Adaptation of bifidobacteria and lactic acid bacteria to nutrient media with increased concentrations of bile (1%) and protein substrates of animal origin allowed the variants resistant to bile and displaying a high production of proteolytic enzymes (active within the pH range of 2.5-9.0) to be selected. Administration of the preparations involving the selected bifidobacteria and lactic acid bacteria assisted in the normalization of the intestinal microflora and activation of protein metabolism in the organism of animals. Specifically, it increased the total protein level in blood serum and redistributed protein fractions, increasing the content of globulins and decreasing albumin concentration.