Functional Requirement of Niacinamide for Blood Profiles, Antioxidant Status, and Intestinal Health in Finishing Pigs Fed a Low-Protein Diet

This study investigated the effects of dietary niacinamide supplementation on blood parameters, antioxidant status, and intestinal health in finishing pigs fed low-protein diets. Sixty-four pigs (Duroc × Landrace × Yorkshire; 80.4 ± 0.1 kg) were randomly allocated to four dietary treatments supplemented with 30 (NAM30), 130 (NAM130), 230 (NAM230), and 330 (NAM330) mg/kg niacinamide for 30 days. Each treatment had four replicate pens and four pigs per pen. Growth performance was not significantly affected. However, the NAM130 group showed higher (<i>p</i> < 0.05) hemoglobin levels, reduced (<i>p</i> < 0.05) serum malondialdehyde and interleukin-1β (IL-1β) concentrations, and altered intestinal microbiota composition, including lower <i>Streptococcus</i> abundance (<i>p</i> < 0.05). Serum alanine aminotransferase levels increased quadratically (<i>p</i> < 0.05) with niacinamide supplementation, with a breakpoint at approximately 221 mg/kg. These results suggest that dietary supplementation with 130 mg/kg niacinamide improves antioxidant status, modulates inflammation, and supports intestinal microbial balance, with a safety threshold to avoid hepatic stress.