Canine aging and frailty
Our understanding of aging in dogs is making great strides forward; in this paper the authors discuss how to assess if a dog comes into the “frail” category and what we as veterinarians can do to help in this situation.
“Frailty syndrome” is a phase that falls between normal and pathological aging, and it is essential that it is detected as early as possible.
The pet population is getting older, and the field of veterinary geriatric medicine is growing in importance.
Management of frailty includes frequent veterinary follow-ups, nutritional evaluation to ensure a suitable diet, and appropriate environmental adaptations.
Two simple methods to assess canine frailty have recently been developed for clinical use in practice.
Aging is currently a popular subject – among scientists, in the media, and for both human and veterinary practitioners. The importance of companion animals in our society has led to an increased pet population, and consequently higher numbers of geriatric animals – for example, one survey showed that the French canine population aged 12 or older had increased by more than 1 percentage point within a two-year period, from 14.5% in 2012 to 15.8% in 2014 1. There is an undoubted need for veterinary medicine to respond to this geriatric population of pets and for dedicated species-specific procedures to evaluate such patients. Fortunately, because dogs are increasingly used as a model for human aging, we now have methods which can be adapted for veterinary geriatric medicine.
What is “aging”?
Aging is a normal, multifactorial physiological process which has been defined as “a decline and deterioration of functional properties at the cellular, tissue and organ levels. This loss of functional properties yields a loss of homeostasis and a decreased adaptability to internal and external stresses, yielding an increased vulnerability to diseases and mortality” 1. However, there are differences between biological aging and chronological aging. The former – also called “senescence” – is a process that affects all individuals of a given species, but not at the same rate 2. “Chronological aging” represents the passage of time 3, and is what we refer to when we talk about a “dog’s age”. This article will focus on canine aging in the biological sense.
What is an “old” dog?
As in human medicine, it can be difficult to get a consensus as to the definition of the geriatric stage in veterinary medicine. Different factors have a part to play (including breed, adult body size, etc.) but two stages can be identified: “pre-geriatric” and “geriatric” (or “senior” in the AAHA guidelines) 4. The pre-geriatric stage is less well-defined than the senior/geriatric stage, although it is essential to start prevention at the first stage. One review has defined the pre-geriatric stage by adult bodyweight: if the breed has an average adult bodyweight over 22.7 kg, a dog is pre-geriatric between 6 and 8 years of age, whereas for breeds with an adult body weight below this, this stage starts between 7 and 10 years old 5. The geriatric/senior stage is defined as the last 25% of the predicted lifespan for a given breed 4, so using these designations a Labrador enters the geriatric stage at 9 years of age, but the pre-geriatric stage starts at 6 years old.
These definitions are entirely based on chronological aging, but dogs go through various changes which can affect their senescence, as older animals are at higher risk of chronic disease such as cardiac pathologies, kidney disease, hormone disorders and tumors 6. There are limited data about the mortality risk factors in pre-geriatric and geriatric dogs, but a retrospective study on service dogs in these categories gave some clues: breed, increased alanine aminotransferase levels (> 102 UI/L) and presenting skin nodules were associated with remaining lifetime 7.
The field of geriatric veterinary medicine is still new, but some essential concepts, like the definition of healthy versus pathological aging, are emerging. Healthy aging in dogs has been defined as “the absence of clinically apparent diseases” and “age-related changes that don’t negatively affect quality of life” 4. Some changes associated with age may be considered to be “healthy”, including greying of the muzzle (Figure 1), mild thinning of the coat, moderate nuclear sclerosis, and even a slight reduction in activity levels (Table 1)48.
