Effect of Niacin on Growth Performance, Intestinal Morphology, Mucosal Immunity and Microbiota Composition in Weaned Piglets

SIMPLE SUMMARY: The protective effect of niacin on growth performance and gut health of weaned piglets and the underlying mechanism remains unclear despite it being a common additive in pig diets. The present study aimed to investigate the effect of niacin on growth performance, intestinal morphology, intestinal mucosal immunity, and colonic microbiota in weaned piglets. Our results show that niacin supplementation significantly improved the growth performance in piglets as compared with those given a niacin receptor antagonist. Niacin also significantly improved the relative abundance of beneficial bacteria in the colon and alleviate the inflammatory response in the intestinal mucosa as compared with control piglets and those given a niacin receptor antagonist. These results provide new insight into the beneficial effects of niacin on growth performance and gut health in weaned piglets. ABSTRACT: This study aimed to investigate the effects of niacin on growth performance, intestinal morphology, intestinal mucosal immunity, and colonic microbiota in weaned piglets. A total of 96 weaned piglets (Duroc × (Landrace × Yorkshire), 21-d old, 6.65 ± 0.02 kg body weight (BW)) were randomly allocated into 3 treatment groups (8 replicate pens per treatment, each pen containing 4 males; n = 32/treatment) for 14 d. Piglets were fed a control diet (CON) or the CON diet supplemented with 20.4 mg/kg niacin (NA) or an antagonist for the niacin receptor GPR109A (MPN). The results showed that NA or MPN had no effect on ADG, ADFI, G/F or diarrhea incidence compared with the CON diet. However, compared with piglets in the NA group, piglets in the MPN group had lower ADG (p = 0.042) and G/F (p = 0.055). In comparison with the control and MPN group, niacin supplementation increased the villus height and the ratio of villus height to crypt depth (p < 0.05), while decreasing the crypt depth in the duodenum (p < 0.05). Proteomics analysis of cytokines showed that niacin supplementation increased the expression of duodenal transforming growth factor-β (TGF-β), jejunal interleukin-10 (IL-10) and ileal interleukin-6 (IL-6) (p < 0.05), and reduced the expression of ileal interleukin-8 (IL-8) (p < 0.05) compared with the control diet. Piglets in the MPN group had significantly increased expression of ileal IL-6, and jejunal IL-8 and interleukin-1β (IL-1β) (p < 0.05) compared with those in the control group. Piglets in the MPN group had lower jejunal IL-10 level and higher jejunal IL-8 level than those in the NA group (p < 0.05). The mRNA abundance of duodenal IL-8 and ileal granulocyte-macrophage colony-stimulating factor (GM-CSF) genes were increased (p < 0.05), and that of ileal IL-10 transcript was decreased (p < 0.05) in the MPN group compared with both the control and NA groups. Additionally, niacin increased the relative abundance of Dorea in the colon as compared with the control and MPN group (p < 0.05), while decreasing that of Peptococcus compared with the control group (p < 0.05) and increasing that of Lactobacillus compared with MPN supplementation (p < 0.05). Collectively, the results indicated that niacin supplementation efficiently ensured intestinal morphology and attenuated intestinal inflammation of weaned piglets. The protective effects of niacin on gut health may be associated with increased Lactobacillus and Dorea abundance and butyrate content and decreased abundances of Peptococcus.