Veterinarians are in the best position to evaluate the nutrient needs of their aging patients and to provide owners with guidance about optimal nutritional support and proper food selection.
Mature adult and senior pets are a significant proportion of your patient population. Approximately 44% of dogs and cats in the United States are 6 years or older, and about one-third of these pets are 11 years or older.1 Naturally, many of these patients are cherished family members whose owners are committed to providing them with the best of care, including optimal nutrition. Veterinarians are in the best position to evaluate the nutrient needs of their aging patients and to provide owners with guidance about optimal nutritional support and proper food selection.
The wide range in size and body type among dog breeds can result in significantly different life spans. Large-breed and giant-breed dogs have life spans that average several years less than those of moderate-sized dogs.2 According to one reference, giant breeds were classified as seniors when older than 7 years and large breeds were classified as seniors when older than 9 years, compared with 10 years for medium-sized breeds and 12 years for small and toy breeds.3 Cats may be considered mature adults or middle-aged when 7 years and older, seniors when 11 years and older, and geriatric when 15 years and older.4 It is important to note that age-related changes may occur before signs of aging are apparent to an owner. For this reason, specific nutrition for older pets should be recommended earlier than when pets are typically considered to be senior, and, for dogs, breed size should be considered. For toy-, small-, and medium-sized dog breeds, as well as cats, age-related changes may start occurring during the mature adult years, and this third midlife stage begins around the age of 7. For giant- and large-sized breeds, the mature adult life stage begins earlier — about 5 to 6 years of age — because of their shorter life spans. Nutritional needs of older pets may not remain static, and an individual's body condition, activity level, and overall health and the presence of chronic disease should always be considered when assessing the need for age-related dietary changes.
Nutritional needs of aging pets Several physiologic changes are associated with aging in animals. These include reduced activity level, a decrease in the body's lean muscle mass, and an increase in the proportion of body fat. Some dogs and cats show signs of hearing loss and decreased visual acuity as they age. Changes in the senses of smell and taste can result in less interest in food and subsequent weight loss. Skeletal and organ changes develop in some animals. These may include mobility problems (most commonly osteoarthritis), periodontal disease, compromised renal or heart function, cognitive dysfunction, and neoplastic disease. Collectively, age-related changes can alter an animal's daily energy needs, change the amounts and type of protein and fat needed, and modify the levels of minerals and vitamins required. The inclusion of functional nutrients such as glucosamine and chondroitin sulfate for joint health, prebiotics for healthy digestion, and ingredients such as L-carnitine to help maintain ideal weight and body condition and sodium hexametaphosphate to help slow tartar buildup in dogs should be considered for their health benefits.
Energy: Most older pets experience a slight to moderate reduction in daily energy needs. For example, a study found that dogs older than 8 years consumed 18% fewer calories than breed-matched dogs that were less than 6 years old.5 While less pronounced, a decline in energy requirements also occurs as most cats age. Regardless of these trends, older pets vary greatly in their energy needs, which are influenced by individual temperament and activity level, the presence of degenerative disease, and the animal's ability to digest and assimilate nutrients. Thus, caloric intake should be carefully monitored in older pets to ensure adequate intake of calories and nutrients while avoiding overweight conditions.
Fat: High-quality dietary fat contributes to a food's palatability, which is especially important in older pets with a diminished sense of taste or a reluctance to eat because of chronic disease. However, adjusting the amount of fat in the diet may benefit both mature adult and senior dogs and cats that are at risk of weight gain. Pets entering the mature adult life stage may require less fat than dogs and cats in the adult life stage, and pets transitioning from the mature adult life stage to the senior life stage may require slightly more fat. In addition to the amount of dietary fat, the source is important. The fat that remains in the diet needs to be both highly digestible and rich in polyunsaturated fatty acids — both omega-6 and omega-3 fatty acids. Senior animals affected by osteoarthritis and several other chronic disorders may benefit from the anti-inflammatory properties of increased dietary omega-3 fatty acids. In addition, the omega-3 fatty acid docosahexaenoic acid (DHA) is worth considering as it has been shown to benefit aging brains in people.6 Interestingly, it has been shown that feeding a diet containing mostly saturated fat can affect the olfactory ability of working dogs in a negative manner.7 This knowledge may be of importance for senior pets with a diminished sense of smell and provide another reason to feed a diet rich in polyunsaturated fatty acids.
Protein: Contrary to persistent popular belief, healthy older dogs and cats do not benefit from reduced dietary protein. In fact, several research studies have shown that older pets require high-quality protein at slightly higher concentrations than the levels found in most adult maintenance diets.8,9 Sufficient dietary protein with an optimal balance of amino acids is essential to support a healthy body condition, to prevent loss of muscle mass, and for a healthy immune system. This is especially importantfor cats that have a naturally high protein requirement and that do not tolerate low-protein diets.