A common sign of “unhealthy” aging is canine dementia, more properly known as canine cognitive dysfunction (CCD). This neurobehavioral syndrome is a clear example of changes that affect a dog’s quality of life, which can be summarized by the acronym DISH (Disorientation, dysfunction in Interactions, Sleep, and Housetraining). Affected animals may present with alterations in activity patterns, impaired learning, and changes in social interaction or sleeping patterns, as shown in (Table 2). Despite recent research, this pathology is still underdiagnosed 4, but interest in pre-geriatric and geriatric animals has increased in recent decades, and new clinical evaluation tools, derived from human medicine, have been recently introduced and adapted for dogs, such as the notion of frailty.
Disorientation: e.g., gets stuck in front of a wall, has difficulty finding food, cannot find the way home on a routine walk
Alterations in interactions: e.g., avoids contact with owners, other pets and the environment, the greeting behavior is absent, changes in interaction with other people
Sleep-wake cycle disturbances; e.g., awake at night and sleeping during the day
House-soiling: e.g., indoor elimination in sleeping area, not asking to go out
Changes in activity: e.g., repetitive locomotor activity, loss of interest in treats or playing
Increased locomotor activity: e.g., aimless pacing at night
New fears (compared with 1 or 2 years before): e.g., phobia of normal locations within the house, fear of other dogs
Memory deficits: e.g., loss of memory, unable to perform a learned task, unable to learn a new task
Changes in personality: e.g., develops neuroses or aggressive signs
The “frailty syndrome”
This concept has developed from the field of human geriatrics 9. The definition of “frailty” has evolved in the last decade, and frailty is nowadays considered as a syndrome associated with an increased vulnerability when exposed to stressor events 10. This clinical state is considered to be a consequence of a cumulative decline in various body systems and is associated with an accelerated and progressive decline in physiological reserves 11, which is quite different from normal aging. Frailty may therefore be defined 12 as:
- A limited capacity to maintain homeostasis
- A clinical state of age-related biological vulnerability to stressors
- Decreased skeletal muscle mass and quality
- Altered hormonal and inflammatory functions
From a practical point of view, frailty is associated with mortality or comorbidity (i.e., the presence of two or more diseases) 13 which is independent from chronological aging 14 but also reversible, as it is a transitional state between normal aging and disabilities 10. However, frailty can be a vicious circle, initiated by multiple factors such as low physical activity, nutritional imbalance, comorbidity, or environmental factors. From a clinical perspective, sarcopenia, weakness or exhaustion can be observed, leading to avoidance of physical activities, and the downward spiral may be initiated by other conditions such as chronic inflammation and hormonal dysfunction. The syndrome has been associated with metabolic abnormalities, increased inflammatory cytokines (e.g., IL-6; CRP, TNF-Alpha) 14 15 or hormonal dysregulation (e.g., Vitamin D, DHEA). There is still a lack of knowledge about the pathophysiological pathway to frailty, but the term “frailty syndrome" is now widely used to indicate aged individuals that have an increased risk of an adverse outcome.
There are two approaches to evaluate frailty in human geriatrics, and both are suitable predictors of mortality in older patients 16. The first is a phenotype model which was created for clinical use, and identifies five basic components 13;
- Poor grip strength
- Slow walking speed
- Low levels of physical activity
- Low energy or self-reported exhaustion
- Unintentional weight loss.
Using this method, a patient can be classified as either Non-frail (where none of the components are abnormal), Pre-frail (where 1 or 2 components are abnormal), or Frail (where 3 or more components are abnormal). However the model does not consider factors such as cognition, mood or social frailty 17. These are taken into account by a second commonly used method, which considers frailty to be an accumulation of deficits including cognitive disorders, depressive syndrome, multiple diseases, and malnutrition. It employs a scoring system to produce a “Frailty Index” which allows for a multidimensional vision of the individual frailty, although it makes no real distinction between frailty and comorbidity 18.
Assessing unhealthy aging in dogs
Both methods have recently been transposed into canine medicine, and both identify frailty as a risk factor for death in aged dogs, independent of their chronological age.
