Briefly, each cecum was ground to powder in liquid nitrogen, dissolved in lysis buffer with 150 µL of radioimmunoprecipitation assay buffer containing 1 mM PMSF and a protease inhibitor cocktail (CST, USA), and then subjected to sonicating. The cellular debris was removed by centrifugation. The concentration of the extracted protein was determined and the quality was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The extracted protein was digested into peptides using trypsin Gold at a protein: trypsin ratio of 30:1 at 37oC for 16h. Following trypsin digestion, the peptides were desalted on a Strata X C18 SPE column, vacuum-dried, resuspended in 0.5M TEAB. Each peptide mixture was labeled using the 8-plex iTRAQ reagent kit (Applied Biosystems, Foster City, USA). The labeled samples were mixed, dried, resuspended and then loaded onto a MacroSpin VydacC18 reverse-phase minicolumn . Following washing and elution, the samples were dried and fractionated using a strong cation exchange column. Each SCX fraction was lyophilized and dissolved in the solvent and 0.01% trifluoroacetic acid. The peptides were loaded onto a C18 capillary trap cartridge and then separated on a 15-cm nanoflow C18 column at a flow rate of 200 nL/min using a Proxeon EASY-nLC system. The peptides were eluted from the HPLC column using a linear gradient including 5% solvent B for 10 min, 5-30% solvent B for 30 min, 30-60% solvent B for 5 min, 60-80% solvent B for 5 min and holding for 5 min, and 80-5% solvent B for 5 min, after which they were maintained in 5% solvent B for 5 min. The flow from the column was directed to a tandem mass spectrometer in the TripleTOF 5600 system operating in positive ion mode. Tandem mass spectra were searched against the chicken protein database (http://www.uniprot.org/proteomes/UP000000539) using ProteinPilotTM V4.5 for computational analysis.