Aging is a complex biological process that is not always easy to define. Aging involves increasing damage and loss of function that occurs over time at both the molecular and cellular level as well as at the level of the entire animal. Many age-related changes can be managed to maintain quality of life (QOL), and age-related diseases may be manageable or curable. In human medicine, the disciplines of geriatrics (the study of diseases of the elderly) and gerontology (the study of the social, psychological, and biological aspects of aging) are well-established. This focus on the unique needs of aging individuals is an emerging field in veterinary medicine. Understanding the changes associated with feline aging opens the doorway for improvements in quality and quantity of life.

Veterinary medicine is starting to consider the concept of frailty, which is important in the care of elderly people. Frailty is a syndrome that is more common in advancing age and describes decreased functional reserve that leads to a decline in physiologic and cognitive performance and increased vulnerability to adverse medical outcomes. In effect, frailty measures may act as proxy measures for aging and mortality. In human medicine, frailty scales based on physiologic, psychologic, and social functions are used to identify affected people.1,2 The concept of “prefrailty” – a clinically silent process that predisposes individuals to frailty – is also taking shape in human medicine.³

Although no studies have been published as of this writing on frailty assessment in cats, some research has been conducted in dogs. In one study, a geriatric health evaluation score that assesses the status of 13 body systems was used to develop a five-component clinical definition of a canine frailty phenotype.⁴ A cohort of guide dogs at least 13 years of age was assessed, and the researchers concluded that signs of frailty appear to be a risk factor for death in dogs, independent of age. In another study where a frailty index was designed for dogs, there was a moderate correlation between increasing age and increasing frailty, and increasing frailty index was strongly correlated to mortality.⁵ Increased awareness of frailty in aging companion animals may help discover risk and predictive factors as well as interventions.⁶

According to published figures, about one-third of American and Canadian households own at least one cat.^7,8 Many of these are older cats. For example, a 2008 Canadian survey found that 35% of owned cats are greater than 8 years of age.⁷ In 2011, it was estimated that over 20% of pet cats in the United States were 11 years of age or older.⁹ In the United Kingdom, a 2017 study reported that over 40% of cats presenting for veterinary consultations were >8 years of age.¹⁰

The 2021 American Animal Hospital Association (AAHA)/American Association of Feline Practitioners (AAFP) Feline Life Stage Guidelines define a mature cat as 7 to 10 years of age and a senior cat as >10 years of age.¹¹ The 2021 AAFP Feline Senior Guidelines Task Force considers the term “senior” to describe age, with the description being patient-dependent.¹² Some patients may meet the criteria of being senior as early as 8 years of age while certain breeds or cats with genetic predispositions may be considered senior even earlier. The AAFP Task Force concluded that the term “geriatric” represents a statement of health status rather than being defined by a specific age. An end-of-life stage as defined by the AAHA/AAFP Life Stage Guidelines Task Force can occur at any age.¹¹

Veterinarians are frequently asked about the human equivalent of a cat’s age. In general, senior cats (11 to 14 years) and geriatric cats (>15 years) are comparable to humans aged 60 to 72 and 76 to 100 years, respectively (see Fig. 8.2). Although these age comparisons are helpful, it is important to remember that the process and speed of aging varies among individuals and may be influenced by genetics, nutrition, environment, and other factors. A cat’s chronologic age is not a good indicator of functional age, and even within an individual, different organs may age at different rates.

It is less than ideal to ascribe signs of illness to aging alone. For example, pain or dehydration might lead to clinical signs that caregivers attribute to the “slowing down” of old age, yet these are physical conditions secondary to underlying disease. Although knowledge of the changes in physiology and prevalence of disease resulting from aging is an important part of health care for senior cats, decisions on disease management should never be made based on age alone. Making a diagnosis and formulating a treatment plan should never be avoided simply because of the age of the patient. Many problems of senior cats are chronic and progressive so that early diagnosis and treatment are important for pain management and preservation of QOL. All living creatures are entitled to the “Five Freedoms” of life (Box 47.1).¹³ The goal for the clinician and caregiver should be to ensure that the senior patient is granted these freedoms and that they are protected and maintained until the end of life. The caregiver will require additional support from the veterinarian and veterinary team when hospice and end of life decisions are being considered.

