The age at which cats and dogs become ‘senior’ is not well defined, but the term typically refers to the last third of the lifespan of the animal. The expected lifespan of cats and dogs differs widely between species, among different breeds, and also among individuals. In dogs, the lifespan of giant and large breeds is typically shorter than smaller breeds (Table 1) (O'Neill et al, 2013). In cats lifespan also differs, though less breed variation is observed (Table 2) (O'Neill et al, 2015). Although maximum lifespan in both species has stayed around the same, advancements in veterinary medicine have allowed for an increase in average lifespan, such that senior pets currently make up around 40% of the population, with approximately 30% being >11 years (Metzger, 2005; Laflamme, 2012).
Table 1. Median lifespan of different dog breeds in the UK
| Breed | Median life span (years) |
|---|---|
| Miniature Poodle | 14.2 |
| Border Collie | 13.7 |
| Miniature Dachshund | 13.5 |
| Jack Russel Terrier | 13.4 |
| Shih-Tzu | 13.3 |
| Springer Spaniel | 13.3 |
| Dalmatian | 13.3 |
| Golden Retriever | 12.5 |
| Greyhound | 10.7 |
| Boxer | 10 |
| Doberman | 9.2 |
| Bulldog | 8.4 |
| Chihuahua | 7.1 |
| Mastiff | 7.1 |
| Great Dane | 6.0 |
| Dogue de Bordeaux | 5.5 |
Table 2. Median lifespan of different cat breeds in the UK
| Breed | Median life span (years) |
|---|---|
| Birman | 16.1 |
| Siamese | 14.2 |
| Crossbred | 14.0 |
| British Shorthair | 11.8 |
| Maine Coon | 11 |
| Ragdoll | 10.1 |
Unlike other life stages where physiological changes are broadly similar, the speed at which these occur, the signs of ageing and the health of senior pets vary greatly among individuals. Factors affecting the changes include:
- Genetics
- Veterinary health care and clinical health
- Nutritional status and/or diet.
Since nutrition plays a key role in the health and potential lifespan of senior pets, a thorough individualised assessment should be performed to inform nutritional recommendations.
Age-related changes
Although signs of ageing vary, there are common changes that are frequently seen (Table 3). Changes are indicative of the declining function of all body organs. Changes in bodily systems determined by clinical signs, together with serological blood parameters, should be used to determine the degree of ageing, as well as the pet's chronological age. Biological age may differ to chronological age.
Table 3. Age-related changes observed in cats and dogs
| Changes to body composition |
| Alterations in energy need |
| Muscle atrophy |
| Reduced kidney function |
| Greying faces – hair pigment loss caused by reduced tyrosinase activity |
| Hair loss, caused by follicle atrophy |
| Reduced ability to groom and care for coat |
| Reduced ability to digest protein and fat (cats only) |
| Reduced bone density because of inadequate calcium absorption |
| Arthritis and associated pain with decreased appetite |
| Reduced cardiovascular function as a result of reduced adaptability |
| Loss of skin elasticity |
| Reduction in sense perception eg smell, sight, taste which may reduce food intake |
| Reduced cognition and behavioural changes (Landsberg and Araujo, 2005) |
| Resisting routine and environmental changes (Landsberg and Araujo, 2005) |
| Pain related altered sitting/sleeping posture and mobility |
| Increase amount of sleep |
| Calmer disposition |
| Decreased ability to thermoregulate |
| Deteriorating dental condition |
| Decreased thirst stimulation |
Body composition
Changes in body composition are a normal part of the ageing process. Sarcopenia (a reduction in lean body mass, muscle quality and muscle strength, in the absence of disease) is observed together with increasing adipose tissue proportions in senior pets (Li et al, 2022). If these changes occur concurrently, the pet's bodyweight can remain relatively stable, hiding the changes to the owner and veterinary team. An optimal nutritional recommendation, designed for the senior pet, can slow the progression of sarcopenia. Cachexia, in contrast, is a loss of lean mass associated with the presence of a chronic wasting disease, such as cardiac disease, chronic kidney disease and cancers. As senior pets are predisposed to chronic wasting diseases, both sarcopenia and cachexia may occur concurrently (Freeman, 2012). Lean body mass can be assessed by performing muscle condition scoring (MCS; Figures 1 and 2). This is a simple and quick assessment which should be performed alongside body condition scoring (BCS; Figures 3 and 4) and body weight. Results of all three assessments should be recorded for each senior pet at every visit. Ideally, seniors should be assessed 3–4 times per year and those who do not present frequently should be encouraged to do so.
In some individuals, assessing muscle mass can be challenging, particularly in the presence of obesity, which is thought to affect 39% of cats (Courcier et al, 2010) and 65% (German et al, 2018) of dogs in the UK. In the USA in 2022, 61% of cats had overweight or obesity (Association for Pet Obesity Prevention, 2022). Abnormal adipose tissue mass can make the muscle mass difficult to palpate; however, the MCS assessment should still be performed because both sarcopenia and cachexia can occur concurrently with obesity. In such patients, muscle mass in the head and hindlimb regions are most helpful because less adipose tissue accumulates in these regions.
