The use of probiotics in animal feed is one of the most promising alternatives to the application of antibiotics. In order to establish the effectiveness of the use of a complex probiotic supplement (Lactobacillus spp., Lactococcus spp., Spirulinaceae, Saccharomyces cerevisiae, Actinomycetaceae, Aspergillus spp. and Penicillium spp.) in pig farming, two groups of pigs of the Poltava Meat breed were formed by the analog method. In the ration of the fattening pigs of the experimental group, 1.0% of the mass of compound feed was replaced with a complex probiotic supplement, which was fed during the 45 days of the experimental period at the age of 135 to 180 days. In experimental pigs, biochemical blood parameters were determined (the content of protein, lipids, cholesterol, triglycerides, activity of aspartate aminotransferase and alanine aminotransferase, the content of creatinine, glucose, calcium, phosphorus, albumins and globulins) using test kits from the company "Filisit Diagnostics" (UA). As a result of the research, it was established that with the use of a complex probiotic feed supplement, the content of total protein in the blood serum of the pigs of the experimental group was higher by 18.4%, glucose by 21.4%, aspartate aminotransferase activity by 20.4%, alanine aminotransferase by 38.0% compared to control group. In both groups, regardless of the established difference, the named indicators were within the physiological norm. The concentration of cholesterol in the blood of pigs receiving the probiotic supplement decreased by 43.2%, but the concentration of calcium (by 26.2%) and phosphorus (by 17.9%) increased. In the experimental group, the blood indicators related to the immunity of pigs improved – the content of α1 and α2 globulins decreased by 4.1% and 7.4%, respectively. Also, in the experimental group, the concentration of albumins increased by 7.5%, which probably indicates an improvement in the functional state of the liver. As a result of feeding with a complex probiotic supplement in the experimental group the albumin-globulin ratio improved, which increased by 35.0%. Thus, the introduction of a complex probiotic feed additive into the ration of pigs changed the structure of the influence of exogenous and endogenous factors on metabolism, had a positive effect on the protein profile of the blood, and caused an increase of average daily gains in experimental animals by 5.8% compared to the control group.