Nutritional Care for Aging Cats and Dogs

KEY POINTS

• Before prescribing a dietary change in any patient, a nutritional evaluation should be completed to include assessment of the patient, the current diet, and feeding management.

• Body condition score to assess body fat and muscle score to assess muscle atrophy are key indicators of nutritional and health status in senior pets.

• Cognitive dysfunction is a common condition in aged pets and may respond to dietary management with antioxidants and alternative energy sources, as well as environmental and behavioral enrichment for mental stimulation.

• Multimodal management of osteoarthritis includes a combination of weight management, physical therapy, diet including long chain n-3 polyunsaturated fatty acids from fish oil, other nutraceuticals, and pharmaceutical agents.

• Obesity is associated with increased oxidative stress, inflammation, and insulin resistance, which contribute to a number of health problems.

• Weight loss can be achieved in most pets by creating a negative energy balance and is best achieved using diets with low calorie density, increased protein content, and an overall increased nutrient: calorie ratio.

SUMMARY

The majority of aging pets are generally healthy but may have special dietary needs. Prior to recommending a diet for a senior pet, a thorough nutritional evaluation should be completed. Over 40% of dogs and cats between the ages of 5 and 10 years are overweight or obese. Such pets may benefit from diets with lower fat and calories and more protein. Although many middle-aged and older pets are overweight, a large percentage of geriatric cats and dogs have a low body condition. Many geriatric cats have a decreased ability to digest fat and/or protein. Thus, geriatric cats (12 years if age) may need a highly digestible, nutrient-dense diet.

Common age-related nutrient-sensitive conditions in dogs or cats include cognitive disorders, OA, and obesity, among others. Age-related cognitive disorders can benefit from a combination of mental stimulation through environment enrichment and mental exercises, plus appropriate diet. Diets that provide an alternate brain energy source, such as MCTs, and antioxidants have been proved helpful in dogs. OA, an inflammatory condition that occurs in many aging dogs and cats, may benefit from both weight management and nutrients that reduce the inflammatory responses, such as long-chain omega-3 fatty acids. Obesity is thought to contribute to a number of health conditions, so weight management is important. Weight loss can be achieved in most pets by creating a negative energy balance and is best achieved using diets with low calorie density, increased protein content, and an overall increased nutrient/calorie ratio. Aging pets should be monitored regularly to confirm that the desired nutritional benefits are being achieved, and to assess any need for new dietary changes.

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According to pet owners, most pets, even senior pets, are healthy or generally healthy and do not require therapeutic diets. But, all pets must eat. And, despite an increase in the influence of the internet, veterinarians remain the top resource for pet owners for information regarding pet health and nutrition. Therefore, veterinarians need to be prepared to provide nutritional advice for healthy pets as well as for pets that are ill. This is especially true for senior pets, due to their unique needs. This article is designed to provide guidance for nutritional assessment of aging pets, with information about feeding healthy older pets as well as addressing some common age-related, nutrient-sensitive conditions in senior dogs and cats. Approximately 40% of pet dogs and cats are 7 years of age or older. Aging brings with it physiologic changes. Some changes are obvious, like whitening of hair general decline in body and coat condition, and failing senses including sight and hearing. However, other changes are less obvious, and these include alterations in the physiology of the digestive tract, immune system, kidneys, and other organs. There is considerable individual variation in age-related changes. With regard to metabolism and normal age-related changes, cats aged 7 to 11 may be considered “mature” or middle aged, while those 12 years and above may be considered “senior” or “geriatric.” For dogs, the effect of age differs, in part, based on breed size. As a general rule, dogs and cats 7 years of age or older may be considered to be at risk for age-related health problems, since this is the age when many age-related diseases begin to be more frequently observed. “Geriatric” screening should be considered as a preventive medicine service, conducted to identify diseases in their early stages, or to head off preventable diseases. An important part of this evaluation is a thorough nutritional assessment.

