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

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.

Comparative study of protease hydrolysis reaction demonstrating Normalized Peptide Bond Cleavage Frequency and Protease Substrate Broadness Index

Two commercial proteases (subtilisin-typed FNA from Bacillus amyloliquefaciens, and chymotrypsin-like NPP from Nocardiopsis prasina), porcine pepsin, porcine pancreatin having protease activity and their combinations were studied in vitro by LC-MS for their ability to digest soy protein isolate (SPI) under conditions close to those found in the stomach (pH 3.7) and small intestine (pH 6.5). The total number of peptides generated, and their size distribution were obtained under each set of the digestion conditions. These peptides were grouped according to their C-terminal amino acid (AA) residue (P1) and mass, based on which two concepts were proposed, i.e., Normalized Peptide Bond Cleavage Frequency (NPBCF) and Protease Substrate Broadness Index (PSBI). At pH 3.7, FNA+pepsin increased PSBI vs. pepsin alone by 2.7 and 4.9 percentage points (p.p.) at a SPI:protease ratio of 20:1 and 100:1, respectively. At pH 6.5, FNA+pancreatin improved PSBI by 9.1 and 10.2 p.p. at SPI:protease 20:1 and 100:1, respectively, vs. pancreatin alone. NPP generated 38% more peptides than FNA when administered with pancreatin at SPI:protease 200:1:1 and pH 6.5, but FNA alone (28.9) or FNA+pancreatin (29.1) gave a higher PSBI than pancreatin (22.2), NPP (20.3) and NPP+pancreatin (22.0). At pH 3.7 FNA generated 59% and 39% of peptides of pepsin at SPI:protease of 20:1 and 100:1, respectively, and both groups of peptides had similar size distribution. At pH 6.5 more small sized peptides were generated by FNA or FNA+pancreatin than pancreatin and NPP alone or pancreatin+NPP. In conclusion, FNA showed complementary effects with pepsin and pancreatin in terms of PSBI and generated more small sized peptides compared to NPP.

Contribution of individual broilers to variation in amino acid digestibility in soybean meal and the efficacy of an exogenous monocomponent protease

A total of 72 male Ross 308 broilers were reared to day 34 on a standard wheat and soy-based diet and then offered one of the four semisynthetic experimental diets, comprising two different soybean meal sources either without or with exogenous protease (treatments therefore offered in a 2*2 factorial arrangement). Each experimental diet was fed to 18 individually housed birds from 34 to 37 D after which ileal digesta were collected and digestibility coefficients were calculated. The two soybean meal sources were found to be nutritionally divergent (P < 0.01), with one having the apparent ileal amino acid digestibility coefficient of 0.80 and the other 0.71. Exogenous protease increased (P < 0.01) apparent ileal amino acid digestibility coefficients from 0.74 to 0.77. There were no interactions between soybean meal origin and protease effect. On an individual bird level, there were substantial differences in the capacity to digest amino acids with the mean total amino acid digestibility coefficients from 0.54 to 0.80 for one of the soybean meal samples. Exogenous protease addition reduced the coefficient of variation for total amino acids from 11.4 to 9.1% in one soybean meal and from 7.7 to 6.3% in the other. It can be concluded that soybean meal digestibility varies and that some of this variance is associated with heterogeneity in the digestive capacity of broilers.