Effects of betaine supplementation in a high carbohydrate diet feed on intestinal health of juvenile largemouth bass ( <i>Micropterus salmoides</i> )

This study aimed to investigate the effects of betaine supplementation in a high-carbohydrate diet on the intestinal health of juvenile largemouth bass ( Micropterus salmoides ). Six diets were formulated: a low-carbohydrate diet (8% corn starch), a high-carbohydrate diet (20% corn starch), and the HC diet supplemented with 0.5%, 1.0%, 1.5%, or 2.0% betaine (HCB1–HCB4). A total of 270 juvenile largemouth bass with an initial body weight of 4.34 ± 0.11 g were subjected to a 56-day feeding trial. The experimental results showed that 0.5% betaine significantly improved the weight gain rate (WGR) and specific growth rate (SGR) of juvenile largemouth bass. In terms of antioxidant capacity, the levels of total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) in the intestine were markedly enhanced in the HCB groups, while 1.0% betaine significantly elevated intestinal glutathione (GSH) levels (P &lt; 0.05). Regarding intestinal histomorphology, betaine supplementation improved the intestinal histological structure, significantly upregulated the expression levels of zonula occludens-1 (ZO-1) and Occludin in the intestine, and notably augmented intestinal Claudin-1 expression in the 1% and 1.5% betaine groups (P &lt; 0.05). Furthermore, betaine reduced intestinal mucosal permeability, as evidenced by a significant decrease in serum diamine oxidase (DAO) levels (P &lt; 0.05). Additionally, betaine alleviated intestinal inflammation: specifically, 0.5% and 1% betaine markedly suppressed the expression of nuclear factor kappa-B (NF-κB), interleukin-8 (IL-8), and cyclooxygenase-2 (COX-2), while the expression level of interleukin-10 (IL-10) was significantly upregulated in the HCB groups (P &lt; 0.05). Concomitantly, supplementation with 0.5% betaine significantly boosted the relative abundance of Actinobacteria, whereas supplementation with 1% and 1.5% betaine significantly decreased the relative abundances of Proteobacteria and Enterobacteriaceae (P &lt; 0.05). In conclusion, dietary supplementation with 0.5%–1.5% betaine can significantly improve the intestinal health of juvenile largemouth bass.