Antioxidative effects of melatonin on kinetics, microscopic and oxidative parameters of cryopreserved bull spermatozoa

Reactive oxygen species generated during the freeze–thawing process may reduce sperm quality. This study evaluates the effects of melatonin supplementation as an antioxidant in the semen extender on post-thaw parameters of bull spermatozoa. Melatonin was added to the citrate–egg yolk extender to yield six different final concentrations: 0, 0.1, 1, 2, 3 and 4 mM. Ejaculates were collected from six proven Holstein bulls. Semen was diluted in the extender packaged in straws, which was frozen with liquid nitrogen. The semen extender supplemented with various doses of melatonin increased (p < 0.05) total motility, progressive motility, linearity, sperm track straightness, lateral head displacement, viability, integrity of the sperm membrane and total normal morphology of sperm after the freeze–thawing process. The most effective concentration of melatonin in microscopic evaluations of the bull sperm freezing extender was 2 mM. The highest (p < 0.05) value of total antioxidant capacity (48.9 ± 2.7) and the lowest value of lipid peroxidation (2.7 ± 0.8) were achieved by inclusion of 3 mM concentration of melatonin in the semen extender and the highest activity of catalase (0.7 ± 0.1) was obtained by 2 mM melatonin. Four millimolar concentration of melatonin were reduced (p < 0.05) the progressive motility and straight linear velocity. In conclusion, supplementation of 2 or 3 mM concentration of melatonin in the semen extender improved the quality of post-thawed semen, which may associate with a reduction in lipid peroxidation as well as an increase in the total antioxidant capacity and antioxidant enzyme activity.