Arthritis is a common problem in performance and older horses.  Dr. Stacey Oke says in The Horse magazine that arthritis simply means joint inflammation. It is also called osteoarthritis or degenerative joint disease.  Classic signs include heat, swelling, lameness, stiffness, and in severe cases enlargement and grinding of the affected joints.  Although any joint can be affected in horses, the most commonly involved are knees, fetlocks, hocks and stifles as these are the highest motion joints.  If your horse is lame you may feel arthritis is the cause, but this cannot be determined without x-rays as there are other conditions that can have similar signs and signs of arthritis may not be found on x-rays in the early stages. 

There are three types of pain including nociceptive pain, which is caused by activating pain receptors in the joint.  Inflammatory pain can also occur due to inflammatory mediators being released in and around the joint, which also prime the nociceptive pain receptors to be more sensitive.  Neuropathic pain is caused by damage to areas of the nervous system that perceive pain. 

These differences are important. As Dr. Sheila Laverty from Quebec indicates, we have to control all three types of pain to treat arthritis.  One treatment is weight loss. if your horse is overweight, weight loss may decrease the amount of pain medication needed.  Joint injections can be used if a few joints are involved, but those are not without risk.  Thousands of joint supplements are available and most have no proof of effectiveness, so check with your vet about the most effective supplements in their experience.  Anti-inflammatories are also useful but unfortunately, there is no current cure for arthritis in animals or people.