Nutrition is increasingly one of the greatest factors cat guardians have some control over when it comes to the health of their senior cat. Yet what constitutes a proper diet for the senior cat remains controversial. This paper is a summary of the latest scientific research and other available data from the veterinary community regarding senior cat diets. Senior cat physiology, disease prevention by dietary means, matching diet to disease, implementing diet adjustments, preservatives, and cat food quality standards are examined. Cat food choices and recommendations from veterinary experts based on the specific medical and behavioral issues of the senior cat will be presented throughout.
Like people, a cat's nutritional needs tend to change with age. Cats are generally termed "older" and "senior" once they hit age 7 and labeled "geriatric" once they reach age 10-12. (Pavia, 2004) Unless otherwise noted, these terms will be used interchangeably throughout this paper. Physiological changes are the primary reason for changing dietary needs of the senior cat. Organs and tissues deteriorate and become less efficient. Nutrition and nutritional history are major contributing factors to the rate of this deterioration. (Agar, 2001) A decreased thirst response and decreased taste sensation are common in older cats. For this reason veterinarians agree that feeding senior cats food that is highly aromatic and warmed to body temperature to increase its palatability are good practices. Keeping the senior cat hydrated is also important.
Chronic dehydration can exacerbate disease and even reduce the cat's ability to regulate body temperature. (Hand, Thatcher, Remillard, and Roudebush, 2000) Digestibility also affects food intake in older cats and decreases by about 10 percent by the time a cat reaches age 14. (Buffington, Holloway, and Abood, 2004) Dental problems are quite common and can lead to a lack of appetite, weight loss and abnormal chewing and swallowing behavior. In the worst cases the issues above combine to lead to anorexia and/or dehydration. Oral examinations and the treatment of oral cavity disorders should not be overlooked during regular veterinary visits for they are often one of the greatest contributing factors to morbidity in geriatric cats. (Wolf, 1999) Decreased immune response, decreased glucose tolerance, decreased renal function, and several other changes commonly develop with age. However, not all cats will experience these age-associated changes and different rates of aging will occur. (Hand et. al, 2000)
It's important to remember that aging itself is not a disease and that the physiological "slowing down" that occurs with aging is a normal part of the life cycle. (Wolf, 1999) There is much less controversy over the nutritional needs of the healthy senior cat versus the nutritional needs of an older cat with kidney disease, for example. Generally agreed upon guidelines for senior cat nutrition include diets that are: nutritionally complete, well balanced, highly digestible and palatable, and with plenty of taurine and potassium. (Wolf, 1999) Like some of the other dietary recommendations from veterinarians cited in this paper, this applies to cats of all ages but even more so to the senior cat. But what does "nutritionally complete" and "well balanced" mean for a senior cat?
Some veterinary experts suggest that due to the lack of studies on nutrient requirements of cats in the last third or quarter of their lives, we must base our decisions on dietary history, a physical exam, and diagnostic testing. They recommend diets that have been "made reputable" by manufacturers and approved by the American Association of Feed Control Officials (AAFCO). (Buffington, et. al, 2004) Perhaps the most helpful advice Buffington and associates offer is to monitor your senior cat's food intake as changes in food intake often serve as a "warning system" or signal for health problems. This is because decreased food intake is a common symptom of disease and illness. They also encourage adequate fresh water intake. There is some consensus that dietary protein need not be restricted in the healthy older cat and that dry foods designed for tartar removal or teeth cleaning can improve oral health. (Hand et. al, 2000)
Veterinarians have yet to develop a "one size fits all" senior cat diet. The task is merely impossible given the enormous diversity of senior cats and their varying health issues. However, some recent studies have shown what not to feed your cat. A 2003 study published in the Journal of Feline Medicine and Surgery proved that healthy cats fed homemade diets consisting primarily of oily fish became depressed, experienced lack of appetite, leukocytosis, anaemia, subcutaneous nodules, and developed Pansteatitis (a disease related to fish-based diets) which is caused by the consumption of high levels of unsaturated fatty acids and/or the insufficient intake of vitamin E, leading to inflammation of adipose tissue. This is a case of diet contributing to or even causing disease.
