As your pet ages, wear and tear can take its toll on his body. Particularly affected will be his highly refined skeletal system and the bones and muscles that make it work. Playing a starring role in the proper functioning of the joints is articular cartilage, which normally provides a smooth, low-friction surface between bones and joints. In older dogs and cats, however, cartilage may become eroded or develop fissures. This is known as degenerative joint disease. Not only does this condition affect a pet's ability to move, it can lead to great pain, swelling and lameness.

Although degenerative joint disease generally affects older dogs, it not uncommon to see this problem in companion canines of all ages. Selective breeding has altered the bone structure in some dogs, leaving many animals-especially large breeds prone to bone disease. Some dogs are born with a defect that inhibits the normal development of articular cartilage, and can lead to permanent lameness in the shoulders, knees and ankles.

And any serious injury can start the degeneration process. Middle-aged and older canines frequently rupture ligaments in their knees, which can result in cartilage breakdown; this also affects overweight dogs with poorly developed musculature. Some young dogs develop fragmentation of their forearm bones at about 5 to 9 months of age. This affects retrievers and rottweilers in particular. Another common inherited bone disorder is hip dysplasia. Because the joint doesn't fit together as snugly as it should, a dog's leg bone will move around too much in its socket. This results in lameness in one or both hind legs and, sometimes, arthritis.

Does your pet feel pain when you touch him in certain areas or hold him in certain positions? If he is showing stiffness of movement or lameness, and if he has trouble getting up and down, we recommends that you ask your veterinarian about the possibility of a bone disorder. Drugs may be used to alleviate the pain. In some cases, surgery may be required. Many doctors prescribe a nutritional supplement that provides the raw materials to help animals replenish articular cartilage.