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More dogs today are living to a ripe old age. Thanks to advances in nutrition and preventive veterinary care and medicine, their owners are able to enjoy their companionship for years after they retire from the performance circuit.

Considering that four out of 10 dogs seen by veterinarians are age 6 or older,1 it is not surprising to see more geriatric health programs providing specialized care. Veterinarians accustomed to working with senior dogs are able to readily recognize physiologic changes and recommend diets suited to the nutritional needs of individual dogs.

Owners should try to learn from their veterinarian whether their dog's nutritional needs are changing as part of the aging process. A common physiologic change in senior dogs is a changing body composition characterized by decreased lean body mass and increased body fat.

Lean body mass accounts for 95 percent of the energy used in metabolic processing.2 In humans, the loss of lean body mass results in a loss in physical strength and motor coordination.3 Loss of immune function also may occur3 as well as higher rates of morbidity and mortality.4

Veterinarians generally advocate bringing a dog in for a medical examination before age 5, or much earlier for large and giant breeds, to establish a healthy baseline medical examination. This examination provides a benchmark for assessing age changes in an individual dog. Genetics, breed size, environment, health care and nutrition all contribute to the aging process in dogs.

Once a dog is 7 years old, owners are advised to visit their veterinarians twice a year. Biannual examinations help to detect health problems early and determine whether a particular dog might need medical care, a dietary change or to be closely monitored.

Geriatric Nutrition Evaluation
Before making a dietary change, a dog should have a geriatric nutrition evaluation by a veterinarian, which helps identify the presence and significance of factors that put dogs at risk for malnutrition or obesity. The evaluation should include a medical examination and complete medical history, detailing vaccinations, prior diseases or injuries, and parasite prevention.

Blood testing and other diagnostic tests, such as cardiology, often help identify problems in early stages. Medical laboratory testing, consisting of a complete blood count, platelet count, biochemical profile, serum chemistry profile, complete urinalysis and fecal flotation, should be taken annually for senior dogs. These tests report signs of disease and nutrient deficiencies that sometimes can be adjusted through dietary modifications.

"For example, a dog that tests low in red blood cells could suffer from parasites, gastrointestinal ulcers, vascular lesions or chronic renal failure," says Ralston Research Fellow Dottie Laflamme, D.V.M., Ph.D. "The veterinarian may recommend special diets to help manage gastrointestinal diseases or chronic renal failure or pharmaceuticals to aid in treating parasites and certain types of vascular lesions."

The nutrition evaluation also should include assessment of body weight and body condition score, as well as an oral examination to determine signs of gingivitis or periodontal disease. "A dog's body weight, body condition and the appearance of its skin and hair coat provide key information about the adequacy of its diet," Laflamme says. "Dry, flaky skin or thin, brittle hair could be the result of nutritional deficiencies. Unexplained weight gain or weight loss also should be evaluated for predisposing causes."

Part of the nutrition evaluation will involve learning detailed information about a dog's current diet and feeding management — what brand of food the dog is eating, how long it has been fed, whether the dog likes the food, the amount of food fed daily, and whether there have been changes in the dog's acceptance of its food.

The nutrient analysis listed on the product label can provide information about the food's content, calories, digestibility and whether it has been evaluated through actual feeding studies to determine nutritional adequacy. A veterinarian also will want to know whether the dog is fed supplements and treats and whether it has access to other foods.

Effect of Age on Nutrition
The nutritional needs of dogs may change along with changes in lifestage, lifestyle or function. Maintenance energy requirements (MER), the energy required for a healthy dog to survive with minimal activity, decrease with age.5 Inactive senior dogs require less energy and have many decreased nutrient needs compared to when they were younger, hardworking or reproducing dogs.

Individual MER, especially in inactive animals, is driven by basal metabolic rate, the energy required to maintain body functioning. Genetics, health, activity and lifestage all influence MER.

Dietary Fat
If energy needs decrease in a dog but energy intake does not decrease accordingly, the dog is at risk for becoming overweight and developing health problems. A dog is considered obese if its weight exceeds optimum by about 20 percent or more due to an accumulation of fat.

To compensate for a general decrease in energy needs, most commercial foods formulated for geriatric dogs contain a reduced concentration of fat and calories. Some foods for senior or overweight dogs also add fiber to further reduce caloric density. It is important to ensure that these products provide adequate protein and other essential nutrients while reducing caloric intake.

