Key Nutritional FactorsP Jane Armstrong, DVM, MS, Diplomate, American College of Veterinary Internal Medicine (Internal Medicine) Professor, Internal Medicine/Clinical Nutrition, College of Veterinary Medicine, University of Minnesota,
Claudia A. Kirk, DVM, PhD, Diplomate, American College of Veterinary Nutrition, Diplomate, American College of Veterinary Internal Medicine (Internal Medicine), Adjunct Faculty Clinical Nutritionist, Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan
Jacques Debraekeleer, DVM, Adjunct Professor of Small Animal Clinical Nutrition, Veterinary Faculty of the State University Gent, Belgium
The below tables summarizes key nutritional factors for young to kittens, gestating and lactating queens, and middle-aged adult cats. The following section describes these key nutritional factors in more detail.
Recommended food levels*
Factors Young To Middle Aged Obese Prone
Energy density (kcal ME/g)
3.3-3.8 3.5-4.5 Energy density (kJ ME/g) 16.7-20.9 13.8-15.9 14.6-18.8 Protein (%) 30-45 30-45 30-45 Fat (%) 10-30 8-17 10-25 Crude fiber (%) <5 5-15 <10 Calcium (%) 0.5-1.0 0.5-1.0 0.6-1.0 Phosphorus (%) 0.5-0.8 0.5-0.9 0.5-0.7 Ca/P ratio 0.9:1-1.5:1 0.9:1-1.5:1 0.9:1-1.5:1 Sodium (%) 0.2-0.6 0.2-0.6 0.2-0.5 Potassium (%) 0.6-1.0 0.6-1.0 0.6-1.0 Magnesium (%) 0.04-0.1 0.04-0.1 0.05-0.1 Chloride (% >0.3 >0.3 >0.3 Average urinary pH 6.2-6.5 6.2-6.5 6.2-6.6 *Dry matter basis. Concentrations presume an energy density of 4.0 kcal/g. Levels should be corrected for foods with higher energy densities. Adjustment is unnecessary for foods with lower energy densities.
Key nutritional factors for growing kittens.*
Factors Recommended food levels* Energy density (kcal ME/g)
Energy density (kJ ME/g) 17-21 Protein (%) 35-50 Fat (%) 10-30 Crude fiber (%) <5 Calcium (%) 0.8-1.6 Phosphorus (%) 0.6-1.4 Ca/P ratio 0.9:1-1.5:1 Sodium (%) 0.3-0.6 Potassium (%) 0.6-1.2 Magnesium (%) 0.08-0.15 Chloride (% >0.45 Taurine (ppm) (extruded) 1,000 Taurine (ppm) (moist) 2,500 Average urinary pH 6.2-6.5 *Dry matter basis. Concentrations presume an energy density of 4.0 kcal/g. Levels should be corrected for foods with higher energy densities. Adjustment is unnecessary for foods with lower energy densities.
Key nutritional factors for Mating - Gestation - Lactation
Recommended food levels*
Factors Mating Gestation
Energy density (kcal ME/g)
4.0-5.0 4.0-5.0 Energy density (kJ ME/g) 19-21 17-21 17-21 Protein (%) 30-45 35-50 35-50 Fat (%) 10-30 18-35 18-35 Carbohydrate (%) - 10 10 Crude fiber (%) <5 <5 <5 Calcium (%) 0.6-1.0 1.0-1.6 1.0-1.6 Phosphorus (%) 0.5-1.0 0.8-1.4 0.8-1.4 Ca/P ratio 1:1-1:1.5 1:1-1:1.5 1:1-1:1.5 Sodium (%) 0.2-0.6 0.3-0.6 0.3-0.6 Potassium (%) 0.6-1.0 0.6-1.2 0.6-1.2 Magnesium (%) 0.04-0.1 0.08-0.15 0.08-0.15 Chloride (% >0.3 >0.45 >0.45 Taurine (ppm) (dry kibble) 1,000 1,000 1,000 Taurine (ppm) (moist) 2,500 2,500 2,500 Average urinary pH 6.2-6.5 6.2-6.5 6.2-6.5 *Dry matter basis. Concentrations presume an energy density of 4.0 kcal/g. Levels should be corrected for foods with higher energy densities. Adjustment is unnecessary for foods with lower energy densities.
