# Proteomic Identification and Quantification of Basal Endogenous Proteins in the Ileal Digesta of Growing Pigs

## TL;DR

This study uses proteomics to identify and quantify endogenous proteins in the ileal digesta of pigs to better estimate nutrient losses based on diet.

## Contribution

The study introduces a proteomic approach to analyze diet-induced variations in endogenous protein composition in pigs.

## Key findings

- A nitrogen-free diet increased proteins linked to intestinal inflammation and autophagy.
- A casein diet increased proteins related to digestive secretions.
- 348 proteins were identified, with 101 showing significant differences between diets.

## Abstract

As variations in the determination of basal endogenous losses can affect the estimation of the nutritional value of diets, this study used a proteomics approach to identify the composition of endogenous proteins in the ileal digesta of growing pigs fed with a nitrogen-free diet and a casein diet. The nitrogen-free diet increased the expression of proteins related to intestinal inflammation, the activation of innate antimicrobial host defense, cellular autophagy, and epithelial turnover in the ileal digesta. In contrast, the casein diet increased the proteins related to pancreatic and intestinal digestive secretions. These findings suggest that a casein diet could provide a more accurate estimation of basal endogenous losses.

The accurate estimation of basal endogenous losses (BEL) of amino acids at the ileum is indispensable to improve nutrient utilization efficiency. This study used a quantitative proteomic approach to identify variations in BEL in the ileal digesta of growing pigs fed a nitrogen-free diet (NFD) or a casein diet (CAS). Eight barrow pigs (39.8 ± 6.3 kg initial body weight (BW)) were randomly assigned to a 2 × 2 crossover design. A total of 348 proteins were identified and quantified in both treatments, of which 101 showed a significant differential abundance between the treatments (p < 0.05). Functional and pathway enrichment analyses revealed that the endogenous proteins were associated with intestinal metabolic function. Furthermore, differentially abundant proteins (DAPs) in the digesta of pigs fed the NFD enriched terms and pathways that suggest intestinal inflammation, the activation of innate antimicrobial host defense, an increase in cellular autophagy and epithelial turnover, and reduced synthesis of pancreatic and intestinal secretions. These findings suggest that casein diets may provide a more accurate estimation of BEL because they promote normal gastrointestinal secretions. Overall, proteomic and bioinformatic analyses provided valuable insights into the composition of endogenous proteins in the ileal digesta and their relationship with the functions, processes, and pathways modified by diet composition.