Geriatric Pets and Their Nutritional Needs

Responsible pet ownership means committing to provide an animal with good food, adequate shelter and space, sources of entertainment, regular veterinary care and living conditions suited to its needs. These efforts have a direct effect on the animal's health and have led to a longer life expectancy for household dogs and cats. As a result, small animal veterinarians are seeing more and more geriatric patients in their practices every day.

Considering all the changes found in geriatric patients, this article focuses on the degenerative changes that can be addressed from a nutritional standpoint.

ANIMALS IN THE SENIOR AND GERIATRIC STAGES

Before discussing geriatric animals, we should be clear that life stages are not strictly defined (Table 1); most are based on the physical and behavioral changes of the animal in question. Yet, despite being arbitrary, they provide an overview that allows us to establish preventive care according to each patient's needs ^{(1, 2, 3, 4, 5, 9)}.

To determine the age at which a dog or cat has reached the senior and geriatric stages, it is important to consider that internal factors (species, breed, adult weight and size ⁽⁴⁾) and external factors (environment, nutrition, etc.) have a direct effect on the animal's rate of aging ⁽²⁾. It is generally known that small dogs have a longer life expectancy than large and giant dogs, which is why they reach the senior and geriatric stages later (Figure 1). In cats, although there is little variation in adult size and weight, there is variation in when each cat reaches the different life stages.

Figure 1. Age at which dogs of different sizes and cats reach the senior and geriatric stages

Aging is not a pathological process, nor is it synonymous with poor health. It refers to the progressive and irreversible changes that take place in a living organism from maturity onward, reducing its ability to meet the demands of its environment and increasing its predisposition to disease and death ^(1,3,4,5).

Some of these changes are obvious, such as limited movement due to joint degeneration, loss of muscle mass, graying of the coat, reduced skin elasticity and diminished response to stimuli. However, changes in metabolic rate, cardiac and pulmonary function, and the reproductive, immune, digestive and dermatological systems, among others, directly or indirectly affect the animal's homeostasis and immune response ⁽¹⁾. Whether visible or not, these changes begin at different times in each pet. It is the veterinarian's responsibility to identify them and, as far as possible, develop a comprehensive plan that helps minimize, prevent and slow down the animal's aging process ⁽¹⁾. This plan must certainly include nutritional management, which will allow us to:

• Maintain an optimal nutritional status (by providing an appropriate diet)
• Improve the patient's quality of life ^(1,5)
• Delay the onset of the aging process ⁽¹⁾
• Extend life expectancy ^(1,5)
• Slow the progression of aging ⁽¹⁾
• Eliminate and/or relieve clinical signs of disease ^(1,5)
• Maintain an ideal body condition ^(1,5,6)
• Preserve joint health to maintain mobility ⁽⁶⁾

Below, we discuss the considerations to keep in mind when developing a feeding plan for senior and geriatric dogs and cats.

1. OVERALL HEALTH STATUS

The first step in developing an appropriate nutritional plan for geriatric pets is undoubtedly to determine the animal's health status. We know that common diseases are highly prevalent in geriatric patients, including heart disease, kidney dysfunction, neoplasia, and cognitive, joint, liver and endocrine disorders, to name a few. These diseases can occur individually or together, with no particular order of onset or severity.

It is important for the veterinarian to gather a complete medical history and perform a thorough clinical examination, including laboratory and imaging studies (ultrasound, radiographs), to define the animal's health status and confirm or rule out underlying disease in an apparently healthy animal ^(4,6,8). This information will be useful for developing a comprehensive program for the pet and identifying areas of opportunity that can be addressed nutritionally ^(5,7).

• CHANGES IN FEEDING BEHAVIOR

Any change in appetite, water and/or food intake, oral health or body condition is especially important in geriatric patients, as it may be an early indicator of underlying disease ^(1,5). The veterinarian must determine the cause of these signs; for example, whether reduced food intake is a sign of painful periodontal disease or anorexia due to a physiological condition.

