Under the influence of microorganisms 95 % of sugars and starch, 70 % of fiber and 40–80 % of protein are broken down in the fore stomachs. Since the microfl ora of the rumen cannot always cope with the digestion of a large amount of coarse feed, enzyme drugs designed to increase productivity and preserve animal health come to their aid. The use of enzyme additives is relevant and allows us to prevent the action of anti-nutritional factors of feed, increase the activity of endogenous enzymes, thereby contributing to the increase in metabolic processes in the body and increase milk productivity. The purpose of this work was to study the features of microbial processes in the rumen of lactating cows when the multicomponent enzyme feed additive Kormomix® Enzyme was included. The use of the enzyme additive aff ected the physics and chemical parameters of the rumen fl uid. The pH concentration in all groups was the same. The volatile fatty acids in the 2nd and 3rd experimental groups were on the same level as the control. In the 1st experimental group, there was a decrease in volatile fatty acids by 1,15 mmol/100 ml compare with control group. The assimilation of ammonia in animals of the 2nd experimental group, which received 50 g /head /day of the enzyme additive, was higher in compare with the control group. The ratio of volatile fatty acids in the rumen fluid of cows of the experimental groups has changed towards the increase in the proportion of acetic acid. The composition of the bacterial community of the rumen improved with the inclusion of 50 g/head/day of the enzyme additive Kormomix® Enzyme. The number of cellulolytic microorganisms exceeded the control level by 6,45 abs.%. Thus, the use of the enzyme additive led to the intensification of microbiological processes in the rumen of cows.