Arthritis is a joint inflammation. It can occur at the early age because of intensive activity. The symptoms are: lameness, pain and reduced performance !
Arthritis must be treated early to avoid bad and irreversible complications.
Arthritis is an inflammatory disease, where the inflammation system of the horse goes a bit mad. Inflammation is a natural response from the body. It gets sent out to deal with damaged or diseased tissues, and infection. However, the body sometimes forgets to shut down the inflammation before it causes damage to healthy tissue. In the cases of inflammatory disease, it doesn't really shut it down at all.
As a result in arthritis, articular cartilage gets damaged and the bones of the joints start to produce more bone. In severe arthritis, there can actually be complete ossification (bone growth) in a joint. Hence why in a hock joint, they usually wait for the bones to fuse.
Symptoms include swelling in the joint (not always noticeable), reluctance to move, lameness. In early stages, the horse may feel just a little bit "off". A xray of the joint will then show up any bone/cartilage changes. It's important to catch arthritis early. The earlier you catch it, the more chance of successful management.