• KEY POINTS IN THE NUTRITION OF GERIATRIC PATIENTS
• Gastrointestinal changes.
  • Secretions. A decrease in the secretion of saliva and gastric juices has been observed.
  • Absorptive surface. Most nutrients are absorbed in the small intestine, mainly thanks to the microvilli of intestinal cells, or enterocytes. In geriatric animals, these microvilli have been reported to shrink, which reduces the available absorptive surface ⁽³⁾.
  • Intestinal motility. Longer gastric emptying time combined with reduced intestinal motility increases the predisposition to constipation ⁽³⁾.
  • Gut microbiota. A balanced intestinal bacterial population is key to the fermentation and absorption of certain nutritional compounds ⁽³⁾.
  • Nutrient absorption capacity. It has been theorized that gastrointestinal changes alter the nutrient absorption capacity of geriatric animals in one way or another; however, studies in healthy geriatric animals conclude that digestive efficiency appears to be maintained as animals age ⁽¹⁾.
  • Function of accessory organs. The liver and pancreas play a very important role in digestion and the subsequent absorption of nutrients ⁽⁵⁾. It is important to monitor the endocrine and exocrine function of these organs in geriatric animals. The gold standard is a complete biochemical profile combined with abdominal imaging.
  • Stool quality. The amount and consistency of the stool should be monitored constantly to detect the onset of a digestive problem in the geriatric animal in time ⁽⁴⁾.
• Changes in physical activity level.

Although physical activity is not a nutritional parameter in itself, it has a direct effect on an animal's energy requirements. Geriatric patients tend to become less active due to various changes, mainly sensory and joint-related. A sedentary lifestyle reduces the energy requirements of geriatric animals by approximately 20%, and since absorption capacity is maintained throughout life, adjusting the diet is recommended to reduce the likelihood of weight gain and the problems that come with obesity ^(3,5).

• Changes in body condition.

The aging process is associated with a loss of muscle and bone mass ^(1,3). Constant monitoring of the patient's body weight therefore allows early diagnosis of weight gain or sarcopenia (loss of lean body mass), so the attending veterinarian can intervene early to slow the progression of the problem and prevent the potential adverse effects of overweight or sarcopenia ^(4,6).

Sarcopenia is often accompanied by an increase in fat tissue; in other words, muscle mass is lost while fat is gained. This is why obesity is highly prevalent among geriatric animals ^(1,3,5).

As mentioned, nutrient absorption capacity is not reduced in geriatric patients, but energy requirements are. If the same energy intake is mistakenly maintained in a geriatric animal that uses less energy due to limited physical activity, it is likely to become overweight or obese ^(1,3). Excess weight can lead to chronic inflammatory diseases, osteoarthritis, pancreatitis, hypertension, insulin resistance and diabetes, among other conditions. In geriatric patients, it considerably reduces quality of life and life expectancy, and it worsens degenerative joint disease by increasing the load on the joints ⁽⁴⁾.

The counterpart of overweight is cachexia, which should not be ignored either. Reduced food intake, decreased appetite, loss of the sense of taste and reduced nutrient absorption due to various diseases must be diagnosed and treated with the same importance as overweight.

Both cachexia and overweight increase the risk of various diseases, shorten life expectancy and raise the likelihood of death. The Body Condition Score (BCS) is a tool that evaluates body shape and the palpation of bony structures to estimate the animal's muscle and fat tissue ⁽⁴⁾.

• NUTRITIONAL REQUIREMENTS OF GERIATRIC ANIMALS.
• Water. Water intake is often taken for granted; however, water is an essential nutrient for maintaining animals' health, especially in geriatric animals. As animals age, their sense of thirst decreases, particularly in cats, which tend to drink small amounts to begin with ⁽⁵⁾. Mature animals often undergo changes in osmoregulation which, combined with the high prevalence of kidney problems, the use of drugs (diuretics) and a reduced ability to concentrate urine, predispose them to greater fluid loss and dehydration, which can even affect their ability to regulate body temperature ^(5,7).

It is important to encourage geriatric animals, particularly cats, to drink an adequate amount of water every day. This can be achieved by offering free access to clean, fresh water in clean bowls and, if necessary, using fountains that encourage animals to drink several times a day. Another way to provide water indirectly is through the diet, either with wet food (canned) with a high moisture content (>75%) or with dry food (kibble) with added water ⁽⁵⁾.

