Although it is often misconstrued as such, aging is not a pathological process but rather comprises the normal, time-dependent changes that occur during the later stages of life in every animal. Today, it is generally accepted that healthy aging is achievable in both humans and animals and should be promoted through effective health-care programs. Aging wellness has been defined as “the development and maintenance of optimal mental, social and physical well-being and function in older adults.”1,2 Important components of healthy aging in humans include a variety of objective and subjective measures of cognitive, physical, and psychological health.3,4 Although there is a paucity of published research on aging in dogs, it seems likely that healthy aging in dogs would involve similar components.
Developing a working definition of healthy aging is essential for future studies of aging in dogs, and identifying clinical methods that can differentiate healthy aging from disease conditions is essential when assessing older dogs in veterinary practice. A standard definition of healthy aging in dogs relies on the assumption that health can be defined as the absence of clinically apparent disease. Dogs naturally undergo a number of changes as they age,5 but dogs with age-related changes that are minimal or do not negatively affect overall quality of life can be classified as healthy aged dogs.
A variety of factors, including breed and adult body size, influence how quickly dogs age. In general, however, both senior and geriatric dogs are considered aged, with giant- and large-breed dogs (ie, dogs with a mature body weight ≥ 22.7 kg [50 lb]) classified as senior when they are 6 to 8 years of age and as geriatric when they are ≥ 9 years of age, and medium- and small-breed dogs (ie, dogs with a mature body weight < 22.7 kg) classified as senior when they are 7 to 10 years of age and as geriatric when they are ≥ 11 years of age.
In humans, successful aging is defined, in part, as having a low probability of disease or disease-related disability,6 and the same definition can be applied to dogs. For veterinarians in clinical practice, differentiating healthy aging from disease and disease-related disabilities is essential when examining aged dogs. The present report provides a review of methods for assessing aged dogs and criteria for differentiating healthy aging from disease.
General Health Assessment
Experts have recommended that dogs in the last 25% of their predicted life span undergo routine health-care visits, including obtaining a minimum laboratory database, every 6 months.7 During these visits, a thorough history should be obtained and a complete physical examination should be performed, including evaluation of physical condition, vital signs, skin and coat, lymph nodes, hydration, the cardiopulmonary system, and the CNS; abdominal and rectal palpation; and a full orthopedic examination. The minimum laboratory database should include a CBC, urinalysis, fecal analysis, and serum biochemical panel, including measurement of BUN, creatinine, glucose, total calcium, total protein, albumin, and bilirubin concentrations and serum alanine aminotransferase and alkaline phosphatase activities. Serial hematologic and serum biochemical testing has been recommended for geriatric dogs as being a more objective and more sensitive method for detecting disease than physical examination alone.8
Ideally, results of hematologic and serum biochemical testing performed on aged dogs should be compared with reference ranges developed specifically for senior and geriatric dogs, rather than with reference ranges developed for all dogs. The Iams Company Pet Health and Nutrition Center maintains a database of results of routine laboratory evaluation of large numbers of healthy dogs, including large numbers of Beagles and Labrador Retrievers. When reference ranges developed for all dogs (including senior and geriatric dogs) were compared with reference ranges developed for senior and geriatric Beagles (considered typical of small-breed dogs) and with reference ranges developed for senior and geriatric Labrador Retrievers (considered typical of large-breed dogs), some important differences were identified (Table 1). Specific differences that could potentially be clinically important included higher upper reference limits for serum alanine aminotransferase, alkaline phosphatase, γ-glutamyltransferase, lactate dehydrogenase, and creatine kinase activities and lower lower reference limits for serum total protein, globulin, triiodothyronine, and thyroxine concentrations and for lymphocyte, monocyte, and neutrophil counts, especially in senior and geriatric Beagles. These findings suggest that healthy senior or geriatric dogs may have some hematologic or serum biochemical values that differ from those for the general population of dogs. Thus, results obtained from commercial laboratories should be interpreted with caution if reference intervals have not been developed by those laboratories for senior and geriatric dogs.
Reference ranges for CBC and serum biochemical profile results for dogs housed at the Iams Company Pet Health and Nutrition Center.
