Arthritis can cause significant discomfort for a senior dog. He may develop a limp, have difficulty lying down or getting up, or no longer be able to make the climb up stairs. Diet supplements can help to keep joints supple, and anti-inflammatory medications can help to ease the pain, but the best way to keep your dog feeling good is to make sure he gets regular, moderate exercise.
If your dog is struggling on a daily basis, it will be difficult for you to watch. You may want to consider purchasing some products made specifically for older or disabled dogs, such as an orthopedic dog bed, heated blankets, or ramps for access to places that normally require climbing stairs or jumping up.