Rabbits breeding is one of the most cost-effective livestock industries, and the investments pay off rather quickly. However, rabbit breeding ensures high economic performance only provided the industry management is carried out on an industrial basis and under condition of high technological level. Rabbit meat is a dietetic product in humans nutrition. One of the important mechanisms of an organism normal development is maintaining a balance of free radical and peroxidation processes different substrates and the antioxidant system condition. Lipid peroxidation increases under the cells damage. Lipid peroxidation intensity increase results in vital enzymes inhibition that can cause violation of biologically active substances synthesis in animals. AOP system is represented with enzymes, foremost of which is the superoxide dismutase (SOD), catalase and glutathione reductase. SOD plays a crucial role in the antioxidant protection of virtually all cell types which contact with oxygen. This enzyme dismutes a super oxide radycal to hydrogen peroxide. SOD is mainly contained in the mitochondrial matrix, the cytosol and cytoplasm. Catalase is an enzyme detoxifying the toxic hydrogen peroxide. Under H₂O₂ high intensity formation in the body, it is neutralized with catalase, and under the low one – with glutathione peroxidase. Glutathione peroxidase is involved in both hydrogen peroxide lipid peroxides inactivation. In these reactions the enzyme oxidizes glutathione. More than 70% of the GPO is localized in the cytosol, the rest – in the mitochondrial matrix. Studying these indicators potency are objective criteria for antioxidant status assessing and is recommended for early detection of oxidative stress in animals.

Modern literature highlights the issues of investigating antioxidant enzyme system age peculiarities in the tissues and organs of different species of animals and birds, while enzymatic activity of antioxidant protection (AOP) in the rabbits body remains less explored. The study of these indicators is an objective criteria for assessing antioxidant status and is recommended for early detection of oxidative stress in animals.

The highest SOD activity is revealed in a day-old rabbits – 12,04 ± 0,9 c.u. / g, which, in part, can be attributed to the transition from the animal intrauterine to independent life and to significant changes in metabolic processes, accompanied by oxidized-reduced processes intensification and free radicals active generation, the level of which is controlled by antioxidant system. SOD activity has been found out to decrease after the rabbits body postnatal period transition. SOD activity increase to 77% was observed in 90 days old rabbits compared to that of a day-old rabbits which indicates peroxidation process strengthening in animals. It has been found that catalase activity was very high – 5,74 ± 0,16 cat / g in a day-old rabbits heart and its activity decreased further. The lowest catalase activity rates were recorded in the 30-days old animals. However, it should be noted that the catalase activity was the highest – 5,84 ± 0,26 kat / g – in 45-days old animals which indicates peroxidation activity increase at this age. The study reveals that GPO activity in the heart of rabbits from the birth to 90-days age had no significant difference and was 17,6–19,7 mmol/min/g. Such stable figures indicate a close relationship of GPO with NADP ∙ H-cofactor production required to replenish the enzyme activity GSH-regulator. The correlation analysis results proved that enzyme components activity indices of SOD and GPO antioxidant system had a moderate feedback (r = -0,49). This can be accounted for GPO participating in both hydrogen peroxide and lipid peroxides inactivation. Also moderate linear relationship between catalase activity and GPO (r = + 0,38) in the heart of rabbits was determined.

Definition of the body antioxidant system enzyme activity indicators provides better understanding the mechanism of the body's antioxidant defense functioning system and organizing cost-effective and economically efficient rabbits.

Having considered the importance of antioxidant protection as a key metabolic processes that have a direct impact on the animals basic physiological systems functioning, one can say the research in this area are promising and need to be continued.

Key words: catalase, superoxide dismutase, glutathione, antioxidant defense system, heart, rabbits.