Regulation of Sturgeon Growth, Immunity, and Intestinal Microbiota by Lactococcus lactis and Its Selenium-Enriched Product as an Alternative to Antibiotic: Advantages and Limitations of Inorganic Selenium

This study evaluated Lactococcus lactis RDN-1 and its inorganic selenium-enriched derivative in hybrid sturgeon, focusing on growth performance, immune responses, and intestinal health. A 21-day feeding trial was conducted with four groups: control (CK), L. lactis RDN-1 (R), inorganic selenium-enriched L. lactis RDN-1 (RX), and enrofloxacin (E). All supplemented groups exhibited significantly improved weight gain. The R group attained the highest levels of most essential and total amino acids, whereas the RX group achieved the highest methionine content. In contrast, the E group exhibited significantly lower levels of most amino acids compared to the R and RX groups. The R group suppressed the abundance of Proteobacteria while enriching beneficial genera such as Lactococcus, thereby enhancing functional capacities related to energy metabolism, amino acid biosynthesis, and signal transduction. The RX group promoted Firmicutes and Bradyrhizobium, and exhibited superior functional characteristics in antioxidant capacity and secondary metabolite biosynthesis. Moreover, the RX group down-regulated IL-6, demonstrating a balanced immunomodulatory effect with anti-inflammatory potential. In conclusion, L. lactis RDN-1 and its selenium-enriched derivative represent promising antibiotic alternatives. L. lactis RDN-1 alone offers more comprehensive effects, whereas inorganic selenium supplementation partially impairs its overall performance but achieves more accurate immune regulation. This work provides a scientific foundation for the precise application of L. lactis.