Reduced digestion ability
Studies have shown that ageing cats have reduced digestive ability for nutrients such as proteins, fats and calcium (Taylor et al, 1995). In the author's experience, senior cats can maintain their bodyweight by consuming more food to compensate for a reduced digestive ability (Harper, 1998).
Reduced kidney function
Kidney function, like the functions of many other organs, decreases gradually with age in both dogs and cats. Since chronic kidney disease (CKD) is a primary cause of death in both dogs and cats (Elliott, 2006), nutritional adaptations should be considered to preserve kidney function and slow the onset of CKD.
Nutritional assessments
A nutritional assessment must be performed for each individual, using a standardised nutritional assessment form. Such an assessment should be performed at every veterinary visit. Information gathered during the assessment can help to identify age-related changes and also inform nutritional recommendations (WSAVA Nutritional Assessment Guidelines Task Force Members et al, 2011; Cline et al, 2021).
Nutritional aims
Key nutritional aims for senior pets are as follows:
- Maintain health
- Slow the effects of the ageing process
- Slow disease progression
- Increase life expectancy, not least when chronic disease is present (eg CKD)
- Alleviate clinical signs
- Maintain an optimal bodyweight and BCS
- Preserve lean tissue mass/slow the loss of lean body mass.
Nutrient adaptations and considerations
Currently, many diets formulated for senior pets are available, and some have similar formulations to standard adult maintenance diets, in terms of macronutrient and micro-nutrient profiles. However, depending on the pet and their known risk factors, specific nutrients should be considered to ensure a tailored dietary recommendation to meet nutritional needs.
Energy
Resting metabolic rate (RMR) decreases as ageing progresses, largely because of the alterations in lean body mass (Mosier, 1989). However, lifestyle and activity should still be taken into account when considering an appropriate energy intake; some senior pets may reduce their overall activity level as they age, but others do not. For those whose activity level is less, restrictions on energy intake may be appropriate to minimise the risk of developing obesity. However, for individuals who remain physically active, this may slow the progression of sarcopenia and so may not require an energy reduction. An individual nutritional assessment is necessary to determine energy requirements.
One of the most influential nutritional factors linked to longevity is BCS (Salt et al, 2019). Evidence from a longitudinal study in dogs suggests that maintaining an ideal BCS of 4–5 on a 9-point BCS scale is associated with the longest average lifespan (Lawler et al, 2005); less evidence is available in cats but, in cross-sectional studies, a BCS of 6/9 was associated with the longest lifespan (Teng et al, 2018a), although a BCS of 4–5/9 was associated with the lowest risk of comorbidities (Teng et al, 2018b).
To determine daily metabolic energy requirements precisely, an accurate bodyweight and BCS must first be recorded. Therefore, it is vital that all senior pets are regularly weighed and body condition scored a minimum of twice a year, although three or four times a year is preferable in the author's opinion, allowing these parameters to be tracked over time. With such monitoring, a change of ≥5% in bodyweight should prompt a closer assessment, and might require adjustments to the daily food allocation or activity level.
Senior pets that have suboptimal condition and/or body weight will require different dietary strategies. Energy requirements and food intake should be assessed on an individual basis and adjusted accordingly to maintain a healthy body weight and lean body condition. For a senior pet that has obesity, a controlled weight reduction plan should be considered, although only modest amounts of weight loss (eg a maximum of 15–20% weight loss) are recommended to prevent excessive reduction of adipose tissue. Studies have indicated in both people and pets that improved survival from wasting diseases such as renal disease (Freeman et al, 2016), heart disease (Donataccio et al, 2021), diabetes (Gravina et al, 2021) and cancer (Martinez-Tapia et al, 2021) is observed when associated with increased body mass – a theory known as the obesity paradox. Any obesity care plan must therefore take into consideration the risks of wasting diseases, which are more prevalent in the senior years, and tailor the weight loss goals accordingly. In general, energy requirements for dogs decrease by an estimated 18–24% as they age, whereas in cats it remains similar to adulthood (Harper et al, 1998).
Protein
There has been much debate about whether protein intake should be restricted in senior pets (Laflamme, 2005) but, currently, there is no evidence that such a strategy is beneficial. Further, senior dogs have an increase demand for dietary protein (Fascetti et al, 2023), while both cats and dogs can lose lean body mass through sarcopenia and because of reduced protein digestibility. Therefore, protein restriction is not currently recommended, unless indicated as a result of a comorbidity (eg CKD) (Elliott et al, 2000). The dietary protein used should be of high biological value and highly digestible, as this will support maintenance of lean body mass, synthesis of new body tissues and immunity.
Fats
Fats provide energy, essential fatty acids and fat-soluble vitamins A, D, E and K in the diet. Fats further increase palatability and so are useful for encouraging voluntary food consumption. Proportions of fat within the diet should therefore be provided based on individual needs. Gram for gram, dietary fats deliver approximately twice the calorie content of proteins and carbohydrates (8.5 kcal/g vs 3.5 kcal/g). Therefore, in senior cats and dogs that are either already overweight or are prone to weight gain, excessive quantities of dietary fat should be avoided. In contrast, underweight individuals may need an increased dietary fat intake.