| Beagles | Labrador Retrievers | ||||
|---|---|---|---|---|---|
| Variable | All dogs | Senior | Geriatric | Senior | Geriatric |
| Albumin:globulin ratio | 0.8–3.7 | 0.8–5.8 | 0–3.0 | 0.8–2.4 | 0.7–2.8 |
| Alanine aminotransferase (U/L) | 21–165 | 16–325 | 20–473 | 27–156 | 24–168 |
| Alkaline phosphatase (U/L) | 14–125 | 12–136 | 12–290 | 17–83 | 18–138 |
| Aspartate aminotransferase (U/L) | 20–64 | 17–221 | 14–137 | 21–57 | 20–64 |
| Albumin (g/dL) | 2.7–4.6 | 2.5–5.1 | 1.9–4.4 | 2.7–4.2 | 2.6–4.4 |
| Calcium (mg/dL) | 9.2–11.3 | 9.1–11.4 | 8.7–11.7 | 9.2–11.1 | 9.2–11.2 |
| Creatine kinase (U/L) | 54–342 | 50–408 | 46–533 | 50–286 | 48–304 |
| Chloride (mEq/L) | 108–124 | 105–125 | 101–119 | 108–124 | 106–124 |
| Cholesterol (mg/dL) | 132–329 | 84–361 | 108–367 | 129–332 | 107–319 |
| Creatinine (mg/dL) | 0.7–1.6 | 0.6–1.3 | 0.5–1.9 | 0.9–1.6 | 0.7–1.6 |
| γ-Glutamyltransferase (U/L) | 3–12 | 3–23 | 3–26 | 3–8 | 3–10 |
| Globulin (g/dL) | 0.9–3.4 | 0.7–3.1 | 0–3.9 | 1.6–3.5 | 1.3–3.6 |
| Glucose (mg/dL) | 72–113 | 71–125 | 65–123 | 71–112 | 75–111 |
| Lactate dehydrogenase (U/L) | 20–321 | 35–399 | 49–460 | 19–324 | 18–350 |
| Magnesium (mEq/L) | 1.4–2.7 | 1.3–2.8 | 1.3–2.6 | 1.4–2.7 | 1.4–2.7 |
| Phosphorus (mg/dL) | 2.8–5.9 | 2.9–6 | 3.1–7.7 | 3–5.8 | 3–6.1 |
| Potassium (mEq/L) | 3.7–5.1 | 3.4–4.9 | 3.3–5.1 | 3.9–5.2 | 3.9–5.3 |
| Sodium (mEq/L) | 142–155 | 140–154 | 141–156 | 143–154 | 142–154 |
| Total bilirubin (mg/dL) | 0.1–0.2 | 0.1–0.3 | 0.1–0.3 | 0.1–0.2 | 0.1–0.2 |
| Total protein (g/dL) | 5.0–6.7 | 4.4–6.7 | 4.6–6.8 | 4.9–6.7 | 4.9–6.8 |
| Triglycerides (mg/dL) | 23–160 | 15–232 | 27–244 | 19–108 | 24–126 |
| Urea nitrogen (mg/dL) | 6.9–25.4 | 5.7–19.9 | 6.5–33.6 | 9–25.0 | 9.9–26.9 |
| Urea nitrogen:creatinine ratio | 7.0–23.9 | 6.7–21.9 | 0–32.4 | 7.5–22.0 | 8.8–23.5 |
| Uric acid (mg/dL) | 0.1–1.1 | 0.1–1.1 | 0.1–0.9 | 0.1–1.1 | 0.1–0.7 |
| Triiodothyronine (ng/mL) | 0.34–1.10 | 0.32–1.30 | 0.2–1.10 | 0.32–1.02 | 0.36–1.00 |
| Free thyroxine (ng/dL) | 0.75–2.40 | 0.59–2.60 | 0.70–2.30 | 0.75–2.10 | 0.61–2.00 |
| Total thyroxine (ng/dL) | 0.66–2.30 | 0.54–2.40 | 0.56–2.10 | 0.76–2.20 | 0.59–2.10 |
| Thyroid-stimulating hormone (ng/mL) | 0.05–0.68 | 0.04–0.81 | 0.04–0.79 | 0.05–0.58 | 0.05–0.73 |
| Hct (%) | 37.2–57.6 | 39.6–60 | 33–51.87 | 35.7–54.2 | 34.5–52.5 |
| Hemoglobin (g/dL) | 12.2–19.0 | 13.2–20.1 | 11–16.9 | 11.9–17.9 | 11.4–17.3 |
| Mean corpuscular hemoglobin (pg) | 21.3–25.3 | 21–24.4 | 20.4–24.8 | 21.6–25.4 | 21.9–25.8 |
| Mean corpuscular hemoglobin concentration (g/dL) | 31.7–34.5 | 31.8–34.5 | 31.3–34.7 | 31.7–34.6 | 31.7–34.8 |
| Mean cell volume (fL) | 65.5–75.7 | 63.7–72.8 | 63–72.54 | 66.4–76.6 | 66.4–76.2 |
| Platelets (× 103/μL) | 153–472 | 147–507 | 145–547 | 166–452 | 163–486 |
| RBCs (× 106/μL) | 5.15–8.36 | 5.82–8.87 | 4.72–7.9 | 4.89–7.84 | 4.84–7.37 |
| WBCs (× 103/μL) | 3.73–11.9 | 3.5–11.1 | 3.45–14.9 | 3.32–10.9 | 3.02–12.0 |
| Band neutrophils | |||||
| Absolute (× 103/μL) | 0.00–0.00 | 0.00–0.00 | 0.00–0.00 | 0.00–0.07 | 0.00–0.05 |
| Differential (%) | 0.00–0.00 | 0.00–0.00 | 0.00–0.67 | 0–1 | 0.00–0.00 |
| Basophils | |||||
| Absolute (× 103/μL) | 0–0.04 | 0–0.05 | 0–0.04 | 0–0.04 | 0–0.04 |
| Differential (%) | 0–0.57 | 0–0.66 | 0–0.55 | 0–0.60 | 0–0.68 |
| Eosinophils | |||||
| Absolute (× 103/μL) | 0–0.72 | 0–0.49 | 0–0.52 | 0–0.63 | 0–0.57 |
| Differential (%) | 0–9 | 0–7 | 0–6 | 0–10 | 0–8 |
| Lymphocytes | |||||
| Absolute (× 103/μL) | 0.61–2.99 | 0.51–3.14 | 0.42–2.93 | 0.61–2.97 | 0.47–2.73 |
| Differential (%) | 9–39.4 | 9–43.5 | 3–38.7 | 10–42 | 7.9–39 |
| Monocytes | |||||
| Absolute (× 103/μL) | 0.03–1.00 | 0.03–1.00 | 0–1.14 | 0.01–1.01 | 0.02–1.06 |
| Differential (%) | 0.44–12 | 0.36–12 | 0–11.9 | 0.13–12 | 0.42–15 |
| Neutrophils | |||||
| Absolute (× 103/μL) | 2.20–8.74 | 1.75–8.9 | 0.25–17.38 | 1.74–7.72 | 1.82–8.5 |
| Differential (%) | 49.5–83.6 | 49.8–85.1 | 51.5–95.7 | 46–82 | 50–86.7 |
Reference ranges were generated on the basis of testing results for 548 healthy dogs, including 81 Beagles (58 between 7 and 10 years of age [senior] and 23 ≥ 11 years of age [geriatric]) and 268 Labrador Retrievers (148 between 6 and 8 years of age [senior] and 120 ≥ 9 years of age [geriatric]), housed at the Iams Company Health and Nutrition Center between February 2002 and July 2011.
