Peritoneal fluid samples were obtained from horses presenting to the Veterinary Teaching Hospital (VTH) with signs of colic. Horses ≥ 2 years of age with no abdominal surgery in the previous 30 days were eligible for inclusion. PF samples were collected by abdominocentesis following standard clinical protocols into sterile blood collection tubes and aliquoted prior to storage at -80°C. Signalment, history, clinical evaluation parameters, diagnosis, treatment, complications, and short-term survival were recorded for each horse treated surgically for colic. After case resolution (discharge or death/euthanasia), horses were assigned to a group (non-strangulating or strangulating disease). Proteins were extracted by chloroform-methanol precipitation followed by digestion with trypsin. Prior to LC-MS analysis, the peptide amount was normalized according to a BCA assay. Dried peptides were suspended in 5% acetonitrile (ACN) with 0.1% formic acid (FA), and 1μg of peptides from each sample injected into an UltiMate 3000 RSLC nanoflow system coupled to a Q Exactive HF-X mass spectrometer (Thermo Scientific, Wilmington, DE). Protein identification and quantitation were performed in MaxQuant v2.010 software using the Uniprot Equus caballus, Bos Taurus, Homo sapiens and common lab contaminants databases. Expressed proteins were annotated with known or predicted functions using UniProtKB/Swiss-Prot.