GERIATRIC NUTRITIONAL EVALUATION

Before instituting a dietary change in any patient, especially an older dog or cat, a nutritional evaluation should be completed. This should include an evaluation of the patient, the current diet, and feeding management. The goal of dietary history taking is to identify the presence and significance of factors that put patients at risk for malnutrition. Understanding how the nutritional needs of older animals may change and a thorough evaluation of the individual patient will allow an appropriate dietary recommendation. Such recommendations should take into account both the needs of the patient and client preferences. Changes in feeding management should be considered a part of total patient management. As with any aspect of medical management, the patient should be reevaluated at appropriate intervals to ensure achievement of desired results.

Patient Evaluation

A complete medical history should be assessed and a thorough physical examination conducted. A comprehensive geriatric evaluation may identify evidence of clinical or subclinical problems that may benefit from dietary modification. For example, anemia, low serum albumin, low potassium, increased serum creatinine, or increased serum glucose may indicate problems that could benefit from dietary modification as part of medical management. Body weight and body condition score (BCS)5– 8 are important to assess. Increases or decreases in body weight or condition should trigger further evaluation. A longitudinal study in cats indicated that weight loss is evident in aging cats approximately 2 to 3 years before death from various causes, often well before clinical signs are apparent.9 Limited data and anecdotal observations suggest that preventing weight loss in no base cats can delay terminal conditions. If weight loss is evident in dogs or cats, further evaluation should determine if this is associated with increased or decreased calorie intake. A detailed dietary history and evaluation are warranted. If the patient shows an increased, or excessive, body condition, it is important to consider current diet and feeding management. Older dogs and middle-aged cats tend to have reduced energy needs. If calorie intake is not adjusted accordingly, weight gain will result. However, unexplained weight gain should be evaluated for predisposing causes, such as hypothyroidism. Animals that are overweight likely will benefit from a weight reduction program. In addition to BCS, it is important to assess changes in muscle mass, using a muscle condition scoring system. Animals, especially those that are sick, may be losing lean muscle mass despite an abundance of body fat. Pronounced loss of lean body mass (LBM) is associated with increased morbidity and mortality

Dietary Evaluation

A complete dietary evaluation should include the normal diet, as well as other foods to which the pet has access. Commercially prepared foods should be identified by brand. Any changes to the diet should be identified, as well as the reason for the change. Since many pet owners provide treats and table food, and about 10% of owners provide nutritional supplements, for their pets, these also should be identified by types and amounts. Once the nutritional characteristics of the total diet are known, it should be compared against the individual patient’s needs. In general, inactive animals or those that are somewhat overweight should be receiving lower calorie foods, yet may need foods with an increased nutrient: calorie ratio formulated to compensate for increased needs of other nutrients. Feeding such animals a high-calorie food may require an inappropriate reduction in volume of food, resulting in lack of satiation as well as restriction of essential nutrients. On the other hand, feeding a low-calorie food to a pet with high energy needs may require excessive food intake, resulting in loss of body weight or excessive stool volume.

Feeding Management Evaluation

It is important to consider how foods are provided and how they are accepted by the pet. Clients should be asked how much and how often each food is fed. It is also important to identify if pets are fed measured amounts of food, or free choice. Within multiple pet households, determine if pets share a food bowl or have access to other pets’ foods. The diet history should determine if there have been any changes in how the patient is fed, or how it eats. This information is not only important in determining the adequacy of the current dietary situation, it can be important in planning a dietary recommendation that will achieve good client and patient acceptance and compliance

EFFECTS OF AGING ON NUTRITIONAL REQUIREMENTS

Energy Needs Maintenance energy requirements (MER) are the energy needs required for the normal animal to survive with normal activity. Individual MER can vary based on genetic potential, health status, and whether the animal is sexually intact or neutered. In addition to these factors, MER appears to decrease with age in most species.15 In dogs, a decrease of about 25% in MER has been documented as dogs age, with the greatest decrease occurring in dogs greater than 7 years of age. Age-related changes in MER in cats are more controversial. Some report no change in MER with age in senior cats. Yet, MER data from cats over a longer period and over a greater age range show a different picture. It appears that MER in middle-aged cats (approximately 7–11 years of age) decreases, similar to that observed in other species. However, by about 11 years of age onward, MER per unit of body weight actually increases, with the greatest increases occurring after 13 years of age. The primary driver of energy requirements in normal pets is LBM, which includes skeletal muscle, skin, and organs and accounts for about 96% of basal energy expenditure. Across species, including dogs and cats, LBM tends to decrease with age. This, plus a decrease in activity, can contribute to the reduction in MER seen in aging dogs and middle-aged cats.