Cognitive and Behavioral Health Assessment
Distinguishing healthy aged dogs from dogs with cognitive or behavioral abnormalities presents several challenges, both because a wide variety of medical conditions can result in behavioral signs (Appendix 1) and because some behavioral changes can normally be expected to occur in dogs as they age. Thus, assessing cognitive and behavioral health in aged dogs should include both routine hematologic and serum biochemical testing and a basic behavior assessment, including questioning owners regarding any recent or sudden changes in behavior or temperament (Appendix 2).
One of the most common cognitive abnormalities in aged dogs is CDS.9–11 Although the clinical criteria defining this syndrome have been evolving, a current consensus has emerged around a collection of clinical signs known as DISH, which stands for disorientation and dysfunctions in interactions, sleep, and housetraining. These descriptors make it clear that this syndrome goes far beyond cognitive impairment and is more akin to advanced dementia in humans, which is often associated with behavioral disturbances.12 The diagnosis of CDS typically relies on questionnaires completed by the owner or handler.
Some investigators11 have suggested expanding the definition of CDS to include alterations in activity, increased anxiety, and impairments in learning and memory, yielding the acronym DISHAAL. In addition, it has been suggested that the severity of any alterations along with the age of onset of clinical signs and their duration be considered when making a diagnosis of CDS. Importantly, in dogs with CDS, activity may be reduced or increased, which complicates assessment.
Many of the behaviors reflected in previous descriptions of CDS can be expected to occur with aging in dogs, including changes in attention (which might manifest as confusion), decreases in social interactions, and occasional sleep problems. It is the number and frequency of these behaviors in aggregate as well as the addition of new behaviors that comprise the syndrome.
Several studies13–16 have attempted to determine the prevalence of CDS among aged dogs, with published estimates ranging from 7% to 68%. Together, these results suggest that the prevalence of CDS naturally increases with advancing age, so that eventually > 50% of dogs > 15 years old are affected. On the other hand, it is clear that many dogs, even at an advanced age, escape this diagnosis and thus can be defined as healthy aged dogs from this behavioral perspective.
A diagnosis of CDS should be made only when all other causes of behavioral changes, including those related to sensory decline (particularly hearing and vision), environmental effects, pain, and other underlying disease processes, have been ruled out. It should also be recognized that many common behavioral problems that occur in aged dogs, although outwardly similar to abnormalities indicative of CDS, are secondary to degenerative disease and other geriatric changes.10,11 Treatable conditions should be excluded before a diagnosis of CDS is made, particularly for owners who find their dog's behavioral changes to be unacceptable. Because CDS is progressive, assessing a dog during several examinations over time will give a broader picture of the dog's behavior.
The current challenge in diagnosing CDS is the lack of a standardized questionnaire that can be used to identify affected dogs. A recent study14 involving nearly 1,000 dogs and their owners identified 13 items that could be used to identify dogs with CDS (Appendix 3), and this scoring system may be useful in distinguishing healthy aged dogs from dogs with CDS.
Weight and Body Condition Assessment
Body weight, BCS, and MCS should be regularly assessed in aged dogs (Appendix 4), and comparing a dog's current body weight and BCS with previous body weight and BCS measurements (eg, measurements obtained shortly after the dog reached adulthood) or with estimated ideal body weight for the breed and ideal BCS (ie, a score of 2.5 to 3.0 on a 5-point scale or a score of 4 to 5 on a 9-point scale) provides a helpful reference for most dogs. In addition, owners should be queried regarding any recent changes in their dog's food intake or body condition.
Early recognition of weight gain or sarcopenia (ie, the loss of lean body mass) allows for appropriate intervention to slow progression and prevent potential adverse effects. Sarcopenia is often accompanied by an increase in fat mass, which means that body weight may not change or may even increase in dogs with sarcopenia. Therefore, as dogs age, it is important to evaluate not only body weight and BCS but also MCS. The MCS differs from the BCS in that it specifically evaluates muscle mass.17,18 Evaluation of muscle mass should include visual examination and palpation of the lumbar vertebrae, scapulae, temporal bones, and pelvic bones. The descriptive elements of this evaluation range from no muscle wasting with normal muscle mass to marked muscle wasting.
Obesity is currently the most common nutritional disorder of pet dogs.19–21 Dogs that weigh 10% to 20% more than their ideal body weight are generally classified as overweight, while those that weigh > 20% more than their ideal body weight are classified as obese. Several health problems, including chronic inflammation,22–24 osteoarthritis,25 pulmonary and cardiovascular disease,26 pancreatitis,27 hypertension,28–32 insulin resistance,29,31,33 glomerular hyperfiltration,32 and increased anesthesia-related morbidity and mortality rates,34 are caused or complicated by obesity in dogs. In addition, increasing body weight as dogs age decreases both quality of life, as indicated by an increased incidence and severity of osteoarthritis, and life expectancy and adversely affects immune status.25 When 48 Labrador Retrievers from 7 litters were assigned to control-fed or restricted-fed groups (dogs in the restricted-fed group were fed 75% of the amount of food provided to the control-fed group), only the dogs in the control-fed group became overweight as they aged. The restricted-fed group had a significantly longer median lifespan, significantly lower incidence and severity of osteoarthritis, and significantly less severe decrease in lymphocyte subtype cell numbers and responses.25
Musculoskeletal Health Assessment
When assessing musculoskeletal health in aged dogs, physical examination should be combined with results of owner assessments concerning the dog's activity level, response to exercise, and signs of pain (Appendix 5).
