What question did this study set out to answer?

This study aims to explore how different dietary protein sources influence nitrogen metabolism and gut microbiota in pigs.

July 12, 2026Open Access

Differential effects of dietary protein sources on nitrogen metabolism and ileal microbiota in pigs correlated with amino acid release rates

WWWenqiang WangNanjing Agricultural University WZWenxuan ZhaoMorgridge Institute for Research LPLong PanNanjing Agricultural University

Key Points

This study aims to explore how different dietary protein sources influence nitrogen metabolism and gut microbiota in pigs.
Twenty-four finishing pigs were housed in metabolic cages and randomly assigned to three diet groups over 8 weeks.
Fish meal and rapeseed meal replaced 50% of soybean meal to create different dietary treatments.
Nitrogen metabolism and gut microbiota were assessed through various biochemical and microbiological analyses.
RPM diet increased fecal nitrogen and reduced urinary nitrogen, blood urea nitrogen, and blood ammonia levels.
RPM group showed higher ileal microbial diversity with changes in relative abundances of specific microbial genera.
Amino acid release rates were negatively correlated with fecal nitrogen and positively correlated with urinary nitrogen and specific microbial abundances.

Abstract

Abstract Background Dietary protein source is one of the primary factors influencing host nitrogen metabolism and intestinal microbiota. However, conventional diet formulations primarily focus on overall nutritional levels, overlooking the differences in amino acid release rates among various protein sources. This study investigates how different protein sources affect nitrogen metabolism and gut microbiota in finishing pigs. Methods The corn-soybean meal diet served as the control (SBM). Fish meal and rapeseed meal isonitrogenously replaced 50% of soybean meal to formulate FM and RPM diets. Twenty-four finishing pigs (DLY; 53.40 ± 2.53 kg) were housed individually in metabolic cages, randomly assigned to three groups ( n = 8), and fed for 8 weeks. Results Feeding the three diets had no significant effect on the growth performance of finishing pigs. Compared with SBM and FM, RPM diet significantly increased fecal nitrogen, but reduced urinary nitrogen, blood urea nitrogen and blood ammonia levels, reduced free amino acids in the small intestinal chyme and plasma, downregulated expressions of amino acid transporters, and showed slower in vitro amino acid release, collectively indicating less amino acid release into the small intestinal lumen and consequently less amino acids into the circulation. In addition, compared with the SBM and FM groups, RPM exhibited increased ileal microbial diversity, characterized by lower relative abundances of Streptococcus , Staphylococcus and higher relative abundances of Lactobacillus , Turicibacter . Additionally, microbial cell amino acids and microbial cell protein concentrations were significantly reduced in the RPM group. Correlation analysis showed that the amino acid release rate was negatively correlated with fecal nitrogen, the relative abundance of Lactobacillus and Turicibacter , while positively correlated with urinary nitrogen, blood urea nitrogen, the relative abundance of Streptococcus and Staphylococcus , microbial cell protein, and total microbial cell amino acid content. Conclusion Dietary protein sources altered host nitrogen metabolism and restructured the ileal microbiota, with the rate of amino acid release appearing to be a key factor associated with these changes.

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