If MER decrease, and energy intake does not decrease accordingly, that pet will become overweight. It is this last point that drives the market position of many foods for older dogs and cats. Most commercial foods for geriatric pets contain a reduced concentration of dietary fat and calories. Some have dietary fiber added to further reduce the caloric density. These products may be appropriate for the large number of pets that are overweight or likely to get that way. Not all older animals are overweight or less active. In fact, while “middle-aged” animals tend to be overweight, a greater proportion of dogs and cats over 12 years of age are underweight compared to other age groups. This effect is especially pronounced in cats. In addition to an increase in MER in this age group, which may partly explain weight loss, older cats may experience a reduction in digestive capabilities. Approximately one third of cats over the age of 12 may have reduced ability to digest fat, and 1 in 5 cats over age 14 have reduced ability to digest protein.9 A reduced ability to digest either protein or fat could contribute to weight loss in aging cats.

Protein Needs

Protein is another important nutrient for aging pets. For many years veterinarians recommended protein restriction for older dogs in the mistaken belief that this would help protect kidney function. However, research has unequivocally demonstrated that protein restriction is unnecessary in healthy, older dogs. On the contrary, protein requirements sufficient to support protein turnover actually increase in older dogs. Protein turnover is the cycle of catabolism of endogenous protein and synthesis of new proteins needed by the body at any given time, including hormones, enzymes, immune proteins, and others. When dietary protein intake is insufficient, the body responds by decreasing both catabolism and synthesis and by mobilizing protein from LBM to support essential protein synthesis. Normal animals can adapt to this low protein intake and maintain nitrogen balance, yet be in a protein-depleted state associated with gradual loss of LBM. In this situation, animals may appear healthy but have a decreased ability to respond to environmental insults including infections and toxic substances. In addition to the direct effect of inadequate protein intake, aging has a detrimental effect on protein turnover and LBM. In one review, 85% of the studies found an age-related decline in endogenous protein synthesis. Inadequate protein intake increases the rate of loss of LBM in aging dogs, while abundant protein slows the loss. There is growing recognition of the importance of this change in body composition. Loss of LBM has been recognized as a predictor of morbidity and mortality in aging subjects. Actual protein needs may vary based on individual factors, such as breed, lifestyle, health, and individual metabolism. In addition, calorie intake affects dietary protein need. Older dogs tend to need fewer calories, thus less food, than younger dogs. Therefore, diets for older dogs should contain a higher percentage of dietary protein, or increased protein: calorie ratio, in order to meet their needs. Diets containing at least 25% of calories from good quality protein should meet the protein needs of most healthy senior dogs. Similar data showing an age effect in cats are lacking; however, cats of all ages have high protein requirements. And, similar to other species, cats need considerably more protein to maintain LBM than is needed to maintain nitrogen balance.

Other Nutrients

All dogs and cats have specific needs for vitamins and minerals, which are normally provided by complete and balanced diets. There is little evidence that the requirements for these nutrients differ in healthy older animals. However, patients with subclinical disease associated with a mild malabsorption syndrome or polyuria may have increased losses of water-soluble nutrients, such as B vitamins, or fat-soluble nutrients, such as vitamins A and E. As noted previously, approximately one third of geriatric cats have a reduced ability to digest dietary fats. In these cats, there is a significant correlation between fat digestibility and the digestibility of other essential nutrients including several B-vitamins, vitamin E, potassium, and other minerals.9 Geriatric cats with gastrointestinal disease are more likely to be deficient in cobalamin (vitamin B12) compared to younger cats.31,32 Thus, older cats should be carefully evaluated for possible nutrient deficiencies and may benefit from supplemental amounts of these nutrients