Although a number of age-related musculoskeletal disorders can affect aging dogs, the most frequently diagnosed is osteoarthritis. Osteoarthritis, or degenerative joint disease, is a progressive condition that affects the synovial joints and is characterized by gradual degeneration of the articular cartilage, hypertrophy of the bone at the joint margins, and changes in the synovial membrane.35 These joint changes ultimately lead to signs of discomfort and pain, a reduced range of motion, muscle atrophy, and decreased mobility.36,37 Changes may be irreversible once the disease process has progressed to the point at which clinical signs are evident.
Osteoarthritis can negatively affect the quality of life in aged dogs and is a common concern of dog owners. Both the incidence and severity of osteoarthritis increase with age in dogs.34,38 Osteoarthritis affects larger breeds of dogs more frequently than smaller breeds, but the incidence and severity vary among joints, and clinical signs can range from nonexistent to incapacitating.39–41
Skin and Coat Health Assessment
Physical evaluation of aged dogs should include thorough examinations of the skin and coat, along with questions to the owner regarding any recent changes in the dog's skin or coat and the presence of new or rapidly growing skin lesions or growths (Appendix 6).
Clinically, sebaceous cysts, papillomas, and lipomas are seen with increased frequency as dogs age. Abnormal flushing of the sebaceous glands or the production of more viscous glandular secretions may be the most common cause of sebaceous cysts. Immune system changes in aged dogs may allow the development of virally induced papillomas. Lipomas, which can occur at any age, are the most common cutaneous tumor in aged dogs.42 The incidence of skin neoplasia increases with age.43
Oral and Gingival Health Assessment
Physical examination of aged dogs should include a thorough examination of the periodontium and teeth, along with questions to the owners regarding signs of pain, changes in eating habits, and halitosis (Appendix 7).
Dental problems such as gingival inflammation, heavy calculus deposits, and periodontal disease are ubiquitous among adult dogs of all ages.44–46 In 1 study,47 for instance, 78% of dogs > 3 years old examined at general small animal practices in the United States had periodontal disease. Increasing age is also positively correlated with increasing severity of periodontal disease as measured by intensity of gingival inflammation, quantity of calculus that is deposited, and degree of bone resorption and tooth mobility.48 Periodontal disease can also potentially predispose aged dogs to heart disease.
Special Senses Health Assessment
Aged dogs should be examined for vision loss and general changes in hearing and olfactory function (Appendix 8). In addition, the owners’ perceptions of any changes to their dogs’ special senses and how these changes are influencing their dogs’ wellness and quality of life should be noted.
Nuclear sclerosis is considered a normal aging change of the lens and typically does not interfere with vision in aged dogs. However, nuclear sclerosis dense enough to impair vision can be seen in some aged dogs. In contrast, cataracts can impair vision in aged dogs, although not all do, including incipient and early immature subcapsular opacities and spoke-shaped opacities in the anterior equatorial cortex. The risk of cataract formation increases with age in dogs,49,50 with mean age of cataract onset ranging from 6.7 to 8.3 years in various studies.50–52
Corneal degenerative diseases occur in aging dogs as well.53 These diseases are characterized by calcium, lipid, or cholesterol infiltrates in the cornea and can be a primary corneal disease or develop secondary to various systemic diseases.54
Indolent ulcers, also known as spontaneous chronic corneal epithelial defects, typically occur in middle-aged to older dogs, with mean age at onset ranging from 8 to 9 years.55–58 These are chronic epithelial erosions that do not undergo proper epithelial-to-mesenchymal transition.59 The underlying predisposing factors for this disease are unknown.
Retinal degeneration is an age-related ocular abnormality. A recent study60 of the effects of aging on retinal function found that for both cone and rod pathways, b-wave amplitude decreases with age.
Gastrointestinal Health Assessment
Quality and quantity of the feces, overall body condition, body weight, and daily amount of food consumed can be indicators of gastrointestinal tract function in aged dogs. Thus, these factors should be regularly assessed in aged dogs. In assessing gastrointestinal health in aged dogs, a BCS and MCS should be assigned and abdominal palpation, rectal examination, and a visual assessment of the abdominal contour should be performed, along with a fecal flotation test for intestinal parasites, CBC, and serum biochemical analyses (Appendix 9). In addition, owners should be queried about any changes in defecation frequency, fecal quality or quantity, appetite, or activity level and asked to report any episodes of vomiting, colic, or borborygmus. Hepatic enzyme activities may be slightly high in aged dogs secondary to extrahepatic disorders such as pancreatitis, inflammatory bowel disease, enteritis, or anemia. Thus, these values should be interpreted cautiously.
Cardiac Health Assessment
Wellness examinations of aged dogs should include auscultation of the heart and lungs, assessment of the jugular and peripheral pulses, and assessment of mucous membrane and skin color; owners should be queried regarding any changes in exercise tolerance or the development of coughing or dyspnea (Appendix 10). Because of the potential link between dental and cardiac health, the oral cavity should also be evaluated for the presence of periodontal disease.
Heart-related diseases are estimated to cause up to a third of illnesses diagnosed in aged dogs.61 Chronic valvular disease is one of the most common acquired cardiovascular diseases in dogs and tends to affect many smaller breeds.62–64 A study63 of cardiac health in Cavalier King Charles Spaniels found that both the incidence and severity of chronic valvular disease increased with age.
Dilated cardiomyopathy is another common cardiovascular disease in aged dogs. The condition is characterized by cardiac dilatation and reduced myocardial contractility. Although any dog can be affected, large-breed and giant-breed dogs are predisposed to develop dilated cardiomyopathy, with increasing age recognized as an additional risk factor. A study65 of Doberman Pinschers reported a positive linear association between age and the frequency of dilated cardiomyopathy.
Although a clear cause-and-effect relationship has not been established, periodontal disease is considered a potential risk factor for heart disease in dogs.28,66–68 Given that the prevalence of periodontal disease in dogs increases with age,48 aged dogs may be particularly prone to develop heart disease.