Veterinarians should be familiar with normal aging changes, as well as the common medical problems of senior cats. Appropriate educational support for the caregiver that highlights the normal changes to expect with aging, as well as early signs of disease is invaluable. The physiology of aging in cats is not well-studied. Most information is extrapolated from other species or learned through observation of disease states. The impact of aging may be obvious (e.g., white hairs, dulling of senses) or it may consist of physiologic changes that are more difficult to appreciate. To understand what is normal and abnormal in the aging cat, clinicians caring for senior cats should be aware of the influence of aging on these organs and body systems:

Studies looking at age-related changes in the feline immune system are currently limited. Data extrapolation from humans and models in other species (e.g., murine, canine) can be challenging. The concept of inflammaging (aging characterized by chronic, low-grade inflammation) is well-developed in human gerontology.14 Immunosenscence (reduced sensitivity to external pathogens) and hypervigilance to autologous tissues are concepts of consideration in the study of feline aging.^15,16 Changes in cats >10 years compared with younger cats include lower total leukocyte counts with specific reductions noted in the number of B cells, CD56+ natural killer cells, as well as numbers of CD4+ and CD8+ T-lymphocytes.¹⁷ An overall reduction in the CD4/CD8 ratio has also been noted.^17,18 Despite a reduction in B cell numbers, cats aged 10 to 14 years were shown to have elevated serum concentrations of IgM and IgA.¹⁷ This suggests a preserved ability to mount humoral immune responses despite an apparent reduction in cell-mediated immunity. Unfortunately, no studies looking at neutrophil function in aging cats are available. Immune function may be further affected by the presence of chronic disease states and immunosuppressive drug therapy, leading to increased risk of infection. Limited studies suggest aging cats can retain effective immunological memory and protective titers against core vaccine viruses.¹⁵ However, in a study of >2000 cats receiving a primary course of vaccination against rabies, older cats had a significantly greater chance of failing to achieve the titer of 0.5 IU/mL required for international travel.¹⁹

Collagen and elastin content is reduced in skin with aging, leading to thinner, less elastic skin. Blood flow to the skin is also reduced. These changes may make assessment of hydration using skin turgor difficult. The coat may become thinner, and some senior cats may exhibit areas of focal alopecia. Senior cats experience changes in sebum production and groom less efficiently than younger cats, leading to dull or greasy coats, dander, and matting (Fig. 47.1).

These changes may increase the risk of skin infection. Decreased grooming may occur secondary to general malaise, arthritis pain, painful oral disease, and/or obesity (Fig. 47.2, e-Fig. 47.1). Increased grooming may occur secondary to external parasites, skin disease, or referred pain. For example, cats with painful conditions such as urolithiasis (Fig. 47.3) or coxofemoral joint arthritis may barber the hair of the ventral abdomen. Nails often become overgrown, thick, and brittle, requiring more frequent care (Fig. 47.4, e-Fig. 47.2). Senior cats are at increased risk of neoplastic skin conditions. This is particularly applicable in the case of white cats and/or chronic solar exposure. Cats may show visible photo damage changes that are non-neoplastic such as sub-epidermal edema, sclerosis, telangiectasia, squamatization of basal keratinocytes, and increased epidermal thickness. These changes may predispose to the development of squamous cell carcinoma or melanoma.¹⁶

Physical and functional changes in the organs of the special senses are known to occur with age. Changes in the eyes may not be pathologic in nature or interfere with vision, but in other cases may be a sign of disease (Fig. 47.5). Lenticular sclerosis is a normal aging change that does not affect vision, but that may be misinterpreted as a cataract. Cataract formation is more common in aging dogs than cats but does increase in prevalence in the aging feline. One study examined 2000 normal cats, 50 cats with diabetes mellitus, and 100 cats with a history of a health crisis associated with dehydration.²⁰ By the age of 17 years, all cats studied were affected by some degree of lens opacity. Pupillary light responses were slower, resulting in part from iris atrophy. Retinal changes may occur secondary to hypertension.²¹ Deposition of melanin in the iris is sometimes difficult to distinguish from melanoma (Fig. 47.6) so referral to a veterinary ophthalmologist may be warranted in some cases. Atrophy of the iris muscle may also occur, in some cases making the iris appear scalloped. When compared with cats 1 to 3 years of age, adult and older cats have increased reactivity to auditory stimuli.²² Decreased olfactory function and taste sensation have not been documented in cats with aging but are likely to occur. The hypothesized changes in smell and taste may impair appetite.