LABORATORY AND OTHER CLINICAL INFORMATION
Laboratory analyses may help develop a complete picture of nutritional status. Results should always be interpreted in relation to the physical examination and historical findings. Complete blood counts, serum biochemistry analyses, fecal analyses and urinalyses may prove useful in assessing nutritional status, depending on the physiologic state, specific nutrient of interest and disease process present. Special diagnostic tests (e.g., plasma aminograms, clotting profiles, urinary clearance ratios and hormone assays) may help assess specific disease processes. Ancillary diagnostic procedures include ultrasonography, radiography and tissue biopsy as dictated by physical and laboratory analyses. Fecal analysis for intestinal parasites and testing for feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) should be routine for healthy adult cats.
Although water is the most important nutrient for cats, a finite water requirement has been not established because:
1) cats adjust water intake to the dry matter content of the diet,
2) cats conserve total body water by forming highly concentrated urine and
3) the water requirement of cats varies with physiologic and environmental conditions.
In general, it is recommended that cats drink 1 ml water/kcal ME requirement. In practice, adult cats should have unlimited access to potable water. Increased water intake is thought to be useful for managing urolithiasis by reducing the urinary concentration of urolith-forming minerals. Feeding moist foods (vs. dry foods) increases water intake and urine volume in most cats. Unlike dogs, cats do not fully compensate for differences in food moisture content by altering free water intake. When allowed free access to water, the total water intake of cats eating dry food was only half that of cats- eating moist food.
The DER of average young to middle-aged adult cats is generally between 60 to 80 kcal/kg body weight/day (251 to 335 kJ/kg body weight/day) or approximately 1.2 to 1.6 x RER, where RER in kcal = 70(BWkg)°75 or RER in kJ = 293(BWkg)0.75. Caloric requirements for neutered or inactive cats are calculated using the lower end of the range (1.2 x RER), whereas the upper end of the range (1.4 to 1.6 x RER) is used for-active sexually intact cats. Most neutered house cats require between 1.2 to 1.4 x RER. Despite the relative uniformity of size within the domestic cat population, there are size-associated differences in energy requirements. Smaller cats consume more calories per kg body weight than larger cats.
Determination of DER for a population of cats results in a bell-shaped curve. Individual cats may have energy requirements that vary by up to 50% or more above or below the average requirement. This range is not surprising considering that the DER of a particular cat is influenced by differences in lean body mass, activity, environmental temperature and genetic traits. Thus, it is important to remember that calculated 'energy requirements are only estimates for individual cats. The true caloric requirement for an individual cat is the amount of food that will maintain an ideal body condition (BCS 3/5) and stable weight.
Controlling energy intake is important in managing and preventing obesity. Approximately 25% of pet cats in the United States are overweight. The prevalence is highest in middle-aged cats (seven to eight years); nearly 50% of this age group are overweight or obese (BCS 4/5 or 5/5). Obesity increases the risk of death in middle-aged cats 2.7 times above that of lean cats, thus preventing obesity has important consequences for long-term health.
Risk factors associated with obesity include:
1) middle age,
2) neuter status,
3) low activity and
4).high-fat, high-calorie foods.
Some cats that are inactive, confined or obese prone may require markedly fewer calories than predicted by equations to determine DER (i.e., 1.0 x RER or 39 to 66 kcal/kg body weight/day or 163 to 276 kj/kg body weight/day). Obese cats may require as few as 0.8 x RER or 44 to 54 kcal/kg ideal body weight (184 to 226 kj/kg ideal body weight/day) to achieve an average weight loss of 1% of body weight per week.
Food digestibility and energy density may influence the risk for FLUTD. Energy-dense foods reduce overall dry matter intake. Lower dry matter intake decreases stool volume, which subsequently reduces fecal water loss. Both features are beneficial in reducing total magnesium intake and increasing urine volume. Controlled food intake should be used when feeding high-calorie foods. Excessive intake of calorically dense foods (e.g., with free-choice feeding) can induce obesity, also a risk factor for urolithiasis. See above for recommended, levels of fat, fiber and energy density of foods for cats at risk for obesity.