Respiratory Health Assessment
Wellness examinations of aged dogs should include auscultation of the lungs and assessment of the mucous membrane and skin color; owners should be asked about changes in exercise tolerance and the development of coughing or dyspnea (Appendix 11).
Respiratory function normally decreases with age in dogs, and this could potentially increase aged dogs’ vulnerability to ventilatory failure. In dogs, aging is associated with an increased likelihood of respiratory conditions such as chronic bronchitis, pulmonary thromboembolism, tracheal collapse, laryngeal paralysis, and chronic rhinitis.7,69
Renal and Urinary Health Assessment
Renal and urinary tract health should be assessed during standard wellness examinations of aged dogs. This should include abdominal palpation, a rectal examination, and a CBC, serum biochemical analyses, and urinalysis. In addition, information regarding the dog's urination habits and water consumption should be obtained from the owners (Appendix 12).
Chronic kidney disease, also known as chronic renal failure, is a leading cause of death in aged dogs. Renal function can be evaluated on the basis of results of serum biochemical analyses and a urinalysis, although these tests may be insensitive at detecting underlying renal disease until it is quite advanced. Serial assessment of serum creatinine concentration is better than a single assessment because it could indicate a progressive decrease in renal function even if values remain within the reference range.70 For example, a serum creatinine concentration of 1.2 mg/dL may be overlooked on a single serum biochemistry profile; however, if previous results indicated a serum creatinine concentration of 0.6 mg/dL, then a loss of renal excretory function may have occurred.
A recent study71 showed that severity of proteinuria tended to increase in smaller dogs as the dogs aged. Both plasma creatinine clearance and endogenous clearance of iohexol also decreased, showing that renal function decreased as the dogs got older. Although all the dogs in the study were overtly healthy, as determined by routine testing, the findings illustrate that many abnormal changes occur in the kidneys as healthy dogs age, and it is not surprising that chronic kidney disease is more common in aged dogs than in younger dogs.70
It is now clear that many otherwise healthy aged dogs have underlying adverse changes in kidney function, even if they do not have overt chronic kidney disease or proteinuria. It is also clear that renal compensatory hypertrophy masks many of these changes until they are quite severe, so many of these dogs have very little reserve renal function that could accommodate additional renal insults. Therefore, it is important that factors that could potentially contribute to a decrease in renal function be minimized in aged dogs. This would include avoiding potentially nephrotoxic drugs when possible; preventing dehydration and renal hypotension, especially during anesthesia; and controlling hypertension when present.
When renal disease develops in aged dogs, it directly affects nutrition and dietary management because chronic kidney disease may be associated with decreased caloric and nutrient intake, weight loss, muscle wasting, altered plasma protein concentrations, anemia, acid-base abnormalities, hypertension, renal hyperparathyroidism, intestinal malabsorption, and reduced assimilation and use of nutrients.72 Accumulation of products of protein metabolism, of which urea is the most abundant, may further contribute to the clinical and physiologic abnormalities associated with renal failure.
Urinary incontinence is also more common in aged dogs. This can occur in either sex but is most frequently reported in spayed females. Although there are several possible underlying causes, hormone-responsive incontinence is one of the most frequently diagnosed disorders of micturition.73 Deficiencies of estrogen in females and testosterone in males lead to reduced muscle tone of the urethral sphincter, which allows involuntary voiding of urine, usually when the dog is resting or asleep. This problem may not become evident until a dog becomes polyuric and is producing larger volumes of urine. Although urinary incontinence can often be managed and is usually not a serious medical problem in most aged dogs, it is often troubling to owners. Therefore, urinary continence should be assessed during wellness examinations of aged dogs.
Endocrine System Health Assessment
To assess endocrine system health, wellness examinations of aged dogs should include a CBC, differential WBC count, serum biochemical profile, urinalysis, thyroid function testing, and, if indicated, adrenal function testing. In sexually intact dogs, the reproductive organs should be examined, and owners of all dogs should be queried regarding any changes in activity level, coat or skin, and urination habits (Appendix 13).
A low serum thyroxine concentration (< 0.5 μg/dL [6 nmol/L]) in conjunction with hypercholesterolemia and typical clinical signs is strongly suggestive of a diagnosis of hypothyroidism, especially if systemic illness is not present. Additional tests of thyroid function and evaluation of thyroid-stimulating hormone (thyrotropin) concentration in combination with thyroxine concentration are helpful in trying to rule out euthyroid sick syndrome. This is especially true in dogs in which the serum thyroxine concentration is < 0.8 to 1.0 μg/dL (10 to 25 nmol/L) but clinical signs and physical examination findings are not strongly supportive of a diagnosis of hypothyroidism and hypercholesterolemia is not present, dogs with severe systemic illness, and dogs that have been given medications known to decrease serum thyroxine concentration.
Conclusions
As with humans, many of the changes that occur with aging in dogs are not considered pathological and do not negatively affect overall wellness or quality of life. However, ruling out disease is essential when attempting to determine whether an aged dog can be considered healthy. Wellness examinations of aged dogs should include measurement of body weight, assignment of a BCS and MCS, and evaluation of mobility and muscle strength, skin and coat quality, oral and gingival health, visual acuity, hearing and olfaction, and general behavior and status. In addition, clinical changes in the gastrointestinal, immune, hepatic, cardiac, respiratory, renal, and endocrine body systems should be evaluated. A CBC, serum biochemical profile, and urinalysis should also be performed as part of the standard wellness examination of aged dogs.