Chronic kidney disease (CKD) is a common clinical finding in aging cats, affecting up to 80.9% of cats over 15 years of age.23 Aging causes decreases in kidney size, blood flow, and glomerular filtration rate. Mineralization of the renal pelvis is not uncommon, although the significance is unknown, and should not be confused with nephrolithiasis. Cats with CKD are 3.5 more times likely to be hypokalemic than cats with normal kidney function.²⁴ In cats >7 years of age, calcium oxalate uroliths are more common than struvite uroliths in many countries.²⁵

Aging cats will have clinically apparent, but age-appropriate, changes in musculoskeletal function including a decrease in lean muscle mass and deterioration of joint components.¹⁶ Although these changes are a normal part of aging, they can cause or contribute to pain, lead to frailty, and predispose to injury or other disease. Aging cats may exhibit signs of decreased agility and flexibility. Aging will naturally lead to some decrease in muscle strength that can be related to loss of muscle mass; however, muscle weakness may also be observed in senior cats with dehydration, severe disease, hypokalemia, anemia, or other pathologic changes. Weakness may also be associated with sarcopenia, which is a gradual decline in muscle mass associated with aging that occurs in the absence of disease. In contrast, cachexia is a pathologic loss of muscle mass that may be more rapid than sarcopenia and is more often associated with disease (Fig. 47.7). The physical manifestations of sarcopenia and cachexia contribute to frailty. Cats >14 years of age have a 15-fold increased risk for being underweight or cachectic compared to young adults.²⁶ Loss of body mass is an important factor in aging cats, as it can be associated with decreased survival. In a study that followed 90 healthy, aging, non-obese cats until death from natural causes found that nearly all cats lost weight in their senior years, with an average loss of almost 50%.²⁷ Loss of body weight, body fat, and lean body mass were all significantly associated with an increased risk of death. The results showed that the risk of death was increased by each 100 grams of weight loss (6.4%), each 100 grams of lean body mass loss (20%), and each 100 grams of fat mass loss (40%).

Musculoskeletal changes noted during the consultation may be indicative of pain related to degenerative joint disease (DJD) and/or other disease processes. Degenerative joint disease includes, by definition, all types of degenerative pathology in any type of joint. This includes osteoarthritis (OA), spondylosis deformans of the intervertebral disc, isolated degenerative lesions (e.g., enthesophytes), traumatic arthritis, and non-OA related degenerative soft tissue mineralization within joints (e.g., menisci, ligament) (Fig. 47.8). Senior cats have a high prevalence of DJD, but radiographic changes may not correlate with clinical signs.²⁸ It is worth noting that bridging spondylosis of the intervertebral disc spaces, also known as spondylosis deformans, is believed to contribute to behavior changes secondary to musculoskeletal pain.²⁹

A healthy mouth in a cat should be free of periodontal disease, tooth resorption (TR), oropharyngeal inflammation, oral masses, and fractured teeth. Enamel layers stay the same thickness as teeth age, while pulp chambers decrease in width and dentin walls thicken. This results in increased tooth density that appears as an off-white to yellow color. The teeth may also have a glassy or transparent look. Periodontal disease increases in frequency and severity with age and the risk of TR increases with age.30,31 The associated pain can diminish overall QOL and contribute to inappetence and weight loss. Age alone should not prevent the pursuit of general anesthesia to treat dental disease in cats. Cats diagnosed with dental pathology should be started on pain management and scheduled for dental surgical care as soon as possible.

There are very little data available on changes in GI tract function in aging cats, although it is evident that they experience a decline in digestibility of energy and other nutrients.³² Appetite may be diminished because of oral disease including pain, periodontal disease, and oral neoplasia as well as difficulty with prehension and/or swallowing; this is called pseudoanorexia. Reduced nutrient digestibility in senior humans has been linked to reduced pancreatic enzyme availability, delayed gastric emptying, and alterations in bile composition.³³ Although GI transit times are similar between young (3.0 ± 0.9 years) and senior (11.6 ± 1.4 years) cats, there is variability in total transit time among senior cats.³⁴ Rapid transit times may predispose to maldigestion, and slow transit times may result in bacterial overgrowth and stool dehydration. This latter may predispose senior cats to constipation. Constipation is a common presentation in older, overweight cats and cats with CKD.³⁵ In a survey that included 43 caregivers of cats with CKD, 42% of cats defecated less than once daily.³⁶ This was significant compared to apparently healthy cats. Elderly humans have reduced colonic motility that may be a predisposing factor for development of constipation if the same change is seen in aging cats.³⁷ In a study of fecal samples from cats in 25 shelters in the United Kingdom, increasing age was associated with decreased risk of diarrhea and increased risk of constipation.³⁸ However, severe diarrhea was associated with being >11 years old. Esophageal function changes noted in elderly humans, such as decreased clearance of esophageal contents, may predispose to dysphagia and gastroesophageal reflux if they also occur in cats.³³