The protein requirements of adult cats have generally been established using experimental foods containing essential amino acids at or above the minimum requirement for growth. From these studies, the National Research Council (NRC) suggested the minimum protein requirement for adult cats is 14% (dry matter basis [DMB] ), or 12% protein calories. Commercial foods prepared from natural ingredients and processed may have lower protein digestibility than the experimental foods used to establish these minimums. To provide a margin of safety and account for differences in protein quality, the Association of American Feed Control Officials (AAFCO) has suggested a minimum dietary protein level of 26% DM for adult maintenance. Protein and amino acid requirements vary with the energy content of a food. The minimum protein allowance suggested by AAFCO is based on foods containing 4.0 kcal/g (16.7 kJ/g) DM and should be corrected in foods with energy densities greater than 4.5 kcal/g (18.8 kJ/g).
Meeting the minimum protein needs of cats is critical because they have minimal capacity to adapt to low levels of dietary protein. However, protein in excess of the requirement is rapidly catabolized and used to provide energy and maintain blood glucose levels. Any excess energy will be stored as fat. Therefore, there appears to be little benefit to feeding large excesses of protein to cats. Conversely, dietary protein excess may increase proteinuria and the progression of subclinical renal disease. Similar to findings in people and dogs, the role of protein and the progression of renal disease in cats is controversial. Nevertheless, avoiding excess dietary protein in cat foods may be beneficial, whereas feeding excess protein simply provides extra energy.
Although cats can be fed vegetable-based foods, most protein in the food should be derived from animal tissues. The amino acid profile of most animal tissues better reflects the nutritional requirements of cats. Moist products usually list animal-based ingredients within the first two ingredients (excluding water), whereas dry products usually list animal-based ingredients in the first three ' ingredients. The recommended protein allowance for normal adult cats is 30 to 45% of the dry matter.
Taurine is a key nutrient for all feline lifestages. Although the requirement varies somewhat throughout the lifestage, variations due to nutritional factors are far greater than those related to age. Although taurine deficiency is no longer common in adult cats, awareness of the nutritional factors that affect taurine availability is important. Sporadic cases of taurine depletion continue to be diagnosed. Therefore, dietary taurine concentrations should be evaluated in cats with signs of deficiency or disease.
Fats and Essential Fatty Acids
Cats use dietary fat for energy and essential fatty acids and to facilitate absorption of fat-soluble vitamins. A minimum requirement for fat has not been established for cats although foods containing less than 5% DM fat have been fed successfully to hyperlipidemic cats. Signs of essential fatty acid deficiency in cats include fatty degeneration of the liver, kidneys and adrenal glands. Scaly skin, mild hyperkeratosis and hair loss have also been noted. Linoleic acid and a-linolenic acid are essential for normal membrane structure and function, including growth, lipid transport, maintenance of the epidermal permeability barrier and normal skin and coat. Arachidonic acid, on the other hand, is important for functions that rely on eicosanoid synthesis. In cats, deficiency of arachidonic acid is associated with impaired platelet aggregation, inflammatory skin lesions and reproductive failure in queens. Male cats are capable of converting linoleic acid to arachidonic acid within the testes, resulting in normal spermatogenesis.
Fatty acids of the n-3 series (linolenic acid, 18:3n-3) are probably required in the diet of all animals. Studies indicate n-3 fatty acids are essential for normal neural development in neonates. Cats would normally consume n-3 fatty acids when eating the neural tissues of their prey. A minimum requirement has not been defined for most mammals, including cats. The role of n-3 fatty acids in companion animal medicine has focused mostly on their pharmacologic -like properties and ability to modulate the immune response and inflammation. Although these effects may benefit some animals, untoward effects are possible. Cats appear particularly susceptible to the deleterious effects of lipid oxidation. Foods high in polyunsaturated fatty acids have been associated with the development of feline pansteatitis when not adequately supplemented with vitamin E. In one study, cats developed increased bleeding times and decreased platelet function when fed foods supplemented with high levels of n-3 fatty acids. However, no adverse effects were found in similar studies. The current understanding of n-3 fatty acid metabolism in cats is limited, thus n-3 fatty acid supplementation should be used judiciously.
