Senior cats: nutritional adaptations and practical feeding considerations

The pet cat population continues to grow. The Pet Food Manufacturer’s Association (2022) estimated in 2022 that there were 12 million cats in the UK, amounting to 28% of households owning at least one cat. The median longevity for cats is 14 years with cross-breed cats having a greater median longevity (14 years) compared to that of pure-breed cats (12.5 years) (O’Neill et al, 2015). International Cat Care (2019) displays six life stages (Figure 1) for cats, three of which pertain to the senior stages: mature, senior and super-senior. This shows that approximately half of a cat’s life is spent within the senior stages, yet pet owners may lack understanding of nutritional adaptations that are recommended at different ages. Comparing the age of cats with the human equivalent age can help pet owners to better understand their cat’s life stage and recognise changes that they may observe, both visibly and subtly, which may be more familiar to them as part of human ageing.

Veterinary professionals have a responsibility to perform nutritional assessments and provide advice as part of the management of animals’ health. In 2011, the World Small Animal Veterinary Association (WSAVA) released nutritional assessment guidelines for dogs and cats to support nutrition as an integral part of a medical healthcare plan, acknowledging it as the fifth vital assessment following temperature, pulse, respiration and pain (WSAVA, 2020).

Nutritional goals and requirements

The ultimate nutritional goal is to provide cats with complete and balanced nutrition appropriate to the life stage and individual, which would include a thorough nutritional assessment. The screening nutritional assessment process should involve body condition scoring (Figure 2) and an assessment of muscle mass. The prevalence of obesity is approximately 30-35% of cats between 7 and 12 years of age (Lund et al, 2005). The incidence of obesity decreases in cats over 12 years old and there is a higher incidence of underweight cats (Perez-Camargo, 2004), which highlights the necessity to assess cats as individuals. In addition to an increased incidence of decreasing bodyweight in cats more than 12 years old, this can be accompanied by a loss in lean tissue, indicating a reduction of muscle mass (WSAVA, 2014). In healthy cats, approximately one third of lean body mass is lost between 10-15 years of age, which is known as sarcopenia (Laflamme, 2018). This differs from cachexia, which relates to the loss of lean body mass because of chronic disease such as congestive heart failure, chronic kidney disease or neoplasia. Many of the chronic diseases are more common in ageing, so sarcopenia and cachexia can occur concurrently (Freeman, 2012). Therefore, another nutritional goal for senior cats is to maintain a healthy bodyweight by assessing energy content and relevant macronutrient levels.

In terms of nutrient requirements for dogs and cats, FE-DIAF (the European Pet Food Industry Federation) periodically reviews the National Research Council (NRC) data in conjunction with existing scientific research and evidence. This results in FEDIAF publishing a set of nutritional guidelines representing industry best practice for pet food manufacturers to follow within the UK and Europe. The guidelines are publicly available for consultation and the most recent version was released in 2021. The guidelines include levels of all essential nutrients required by dogs and cats and, where relevant, minimum and maximum recommended amounts at different life stages or physiological states, such as gestation. There is no clear definition or agreement on the nutritional requirements for senior cats. However, scientific evidence shows it is beneficial to adapt nutrition to support biological changes that occur as part of the ageing process, some of which will be examined here. There are also several diseases that are frequently diagnosed in older cats, notably chronic kidney disease, diabetes mellitus and osteoarthritis; in these pets, nutritional adaptation may be beneficial.

Nutrients of interest

Bioavailability is the degree to which nutrients are absorbed and become available at the site of action in the body (Hoag and Hussain, 2001). The bioavailability of protein and fat must be considered in diets for senior cats as they can become less adept at digesting these nutrients in the latter stages of life (Fahey et al, 2008). Both the ingredients used to deliver these nutrients and the processing of these ingredients will affect the overall digestibility. Several vegetable proteins, such as wheat gluten, corn gluten and soy protein isolate, are more digestible than some animal sources of protein. By balancing the types of proteins used, higher digestibility can be achieved with a wider amino acid profile. From the eleven essential amino acids required by cats in their diet, some are of particular interest for senior cats. For example, leucine, a branched-chain amino acid, is specifically involved with stimulating the synthesis of proteins and helping to slow down their degradation in the muscles (Grandjean, 2006). This is beneficial to try to preserve the lean muscle mass in senior cats considering the increased incidence of muscle wastage.

