In their review, the authors present the results of research evaluating the effect of fermented liquid feed on the performance and digestive health of weaned piglets and fattening pigs. Based on the available literature, it is advisable to carry out controlled fermentation instead of spontaneous fermentation, because by inoculating the feed / raw materials with specific lactic acid bacteria, the fermentation process goes in the right direction, lower pH values can be achieved within the same timeframe, which all help to control the acid-sensitive pathogenic microbes. The fermentation of only certain raw materials, as opposed to a complete diet, has the advantage of better controllability, and the incorporation of these fermented end products into final diets provides farms with increased flexibility. During fermentation, the particle size of the feed / raw materials and the levels of antinutritive substances are reduced, thereby increasing their digestibility. Feeding studies have shown that improvement in nutrient utilization is primarily due to better bioavailability of nutrients, as opposed to increased feed intake. Several works have demon-strated that fermented liquid feeds significantly reduce the pH of gastric juice, Salmonella spp. levels and the chance of developing diarrhoea caused by coliforms in piglets. Fermented feeds support gut health, thus also playing an immunomod-ulatory role. Taking all this into account, the authors believe that fermented liquid feeds in nutrition of pigs may be an effective alternative after the antibiotic reduction provisions come into force in the European Union in 2022.