Fat levels above 9.0% DM are recommended for most cats. When both fatty acids are present, linoleic acid is required at 0.5% of the food and arachidonic acid at 0.02% of the food, or 5% and 0.04% of the dietary energy as linoleic acid and arachidonic acid, respectively. Fat enhances the palatability of food; cats prefer foods with levels near 25% DM vs. foods at 10 or 50% DM.
High-fat foods have been associated with an increased incidence of obesity in cats. Most cats do well on foods with 10 to 30% fat. However, cats prone to obesity should be fed foods with lower levels of dietary fat (8 to 17% DM)..
Although cats do not require dietary fiber, small amounts in commercial foods enhance stool quality and promote normal GI function. The natural foods of cats typically contain less than 1% dietary fiber although much higher levels are well tolerated. Fiber concentrations less than 5% DM are recommended for normal adult cats. Obese-prone cats may benefit from foods that contain up to 15% crude fiber (DM). Fiber supplementation may benefit cats with frequent hairballs, but its effects for this problem have not been well studied. Clinical evidence and field trials have demonstrated a reduction in the frequency of hairball vomiting with fiber supplementation.
Calcium and Phosphorus
Deficiencies of calcium and phosphorus are uncommon in cats fed commercial foods. Most cases of calcium deficiency have occurred in cats eating only unsupplemented meats, in which the calcium concentration is excessively low and the phosphorus concentration excessively high. Phosphorus excess appears to be of greater concern for adult cats fed commercial foods, especially as related to lower urinary tract and renal disease. The calcium requirement for growing kittens is 0.5% (DM) of the diet. Adult needs are typically less than those for growth. Calcium and phosphorus requirements of adult cats have recently been determined. The minimum calcium requirement was reported as 132 mg/MJ (60 mg/100 kcal or 0.25% DM at an energy density of 4.5 kcal/g). The minimum phosphorus requirement was 143 mg/MJ (55 mg/100 kcal or 0.27% DM at an energy density of 4.5 kcal/g). Both values are nearly half the AAFCO minimum allowance (i.e., 0.6% DM for calcium and 0.5% DM for phosphorus). Typical commercial foods contain calcium and phosphorus levels well in excess of these guidelines.
Daily calcium intakes of 200 to 400 mg per day meet the needs of adult cats when fed foods with a calcium-phosphorus ratio of 0.9:1 to 1.1:1. Although foods with much broader ratios of calcium to phosphorus have been fed successfully, ratios near 1:1 calcium to phosphorus optimize the availability of phosphorus. When the calcium-phosphorus ratio is increased to 2:1, phosphorus availability declines by 41%. Calcium-phosphorus ratios between 0.9:1 to 1.5:1 appear optimal for most feline foods.
Dietary phosphorus is a key nutrient in the management of two common feline diseases: struvite-mediated FLUTD and renal disease. The mineral constituents of struvite are magnesium, ammonium and phosphate. Although the primary objectives for preventing FLUTD due to struvite precipitates are to reduce urinary pH and, to a lesser extent, restrict dietary magnesium, limiting dietary phosphorus may be beneficial. The kidneys excrete excess dietary phosphorus to maintain phosphorus balance. The risk of clinically apparent struvite crystalluria and urolithiasis appears highest in adult cats from two to five years of age. Controlling phosphorus intake in combination with appropriate reductions in dietary magnesium concentrations and urinary pH reduces the risk of struvite-associated FLUTD in cats of this age group.
In one survey among pet owners, renal disease was the second most common cause of non-accidental death in cats; its prevalence increases with age. Excess dietary phosphorus is not considered a cause of renal damage but accelerates the progression of renal disease toward failure and death. High levels of dietary phosphorus (1.2 to 1.8% DM) lower creatinine clearance values and possibly reduce renal function in young, healthy cats. Phosphorus reduction is advised in the early nutritional management of renal disease in cats to decrease the renal excretory workload and avoid phosphorus retention. Cats with renal insufficiency are often not diagnosed until three-fourths or more of kidney function has been lost and older cats have an increased prevalence of kidney disease. Generalized phosphorus reduction may slow progression of renal disease in cats with subclinical or undiagnosed disease. Dietary phosphorus may be reduced as low as 0.3% DM in cats with overt renal disease, otherwise levels of 0.5 to 0.7 % are recommended.
