty, livability, and membrane integrity after equilibration, as well as increasing progressive motility, livability, and membrane integrity, and decreasing abnormality of sperm cells after thawing. Also, recovery rate of progressive motility, livability, and membrane integ-rity after equilibration and thawing was the highest for semen supplemented with 1µL nano-oleic acid. Supplementing Tris-extender with nano-oleic acid at a level of 5 or 2µL decreased (P<0.05) AST and ALT activities, and increased (P<0.05) TAC level and GPx activity as compared to free-extender. Pregnancy rate of cows inseminated with 1µL nano-oleic acid showed higher (P<0.05) pregnancy rate (57.5%) than in free-extender (32.5%) or other nano-oleic acid levels (25-42.5%).
In conclusion, addition of 1µL NOA in Tris-extender of bull semen can be used as a strategy for improving freezing ability and fertilizing capacity of cryopreserved bull sper-matozoa.