The intensive development of animal husbandry at the present stage requires new approaches to organizing the feeding of farm animals and the introduction of modern feed additives, which are not normally used purely as feed, but are deliberately added to feed or water to improve their quality, increase productivity and animal welfare. To prevent the development of oxidative stress in animals, we used the feed additive "Butaselmevit-plus", which in its composition contains the fruits of milk thistle, selenium, methionine and vitamins A, E and D3. The aim of the study was to investigate the effect of feed additive Butaselmevit-plus on blood morphological parameters and protein synthesis of rat liver under tetrachloromethane poisoning. For research, we used Wistar male rats, which were divided into three groups of 20 animals each. Control rats were intact. The first and second experimental group of rats were administered tetrachloromethane. Experimental intoxication in animals was performed by twice (after 48 h) intragastric administration of tetrachloromethane at a dose of 0.1 ml per 100 g of rat body weight in the form of a 50% oil solution. Experimental group R2 was fed a feed additive of Butaselmevit-plus for a dose of 0.1 g per 100 g of body weight together with the feed for experimental toxicosis for 30 days. On the basis of the conducted researches positive effect of feed additive "Butaselmevit-plus" on the organism of rats, which were intoxicated with tetrachloromethane, is shown, which is shown by normalization of hematological parameters and protein synthesis of liver function. Restoration of hematopoietic function of bone marrow of rats by intoxication with tetrachloromethane is due to the fact that the feed additive "Butaselmevit-plus" contains in its composition fruits thistle, which have a high level of vitamins A and K, and trace elements, namely: Ferum, Cuprum and Cobalt that are directly involved in hematopoiesis. When feeding Butaselmevit-plus as feed supplement, the number of red blood cells in the blood of the second experimental group of rats was higher than that of the first experimental group, but the control values reached only on the 30th day of the experiment. When using the feed additive Butaselmevit-plus in rats under conditions of oxidative stress development, the leukocyte count decreased to the optimum level.