Sodium and Chloride
The long-term effects of high sodium or salt intake by cats have not been studied. In people, limiting sodium intake to levels that meet the requirement without significant excess reduces the risk of hypertension and is considered important to long-term health. This same nutritional practice has been advocated for cats. In a study involving feline hypertension, nearly 50% of hypertensive cats fed a low-sodium food had a significant reduction in blood pressure. This response is similar to that seen in people in that not all people are "salt-sensitive." In cats, hypertension is commonly associated with renal failure, hyperthyroidism, cardiac disease and possibly obesity. High blood pressure has been associated with significant end-organ damage in hypertensive cats. Blindness, retinal hemorrhage, stroke, cardiac dilatation and murmurs and renal damage were common findings among the cats studied. Avoiding excess sodium chloride seems prudent because: 1) hypertension has significant deleterious health effects, 2) diagnostics to detect hypertension are not commonly performed and 3) the medical conditions associated with hypertension are common in cats. Chloride has been implicated more recently as a major determinant in the development of hypertension in salt-sensitive people. The interaction of sodium with chloride appears to cause the greatest increase in blood pressure compared with sodium combined with other anions. The minimum chloride requirement is not known for cats, but the NRC recommended concentration (i.e., 0.19% DM) appears sufficient.
In addition to exacerbating hypertensive disorders, high dietary sodium is reported to enhance urinary calcium excretion. Whether excess dietary sodium plays a role in the development of calcium oxalate urolithiasis in cats is unknown. However, the negative effects of high sodium intake outweigh the benefits; therefore, sodium excess, particularly in the form of sodium chloride, should be avoided.
The minimum sodium requirement for adult cats is estimated at 9.2 mg/kg body weight/day or approximately 0.08% DM; however, the optimal sodium content of cat foods has not been established. The average sodium content of prey is relatively low (e.g., approximately 0.25% DM in whole rat carcasses). Short-term studies have shown adult cats tolerate a wide range of dietary sodium intakes (i.e., 0.04 to 2.0%). Dietary salt (sodium chloride) added at concentrations of 4% DM or greater will markedly enhance water intake and increase urine volume when fed to cats. However, the long-term consequences of feeding such high levels of sodium chloride are unknown. Sodium concentrations from 0.2 to 0.5% DM will satisfy the needs of healthy adult cats without providing excessive levels.
The potassium requirement of cats varies with the dietary protein concentration and the effect of the food on urinary pH. High-protein foods and foods that result in an acidic urinary pH increase the potassium requirement of cats. Previously recommended levels of 0.4% DM resulted in hypokalemia in adult cats and kittens when combined with dietary acidification. Dietary potassium levels in foods for normal adult cats should be greater than 0.5% DM and ideally between 0.6 to 1.0% DM to prevent hypokalemia. Increased potassium losses occur in cats with certain metabolic abnormalities (e.g., renal insufficiency, renal tubular acidosis, diabetes mellitus and enteritis). Potassium supplementation may be necessary to maintain normal potassium balance in cats with these conditions.
Magnesium is an essential nutrient, but is also a major constituent of struvite crystals (magnesium ammonium phosphate). Struvite precipitation in the urinary tract contributes significantly to the development of FLUTD. Struvite-mediated FLUTD has declined following the industry-wide reduction of dietary magnesium and inclusion of acidifying ingredients in commercial cat foods. To reduce the risk of FLUTD due to struvite, dietary magnesium concentrations should be less than 20 mg/100 kcal of food (or less than 0.10% DM) in conjunction with a reduced urinary pH (i.e., average pH values <6.5 pH units). These levels are similar to those found in the natural food of cats.
Magnesium concentrations of 0.08% DM were measured in whole rat carcasses." The minimum magnesium requirement for adult cats is 4.1 mg/100 kcal (9.7 mg/MJ or 0.016% DM). Excessive magnesium restriction may be associated with the increasing prevalence of calcium oxalate uroliths in cats. Therefore, excessive restriction of magnesium (i.e., less than 0.04% DM) is not recommended.
