Although oxygen is a necessary molecule for catabolic and anabolic processes in animals and humans, it is also a main source of reactive oxygen species (ROS). Oxidative stress occurs when the amount of generated ROS exceed cellular antioxidant defences, causing oxidative damage of DNA structure and consequently failure of essential pathways of lipids, proteins and carbohydrates metabolism. Mitochondrial respiratory chain is the main site of free radicals with genotoxic properties. ROS is genotoxic not only in relation to sensitive mitochondrial DNA but also to nuclear DNA and much attention has been paid to its oxidative damage. It is supposed that the increase of a lifespan can be achieved by energy restriction causing decreased metabolic rate and therefore reducing intensity of oxidation and generation of ROS. The paper describes our recent results concerning oxidative effects of restricted energy supply and administration of ubiquinone, vitamins C and E, and taurine on different cellular and morphological parameters of oxidative stress in rats, pigs and horses. Based on the novel literature and own experiments it is concluded that ROS generation is a necessary element of life and the action of antioxidative network, being related to all essential life processes, is orchestrated by requirements for ROS.