This has recently been evaluated with a study on service dogs (mostly Retrievers) using a simple geriatric scoresheet (Table 3) 19. Any animal having two or more of the five components on assessment was considered to be frail, and the study noted that affected dogs were more likely to die, even when age was taken into consideration. However, this method has only been studied in a single population subset so far, and (unlike the human frailty phenotype) it currently involves no real physical evaluation. A protocol of frailty phenotype assessment with physical evaluation is currently being tested at the French National Veterinary School of Maison-Alfort.
Evaluation of muscular mass (normal or abnormal)
Estimation of exercise (in)tolerance, which may appear as fatigue or marked breathlessness
Low physical activity
Evaluation of perceived activity level (as reported by the owner)
Appraisal via a combination of body condition, appetite, and coat quality; considered to be present if any one of these components is suboptimal
Detection of abnormal gait evaluation and joint pain; considered to be present if either is noted
Frailty is associated with mortality or comorbidity and is independent from chronological aging, but it is also reversible, as it is a transitional state between normal aging and disabilities.
1. Assistance when standing up
2. Decreased appetite
3. Assistance when eating
5. Assistance when climbing stairs
6. Decreased activity over the last year
7. Reduced cognitive ability
8. Reduced vitality over the last year
9. Weakness during exercise
10. Congenital defects
11. Weight loss (not due to diet or exercise)
12. Weight loss (not due to diet or exercise)
13. Chronic therapies
15. Episodes of disorientation
16. Chronic infectious disease
17. Endocrine disease
18. Chronic inflammation
19. Acute vascular problems
23. Hearing impairment
25. Chronic respiratory disease
27. Neurological deficits
28. Disease of the oral cavity
29. Visual impairment
30. Chronic digestive disease
31. Disease of the hematopoietic system
32. Dermatological disease
33. Chronic kidney disease
Items 1-21 are scored as No (scoring 0) or Yes (scoring 1); items 22-33 are assessed as No (scoring 0), Mild (scoring 0.5) or Severe (scoring 1). The Frailty Index corresponds to the sum of the score divided by 33. A score of 0.25 is the entry point to the frailty state.
This method has recently been adapted for dogs and has been tested on a bigger group of individuals (age above 2 years, various breeds) 20. It assesses 33 potential health deficits, as shown in Table 4, with a score attributed to each factor; the overall total (with a range between 0 and 1) indicates a dog’s status, where 0.25 is the entry point to the frailty state. The study concludes that dogs that score above this level should have more frequent follow-up visits to the veterinary clinic.
Such assessment tools are inexpensive and can facilitate a standardized follow-up of at-risk or frail patients. However, they do not really explore the cognitive aspects of aging, and if one of the two methods outlined above is used to evaluate a dog’s frailty, an appraisal of its cognitive abilities should also be performed at each and every routine geriatric consultation.
Assessing cognitive dysfunction
A diagnosis of canine cognitive dysfunction (CCD) must be made only after exclusion of medical causes (e.g., epilepsy, hypothyroidism, joint pain), as such diseases may cause similar clinical signs. Various questionnaires can be used to assess for the condition in the clinic; one of the most common is the CCDR (Canine Cognitive Dysfunction Rating scale) as shown in Table 5 21. This tool assesses 13 factors related to behavior impairment, with each factor scored depending on the frequency of each behavior. The maximum score is 80, but any dog that is assessed as over 50 is likely to have CCD.
1. How often does your dog pace up and down, walk in circles and/or wander with no direction of purpose?
2. How often does your dog stare blankly at the walls or floor?
3. How often does your dog get stuck behind objects and is unable to get around?
4. How often does your dog fail to recognize familiar people or pets?
5. How often does your dog walk into walls or doors?
6. How often does your dog walk away while, or avoid, being patted?
7. How often does your dog have difficulty finding food dropped on the floor?
8. Compared with 6 months ago, does your dog now pace up and down, walk in circles and/or wander with no direction or purpose?