Food ingredients and feeding methods contribute to the urinary pH produced by cats. The risk of struvite precipitation and FLUTD is greatly reduced at urinary pH values less than 6.5. Many cats develop metabolic acidosis when the urinary pH is less than 6.0. Metabolic acidosis may promote bone demineralization, urinary calcium and potassium loss and increase the risk of calcium oxalate urolithiasis. Free-choice food intake modulates urinary pH by dampening the postprandial alkaline tide that occurs three to six hours following larger meals. Meal feeding promotes a much greater alkaline tide and higher average urinary pH. Commercial foods commonly balance dietary cations and anions to achieve the appropriate urinary pH. Animal proteins, corn gluten meal, certain mineral salts, methionine and phosphoric acid are common ingredients that reduce urinary pH when added to feline foods.
Foods that produce average urinary pH values of 6.2 to 6.5 when fed free choice reduce the risk of st stuvite-medi-ated FLUTD and avoid metabolic acidosis in most adult cats. The normal urinary pH of cats eating mice and rats is 6.2 to 6.4. Thus, 6.2 to 6.4 is the "normal acidic urinary pH" of cats fed a wild-type food and the recommended range for healthy adult cats.
Recently, very hard foods have been implicated as a potential factor in the etiology of feline odontoclastic resorptive lesions (i.e., neck lesions). Chronic tooth trauma may result in abfraction (fractures) of the enamel at the gum line. This trauma alone or together with poor oral hygiene may initiate odontoclastic resorptive lesions in cats. Although a direct association has yet to be demonstrated, it seems prudent to avoid very hard foods when possible, especially in cats with dental disease.
Food texture also influences the palatability and acceptability of foods for cats. A sudden change in texture may result in reduced food intake or food refusal. Cats accustomed to eating only dry foods may refuse moist foods and vice versa. Recognizing the preferred food texture from the dietary history will help identify textural change as a cause of inappetence
Key Nutritional Factors For Older Cats
For nutritional purposes, cats are often considered as being senior at seven to eight years of age and geriatric or very old beginning at 10 to 12 years of age There is an increasing prevalence of age-related diseases around seven years of age coupled with the gradual onset of behavioral, physical and metabolic changes related to aging. Interestingly, age seven in cats roughly corresponds to the age at which people are considered senior (51 years), whereas 12-year-old cats correspond to very old or geriatric people (i.e., 69 years). Outwardly, a seven-year-old cat may not appear old, but changes in nutritional management and preventive care are important to reduce risk factors for common age-associated diseases, maintain good health and maximize longevity. It is important to remember the aging process is influenced by genetics, nutrition and environment. Further, an animal's chronologic age may not accurately reflect the animal's physiologic age (e.g., an eight-year-old cat with kidney disease and poor nutritional status is likely to be "physiologically older" than a healthy 11-year-old cat).
The minimum nutrient requirements of older cats are probably similar to those of young and middle-aged adult cats. The few studies evaluating the effect of aging on the nutritional needs of cats have shown minimal changes in nutrient requirements. Therefore, nutritional recommendations for older cats are based on risk factor management, extension of learning from other species and prudence. However, it is important to recognize the only nutritional modification known to slow aging and increase the life span is caloric restriction. Reducing caloric intake by 20 to 30% of normal while meeting essential nutrient needs reduces the aging process, cancer, renal disease and immune-mediated diseases in the animal models tested to date. This level of caloric restriction is difficult to achieve in the long term and has not been incorporated into mainstream nutritional advice.
Older cats become less active and have reduced lean body mass. Together, these changes reduce the basal metabolic rate. Additionally, changes occur in virtually all body systems. Age-associated changes in physiologic function include reduced digestive function, immune response, glucose tolerance, renal function, smell, taste perception and numerous other changes. Not all cats develop all age-associated changes nor will the changes that develop necessarily occur in any predictable sequence. Aging cats become less adaptable and have reduced physiologic reserve to withstand perturbations in their health and environment, including changes in their food. Different rates of aging occur among older cats, thus there is greater diversity in individual animal needs than at any other lifestage. Individualization of nutritional management becomes even more important because of the poor adaptability of older cats. The goals for the nutritional management of older cats are:
Maintenance of optimal nutrition (i.e., maintenance of ideal body condition and weight, adequate
intake of a nutritious food and good hydration)
Risk factor management (i.e., minimization of associated disease risks)
Disease management (i.e., amelioration of clinical signs of common diseases, slowing progression of
certain chronic diseases)
Improvement in the quality and longevity of life.
