Dogs and cats begin to show visible age-related changes when they are seven to twelve years old. Before those changes become visible, though, there are metabolic, immunologic and body composition changes that slowly begin. Some of the changes are unavoidable. Others can be managed with diet. If, however, the timing of those dietary changes waits until the overt signs are visible, the opportunity to prevent or slow those changes is past.

Nutritional adjustment should begin early, but the exact age in dogs is not as simple as it is in cats. Cats should start eating a senior diet at about 7 years of age. The age for dogs depends upon the dog’s size. Since smaller dogs live longer and don't experience the age-related changes as early as bigger dogs, size is used to determine the time to change diets.

As a dog or cat ages, changes in body tissues may result in health issues, including:

• Deterioration of skin and coat
• Loss of muscle mass
• More frequent intestinal problems
• Arthritis
• Obesity
• Dental problems
• Decreased ability to fight off infection

The main objectives in the feeding of geriatric dogs and cats should be to maintain health and optimum body weight, slow or prevent the development of chronic disease and minimize or improve clinical signs of diseases that may already be present.

Older dogs and cats have been shown to progressively put on body fat in spite of consuming fewer calories. This change in body composition is inevitable and may be aggravated by either a reduced energy expenditure or a change in metabolic rate. Either way, it is important to feed a diet with a lower caloric density to avoid weight gain from fat and with a normal protein level to help maintain muscle mass.

Studies have shown that the protein requirement for older dogs does not decrease with age and that protein levels do not contribute to the development or progression of renal failure. It is important to feed older dogs diets that contain optimum levels of highly digestible protein to help maintain good muscle mass. Avoid "senior" diets that have reduced levels of protein.

Other special nutrients have been shown to be beneficial in older animals:

• Increased vitamin E for senior cats. Antibody response decreases as cats age. Increasing the intake of vitamin E in cats over seven years of age can increase their antibody level back to levels seen in younger cats.
• Gamma-linolenic acid (GLA). GLA is an omega-6 fatty acid that acts like an omega-3. It also plays a role in the maintenance of a healthy skin and coat. It is normally produced in the dog's liver. In older dogs, GLA levels may be diminished because the activity of the enzyme responsible for its production decreases with age.
• Fructooligosaccharides (FOS). Older dogs often have changes in the intestinal bacterial population which can result in clinical signs of gastrointestinal disease (e.g. diarrhea). Senior diets for dogs should contain FOS to promote the growth of beneficial bacteria at the expense of detrimental ones.
• Antioxidants. As dogs age, free radical particles accumulate and can damage body tissues and contribute to the signs of aging. Antioxidants such as vitamin E and beta-carotene help eliminate the free radical particles. Senior diets should contain higher levels of these antioxidant compounds to help nutritionally manage the free radical particles at the cellular level. Antioxidants can also increase the effectiveness of the immune system in senior cats and dogs.

Routine care for geriatric pets should involve the adherence to a consistent daily routine, regular attention to normal health care procedures and periodic veterinary examinations for assessment of the presence or progression of chronic disease. Stressful situations and abrupt changes in daily routines should be avoided. If a drastic change must be made in an older pet's routine, attempts should be made to minimize stress and to accomplish the change in a gradual manner.