Effect of oxidative-stress (OS) on male fertility is much as it reduces fertility to a substantial low level. In bulls, a variety of testicular insults, such as exposure to toxins, X-ray and environmental chemicals, pollutants or specific physical ailments (varicocele) can result in OS which is then reflected in the spermatozoa health. The free-radicals induced damage can be either due to reactive oxygen or nitrogen species. The measures to alleviate such OS include either preventive measures to suppress the production of free-radicals or addition of supplements to counteract the negative effect post-facto. Since detrimental effect of free-radicals is well documented estimation of its presence in semen and effect on spermatozoa need to be carried out precisely to chalk out a strategy to counterbalance the OS. This review briefly touches upon aetiology, methods of combating OS and comparative analysis of various available determinative assays.