Cardiac changes can vary among aging cats and may or may not indicate a pathologic process. Physical examination may be unremarkable, but new auscultatory findings such as a murmur, gallop rhythm, or an arrhythmia may be cause for concern. Murmurs detected for the first time or murmurs that have progressed in grade from previous assessments are of more concern than previously detected, stable murmurs. It is important to realize that the grade of murmur is not necessarily consistent with the severity of the disease, such that any cat with a murmur should have an echocardiogram. Certain changes in the radiographic cardiac silhouette may be age-related and not necessarily a sign of disease. These include a tipped heart with increased sternal contact in the lateral view (Fig. 47.9), as well as a prominent and/or wavy aortic arch.³⁹

The prevalence of hypertension increases with age in cats.40,41 Target organ damage associated with the retina, central nervous system, heart, and/or kidneys may be observed. Presenting complaints associated with hypertension include abnormal behaviors, such as abnormal howling, particularly at night, that might be mistaken for an aging change. Cats with CKD are at increased risk of developing hypertension,⁴⁰ and therefore should have more frequent blood pressure evaluations than younger cats.

Very little is known about specific respiratory system changes that occur in aging cats. Changes likely reflect those found in humans, including decreased pulmonary elasticity, respiratory muscle strength, and chest wall compliance. Increased bronchointerstitial patterns may be seen in senior cats.⁴² Based on decreased cellular immune function and decreased incidence of asthma in older cats, it has been proposed that airway reactivity may decrease with age in cats.⁴³ Finally, the presence of thoracic tumors may negatively impact normal respiratory and/or esophageal function.

Unfortunately, the AAHA estimates that only 14% of senior pets receive regular health screenings recommended by veterinarians.44 The main obstacle identified is lack of clear recommendations from the veterinary health care team.

Components of preventive health care by life stage are found in Table 8.1. A comprehensive examination, history assessment, and minimum database (MDB; Table 47.1) are recommended every 6 months for senior cats.¹¹ An increased frequency of examination is warranted because an individual’s health status may change rapidly in this age group and early detection and treatment of problems is important to preserve QOL and diminish the risk of frailty. As well, the signs of illness in cats are often subtle and may go unnoticed by caregivers until the problem is well-advanced (Box 47.2). Senior cats with chronic diseases may require even more frequent evaluation and laboratory testing. The frequency will depend on health condition(s), disease(s), and the medication(s) in use.

Consultations and physical examinations for senior cats should follow recommended guidelines, as outlined in Chapter 8: Preventive Health Care for Cats. A feline-friendly approach should always be utilized. To implement feline-friendly interactions and provide a thorough consultation and physical examination, 30-to-40-minute appointments are appropriate for senior cats. This will allow sufficient time for the necessary assessments. Physical examination of a senior cat is similar to that for younger cats but there should be a focus on certain aspects. For example, retinal examination is critical to detect evidence of hypertensive retinopathy, and the ventral neck should be palpated for the presence of cervical nodules suggestive of goiter.

Assessments that are important in health care for all cats (e.g., nutrition, pain) are even more important for senior cats. A nutritional assessment should focus on the needs of the senior cat that are influenced by age and disease. Health conditions in senior cats are frequently associated with pain (Box 47.3). A pain assessment should be performed at every visit and should always be performed first so that an analgesic may be administered promptly to facilitate the rest of the examination. More information on pain management for chronic conditions is found in Chapter 6: Assessment and Management of Pain. As previously mentioned, the prevalence of hypertension increases with age so blood pressure measurement should be performed (Fig. 47.10). More information on hypertension and assessing blood pressure is found in Chapter 23: Cardiovascular Diseases.

In addition to routine measurement of body weight, the patient’s body condition score (BCS; see Fig. 3.3) and muscle condition score (MCS; see Fig. 3.4) should be evaluated and recorded at each visit. This is particularly important with senior cats, but valuable at all life stages. Body condition scoring is useful for identifying obese patients that will require weight loss as well as those patients that are poorly conditioned for their body size. As previously mentioned, unintended loss of lean and fat body mass may be an indicator of disease. Cats with chronic diseases should have body weight, BCS, and MCS monitored regularly. Careful assessment of muscle condition is important as some senior cats have an increased BCS combined with muscle wasting (Fig. 47.11).