Given current thinking on healthy aging in people, it appears that healthy aging in dogs can be defined as cognitive and behavioral health in conjunction with normal function of individual body systems (Appendix 14) and that these criteria could be used as a standard for clinical studies of aging in dogs. By understanding healthy aging, veterinarians and pet owners alike can help reduce the potential for development of certain diseases in aged dogs. Veterinarians are a primary education resource for dog owners and play a central role in helping clients provide the best care for their aged dogs. Possessing a clear understanding of normal and abnormal changes associated with aging in dogs can help practitioners make decisions regarding medical management, nutritional and feeding interventions, and additional testing procedures for aged dogs.
ABBREVIATIONS
| BCS | Body condition score |
| CDS | Cognitive dysfunction syndrome |
| MCS | Muscle condition score |
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Appendix 1
Behavioral signs potentially associated with various medical conditions in aged dogs.
| Medical condition | Potentially associated behavioral signs |
|---|---|
| Sensory dysfunction (ie, loss of sight, hearing, or smell) | Increased irritability, fear, or aggression |
| Decreased appetite | |
| Increased vocalization | |
| Disrupted sleep-wake patterns | |
| Disorientation | |
| Decreased greeting behaviors | |
| Inattentiveness | |
| Decreased responsiveness to verbal commands | |
| Urinary tract disease | Incontinence |
| Loss of housetraining | |
| Renal disease | Polyuria |
| Polydipsia | |
| Lower urinary tract infection | Dysuria |
| Stranguria | |
| Pollakiuria | |
| Osteoarthritis | Weakness |
| Reduced mobility and activity | |
| Increased pain and irritability | |
| Loss of housetraining | |
| Reluctance to engage in normal daily activities | |
| Hypothyroidism | Decreased activity |
| Increased irritability or aggression | |
| Reduced tolerance to cold | |
| Hyperadrenocorticism | Decreased social interaction |
| Decreased responsiveness to verbal commands | |
| Decreased greeting behaviors | |
| Disrupted sleep-wake patterns | |
| Loss of housetraining | |
| Panting | |
| Polyphagia | |
| Polydipsia | |
| Polyuria | |
| Restlessness | |
| Reduced activity | |
| Neurologic disorders (eg, primary or secondary intracranial neoplasia) | Disrupted sleep-wake patterns |
| Increased or decreased appetite | |
| Loss of housetraining | |
| Increased aggression | |
| Increased docility | |
| Peripheral neuropathy | Self-mutilation |
| Increased irritability or aggression | |
| Circling | |
| Hyperesthesia | |
| Pain | Altered response to stimuli |
| Decreased activity | |
| Restlessness | |
| Vocalization | |
| Loss of housetraining | |
| Increased irritability or aggression | |
| Self-trauma | |
| Disrupted sleep-wake patterns | |
| Gastrointestinal | Excessive licking |
| Polyphagia or hyporexia | |
| Pica | |
| Coprophagia | |
| Loss of housetraining (feces) | |
| Disrupted sleep-wake patterns | |
| Restlessness | |
| Lip smacking | |
| Vocalizing | |
| Prayer posture | |
| Urogenital | Dysuria |
| Loss of housetraining (urine) | |
| Pollakiuria | |
| Polydipsia | |
| Polyuria | |
| Stranguria | |
| Disrupted sleep-wake patterns | |
| Dermatologic | Acral lick dermatitis |
| Nail biting | |
| Hyperesthesia | |
| Other self-trauma | |
| Metabolic disorders | Anxiety |
| Increased irritability or aggression | |
| Disrupted sleep-wake patterns | |
| Loss of housetraining | |
| Mental dullness | |
| Decreased activity | |
| Restlessness | |
| Confusion |
Appendix 2
Recommended methods for assessing cognitive and behavioral health in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Assess general behavior and interactions | Normal and responsive | Abnormal or nonresponsive |
| Perform a CBC and serum biochemical profile | Normal | Abnormal |
| Query owner regarding recent or sudden changes in temperament temperament | No changes in temperament | Sudden changes in temperament or behavior, especially if concerning to the owner |
| Test for CDS | No CDS | CDS |
Appendix 3
Rating scale for identifying CDS in aged dogs.
| For the 7 following items, owners are asked to assign a score from 1 to 5, where 1 = never, 2 = once a month or some of the time, 3 = once a week or half the time, 4 = once a day or most of the time, and 5 = once a day or always. |
| How often does your dog: |
| • Pace up and down, walk in circles, or wander with no direction or purpose? |
| • Stare blankly at the walls or floors? |
| • Get stuck behind objects? |
| • Fail to recognize familiar people or pets? |
| • Walk into walls or doors? |
| • Walk away while being petted or avoid being patted? |
| • Have difficulty finding food dropped on the floor? |
| For the 5 following items, owners are asked to assign a score from 1 to 5, where 1 = much less, 2 = slightly less, 3 = the same, 4 = slightly more, and 5 = much more. |
| Compared with 6 months ago, does your dog: |
| • Now pace up and down, walk in circles, or wander with no direction or purpose? |
| • Now stare blankly at the walls or floor? |
| • Now urinate or defecate in an area previously kept clean? |
| • Have trouble finding food dropped on the floor? |
| • Fail to recognize people or pets? |
| For the following item, owners are asked to assign a score from 1 to 5, where 1 = much more, 2 = slightly more, 3 = the same, 4 = slightly less, and 5 = much less. |
| Compared with 6 months ago, how much time does your dog spend being active? |
| Scores for the 13 items are summed, and dogs with a score ≥ 50 are considered likely to have CDS. |
| (Adapted from Salvin HE, McGreevy PD, Sachdev PS, et al. The canine cognitive dysfunction rating scale (CCDR): a data-driven and ecologically relevant assessment tool. Vet J 2011;188:331–336. Reprinted with permission.) |
Appendix 4
Recommended methods for assessing weight and body condition in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Measure body weight and compare with previous weight | Appropriate weight No sudden change in weight | Recent or sudden weight gain or loss |
| Palpate body conformation | Appropriate for breed and size | Excessively thin or overweight |
| Assign BCS | BCS of 2.5–3.0 on a 5-point scale; BCS of 4–5 on a 9-point scale | BCS < 2.5 or > 3.0 on a 5-point scale; BCS < 4 or > 5 on a 9-point |
