The objective of the study was to evaluate the influence of dietary vitamin E and olive polyphenols on the oxidative stress caused by a high intake of n-3 PUFA in broiler chickens and growing pigs. Research was divided into three sections: the synergistic effect of vitamin E with vitamin C and Se on broilers, the effect of olive leaf extract rich in olive polyphenols versus vitamin E in growing pigs, and the influence of olive leaf and marigold extract on the apparent digestibility of nutrients in broilers. In these studies, vitamin E was the most effective antioxidant for the prevention of oxidative stress caused by the dietary intake of n-3 PUFA, and vitamin C and Se did not have a synergistic effect with vitamin E in chickens. Similar results were obtained in growing pigs, in which vitamin E was a more effective defence than the olive leaf extract, and the effect of the extract was not concentration-dependent. In the third part of the thesis, we observed that the olive leaf extract did not affect the utilization of nutrients in broiler chickens, nor did it affect the mineralization of bones. From the results of the research we concluded that the most effective antioxidant to protect animals against oxidative stress is vitamin E, and that it is still premature to replace it with the olive leaf extract, although extract does not negatively affect the animals.
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