Incorporating vegetable protein sources helps achieve a moderated phosphorus content overall. Phosphorus is an essential mineral required by the body; it has an inter-relationship with calcium and the ratio in adult cats needs to be balanced at 2:1 (calcium:phosphorus) (FEDIAF, 2021). Phosphorus has multiple roles in the body; the majority is retained in the bones and skeletal system, and it is also a constituent of cell membranes, where it is needed to dispense energy (Grandjean, 2006). Phosphorus restriction is one of the key aspects of nutritional management for cats with chronic kidney disease.

It has been estimated that over 30% of cats older than 10 years of age are affected by chronic kidney disease (Sparkes et al, 2016), making it a significant progressive disease of older cats. Frequently, by the time a cat is showing clinical signs of chronic kidney disease and a diagnosis is made, a significant amount (two thirds to three quarters) of functioning kidney tissue has already been lost (International Cat Care, 2018). As a result, it is deemed prudent to moderate the level of phosphorus in diets for senior cats. Feeding foods designed for kittens, that have higher levels of phosphorus to meet growth needs, is inappropriate in senior cats. In the author’s experience, some cat owners feed older cats with kitten food because they perceive it to be more palatable or because of a desire for dry kibbles of a smaller size because of dental issues.

Mobility and joint issues in older cats can be challenging to diagnose as there are a variety of symptoms, many of which can be subtle so go unnoticed by owners or are disregarded as natural advancements of old age. There have been several studies in cats combining radiographic interpretation alongside the presence of lameness, which is not always apparent even where radiographic changes have occurred. One study of 100 cats by Hardie et al (2002) found that 90% of cats more than 12 years old showed a radiographic prevalence of osteoarthrosis, but that only 4% of those cases reported lameness as a clinical sign. As a result of the high prevalence and low recognition of joint disease, it is beneficial to include nutrients known for their qualities in supporting joint health. Glucosamine and chondroitin sulphate are commonly included to provide synergistic benefits in supporting joint health. Both are included in the composition of glycosaminoglycans which are base components in the formation of joint cartilage. Glucosamine helps to promote the production of new cartilage and chondroitin sulphate helps to inhibit the effect of enzymes that cause the permanent degradation of cartilage (Grandjean, 2006). Long-chain omega-3 fatty acids, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from marine sources, have many uses within the body, one of which relates to joint health in terms of the positive effect on inflammatory pathways (Lascelles et al, 2010).

Free radicals or reactive oxygen species are metabolically produced resulting from exposure to sources such as ultraviolet light, pollution, inflammation, disease and because of exercise, among other reasons. In healthy animals, antioxidants are used within the body to help restore the balance and neutralise the free radicals to help limit potential cellular changes such as cell death and mutation. As part of the natural ageing process, the antioxidant defence declines and the amount of reactive oxygen species increases, causing an imbalance and placing the animal in oxidative stress (LaFlamme, 2005). Nutrients that are frequently included at higher levels in senior diets for their antioxidant properties include vitamins C and E, and carotenoid pigments such as lutein and lycopene. Taurine, an essential amino acid for cats, primarily has roles relating to vision and reproductive function but also carries antioxidant properties within cells (Grandjean, 2006).

Cognitive changes are noted in a significant proportion of geriatric cats in the latter stages of life. Gunn-Moore et al (2007) estimated that 28% of cats more than 12 years old are affected, increasing to 50% of cats more than 15 years old. Behavioural changes exhibited can be varied and displayed to different degrees depending on the individual. Many of the most common signs of cognitive dysfunction syndrome (Table 1) may be distressing to both pet and owner. It is vital that medical causes of such symptoms are ruled out or treated as necessary. In terms of dietary support for such changes, increased antioxidant inclusion as described above may assist in reducing the activity of reactive oxygen species and potential brain cell damage. Other supportive nutrients including phosphatidylserine and omega 3 and 6 fatty acids are also believed to reduce oxidative damage and improve cognitive function (Milgram et al, 2004). Much of this research has been conducted in dogs so further studies in cats are warranted. Many aspects of helping to manage the symptoms of cognitive decline relate to the pet’s environment and minor adaptations may help to aid difficult situations. For example, the provision of more litter trays with lower sides may help with inappropriate toileting issues. Senior cats in particular value consistency in their environment and so inconsistency can cause stress and negatively impact their health and behavioural wellbeing (Landsberg et al, 2012b).

Water is also an essential nutrient, although fluid intake is not discussed in this article.

Respecting eating behaviours

There are many factors that impact the palatability of food to an individual cat, including those that are not physical factors of the food itself, for example routines, feeding receptacles and feeding environment. Natural feeding preferences should be respected, partly because cats respond to consistency as they age. This should include replicating feeding practices within the veterinary environment, where possible by enquiring into a cat’s preferences in discussions with owners during admittance.

