PSVII-21 Functional requirement of niacinamide for intestinal health and growth performance of nursery pigs.

Abstract Weaning stress impairs intestinal health and growth in nursery pigs. Niacinamide, a bioavailable form of niacin, supports energy metabolism and cellular function, and shows promise as a nutritional intervention during the post-weaning phase. However, the use of low-protein diets to reduce nitrogen emissions and diarrhea risk has decreased dietary niacin intake from conventional sources, such as soybean meal, highlighting the need to reassess optimal niacinamide supplementation levels. This study aimed to evaluate the functional requirement of niacinamide in low-protein diets and its effects on growth performance and intestinal health in nursery pigs. Sixty-four pigs (7.9 ± 0.7 kg, weaned at d 28) were randomly assigned to four dietary treatments with increasing levels of niacinamide (30, 130, 230, and 330 mg/kg) for 28 days. Each level had four replicate pens, each containing four pigs. On d 28, one piglet per replicate with a body weight closest to the treatment average was selected and euthanized to sample duodenum, jejunum, and ileum tissue and colonic digesta (n = 4). Parameters assessed included growth performance, gut morphology, colonic volatile fatty acids (VFA), colonic microbiome, and metabolomic profiles. Data was analyzed using SAS 9.4 (Cary, NC, USA), and polynomial contrasts were used to assess linear and quadratic effects of increasing niacinamide levels. Niacinamide supplementation linearly increased (P < 0.05) villus height and villus-to-crypt ratio, while reducing (P < 0.05) crypt depth across all intestinal segments. Total colonic VFAs and acetic acid concentrations also increased linearly (P < 0.05) with the increasing niacinamide levels. Additionally, the abundance of Lactobacillus in the colonic content was highest (P < 0.05) in the 330 mg/kg group, whereas the proportions of Streptococcus and SMB53 were lower (P < 0.05) than in the other groups. Metabolomic differences between the 30 and 330 mg/kg groups were enriched in pathways related to protein digestion and absorption, amino acid metabolism, and glutathione metabolism. The gain-to-feed ratio (G:F) showed a quadratic response (P < 0.05), with the highest value at 139 mg/kg niacinamide in feed on d 1-28. The diarrhea occurrence showed a quadratic response (P = 0.072), with the lowest value at 314 mg/kg in feed. In conclusion, nicotinamide requirements in nursery pigs fed low-protein diets vary by functional objective: a supplementation level of 130 mg/kg is sufficient to optimize feed efficiency, whereas 330 mg/kg is required to achieve maximal improvements in intestinal morphology, microbial fermentation, and gut microbial composition. These results highlight the importance of selecting nicotinamide inclusion levels based on specific health and performance targets.