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

## TL;DR

Adding 360 mg/kg niacinamide to low-protein pig diets improves nitrogen and energy metabolism and changes gut microbiota.

## Contribution

This study reveals how niacinamide supplementation modulates metabolism and microbiota in pigs on low-protein diets.

## Key findings

- Niacinamide reduced urea nitrogen and enhanced glucose and amino acid absorption in pigs.
- Supplementation improved intestinal morphology and enzyme activity in the ileum.
- Niacinamide altered gut microbiota, reducing Lactobacillus and increasing nucleotide metabolism.

## Abstract

Enhancing nutrient metabolism, particularly amino acid metabolism, in animals is a crucial strategy for improving protein utilization efficiency, reducing nitrogen excretion, and conserving protein feed resources. In this study, we found that the use of high levels of nicotinamide effectively reduced urea nitrogen production in the liver of growing–finishing pigs, enhanced glucose and amino acid absorption in the ileum, and altered microbial nucleotide and purine metabolism. These metabolic alterations were accompanied by improved intestinal morphology and elevated activity of key tricarboxylic acid cycle enzymes in the ileum. These findings not only enhance our understanding of the role of dietary nicotinamide in modulating host–microbiome interactions but also establish a theoretical foundation with minimized nitrogen excretion.

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.