| Assign MCS | Normal MCS for age and breed (ie, normal muscle mass | Low MCS (ie, muscle wasting) |
| Query owner regarding recent or sudden weight changes or changes in food intake | No recent or sudden changes | Change in weight or food intake |
Appendix 5
Recommended methods for assessing musculoskeletal health in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Perform an orthopedic examination | Normal findings; no lameness or inconsistent lameness that is difficult to observe | Evidence of lameness or needs assistance to ambulate |
| Palpate joints for signs of swelling | No swollen joints | One or more swollen joints |
| Evaluate for signs of pain | No signs of pain or rare signs of pain as indicated by comfortable resting and movement and no resistance to palpation | Signs of pain as indicated by restlessness, hesitation to move, and objection to palpation |
| Query owner regarding | ||
| Ability to ascend and descend stairs | Needs no assistance | Needs assistance from the owner or cannot ascend or descend stairs |
| Ability to walk | Can manage a 20-min walk | Cannot manage a 20-min walk |
| Ability to rise from lying down | Can rise without assistance | Cannot rise without assistance |
| Ability to posture for elimation | No difficulty posturing or ability to posture without falling | Inability to posture for elimination |
| Pain relief | No analgesics given or analgesics given ≤ 2 times/wk | Analgesics given > 2 times/wk |
Appendix 6
Recommended methods for assessing skin and coat health in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Evaluate coat color | Graying of muzzle, face, and possibly trunk and legs | Not applicable |
| Assess coat density, texture, and luster | Slight thinning; normal to slightly dry coat; slightly dry coat; no detectable alopecia or hyperpigmentation | Severely dry, brittle, and dull coat; excessive skin flaking (dander); areas of alopecia with hyperpigmentation |
| Examine for skin lesions and growths | Rare to occasional warts or cysts in dermis; presence of lipomas that do not impede function; mild skin wrinkling around the face or neck | Multiple warts or cysts; presence of lesions or growths rapidly changing in size or with an abnormal appearance; severe skin wrinkling |
| Query owner regarding recent hair loss, sudden growth of skin lesions or skin bumps, and changes in the shedding cycle | No recent changes or growth | Sudden change in coat density, shedding cycle, or texture; appearance of new or unusual lesions or growths |
Appendix 7
Recommended methods for assessing oral and gingival health in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Conduct periodontal probing | Normal results (ie, probing depths ≤ 2 mm in medium-sized dogs) | Abnormal results or bleeding on probing |
| Evaluate the mouth for oral masses | No masses seen | Oral masses or abnormal facial swelling identified |
| Evaluate the mouth for fractured teeth with or without pulp exposure | No fractured teeth | Fractured teeth with or without pulp exposure |
| Query owner regarding signs of mouth pain, changes in chewing or eating habits, and the presence of malodorous breath | No signs of pain or changes in eating or chewing habits; no or minimal mouth odor | Frequent signs of pain or refusal to eat; change in chewing habits; moderate to severe mouth odor |
Appendix 8
Recommended methods for assessing health of the special senses in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Measure intraocular pressure | Pressure < 20 mm Hg | Pressure > 20 mm Hg; diagnosis of glaucoma |
| Perform external examination of the eye and surrounding tissues | Normal examination results; presence of minor cysts or warts on the eyelids that do not interfere with function | Presence of abnormal growths; diagnosis of entropion |
| Perform internal examination of the eye | Normal or near normal vision; presence of nuclear sclerosis not affecting vision | Presence of cataracts, other lens abnormalities corneal ulcers, retinal degeneration, or blindness |
| Conduct Schirmer tear test | Normal results | Diagnosis of keratoconjunctivitis sicca |
| Conduct hearing examination (eg, brainstem auditory evoked response test) | Normal hearing or moderate hearing loss | Severe hearing loss that adversely affects quality of life |
| Perform external ear and otoscopic examinations | Normal results | Abnormal findings or ruptured tympanic membrane |
| Query owner regarding sudden changes in vision, hearing, or smell and, if present, whether these changes had any effect on daily activities or quality of life | No changes or slight to moderate changes that do not appreciably affect daily activities or quality of life | Severe changes that alter daily activities and reduce quality of life |
Appendix 9
Recommended methods for assessing gastrointestinal health in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Assign BCS | BCS of 2.5–3.0 on a 5-point scale; BCS of 4–5 on a 9-point scale | BCS < 2.5 or > 3.0 on a 5-point scale; BCS < 4 or > 5 on a 9-point scale |
| Assign MCS | Normal MCS for age and breed (ie, normal muscle mass) | Low MCS (ie, muscle wasting) |
| Examine mucous membrane and skin color | Normal color | Poor color of mucous membranes or skin (pale or jaundice) |
| Palpate abdomen | Normal results | Pendulous abdomen; abnormal size or shape of the liver or intestines |
| Perform a rectal examination | Smooth colorectal muscosa; no masses or strictures; no evidence of pain during palpation; no evidence of hematochezia or melena | Evidence of masses, blood, strictures, or pain during rectal examination |
| Evaluate appearance and volume of feces | Formed feces; no evidence of blood or excessive mucus | Watery to loose or very dry feces; presence of blood or excessive mucus |
| Perform fecal flotation test | Negative results | Positive for intestinal parasites |
| Perform a CBC and serum biochemical profiles | All values within reference limits for age and breed (hepatic enzyme activities may be up to twice the upper reference limit) | Abnormal results |
| Query owner regarding changes in defecation frequency, fecal quality and quantity, appetite, and activity level and any episodes of vomiting, colic, or bororgymus | No or minimal changes in defecation frequency; normal fecal quality and quantity; no signs of of colic; normal appetitie | Increase or decrease in defecation frequency; abnormal fecal quality or quantity; signs of colic, vomiting, diarrhea, or increased borborygmus; decreased appetite |
