Updated project metadata. Osteoarthritis (OA) is the most common equine joint disease characterised by cartilage degradation and changes to other joint tissues severely effecting welfare and performance leading to early retirement. It results in substantial morbidity and mortality, but our understanding of the pathophysiological mechanisms involved is limited. There are no disease modifying therapeutics available, with OA medication offering symptomatic relief only. Early diagnosis is thus important, as substantial joint pathology is usually present at the time of clinical diagnosis. Thus, biomarkers of early-stage OA are actively sought, and among these, extracellular vesicles (EVs) are emerging as potential candidates. Here we use a SWATH MS approach to profile the protein cargo of EVs derived from equine plasma and synovial fluid.