Carbohydrates (starch): As pets age, they may experience problems with glucose metabolism. Dietary interventions that blunt the postprandial blood glucose surge can improve glycemic control in dogs and cats. Because dietary starches differ in their effects upon postprandial glucose levels, the type of starch included in the diet is important. Studies have revealed that including sorghum or barley as starch sources in the diet of dogs results in a lower blood glucose response when compared with glycemic response to diets containing wheat or rice.10
In addition, feeding a food that contained barley resulted in a blunted insulin response when compared with the insulin response to diets containing other grains. Similar results have been reported in cats.11
When overweight cats were fed one of two diets formulated to contain a similar starch content from different sources (sorghum and corn vs. rice), cats fed the food with rice were more likely to have higher blood glucose and insulin levels after a meal than cats fed the diet containing sorghum and corn. Thus, improving glucose control via diet may help maintain more normal glucose metabolism in older pets.
Fiber: Mature adult and senior pets may be more prone to digestive challenges. Thus, providing a diet with moderate fiber levels may promote a healthy digestive tract. The optimal fiber system for dogs and cats should contain a fermentable component to facilitate short-chain fatty acid generation and a nonfermentable component to provide bulk. Beet pulp is an excellent source of moderately fermentable fiber, which enhances intestinal health12 by providing short-chain fatty acids as an energy source for intestinal cell repair and maintenance. Another type of fiber called fructooligosaccharides (FOS) works as a prebiotic by promoting the growth of beneficial bacteria and inhibiting nonbeneficial bacteria in the digestive tract.12
Vitamins and minerals: Older animals have the same vitamin and mineral requirements as young adults. Because some vitamins, such as vitamin E and beta-carotene (provitamin A), have antioxidant functions, they are especially important for senior animals. These nutrients support a healthy immune system and reduce free-radicalproduction, which may contribute to aging and the onset of chronic disease. There is also some evidence that a diet enriched with antioxidant vitamins and related compounds improves cognitive function in older dogs.13
Although dietary modification can promote wellness in older pets, a senior food will only be helpful if it is properly formulated for a pet's age and state of health and if the owner elects to feed it. A 2011 survey examined the perceptions of more than 1,200 respondents regarding nutrition in senior dogs.*14
The majority of participants (85%) believed that senior dogs have different nutritional needs than do adult dogs. A majority believed that senior diets should contain reduced levels of protein, fat, energy, and sodium and an increased level of fiber. However, among those who owned a senior dog, only 42% were actually feeding a senior diet. Moreover, almost all of the participants identified ingredient quality (not the above-mentioned changes in nutrient content) as the most important consideration when choosing a senior diet for their pet.
This apparent disconnect between reported beliefs about nutrition and actual pet food selection for senior pets means there is a need for pet owner education and guidance.
The study also collected nutrient analysis information from pet food manufacturers of 37 over-the-counter foods that are marketed for senior dogs. Energy and nutrient content varied markedly among the products, and nutrient content was often not consistent with pet owner beliefs about the needs of senior pets. The most significant incongruities related to energy and protein levels. The caloric content of senior foods ranged between 246 and 408 kcal/cup in dry foods and between 312 and 411 kcal/can (can size not specified) in wet foods. This wide range is not consistent with the perception that senior diets all contain reduced calories. Therefore, poor diet selection could lead to unintentional over- or under-feeding and subsequent weight change in senior pets whose needs were not matched with diet. A wide range in protein level was also found, and the mean protein content of the 37 foods was higher than the AAFCO minimum for adult foods. Almost all of the commercial senior diets had protein levels higher than the protein amount in a representative adult maintenance food. These levels undoubtedly reflect the correct response by pet food manufacturers to research that has shown that pets do not automatically need less protein as they age and benefit from moderately increased amounts of quality protein. However, the persistence of the myth that older dogs need less protein shows that veterinarians need to be involved in their patients' diet selection.
The 2011 study by Hutchison et al reported that only 30% of owners who were feeding a senior dog food based their choice on a veterinarian's recommendation.14 Owner misperceptions about senior pets' needs and the abundance of highly variable over-the-counter senior pet foods show that veterinary guidance is needed. Such intervention need not take extra time or effort and can be seamlessly integrated into your regular wellness appointments. The American Animal Hospital Association's recently published "Nutritional Assessment Guidelines for Dogs and Cats" provides helpful protocols and forms to use during nutritional assessments of patients.15 For example, the screening evaluation includes a review of age-related changes in senior pets that may influence their nutritional status. Senior patients that are identified as "at risk" can undergo an extended evaluation to prevent or rectify nutrition-related health problems.
When advising clients, your primary objectives are to educate them about the nutrient and energy needs of mature adult and senior pets and to help them select a food that is best formulated to meet the unique needs of an individual pet. Given the number of older pets and their importance to pet owners, this is time and effort well spent during routine appointments. Your input about your mature adult and senior patients' diets will contribute to their long-term health and vitality.
*For this survey, giant-breed dogs were classified as seniors when they were > 7 years old, large-breed dogs when > 9 years old, medium-breed dogs when > 10 years old, and small-and toy-breed dogs when > 12 years.3
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