Obesity may be the most common problem among older cats between the ages of 7 and 12. A variety of health problems may result from obesity including diabetes, heart disease, cancer, skin disease, urinary tract disease, and more. (Wolfson, 2004) Veterinary nutritional experts have yet to come to a consensus regarding what diet is best for the obese feline. Low carbohydrate diets termed "Catkins" have recently gained in popularity but even a low carbohydrate diet will not lead to weight loss if consumed in large amounts. (Wolfson, 2004) Because cats are carnivores and require a higher level of protein there may be some benefit to the Catkins diet. Studies of obese and diabetic cats show that most cats that were put on low carbohydrate, high protein diets lost weight gradually and about half of the diabetic cats went into remission and no longer needed insulin injections. (Wolfson, 2004)
The veterinary nutritional expert quoted in the Wolfson article recommends that what cat guardians should look for on supermarket shelves are diets that are meat based, canned or wet foods because they are higher in moisture than dry cat foods, and foods that mimic an "all-prey" diet. A typical mouse contains 65-85 percent moisture versus typical dry cat foods that contain only 10 percent moisture. Dry foods can contain up to 50% carbohydrates while a mouse generally contains less than 10 percent. (Wolfson, 2004) Extra carbohydrates mean extra calories and weight gain for most sedentary older cats ages 7-12. Excessive feeding of any food will not result in effective weight control. Yet just like humans, each cat is different and a diet that is right for one obese older cat may be wrong for another.
Some of the confusion over diet advice may be based on the fact that we are often told that "geriatric" cats need more calories. The problem lies with the definitions. Generally, older cats between the ages of 8 and 12 tend to grow heavier and after age 12 tend to become thinner and metabolically old. (Pavia, 2004) Strategies to increase calories in a healthy way for thinning cats well into their senior years include buying cat foods with higher protein content and cat foods that are used for growth. (Deneen, 2004) Some studies also show that decreasing fat content may improve insulin sensitivity. Impaired glucose tolerance is often age related and can be controlled by decreasing carbohydrates and fat content in the diet. (Rand, Farrow, Fleeman, and Appleton, 2003)
Other recent studies with promising results for the treatment and prevention of obesity and diabetes in cats include cat foods with added supplements of vitamin A, chromium, and carnitine. Studies to determine the appropriate fiber content of cat foods have been inconclusive and contradictory. (Rand et. al, 2003) Reading cat food labels carefully and visiting a veterinarian for geriatric laboratory tests to determine a cat's ideal weight and diet are wise decisions. Once you and your veterinarian have decided on the best diet for your older cat, the cat's diet must be adjusted gradually and carefully. How to properly go about making adjustments to your senior cat's diet will be discussed later in this paper.
Veterinarians have observed a recent increase in the prevalence of hyperthyroidism in older cats. The current debate in the veterinary community is if the increase is the result of the aging of the cat population or the consumption of commercial canned foods. One recent study looked at 169,756 feline medical records and on the basis of owners' questionnaire responses determined that age-specific hospital prevalence of feline hyperthyroidism has indeed increased greatly from 1978 to 1997. (Edinboro, Scott, Janovitz, Thacker, and Glickman, 2004) The researchers also found an association between increased risk of hyperthyroidism and the consumption of cat food in pop-top cans. They conclude that feline hyperthyroidism is not solely the result of aging and that canned cat foods may play a role. (Edinboro et. al, 2004)
It is now generally accepted that diet and lifestyle are risk factors for chronic renal failure (CRF) in pet cats. (Hughes, Slater, Geller, Burkholder, and Fitzgerald, 2002) A case-controlled study examining dietary risk factors for chronic renal failure in pet cats found that higher ash intake increased the odds of CRF while higher dietary fiber, magnesium, protein, and sodium intake were associated with decreased odds of CRF. (Hughes et. al, 2002) The deterioration of the kidneys may lead to an increased loss of vitamins, thereby requiring an increased supply of vitamins from the diet. (Agar, 2001) It is sometimes recommended to reduce protein levels in older cat diets, particularly those experiencing any degree of kidney failure. However, cats are known to be particularly sensitive to protein restriction so this approach to kidney disease prevention and treatment is extremely controversial. A level of 30 percent protein has been suggested for cats young and old to maintain lean body mass. Some researchers suggest we focus instead on the quality rather than the amount of protein we feed our senior cats. (Agar, 2001)
Older cats are less adaptable to changes in their diet. (Pavia, 2004) Whether or not dietary changes are even necessary depends on the health status of the individual senior cat. A 2002 study by Peachey and Harper found that aging does not influence actual feeding behaviors in cats such as the number of meals consumed, amount consumed, or duration of each meal. They did find that cats were more attracted to food with higher fat contents. Because no differences were observed between the young and senior cats' dietary habits, Peachey and Harper concluded that it cannot be assumed that feeding patterns are responsible for the previously observed age-related decreases in apparent digestibility. Their finding that foods with higher fat contents are more palatable to cats is a common one. Factors influencing the food preference of cats are important considerations.
