Standardized feeding of young cattle should be based on scientifically based standards, guaranteeing their genetic productivity potential, rational use of fodder resources, and proper feed payment with meat products. The current situation regarding the rationing of livestock feeding in global and domestic, both scientific and industrial practices, has fundamentally changed, which requires a significant revision of the traditional provisions on the organization of standardized feeding and feeding of farm animals. At the same time, the conceptual requirements for the organization of standardized feeding of young livestock should be based on the generalization of world experience in need of animals for energy, nutrients, and biologically active substances, taking into account the age period of fattening with an emphasis on the quality and biosafety of products. In the conditions of intensive production of meat products, to ensure high productivity, it is impossible to do without using feed products of natural substance, which should include additives with a purely biological effect. One of these includes the feed additive “EnzActive”, which contains a unique formula of a combination of biotic and enzymatic action, which consists of live yeast of the genus Saccharomyces cerevisiae, and a complex of six enzymes: protease, cellulose, xynalose, α-amylase, ß-gluconase and phytase. The research was based on optimizing the standardized feeding of fattening young animals on hay-type rations using the probiotic feed additive “EnzActive” based on 8 g/head per day. The research was conducted on Simmental bulls in the conditions of the “Pchany-Denkovych” farm of the Stryi district of the Lviv region. It was established that the use of the probiotic supplement “EnzActive” against the background of hay-type feeding contributed to the improvement of the intensity of the vital activity of the physiologically helpful microflora of the rumen, which had a stimulating effect in the processes of additional assimilation of nutrients. A positive result was obtained regarding the level of average daily growth and functional features of rumen microflora, the final period of fattening. Thus, based on the results of our research, it is possible to recommend introducing the hay type with the inclusion of probiotic feed additive “EnzActive” at the rate of 8 g/head into the intensive livestock technology fattening a day. No adverse side effects of “EnzActive” bio-additives on the general functional condition of young bull's residents were found.