While this article is focusing on the senior life stages, it is important to note that an individual cat’s feeding preferences can be strongly influenced by the types of food they consume during the weaning process and throughout the first year of life (Bradshaw, 2006). Food neophobia is the reluctance to eat or complete avoidance of a new food stuff if the individual has not been exposed to that type of food before. It can be beneficial for kittens to experience variety in food textures to help avoid food neophobia later in life, provided foods are offered in a balanced way, respecting mixed feeding guidelines and selecting compatible foods.

Clinical diets may be required long term to help support specific health conditions which, because of the nature of the diseases, may be more commonly required in middle to older age. It is strongly recommended that these are not introduced during periods of hospitalisation. Doing so can increase the risk of stress-related food aversion and may cause the cat to refuse the food for an indeterminate length of time. Instead, it is advised to commence the dietary change in the cat’s home environment and to start by offering the new diet in a separate, adjacent receptacle to allow the cat to express its preference and encourage a gradual transition (Quimby et al, 2021).

There are several other practical recommendations that can be discussed with owners of senior cats to aid their feeding habits. From studies in humans, it is hypothesised that cats experience a decline in both smell and taste with age that may contribute to inadequate food intake and subsequent loss of bodyweight. In a study of ageing domestic shorthair cats (more than 7 years old) a preference was shown for the cats to eat wet food that was served at an average temperature of 37°C, when compared with the same food being served at 6°C or 21°C (Eyre et al, 2022). This is thought to be because of the increased aroma and potential for the taste compounds to be changed or enhanced by warmth. The simple act of warming wet food may be enough to increase spontaneous food intake in healthy senior cats that may be experiencing a reduction in appetite and loss of condition, when other medical causes have been ruled out.

Another aspect of feeding that could be relevant to cats of all ages is the positioning of resources such as resting areas, litter trays, food and water bowls. These should be situated away from each other at a recommended minimum distance of 50 cm and ideally multiple sites of each should be available (Horwitz et al, 2010). Although difficult to achieve in the veterinary practice setting, efforts should be taken to separate out these resources, particularly where there are larger cages and for long-stay patients.

Nursing interventions

It is widely accepted that cats are experts at hiding symptoms and that many find visits to the veterinary practice stressful which in turn can make owners anxious and reluctant to bring their cat to the practice. According to a survey of cat owners by Cats Protection, separate to those cats that visit for routine checks, 36% of cats only visit a veterinary practice when their owner feels they need to and 4% never go to a practice (Cats Protection, 2022). Additionally, there are approximately 1.2 million cats in the UK that are not registered with a veterinary practice (Cats Protection, 2022).

Veterinary practices and veterinary nurses can be proactive in providing tips to owners on how to make the cat’s journey to the practice more comfortable. Within the practice itself, initiatives such as the Cat Friendly Clinic programme are widely recommended. Developed by the International Society of Feline Medicine (ISFM), the programme provides a framework and accreditation system reflecting changes that practices make, both physically and behaviourally, with the aim of making the practice more welcoming to cats and their owners to help reduce the stress of veterinary visits. The goal is for owners to understand the importance of cats having a regular veterinary examination in order to pick up on changes or abnormalities early, leading to a better clinical outcome. Qualified veterinary nurses can play a pivotal role in coordinating senior pet clinics, which provide an ideal opportunity for assessing nutrition and making appropriate recommendations. It is important for consistency of advice that standard operating procedures are set out, agreed and adopted across the whole team so that there are clear distinctions about when the veterinary surgeon should be consulted and what predetermined recommendations can be made based on various clinical scenarios. Explaining to owners the reasons behind all the recommendations made, in conjunction with identifying the needs of their individual cat, can lead to greater compliance and better outcomes.

Conclusions

Ageing is inevitable but there are many interventions available to help smooth the process and maintain vitality throughout a cat’s life. Nutrition plays a significant role in supporting a healthy ageing process and veterinary nurses are ideally positioned to instigate conversations with pet owners nutritional interventions, making appropriate recommendations and providing support.

KEY POINTS

• It is beneficial to adapt nutrition to support biological changes that occur as part of the aging process.
• Some diseases of older cats may benefit from nutritional adaptations.
• The cat’s eating behaviours should be taken into account when considering changes to nutrition.
• Veterinary nurses can be proactive in helping owners understand their cat’s nutritional requirements.