Appendix 10
Recommended methods for assessing cardiac health in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Auscultate heart and lungs | Normal results | Abnormal results |
| Assess jugular and peripheral pulses | Jugular vein distends when pressure is placed in thoracic inlet, but quickly collapses when pressure is released; peripheral pulses easily felt | Jugular vein collapses slowly when thoracic inlet pressure is released or jugular vein is is distended even when no pressure is applied; weak or absent peripheral pulses or increased peripheral pulses |
| Examine mucous membranes and capillary refill time | Normal mucous membrane color; capillary refill time ≤ 2 s | Abnormal mucous membrane color (blue, bluish-gray, pale, dark red, or icteric); prolonged capillary refill time |
| Query owner regarding changes in exercise tolerance or development of a cough or dyspnea | Normal exercise tolerance; no cough or dyspnea | Reduced exercise tolerance; development of cough or dyspnea |
Appendix 11
Recommended methods for assessing respiratory health in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Auscultate lungs | Normal breath sounds | Abnormal breath sounds (eg, rales or rhonchi); abnormal respiratory rate (eg, tachypnea or hypopnea) |
| Evaluate respiratory effort | Normal | Abnormal |
| Examine mucous membrane and skin color | Normal | Cyanosis |
| Query owner regarding changes in exercise tolerance or development of a cough | Normal exercise tolerance; no cough or dyspnea | Reduced exercise tolerance; development of cough or dyspnea |
Appendix 12
Recommended methods for assessing renal and urinary health in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Palpate abdomen, especially size and shape of kidneys and bladder | Normal | Abnormal kidney size or shape; bladder mass |
| Perform serum biochemical profile | BUN and creatinine concentrations within reference limits and unchanged from preious values; serum electrolyte concentrations within reference limits; normal acid-base status | Abnormal BUN or creatinine concentrations or increase in values; abnormal serum electrolyte concentrations or acid-base status |
| Perform a CBC | Normal results | Nonregenerative anemia; microcytic, hypochromic RBCs; abnormal WBC or platelet count |
| Perform a urinalysis | Normal results | Abnormal results |
| Perform a rectal examination to evaluate pelvic urethra and, in males, the prostate gland | Smooth colorectal mucosa; no masses or strictures; no evidence of pain during palpation; no evidence of hematochezia or melena | Evidence of masses, blood, strictures, or pain during rectal examination |
| Query owner regarding urination habits, water consumption, urinary continence, and any changes in appetite or recent weight loss | Normal; no history of polyuria or polydipsia; no incontinence or changes in appetite or recent weight loss | History of polyuria or polydipsia; presence of urinary incontinence; recent change in appetite or weight loss |
Appendix 13
Recommended methods for assessing endocrine system health in aged dogs.
| Assessment | Healthy | Not healthy |
|---|---|---|
| Perform a serum biochemical profile | Normal results or mild stress hypergylcemia | Abnormal results |
| Perform a CBC | Normal RBC count and morphology; normal WBC and platelet counts | Nonregenerative anemia; microcytic, hypochromic RBCs; abnormal WBC or platelet count |
| Perform a urinalysis | Normal results | Abnormal results (eg, dilute urine or glucosuria) |
| Perform thyroid function testing | Normal results | Abnormal results |
| Examine reproductive tract in sexually intact patients, including per rectal prostate palpation | Normal results | Abnormal results |
| Query owner regarding changes in activity, coat or skin, or urination habits | Normal activity or age-appropriate reduction in activity level | Reduced activity; poor coat quality; skin changes; polyuria and polydipsia |
Appendix 14
Criteria for healthy aging in dogs, classified on the basis of body system.
| Body system | Criteria indicative of healthy aging |
|---|---|
| Cognitive and behavioral health | Absence of CDS |
| Body weight and condition | Normal BCS and MCS; absence of overweight or underweight |
| Musculoskeletal health | Able to ascend and descend stairs, walk for 20 min, and posture for elimination without assistance; absence of consistent or easily observed lameness; absence of signs of pain involving the joints |
| Skin and coat health | Absence of clinically important skin growths or lesions or masses that impair locomotion or other normal functions; no reports of sudden or severe changes in coat density or texture |
| Oral and gingival health | Absence of periodontal disease, oral masses, and fractured teeth |
| Special senses health | Absence of ophthalmologic problems that require observation or medical attention, hearing loss that impairs normal social interactions, or loss of smell that impairs daily activities or leads to weight loss |
| Gastrointestinal health | Normal, nonpendulous abdomen and formed feces produced 1–3 times/d; absence of clinical signs of liver disease and clinically relevant increases in hepatic enzyme activities; absence of rectal masses; no evidence of blood or excessive mucus in feces |
| Cardiac health | Normal heart and lung auscultation results, jugular and peripheral pulses, mucous membrane and skin color, and exercise tolerance; absence of cough and dyspnea |
| Respiratory health | Normal lung auscultation results, respiratory effort, and exercise tolerance; absence of cyanosis, cough, and dyspnea |
| Renal and urinary health | Normal kidney size and shape; BUN and creatinine concentrations within reference limits; normal urinalysis results; normal rectal examination results; absence of bladder masses, nonregenerative anemia, urinary incontinence, polyuria, and polydipsia |
| Endocrine health | Normal reproductive organs in sexually intact animals; normal thyroid function testing and urinalysis results; normal activity level or age-appropriate reduction in activity level; absence of clinically important increases in alkaline phosphatase activity and serum glucose concentration; no evidence of hypothyroidism, polyuria, polydipsia, or changes in the skin or coat |