Updated publication reference for PubMed record(s): 31028944. Presently few studies have investigated the proteomic profile of equine synovial fluid (SF) using high mass resolution mass spectrometer and in-solution trypsin digestion and to our knowledge none have investigated protein profile changes septic SF in any species. In this study we have used mass spectrometry and label-free quantification to identify potential protein biomarkers that allow differentiation between equine articular joint pathologies, potentially aiding accurate diagnosis and enabling increased understanding of the effect of septic synovitis on the joint environment. Identification of characteristic proteomic profiles in synovial sepsis would increase the understanding of the molecular basis of the condition and also allow the identification of potential biomarkers for early diagnosis and treatment of the disease. We hypothesised that proteomic profile characteristics will distinguish septic from non-septic equine arthropathies and between the non-septic common arthropathies osteochondrosis and OA.