One 2001 study concludes that smell is the primary factor influencing food preference although cats will make decisions about food based on both smell and taste. Diets having one dominant taste (versus a mix of different flavors) resulted in a higher feed intake. (Hullar, Fekete, Andrasofsky, Szocs, and Berkenyi, 2001) Other studies show that sick geriatric cats benefit from being petted while they eat, wider and shorter bowls, warming and moistening the food, and feeding favorite foods. Another consideration is that for cats on medications, dietary intake and nutritional requirements may be affected by interactions between drugs and certain nutrients. It's also important to note that for a sick cat that is supposed to be on a veterinary prescribed diet, it is better for the cat to eat something than nothing at all if the prescribed diet is rejected. (Buffington et. al, 2004)
The content and quality of cat food diets has changed significantly over the years. The unfortunate general rule of the past has been to base the diet of domesticated cats on whatever ingredients are easily processed, cheap, and convenient while an actual understanding of the unique nutritional requirements of cats is seriously lacking. (Wolfson, 2004) This seems to have changed in recent years as the number of veterinary nutritionists grows and the role different cat food ingredients play is studied and explained to consumers so that we can make educated decisions about what we're feeding our cats. Yet there are still no officially recognized criteria against which the nutritional adequacy of a geriatric diet can be judged. The AAFCO and publications on nutrient requirements for dogs and cats as recommended by the National Research Council do not address the geriatric life stage. (Hoskins, 2004)
The role of preservatives in cat food has come under fire and is still frequently debated among traditionally-minded veterinary professionals and those with a more "holistic" approach. Preservatives have been blamed for everything from allergies to cancer in cats. For example, a study for the FDA's Center for Veterinary Medicine concluded that the preservative propylene glycol reduces red blood cell survival time and renders the cells more susceptible to oxidative damage among other adverse effects in cats when consumed at the level found in soft-moist cat foods. Another preservative called ethoxyguin has been shown to increase liver-related enzymes in the bloodstream and accumulation of hemoglobin-related pigment in the liver. These are preservatives that need to be studied further. (Bonham, 2004)
On the other end of the debate are veterinarians and researchers who warn that the lack of preservatives, or so-called "natural" preservatives may cause food to become rancid more easily. Rancid cat food has been linked to cell abnormalities that lead to cancer. (Bonham, 2004) Bonham also points out that canning seals in freshness and therefore usually requires less preservatives than other types of packaging. She concludes that fresh is always best and that food sensitivities are more likely due to protein or grains than preservatives in amounts as miniscule as those found in most commercial cat foods (around 50 parts per million).
Agar says it best in her book Small Animal Nutrition where she states "all animals are individuals and it is therefore difficult to generalize (even though this book attempts to do so), and it is in the geriatric phase where generalizations are least appropriate." Tailoring the diet to the individual senior cat based on the cat's age (senior versus geriatric), health issues, and veterinary lab diagnostics is key. New studies are emerging daily and it is not uncommon for them to contradict each other proving that the study of feline nutrition is just as complicated as the study of human nutrition.
Based on the journals, books, and articles summarized in this paper, it seems appropriate to conclude that for healthy cats of all ages: the current trend toward meat-based, high moisture or wet food diets with higher protein and lower carbohydrate content, or diets that imitate the moisture and nutritional content of a cat's typical prey, seem to be gaining a high level of acceptance among many veterinary nutritional experts. It is clear that more research is needed to determine the specific nutritional requirements of senior cats. Perhaps consumer demand for products specialized for the geriatric cat will drive this research as the cat becomes more popular, gains higher status as a pet, and the cat population continues to age.
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