摘要Objective: To assess the effect of melatonin (MT) at different seasons of the year on sperm motility, viability, total sperm abnormality, acrosomal membrane, plasma membrane and nuclear integrity, antioxidant profiles such as superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) and total antioxidant capacity (TAC), enzymatic profiles such as aspartate amino transaminase (AST), alanine amino transaminase (ALT) and biochemical profiles such as malondialdehyde (MDA) production. Methods: Total numbers of 80 ejaculates (20 ejaculates in each season) were collected twice a week from mithun bulls and semen was split into five equal aliquots, diluted with the tris egg yolk citrate (TEYC) extender. Group 1:semen without additives (control), group 2 to group 5:semen was diluted with 1 mM, 2 mM, 3 mM, and 4 mM of melatonin, respectively. These seminal parameters, antioxidant, enzymatic and biochemical profiles were assessed at liquid storage of mithun semen (5 ℃). Simultaneously, retrospective study was conducted on birth rate of calf at different seasons from 2002 to 2012 from farm birth register of mithun farm. Results: Inclusion of melatonin into diluent resulted in significant (P<0.05) decrease in percentages of dead spermatozoa, abnormal spermatozoa and acrosomal abnormalities at different seasons of the year as compared with control group. Additionally, spring season has highest seminal and antioxidant profiles followed by autumn and winter season, whereas lower values were observed in ejaculates collected from summer season. Similarly retrospective study revealed that highest birth rate was in winter followed by autumn, spring and summer season and breeding was occurred in spring, winter, summer and autumn season, respectively with gestation period of 270- 290 days. Conclusions:The result of present study indicates that the melatonin protects seminal and antioxidant profiles varied in different seasons, semen quality also varied from different seasons and was highest in spring and lowest in summer season. It was concluded from the present study that breeding takes place throughout year but the peak breeding season is from November to April (spring and winter season) in mithun.