• Energy. As animals age, they undergo changes that directly affect their energy requirements: they begin to lose muscle mass (sarcopenia), and their basal metabolic rate and body temperature gradually decrease ⁽³⁾. Mature dogs and cats tend to be slower ⁽¹⁾, less active and may have compromised thyroid function. All of these changes result in a decrease (approximately 20–30%) in the energy requirements of geriatric animals ^(1,3). There are several methods for calculating an animal's energy requirements, but all agree that weight is key to the calculation; therefore, if the activity level, loss of lean mass and/or increase in fat tissue are not taken into account, errors can be made in the calculations ^(3,5,7).

The choice of diet, feeding regimen and recommended amount must ensure that all nutrients are provided in the right quantities (a complete and balanced diet) to avoid nutritional imbalance, while supplying the energy needed to maintain an adequate body condition.

• Fat. Fat serves several nutritional functions: it is a source of reserve energy, adds palatability to food, aids the use of fat-soluble vitamins, provides essential fatty acids ⁽¹⁾ and largely determines a food's caloric density. Eliminating fat completely from the diet of geriatric animals would lead to nutritional imbalance. The key to providing enough nutrients and energy while preventing overweight is to choose a diet with quality ingredients and a balanced nutritional profile designed for geriatric patients.
• Fiber. As mentioned above, geriatric animals often have slower gastric emptying, reduced intestinal motility, low water intake and limited physical activity, which predisposes them to constipation ^(1,5). Fiber promotes gastrointestinal health through several mechanisms: it stimulates intestinal motility (peristalsis) and provides nourishment for the gut microbiota ⁽⁵⁾.
• Protein. There is some controversy regarding protein, mainly concerning the level provided in the diet. Rather than increasing or decreasing the inclusion level, what really matters is protein quality, as this determines the availability of amino acids to meet the animal's needs ^(1,5,7). Modifying the protein content of a diet can lead to a nutritional imbalance that puts the animal's health at risk.
  • Healthy patients. Research shows that there is no reason to reduce protein intake in healthy geriatric patients, especially considering that protein not only helps maintain muscle mass but is also needed for protein synthesis and a good immune response ⁽⁵⁾.
  • Patients with kidney disease. Without going too deeply into the pathophysiology of the disease, we know that protein intake should be reduced in animals with kidney disease. Although this article is not about the nutritional management of these patients, the first step for the attending veterinarian is to determine the animal's health status in order to have enough information to establish appropriate nutritional management.
• Micronutrients
  • Vitamins. Any imbalance in dietary vitamins, whether deficiency or toxicity, can trigger a health problem. Commercial foods labeled as complete and balanced should, in theory, have the right vitamin profile to meet the requirements of the animal they are intended for, which is why the use of vitamin supplements is somewhat controversial ⁽¹⁾.
  • Minerals. Minerals play a very important role in the diet of a geriatric animal. For example, a calcium deficiency can predispose to osteoporosis, while an excess predisposes to calcium oxalate urolithiasis. Another example is phosphorus, which plays an important role in kidney function ⁽¹⁾ and works in relation to calcium.

Minerals often have a direct effect on urine pH, which in turn affects the likelihood of developing uroliths. These can be prevented by adding sodium chloride to encourage water intake and thus promote urine dilution.

In conclusion, it is important to know in detail the specific function of each mineral and the effects of its deficiency and toxicity, and to determine the mineral requirements of the patient in question ^(5,7).

• Antioxidants

The consequences of oxidative stress (free radical damage) to cell membranes, proteins and DNA (deoxyribonucleic acid) contribute to worsening a wide variety of degenerative diseases. Free radicals can be produced for many reasons, such as pollutants and radiation, although the main source is oxidative metabolism. Antioxidants are molecules that protect the body by “trapping” free radicals to reduce the damage they can cause.

• USE OF SUPPLEMENTS AND/OR NUTRITIONAL ADDITIVES (NUTRACEUTICALS).

A functional ingredient or nutraceutical is commonly defined as an ingredient that provides physiological benefits beyond nutrition. So-called specialized, prescription or veterinary diets not only meet animals' nutritional requirements but, thanks to the inclusion of nutraceuticals, also have preventive and/or therapeutic effects ⁽⁶⁾, such as improving intestinal health or supporting the joints and heart function. Figure 2 shows some of the systems affected in senior cats and the functional ingredients that can help in treating these conditions.