DIET-SENSITIVE CONDITIONS IN GERIATRIC DOGS AND CATS

Few diseases in modern pets are “diet-induced.” One possible exception to this is obesity, which, while many interactive factors are involved, is ultimately caused by consuming more calories than needed by the dog or cat. However, many other diseases are “diet-sensitive,” meaning that diet can play a role in managing the effects of the disease. Examples of diet-sensitive diseases common in aging dogs or cats include chronic renal disease, diabetes mellitus, heart failure, and many others. Information on the management of many of these diseases can be found in other articles in this issue. The remainder of this article will focus on the role of diet in some common problems in aging pets: aging-related cognitive disorders, osteoarthritis (OA), and obesity

COGNITIVE DYSFUNCTION OF AGING

Older animals often undergo personality changes. Elderly pets can be less mentally alert, have altered sleep patterns and sleep more, and may exhibit varying degrees of cognitive decline. The main behavioral changes associated with cognitive dysfunction in dogs can be grouped into 4 categories: disorientation in the immediate environment; altered interactions with people or other animals; disturbed sleep-wake cycle patterns; and loss of house training. Studies suggest that signs of cognitive dysfunction occur in 20% to 30% of dogs over 7 to 9 years of age, increasing to 68% in dogs over 14 years of age. Similar categories of behavioral changes have been reported to occur in cats with cognitive dysfunction. Behavior problems increase Nutrition for Aging Cats and Dogs 773 in frequency in aging cats as well, occurring in 50% to 88% of cats 15 to 19 years of age.46 The severity of cognitive decline in dogs and cats may range from minimal changes to severe dementia and is suggested to be progressive.

Dietary Factors

The amount of calories needed to induce weight loss will vary greatly among individual animals due to differences in MER as well as their level of activity. In addition, MER decreases in response to calorie restriction and weight loss. This appears to be due, in part, to metabolic adaptation, as indicated by reduced diiodothyronine concentrations, and reductions in LBM which drive basal metabolism. It is, therefore, important that adjustments in calorie allowance are made on a regular basis, such as every month, to maintain ongoing weight loss. Use of an appropriate diet for weight loss is important, and there are several criteria to consider. While it is ultimately calorie restriction that induces weight loss, it is important to avoid excessive restriction of essential nutrients so a low-calorie product with increased nutrient: calorie ratios should be considered. Further, an important goal for weight loss is to promote fat loss while minimizing loss of LBM, which can be influenced by dietary composition, especially protein.

Behavioral Factors and Feeding Management

In addition to diet, changes in feeding management are critically important to successful weight management. In both human and pet obesity management, behavioral changes regarding food intake and activity are important for both weight loss and long-term weight management. Owners of obese pets are likely to unintentionally feed their pet excessive calories. Effective control strategies are those that will increase the owners’ mindfulness regarding feeding behaviors. Dog owners report that veterinary guidance is important in managing their pet’s obesity. Effective weight management programs have included specific feeding guidelines, appropriate guidance on feeding of treats, and frequent monitoring with adjustments in food allowance. Given the intensity of work involved with supporting weight management, the concept of veterinary “obesity clinics” has been explored. Obesity clinics can be run by trained technicians to perform such important functions as client education, ongoing client support, rechecking of body weight and BCS, updating feeding guidelines, and dispensing food. Clinics can be managed as individual appointments, or as group sessions that provide owners with the additional benefit of a peer support group. Among practices that offer such clinics, 79% noted that it was a valuable service. Provision of a handout that details the portion of cups or cans of a specific diet (with client input on diet selection) to be fed daily was found to be helpful for clients. There is a limitation to this, however, as there is considerable imprecision even when using measuring cups to weigh food.180 In small pets, this imprecision could be sufficient to compromise the weight management plan, so it is recommended to use an accurate weight scale rather than measuring cups whenever possible. Monitoring food intake and activity via use of a daily log is a principal pillar of behavioral modification for human obesity management. Many clients find that keeping a daily diary regarding their pet’s food intake and activity is helpful. Where multiple people in a household might feed the pets, use of a daily log can be especially useful to avoid accidental overfeeding.

Most dog owners and many cat owners provide treats to their pets on a regular basis. The creation of a “treat allowance” equal to 10% of the daily calories allows owners to continue this pleasurable activity while also achieving appropriate energy balance. Owners may benefit from a menu of low-calorie foods or commercial treats that would be appropriate to use within the allowed calories

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