9. Compared with 6 months ago, does your dog now stare blankly at the walls or floor?
10. Compared with 6 months ago, does your dog urinate or defecate in an area it has previously kept clean? (if your dog has never house-soiled, tick “the same”)
11. Compared with 6 months ago, does your dog have difficulty finding food dropped on the floor?
12. Compare with 6 months ago, does your dog fail to recognize familiar people or pets?
13. Compared with 6 months ago, how active is your dog?
The scores are totaled to give the dog’s rating; the maximum possible score is 80, but any score above 50 is indicative of CCD.
Evaluation of pain linked to osteoarthrosis is also recommended during these consultations, and this can be easily performed in a clinical context using a validated questionnaire, such as the Canine Brief Pain Inventory 2.
Practical geriatric support in the clinic
Frailty and CCD must be evaluated as soon as signs become evident to allow more precise observation of the patient and possible progression of the condition. It is therefore suggested that the veterinary clinic can institute several proactive steps to allow good clinical care of their older patients (Table 6).
Frailty phenotype 19
Frailty index 20
|Canine cognitive assessment||
(in the waiting room)
|Muscle condition score||
WSAVA Muscle condition score
|Body condition score||
WSAVA Body condition score
(in the waiting room)
|General clinical evaluation||10 min||Veterinarian
Feed ration calculator
|Veterinarian and nurse|
In-house diagnostic equipment
In-house diagnostic equipment
|Assessing pain linked to osteoarthritis||
Canine Brief Pain inventory 3, Helsinki chronic pain index 4
(in the waiting room)
|Quality of life||
HHHHHMM scale/Grey muzzle app
(in the waiting room)
Frequent follow-up consults
A yearly routine geriatric examination is recommended for every dog in the pre-geriatric category 22, whilst animals in the geriatric stage should be assessed at least every 6 months, or every 3 months for frail dogs 4. This involves performing a Frailty assessment, a Cognitive assessment (using the CCDR) and laboratory tests. A minimum blood panel (urea, creatinine, total calcium, total protein, albumin, cholesterol, bilirubin, serum alanine aminotransferase and alkaline phosphatase) should be done every 6 months for asymptomatic geriatric canine patients 4 22, or more frequently if necessary. Urinalysis, blood glucose levels and hematology should also be included if possible. A questionnaire about the dog’s environment and habits (which can be completed by the owner in the waiting room) may also help the veterinarian to make recommendations.
Nutritional evaluation and recommendations
Nutritional assessment should be at the heart of all geriatric consults. Body weight, Muscle Condition Score (MCS) and Body Condition Score (BCS) – both created by the WSAVA – should be evaluated from birth to construct a weight curve for each patient. The goal is to recognize the onset of sarcopenia, although this can sometimes prove to be difficult as it can be masked by an increased fat mass. Evaluation of MCS includes palpation of the lumbar vertebrae, the temporal bones, the scapulae and the pelvic bones 4. Any obesity or weight loss should be noted.
An evaluation of the nutrient intake and energy provided by the daily ration is essential. Ideally the dog’s nutritional history should be detailed and assessed with a feed ration calculator, although analysis using an appropriate software program allows for a more precise assessment of the food offered. Pre-geriatric and geriatric dogs have special needs and adequate nutrition is always to be recommended 23: indeed, sarcopenia and malnutrition are cornerstones of the frailty circle. With aging and increased protein turnover, unless chronic kidney disease (CKD) or other pathologies are present, a dog’s protein requirement may increase. Protein quality should therefore be optimal (using a commercial petfood or home-prepared ration calculated by a nutritionist), and protein hydrolysates may be useful. One study has recommended 25% of the calorie intake for healthy senior dogs should come from good quality protein 24 and this quantity may be increased if sarcopenia is present and there are no contraindications (such as CKD). Note that BARF-type diets are not recommended for pre-geriatric and geriatric dogs.
