Impacts of 360 mg/kg Niacinamide Supplementation in Low-Protein Diets on Energy and Nitrogen Metabolism and Intestinal Microbiota in Growing-Finishing Pigs.

This study aimed to investigate the effects of adding 360 mg/kg niacinamide (NAM) to diets on nutrient metabolism, providing insights into how dietary NAM supplementation enhances nitrogen utilization and growth performance in pigs. Forty growing-finishing pigs were randomly assigned to one of four experimental diets as follows: basal diet + 30 mg/kg NAM (CON), basal diet + 360 mg/kg NAM (CON + NAM), low-protein diet + 30 mg/kg NAM (LP), and low-protein diet + 360 mg/kg NAM (LP + NAM). Results showed that supplementation of both the CON and LP diets with 360 mg/kg NAM resulted in decreased urea nitrogen concentrations and carbamyl phosphate synthetase-I activity (p < 0.05). The pyruvate dehydrogenase activity in the serum and liver, as well as the activity of pyruvate dehydrogenase, citrate synthase, and glutamate dehydrogenase 1 in the ileum mucosa, was increased by supplementing the LP diet with 360 mg/kg NAM (p < 0.05). The LP diet with 360 mg/kg NAM increased the villi length to crypt depth, mRNA expression of glucose transporters 1 and 2 and alanine-serine-cysteine transporter 1, and mRNA expression of mechanistic target of the rapamycin 1 in the ileum (p < 0.05). Additionally, 360 mg/kg NAM supplementation in the LP diet reduced ileal Lactobacillus abundance (LDA > 4) and increased ileal microbial nucleotide and purine metabolism (p < 0.05). Our findings suggest that addition of 360 mg/kg NAM to the LP diet reduced urea production in the liver, enhanced glucose and amino acid absorption and transport in the ileum, and improved glucose metabolism.