Simple Summary
Prolonged feeding of high-concentrate diets to ruminants often promotes the overgrowth of Gram-negative bacteria within the rumen, thereby increasing the risk of lipopolysaccharide (LPS) release and subsequent low-grade systemic inflammation. While antibiotics can mitigate some of these effects, their use as growth promoters is now restricted or prohibited in numerous countries. Consequently, attention has shifted toward finding safer alternatives. Astragalus membranaceus (AM) is one of the most promising plant-based additives in this category. This study employed a combined analysis of the rumen-fluid microbiome and metabolome to explore associations between AM-containing diets and immune markers in lambs on a high-concentrate finishing diet. The results indicated that changes in inflammatory and humoral immune markers were associated with AM-containing high-concentrate diets and concurrent changes in rumen fermentation, remodeling of the microbial community, and regulation of immune-related metabolic pathways on a high-concentrate diet. These correlative findings point to parallel associations among rumen-fluid microbiome shifts, metabolic alterations, and immune marker changes. However, as these findings are correlational, direct causal relationships within this triad remain to be established.
Abstract
This exploratory study was designed to investigate associations between AM-containing high-concentrate diets and immune markers in Dumeng lambs and to generate hypotheses regarding concurrent changes in rumen fermentation, liquid-associated rumen microbial community structure, and metabolic profiles. Eighteen healthy male Dumeng lambs were randomly assigned to three groups with six lambs per group (n = 6). The CON group served as the control, while the T1 and T2 groups were supplemented with 1% and 2% AM, respectively. The results showed that compared with CON, lambs fed AM-containing diets had higher ruminal NH3-N (10.88 vs. 12.01 and 12.10 mg/100 mL, p < 0.01) and TVFA (73.78 vs. 85.39 and 87.22 mmol/L, p < 0.05) concentrations, lower acetate proportion (52.16% vs. 47.64% and 46.55%) and acetate-to-propionate ratio (p < 0.01), and higher butyrate proportion in the 1% and 2% AM groups (5.58% vs. 8.55 and 9.31%, p < 0.01). Endpoint-level immune effects survived BH-FDR correction (q < 0.05); Tukey-adjusted pairwise comparisons showed that T2 lambs had lower IL-6 (58.97 vs. 91.35 pg/mL), TNF-α (137.80 vs. 182.38 pg/mL), rumen LPS (109.33 vs. 141.25 ng/mL), and serum LPS (59.67 vs. 81.07 ng/mL), and higher IL-10 (123.14 vs. 87.88 pg/mL), TP (73.50 vs. 67.72 g/L), ALB (28.69 vs. 24.47 g/L), IgA (15.42 vs. 8.52 μg/mL), and IgG (18.38 vs. 11.73 μg/mL) than CON. Exploratory 16S rRNA analysis showed nominally lower Proteobacteria and higher Shuttleworthia in T2; however, no taxon survived BH-FDR correction (q ≥ 0.05), and ANCOM W and LEfSe LDA results are exploratory sensitivity findings only. Exploratory metabolomics suggested associations with purine and nucleotide metabolism; KEGG analysis used uncorrected p values and is hypothesis-generating only. These correlational findings indicate that AM-containing high-concentrate diets are associated with changes in several immune markers; because diets also differed in ingredients other than AM, causality, clinical benefits, and the independent effect of AM remain to be established.