Dietary phosphorus levels should be reduced where necessary (aiming for 0.3-0.7% of DM diet, i.e, a maximum of around 1.6 g/1000 kcal) for senior dogs, and omega-3 products such as EPA (Eicosapentaenoic acid) and DHA (Docosahexaenoic acid) are recommended for joint pain. 2.5 g/1000 kcal of omega-3 from marine sources has been recommended for canine osteoarthrosis 24 and in practice at least 2 g/1000 kcal of omega-3 from marine sources is necessary. These polyunsaturated fatty acids (PUFAs) have an anti-inflammatory action, which is important, as frailty is linked to inflammation. However, no study has been conducted on dogs combining nutrition and frailty, and most of the recommendations are extrapolated from human medicine 25. It is also important to ensure appropriate levels of dietary vitamins and minerals, and a supplementary source should always be used if a home-prepared diet is fed.
As cognitive dysfunction is part of frailty, nutritional supplementation should also focus on this aspect; antioxidants are recommended for dogs with CCD (and the diet should therefore be supplemented as necessary), in combination with environmental enrichment (as discussed below) 23 26. Recently, medium-chain triglycerides have been shown as a good alternative energy source for the brain as a nutritional strategy for cognitive dysfunction 26. Some drugs may also be useful for dogs showing clinical signs of CCD; these include selegiline (0.5-1 mg/kg PO q24H in the morning) and propentofylline (2.5-5 mg/kg PO q12H) 26. Remember that the clinician should always consider potential risks, such as the presence of concomitant pathologies, before administering such drugs.
Environmental management and cognitive stimulation
The environment and quality of life offered by the owner are also important for frail dogs. Activity should be encouraged, and walks of variable duration (depending on the clinical status) are generally recommended (Figure 2). Exercise may be adapted as necessary (e.g., short, gentle walks or swimming) to help to maintain muscular mass.
Sarcopenia and malnutrition are cornerstones of the frailty circle… senior and geriatric dogs have special needs, and adequate nutrition is therefore to be recommended for all animals in this category.
Sensorial stimulation and cognitive motivation may be achieved by offering a variety of odor or tactile stimulations (Figure 3), food enhanced toys (e.g., puzzle feeders) and positive interactions (such as play sessions with the owner or social interaction with other dogs), combined with continuous learning, can be useful. Exploring new places to walk can also help. Offering multiple sleeping areas may be useful, although frequently moving the sleeping and feeding areas should be avoided. At the same time creating a predictable and safe environment is essential; this can be achieved by ensuring consistent feeding and walking times, and avoiding stressful noises 26. The dog’s quality of life must be discussed regularly with the owner, and tools like the HHHHHMM scale (you can download the PDF below) or IT solutions (such as the VetMetrica questionnaire or “Grey Muzzle” app) can help assess how a dog is affected by his age and condition, and may also be useful for some end-of-life considerations.
The authors thank Dr. Delphine Moniot, Dr. Charlotte Devaux and Prof. Loïc Desquilbet for their valuable comments whilst preparing this article.
Interest in geriatric canine medicine is increasing, and in particular the frailty syndrome – and simple methods that can assess this problem – offers an opportunity for practitioners to approximate the biological aging of canine patients and to go beyond chronological aging. Being able to rapidly adjust the care and medication for old dogs with specific, dedicated consultations should promote owner adherence and help dogs to age healthily. There are still a lot of questions to be answered, such as the impact of the microbiome on canine frailty, but future long-term studies will provide new answers to the veterinary community and help our dogs to achieve healthier aging.
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Dr. Péron graduated from Alfort Veterinary School and then studied animal cognition before specializing in neurosciences, gaining his PhD from Paris Ouest University. He achieved board-certification in Animal Welfare in 2016. Read more
Dr. Hoummady graduated from Alfort Veterinary School (ENVA) in the Paris region and went on to study canine ethology and behavior in working dogs. She then specialized in canine geriatrics, with a PhD carried out at CNRS (the French National Centre for Scientific Research) before training in veterinary nutrition within the petfood industry. Read more