The aim of the current study was to analyse the effect of different doses of a new probiotic (produced in Ukraine from Saccharomyces cerevisiae) in the feed on the production of nitrogen metabolites in the rumen, enzymatic activity of the digestive tract microbiota and growth rate of young ewes. The experiments showed that the supplementation of the probiotic EnzActive at doses of 0.4, 0.8 and 1.2% (w/w) to concentrate feed for 11–12 month old sheep had a positive effect on the production of nitrogen compounds, enzymatic activity of the rumen microbiota and animal growth intensity. It was proven that the introduction of the specified probiotic at a dose of 1.2% significantly increased the production of total nitrogen and amylolytic, proteolytic and cellulolytic activity of the rumen microbiota compared to animals that did not receive it. It was also found that the highest significant indices of animal growth rate during the experimental period were obtained for 0.8% probiotic supplementation.