Previous feeding habits also can influence a dog's weight as it ages. In a study of the effect of aging on body condition, dogs fed limited quantities of food starting when they were puppies had less body fat and a higher percent of lean body mass compared to overfed dogs. The research, conducted at the Purina Pet Care Center, involved pairing 24 Labrador retriever littermates from seven litters. The control group was fed without restriction, and pairmate dogs in the limit-fed group were fed 75 percent of the food their littermate ate.

When the overfed dogs were 3.25 years old, food was reduced and fed at a constant amount. The limit-fed group continued to receive 25 percent less food than the overfed group. When the dogs were from 6 to 10 years old, those in the overfed group showed a decline in percent of lean mass and increase in fat mass, while the limit-fed group showed significantly lower body fat along with significantly higher percent of lean body mass.

While this study shows the potential benefit of limiting the amount of food fed to result in a higher percent of lean body mass and lower percent of fat as an older dog, it is important to note that not all older dogs are overweight or less active. In fact, a greater proportion of older dogs are underweight than any other age group.6

These dogs could be highly active, have a reduced food intake or have developed medical problems. Dogs in this nutrition group may benefit from a more energy-dense, high-fat product.

High-quality dietary fat helps to increase palatability, which is especially important in older dogs because they may have a diminished sense of smell or taste. Caloric intake also may be decreased because senior dogs may lack the desire to eat. In addition, intake may be normal, but the dog may be less efficient at digesting or absorbing nutrients.

A diet rich in protein is especially important for older dogs. Senior dogs appear less efficient at metabolizing protein, so they require additional protein in their diets to help compensate. In fact, research has shown that healthy older dogs may need as much as 50 percent more protein than normal young healthy adult dogs.

The additional protein is required to maintain a geriatric dog's protein reserves and support protein turnover, which are important in helping the dog's immune system function at full capacity, Laflamme says. "Dogs that do not receive adequate protein are more susceptible to stress," she says.

The specific amount of protein needed, as a percent of diet, depends on factors such as organ function, individual dietary needs and energy requirements. In otherwise healthy animals, even mild protein-calorie malnutrition can significantly impair immune function.8 Unless a dog has clinical evidence of kidney disease or other problems for which protein restriction is beneficial, there is no reason to recommend a change to a low-protein diet.

The importance of providing adequate dietary protein to senior dogs was brought out in research conducted at the Purina Pet Care Center. In this study, 26 English pointers, ranging from 7 to 9 years old, were fed diets that were either 15 percent or 45 percent protein over several years. Dogs fed the high-protein diet maintained a directionally higher percent of lean body mass and lower percent of body fat.

Other Nutrients
All dogs have specific needs for vitamins and minerals, such as calcium, phosphorus, copper, magnesium, potassium, sodium and chloride. Though older dogs do not commonly suffer vitamin and mineral deficiencies, it still is important they receive adequate amounts in their food since the diet usually is their sole source of nutrients. Healthy older dogs eating adequate quantities of a nutritionally complete and balanced quality diet usually do not need vitamin or mineral supplements.

Making Dietary Changes
Healthy dogs do not experience a significant age-related decline in their ability to digest and absorb nutrients. If a dog generally is healthy and is fed an appropriate diet, a dietary change is unlikely to be necessary.

On the other hand, dietary modifications sometimes can help dogs experiencing changing nutritional needs. Your veterinarian can help you determine whether a change in diet is necessary.

Whenever a diet change is necessary, a new product should be introduced gradually. Dietary changes, especially those made for medical reasons, should be re-evaluated periodically and adjusted if necessary.

1 Goldston RT, Norsworthy GD, Willard MD, et al. Establishing a geriatrics management program. Ralston Purina, St. Louis. 1996.
2 Roubenoff R. Hormones, cytokines and body composition: Can lessons from illness be applied to aging. J. Nutr. 1993; 123: 469-473.
3 Castaneda C, Charnley JM, Evans WJ. Elderly women accommodate to a low protein diet with losses of body cell mass, muscle function and immune response. Am. J. Clin. Nutr. 1995; 62: 30-39.
4 Baumgartner RN, Kochler KM, Romero L, et al. Serum albumin is associated with skeletal muscle in elderly men and women. Am. J. Clin. Nutr. 1996; 64: 552-558.
5 Taylor EJ, Adams C, Neville R. Some nutritional aspects of aging in dogs and cats. Proc. Nutr. Soc. 1995; 54: 645.
6 Armstrong, PJ, Lund EM. Changes in body composition and energy balance with aging. Vet. Clin. Nutr. 1996; 3:83.
7 Redmond HP, Shou J, Kelly CJ, et al. Immune responses in mild and severe protein-calorie malnutrition. J. Parenteral and Enteral Nutr. 1991; 15 (Suppl.):21S

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