Figure 2. Supporting ingredients

1. NUTRITIONAL MANAGEMENT
   1. Palatability. Geriatric patients commonly show diminished senses ⁽³⁾, particularly smell and taste, which are essential for detecting the flavor of food and can therefore affect food acceptance. Food for geriatric animals should be highly palatable (pleasant to the taste) so that it is appealing to the animal. If necessary, wet food or mix feeding (a combination of dry and wet food) can be used to encourage intake and ensure the patient consumes all the nutrients it needs for its life stage ⁽¹⁾.

Remember how important it is to prevent young or geriatric cats from going through episodes of anorexia, as the risk of developing hepatic lipidosis is very high.

• Digestibility. Digestibility is the fraction of food consumed that does not appear in the feces and is therefore absorbed in the gastrointestinal tract. Nutrient bioavailability is the main requirement for evaluating the nutritional quality of a food.

A food's digestibility is determined by its formulation, the quality of its raw materials and the production process. The higher the quality of the raw materials, the greater the digestibility and use of nutrients, ensuring the animal's nutritional intake.

• Texture. There are different types of food on the market: dry (kibble), wet (canned meats) and semi-moist (treats), each with its own benefits and limitations. One of the main differences is palatability: wet foods tend to be more palatable, which is a great advantage in geriatric patients whose appetite is sometimes reduced ⁽¹⁾.

Periodontal disease is highly prevalent in geriatric patients ^(5,7). As mentioned, it can significantly affect their feeding behavior, since it can cause pain and inflammation, tooth loss and a consequent decrease in food intake.

The texture of dry food (kibble) can have an abrasive effect that helps reduce the formation of dental calculus (tartar) and the resulting periodontal disease. Wet food lacks this abrasive action, so tartar tends to build up; however, its contribution to indirect hydration, which is especially important in cats, and its high palatability are reasons enough for owners and veterinarians to keep offering wet food to pets.

When developing food for geriatric patients, manufacturers usually take this important aspect into account and design kibble specifically for these patients; however, the individual animal's preference and circumstances will be decisive ⁽¹⁾.

• Feeding regimen. The key is to meet nutritional requirements and prevent weight loss and/or gain. Given the predisposition to weight changes, and to make sure the animal eats the right amount of food, the feeding regimen should be chosen according to each patient's needs. Some patients will be thin, and free-choice feeding may be the best option, while others will be obese or prone to overweight and will need controlled feeding ⁽¹⁾. The reality is that nothing is general in geriatric patients: everything must be individualized according to each animal's needs. Remember that any stressful situation can cause a cat to stop eating, so in geriatric animals, and especially cats, changes should be made gradually ⁽¹⁾.
  • Choosing the diet. As with any nutritional management, the first step is to evaluate the current diet and determine whether the formula's nutrient concentration meets the specific requirements of the animal in question. If necessary, change the food.

Review the diets available on the market and choose the one that provides the necessary nutrients according to the animal's needs. An important point to consider is cost: the food chosen should not only meet the animal's nutritional needs but also fit the owner's budget.

Considering that many factors (species, size, weight) determine when and how fast aging occurs, it becomes clear that each geriatric patient is unique and its management must be personalized ⁽¹⁾. A comprehensive plan that includes preventive medicine, drug therapy and nutrition will allow the attending veterinarian to improve patients' quality of life. Once the plan is in place, the veterinarian should carry out periodic check-ups, preferably every six months ⁽⁴⁾, to evaluate the results and, if necessary, make adjustments to reach the goal: improving the geriatric patient's quality of life ⁽⁶⁾.

CONCLUSIONS

It is very important for veterinarians to dispel the common idea that aging is synonymous with disease. Aging is a natural process that, although it brings changes that somewhat reduce the animal's ability to meet the demands of its environment, does not mean its quality of life must decline in any way.

Early detection and treatment of these changes give the attending veterinarian the opportunity to develop comprehensive plans that help counteract, lessen or slow them down. A complete and balanced, high-quality diet with functional ingredients that benefit the animal's health has great potential to prevent many diseases.

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