The work concerns the study of the reproductive qualities of sows that received, in addition to the main diet, a biologically active preparation (monoprotein) synthesized from brewer’s yeast waste. For this purpose, two groups of sows were formed, experimental and control ones containing 5 animals in each group. The preparation was administered in addition to the main diet of sows 30 days before farrowing and 10 days after farrowing at 3.3 mg per 1 kg of feed. It was found out that the enrichment of rations for pregnant sows with a biologically active preparation (monoprotein) allows an increase in the number of born piglets by 1.6 heads more than in the control group. There were 0.8–0.31 stillborn piglets in the experimental group or 1.0 piglets less compared to the control group. Enrichment of the diets of sows 30 days before farrowing with a biologically active agent had a positive effect on the live weight of the nest at birth and on the 21st day. The average live weight of piglets in the nest of the experimental group was 0.85 kg higher than the average live weight of piglets in the nest of the control group. The average live weight of one piglet at birth in the experimental group was 1.7 kg, and in the control group 1.4 kg, which is 0.3 kg less. Hematological and biochemical blood tests were studied at the beginning and at the end of the experiment, as well as the amino acid, macro and microelement composition of the preparation.