While no frailty scales or tools have been developed in veterinary medicine as of this writing, simple scales used in human medicine may serve in the meantime to help veterinarians identify and acknowledge frailty in senior cats. Table 47.2 is a phenotype frailty scale based on specific physiologic factors² and Table 47.3 is an index frailty scale that incorporates psychological factors and social function which may help identify cognitive decline.¹

The MDB (Table 47.1) for evaluation of senior cats includes a complete blood count (CBC), serum chemistry panel, urinalysis including microscopic sediment examination, and total thyroxine concentration (TT₄). In-house equipment and reference laboratories should use reference ranges specific to senior cats, as many components of the MDB vary with age. In a study of 100 apparently healthy cats, those >10 years of age had significantly higher platelet, blood urine nitrogen, and bilirubin values compared to cats 6 to 10 years of age.⁴⁵ They also had lower packed cell volume, albumin, and calcium values with some overlap between the groups.

Depending on risk factors and clinical signs, fecal examination and retrovirus testing may also be indicated. Trending of creatinine values and assessment of other kidney function tests in association with muscle condition scoring is essential to properly assess the patient’s renal function.

More research is needed to understand the response of aging cats to primary vaccination and revaccination. Based on the available data, the 2020 AAHA/AAFP Feline Vaccination Guidelines recommend healthy senior cats and those with stable chronic diseases receive vaccinations according to the same principles as younger cats.⁴⁶

As mentioned earlier, senior cats tend to lose body weight, fat mass, and lean body mass as they age. An investigation of changes in body composition with aging found that lean body mass drops dramatically after 12 years of age, and that by age 15, cats may have a mean lean tissue mass <2 kg (4.4 pounds), one-third less than cats 1 to 7 years of age (mean, 3 kg [6.6 pounds]).47 Mean percentage body fat also decreases progressively after 12 years of age so the lean body mass to fat ratio does not show significant changes with aging.⁴⁷ The combination of reduced lean body mass and body fat contributes to the frail look of many elderly cats (Fig. 47.7).

The prevalence of obesity decreases with age in cats; in fact, senior cats tend to be underweight. In a report of 191 cats at the Waltham Centre for Pet Nutrition (Melton Mowbray, United Kingdom) ranging in age from 1 to 13 years, the heaviest cats were neutered males aged 5 to 8 years, while cats >11 years had a tendency to exhibit lower body weights than younger cats.⁴⁸ In a survey of >2000 cats presented to veterinary hospitals in the northeastern United States, the proportion of overweight cats increased until 7 years of age, after which it declined, especially in cats >10 years of age.⁴⁹ Longitudinal data collected on 53 healthy cats >11 years of age at the Waltham Centre indicates that for most cats weight loss or weight maintenance, rather than weight gain, is a feature of old age.⁴⁸ After 8 years of age, 50% of cats in that report maintained weight and 30% lost weight. It appears that a significant proportion of obese middle-aged cats die before reaching old age (e.g., from diseases such as diabetes mellitus or hepatic lipidosis), and a similar proportion lose weight into their senior years. Senior cats that are obese have probably been obese for most of their lives.

Changes in digestive efficiency occur with age and may contribute to weight loss. Older cats are less efficient at digesting fats and proteins. In one study, 22% of cats >14 years old had protein digestibility of <77%, and 33% of cats >12 years old had fat digestibility of <80%.⁵⁰ To compensate, senior cats may need to increase daily food intake by as much as 25%. In a study of 85 senior cats on a long-term feeding study spanning 7 years, there was a significant increase in total kcal/kg body weight ingested and total daily food consumption in cats from 10 to 15 years of age.^51,52 Despite the increase in caloric intake, body weight decreased with age, particularly after age 13. Reasons for this susceptibility to weight loss may include changing physiology, presence of diseases, and decreased appetite because of dulling senses of taste and smell.

Until about 11 years of age, a cat’s maintenance energy requirement (MER) decreases by about 3% per year.⁵³ After 11 years of age, the MER increases. This may contribute to the tendency of senior cats to be underweight if their energy needs are not met. In contrast, humans and dogs experience a decline in MER of about 20% with aging.⁴⁸

Many senior cats, especially those 12 years of age and older that are not obese, will benefit from being fed a palatable food that is highly digestible, and energy dense with high-quality protein. Ideally food should be offered in small amounts frequently to maintain body weight and lean tissue mass and to avoid protein:calorie malnutrition.⁵⁴ Protein:calorie malnutrition is associated with important detrimental effects, such as muscle wasting, anemia, hypoproteinemia, delayed healing, decreased immune function, and compromised function of major organ systems (GI, pulmonary, cardiovascular).⁵⁵ More information on nutrition for senior and geriatric cats is found in Chapter 19: Nutrition for the Normal Cat.