With old age comes a wearing out of the bearing surfaces (joints) and the muscles and bone. Muscle fibers cannot reproduce, therefore, like with nerve cells, the dog does not get to replace those that are lost. This explains the characteristic loss of muscle mass and strength as the dog ages.
Muscle--Mysathemia gravis, an autoimmune condition which prevents transmission of nerve impulses to muscle cells, is more common in old age and manifests as general weakness. In the larger breeds, there is an association of polymostitis (unknown origin but manifesting with general weakness) and age. Also fairly common in old dogs is progressive myopathy, a condition resembling multiple dystrophy in humans which also manifests as generalized weakness. A loss of oxidative capacity of skeletal muscle occurs with age, but may be partially offset and to some degree restorated with endurance exercise.xii
Joints--Canine hip dysplasia is the most common of all joint diseases, especially in old age. This is a potentially crippling, exceedingly painful condition and will be discussed in detail later on in this series. Osteoarthritis, just as in humans, is a way of life in the aged and affects most commonly the weight bearing joints. There are numerous approaches to ameliorating the problem, but for the foreseeable future, osteoarthritis is a very real fact of life in dogs, though various nutritional approaches hold great promise. In some breeds, such as German Shepherd Dog and Dachshund, intervertebral disease and and spondylosis, a degenerative disease most commonly involving the lumbar vertebrae. Patellar luxation (dislocation of the kneecap), a common problem in many breeds, especially the smaller ones, just gets worse with age. Old age obesity takes its toll on both the muscles and the joints. Often the best solution to many of the old age aches and pains is weight reduction.
Bones--As in humans, with aging comes a loss of mineralization in bones. Bones need to be stressed to maintain their calcification, and in older dogs with limited activity, the demineralization of the bones may become serious. Fortunately, osteoporosis (loss of bone) while increasing in older dogs, is not commonly a problem given a complete and balanced diet, and normal absorption of minerals and vitamins.
Aging is a normal function. Without aging, overpopulation by all species would quickly choke the eco-system. Nonetheless, one can age "hard" or one can age "easy." With an understanding or the aging process, and with learning to plan for and make accommodations for the diminished physical and mental capacity that accompanies aging, it is possible to minimize the disruption of living a normal life, and to extend the length of useful life in our dogs. In the next article in this series we will take a look at the chronic ailments of old age and what you can do keep your dog as young and healthy as possible.