Alanyl-Glutamine Attenuates Soybean Meal-Induced Intestinal Dysfunction and Growth Retardation in Largemouth Bass...

This study investigated the mitigating effects of alanyl-glutamine (AG) on soybean-meal-induced enteritis (SBMIE) in largemouth bass (Micropterus salmoides). Three experimental diets were prepared: a fishmeal (FM) diet as a positive control, a 50% soybean meal (SBM) replacement FM protein (SBM50) diet as a negative control, and the SBM50 diet supplemented with 1% AG (SBM50 + 1% AG). Fish (initial weight: 10.20 ± 0.20 g) were distributed into three groups in triplicate (25 fish per tank) and fed for 8 weeks. Results demonstrated that the SBM50 + 1% AG group exhibited markedly higher final body weight, weight gain rate, and specific growth rate compared to the SBM50 (p < 0.05). The SBM50 + 1% AG group markedly elevated serum levels of free glycine, lysine, and total essential amino acids compared to the FM group (p < 0.05). In addition, the SBM50 + 1% AG group markedly increased the intestinal plica height (PH) and goblet cell numbers compared to the SBM50 group (p < 0.05). Pathological alterations, including villous atrophy, nuclear pyknosis, mitochondrial matrix dissolution, and inner membrane disruption, were shown in the SBM50 group, all of which were ameliorated by AG supplementation. In addition, the addition of AG significantly reduced Caspase3 activity compared to the FM group (p < 0.05). Microbiome analysis revealed dietary AG significantly increased α-diversity and the proliferation of potentially beneficial taxa (Bacteroidota, Bacteroides, and Prevotella) (p < 0.05). Transcriptomics showed dietary AG upregulated intestinal barrier-related pathways (including focal adhesion, cell adhesion molecules, and adherens junction), along with tight junction gene expression (zo-1, claudin-3, and filamin-B). In conclusion, high dietary SBM inclusion impairs growth performance and induces intestinal inflammation in largemouth bass. Dietary AG effectively mitigates SBMIE by remodeling the intestinal microbiota, enhancing intestinal barrier integrity, and modulating immune responses.