Like us, dogs don't stay young forever - they age. While some aspects of getting old may not be much fun, getting old is not all bad. Each stage of life has its joys, pleasures and drawbacks. Middle age for a dog, which is between 5 and 9 years of age, is a kind of gray zone during which the dog is busily engaged in the process of life without any particular physical or mental deterioration to hamper him. But somewhere towards the end of middle age, dogs start acting and feeling their age.
The effects of the aging process are both physical and mental. Physically, structural and functional changes occur in virtually all organ systems throughout the body, affecting vision, hearing, stamina, susceptibility to drugs and locomotor activity. Mental changes are secondary to decreasing brain size and a reduced number of brain cells. In some cases, canine Alzheimer-like changes hasten deterioration. Aging does not affect all dogs in precisely the same way. Some dog breeds, and some individuals, are more successful agers than others. Some dogs, at the age of 10 years, may have no noticeable physical or mental incapacitation. Others of the same age, however, are already handicapped by age-related internal organ failure, failing senses or orthopedic problems.
Age-Related Physical Changes
Dogs' hearing deteriorates progressively with age so that many older dogs appear not to hear you when you issue commands, and they do not respond to outside sounds that formerly would have aroused them. Loss of hearing can be either peripheral, due to changes in the ear itself or, as with failure of vision, related to changes in central processing.