# Moderate Reduction in Dietary Protein Improves Muscle Composition and Modulates Gut Microbiota and Serum Metabolome Without Compromising Growth in Finishing Pigs

## TL;DR

Reducing dietary protein in finishing pigs improves muscle composition and gut health without harming growth, offering a sustainable approach for pork production.

## Contribution

The study shows that moderate protein reduction, when balanced with essential amino acids, can enhance pork quality and gut microbiota while reducing nitrogen emissions.

## Key findings

- Moderate protein reduction maintained growth performance and nutrient digestibility in pigs.
- Low-protein diets altered muscle fatty acid composition and amino acid profiles.
- LPDs reshaped gut microbiota and serum metabolites, affecting lipid and amino acid metabolism.

## Abstract

Reducing dietary protein is an effective way to decrease nitrogen emissions and feed costs in pig production, but concerns remain about whether this affects growth performance and meat quality. This study examined how low-protein diets (LPDs) affect growth, meat quality, gut microbiota, and metabolism in finishing pigs. Results showed that moderate protein reduction, when balanced with essential amino acids, maintained growth and nutrient digestibility. However, protein levels influenced muscle fatty acid composition and amino acid profiles. LPDs also reshaped gut microbiota and serum metabolites, indicating adjustments in lipid and amino acid metabolism. Overall, moderate protein reduction can improve meat quality and gut health while reducing nitrogen output, offering a sustainable nutritional strategy for swine production.

Reducing dietary crude protein (CP) while sustaining growth performance and minimizing nitrogen emissions is a critical challenge in swine production. Beyond growth efficiency, the influence of low-protein diets (LPDs) on meat quality traits, gut microbiota, and systemic metabolism in finishing pigs remains insufficiently understood. In this study, 180 healthy crossbred finishing pigs (Duroc × Liangguang Small Spotted; initial body weight 85.49 ± 4.90 kg) were assigned to three dietary regimens for 35 days (six replicate pens per treatment, ten pigs per pen, male/female = 1:1): Control (CON, 15.5% CP), Low-Protein 1 (LP1, 14.5% CP), and Low-Protein 2 (LP2, 13.5% CP). Growth performance and nutrient digestibility were not impaired by protein reduction. Notably, LP1 pigs exhibited thicker backfat (p < 0.05), while LP2 pigs showed decreased concentrations of specific fatty acids (C12:0–C22:1n9) and essential amino acids (aspartic acid, glutamic acid, lysine) compared with LP1 (p < 0.05), indicating that dietary protein levels affected muscle composition. Cecal microbiota analysis revealed distinct shifts, with Prevotella spp., Faecalibacterium spp., and Plesiomonas spp. enriched in CON, whereas LP1 promoted Eubacteriaceae spp., Christensenellaceae spp., and Clostridia spp. (p < 0.05). Serum metabolomics further distinguished groups: LP1 reduced bile secretion and cholesterol metabolism pathways (p < 0.05) and LP2 further suppressed cholesterol metabolism and primary bile acid biosynthesis (p < 0.05), with a trend toward reduced phenylalanine metabolism (p = 0.07). Collectively, these findings demonstrate that moderate dietary protein reduction, when balanced with essential amino acids, maintains growth, reduces nitrogen output, and beneficially alters muscle composition, gut microbiota, and host metabolic pathways, offering nutritional strategies to enhance pork quality and promote sustainable pig production.