Carbohydrates
Although carbohydrates can be used in diets for senior pets, cats have a reduced ability to use them in comparison to dogs (Verbrugghe and Hesta, 2017). Carbohydrates provide a source of energy, which can spare proteins for use in other processes as detailed above. Carbohydrates are also a source of dietary fibre, which help to maintain gastrointestinal health and regulate gut motility. Both fermentable and non-fermentable fibre is important for maintaining gut health; fermentable fibre (eg beet pulp) is a source of butyrate (a short chain fatty acid (SCFA)), a key energy source for colonocytes, while non-fermentable fibre (eg cellulose) can help regulate gut motility by providing faecal bulk (Fahey et al, 2004). However, as constipation is more common in older pets, fibre is an important inclusion in diets for seniors. There are three main ways in which constipation can be managed with dietary fibre (Table 4).
Table 4. Three ways in which constipation can be managed with differing dietary fibre types.
| Fibre type | Management of constipation |
|---|---|
| Higher non-fermentable content | Increases stool bulk and frequency of elimination |
| Low non-fermentable content | Increased digestibility of the diet Reduced faecal volume and colonic distension |
| Higher digestible content, eg lactulose | Draws water into the colon to moisten the faeces and ease defecation |
Phosphorus
As described above, not only will renal function deteriorate over time as pets age, but renal disease is a primary cause of death in ageing cats and dogs. One of the main functions of the kidney is the removal of nitrogenous waste from the blood. As functional nephron numbers decline, the efficiency of glomerular filtration also will decrease, leading to toxic build-up of nitrogenous waste in the blood which, if left unmanaged, will eventually result in uraemic syndrome, affecting all other organs. Through correct dietary management, nitrogenous waste build-up can be minimised, functional nephrons can be preserved, and further progression of CKD can be slowed. Therefore, restriction of dietary phosphorus intake is important in the management of CKD, and might slow its progression (Böswald et al, 2018).
Antioxidants
Antioxidants, such as vitamin E or Beta-carotene, are frequently added to the diets of senior pets to support immune function (Massimino et al, 2003); theoretically, they might also delay the ageing process by combating free radical production caused during oxidative stress, a normal part of physiological ageing (Ray et al, 2021). Dietary supplementation with antioxidants has also been shown to enhance cognitive function and slow cognitive decline in several species, including dogs (May and Laflamme, 2019). However, although the addition of antioxidants to the diets of senior cats and dogs is unlikely to be harmful, there is limited evidence to support any meaningful benefit. Longterm, prospective cohort studies would be required to determine any such benefits as well as to determine which antioxidants are most suitable.
Water
Access to clean and fresh water should constantly be available, and the amounts consumed by a senior pet assessed periodically. If a change in water intake is observed (particularly an increase), further investigations would be indicated. There is no requirement for additional electrolytes to be added to water because, unlike with humans, cats and dogs do not lose significant amounts of electrolytes through sweating.
As detailed above, thirst stimulation in cats decreases with age (Churchill and Eirmann, 2021); to counter this and prevent dehydration, adequate intake of fluids should be promoted, and this can be achieved by providing multiple sources of water within the household, providing water fountains (as some cats prefer to drink from a running water source) and feeding wet foods which typically contain ≥80% moisture.
Access to food and water
Chronic pain from osteoarthritis is common in senior pets, and this can reduce their mobility, which might affect their ability to access food and water. Cats, in particular, can start to restrict their environment when their mobility is affected (especially if they need to jump up to gain access), no longer using favourite eating places which may then affect food consumption. Similarly, dogs with orthopaedic pain might find it difficult to access food and water from bowls positioned on the floor. Such issues can be addressed by making simple environmental changes, such as raising food and water bowls (using a stand, placing bowls on a step or chair). Further, if cats consume food from a bowl placed on a work surface, providing steps or a ramp might improve access. Small alterations such as these are important for maintaining good quality of life for all senior pets with arthritic changes or reduced mobility.
Conclusions
A detailed dietary history and nutritional assessment are required in order to make an optimal dietary recommendation for a senior pet. In addition to considering chronological age, lifestyle, environmental factors and comorbidities are all important. The dietary recommendation should be reviewed frequently because requirements may change more often in senior pets. Whatever the recommendation, the diet should be complete and balanced with appropriate modulation of nutrients according to the needs of the individual animal.
KEY POINTS
- Ageing is not a disease but a normal biological process that occurs as pets increase in years.
- Senior age is assumed to start when cats and dogs reach their last third of life, though this can vary according to species and breed as well as among individuals.
- Senior pets age in many diverse ways and, therefore, clinical signs of age rather than chronological age should be managed.
- Optimal nutrition has the potential to support all ageing body systems and delay the onset of diseases more likely to occur during the senior years.
- Simple environmental adaptations can also assist senior pets to consume their food more easily.