Our laboratory seeks to improve the ability of equine practitioners to diagnose and treat osteoarthritis (OA) in horses. OA is the primary cause of lameness in horses of all ages, breeds, and disciplines. While the area of therapeutics for managing joint disease in horses continues to expand it can easily outpace the current body of knowledge, and this proposal seeks to fill some of this gap. First, we propose expanding our ability to measure alpha-2 macroglobulin (A2M) through creation of an equine-specific antibody. A2M is an anti-inflammatory protein currently available for treating OA in humans and horses, and in several species in increased in OA-affected joints. This protein can be measured in humans, however there are no reagents available to measure A2M in horses. By developing an antibody that recognizes equine A2M we will expand our ability to quantitate this protein. Additionally, we seek to expand our previous work evaluating proteins present within joint fluid from horses with knee (carpal) OA to the joint fluid and blood from horses with ankle (fetlock) OA. This expansion will confirm the validity of potential diagnostic and therapeutic protein markers across multiple joints and determine whether any systemic blood markers of OA exist in the horse.