Effects of adding niacinamide to diets with normal and low protein levels on the immunity, antioxidant, and intestinal microbiota in growing-finishing pigs

This study aimed to investigate the effects of nicotinamide (NAM) applied to diets with different crude protein levels on immune function, antioxidant capacity, and intestinal flora in growing-finishing pigs. Forty barrows (37.0 ± 1.0 kg) were randomly allocated to one of four dietary treatments (n = 10 per group). The diets in the two phases consisted of a basal diet with 30 mg/kg NAM, a basal diet with 360 mg/kg NAM, a low-protein diet with 30 mg/kg NAM, and a low-protein diet with 360 mg/kg NAM. The results showed that dietary addition of 360 mg/kg NAM decreased IL-12, malondialdehyde, IgG and IgM contents in the plasma and increased total superoxide dismutase activity and total antioxidant capacity in the colonic mucosa (P < 0.05). Supplementing the diet with 360 mg/kg NAM increased mRNA expression of the nucleotide-binding oligomerization domain containing 2 and nuclear factor erythroid 2-related factor 2 and protein expression of nuclear factor kappa-B and toll-like receptor 4 in the colonic mucosa (P < 0.05). The concentrations of acetic acid and butyric acid in the colonic contents and the abundance of Actinobacteriota in the colon at the phylum level were significantly decreased by feeding low-protein diets (P < 0.05). Additionally, the addition of 360 mg/kg NAM to diets increased (P < 0.05) the Sobs, Ace, and Chao indices of colonic microorganisms in pigs. Overall, the rational use of NAM can improve inflammatory status, enhance antioxidant capacity and intestinal barrier function, and increase colonic microbial diversity in growing-finishing pigs.