This section describes how to assess older cats and meet their nutritional needs.
Assess the Animal
HISTORY AND PHYSICAL EXAMINATIONA complete history should be taken and physical examination performed, as described for young to middle-aged adult cats. Of particular interest are physiologic changes associated with aging and age-related diseases. Note any changes in appetite, food or water intake, activity, oral health and body condition. Abnormalities in these parameters are often early indicators of underlying disease. Oral disease is the most prevalent disease in older cats; however, weight loss, renal disease, cardiac disorders, diabetes mellitus and hyperthyroidism are frequently diagnosed in this age category. Kidney disease may affect nearly 30% of older cats and is a major cause of feline death. Physical evaluation of renal size, shape and firmness may uncover kidney abnormalities, whereas thoracic auscultation may expose cardiac disease. Hyperthyroidism may be detected by palpating enlarged thyroid glands or may be suspected based on the history and other physical findings. A fundic examination may help detect hypertension, which is often secondary to renal, cardiac or thyroid disease in older cats. Retinal hemorrhage was a common finding in a group of older hypertensive cats. LABORATORY AND OTHER CLINICAL INFORMATION
Specific abnormalities in the physical and historical examination should be pursued further using appropriate diagnostic procedures. A geriatric-type blood panel to screen for common age-associated diseases should be performed annually. The minimum database should include a complete blood count, urine specific gravity and sediment examination and a serum biochemistry profile. The biochemistry panel should include measurements of albumin, globulin, urea nitrogen, creatinine, glucose, alkaline phosphatase, alanine aminotransferase, calcium, potassium, phosphorus, sodium, chloride and bicarbonate. Serum total thyroxine (T4) concentrations should be assessed if clinical or biochemical abnormalities suggest hyperthyroidism. FeLV and FIV testing should be current and repeated if potential exposure has occurred or suspicious clinical signs are present. Specialized diagnostics may be indicated by the physical or biochemical findings (e.g., electrocardiography, ultrasonography, radiography, blood pressure monitoring).
KEY NUTRITIONAL FACTORS
The nutrient requirements of older cats are unlikely to be significantly different from those of young to middleaged adult cats. However, the recommended range of nutrient allowances can be optimized to support changes in physiologic function and reduce risk factors for common age-related diseases.
Age-related changes Associated conditions and diseases Decreased thirst sensitivity Dehydration Decreased thermoregulation Hypothermia or hyperthermia Decreased immunocompetence Susceptibility to infections, disease and cancer Decreased rate of drug metabolism Drug intolerance Increased sleep Irritability Decreased activity and metabolic rate Loss of body mass, reduced BMR and obesity Special senses Decreased olfaction Reduced food intake and weight loss Decreased taste perception Reduced food intake and weight loss Decreased hearing Decreased visual acuity Oral cavity Decreased salivary secretion Increased oral disease Increased tooth loss, dental calculus Painful or difficult prehension Reduced food intake and weight loss Increased periodontal disease Susceptibility to sepsis and end-organ damage Gastrointestinal Decreased liver function Reduced nutrient assimilation Increased cellular infiltrates Decreased digestive function Reduced nutrient digestibility Decreased colonic motility Constipation Decreased pancreatic function Reduced nutrient digestibility Endocrine Decreased pancreatic function Glucose intolerance and diabetes mellitus Decreased adrenal function Reduced ability to respond to stress Alterations in thyroid structure and function Hyperthyroidism Integumentary Loss ofelasticity, dry, thin coat, hyperplasia
of sebaceous glands with decreased sebum
and increased waxy secretions
Dry, flaky coat
Urinary Decreased total renal function Chronic renal failure
Alterations in acid excretion Decreased acid-base regulation
Reproductive Testicular tumors and atrophy, mammary gland nodules Reproductive gland neoplasia
Irregular estrous cycles Pyometra Decreased conception rates Cystic endometrial hyperplasia Musculoskeletal Decreased lean mass and tone Decreased BMR, weakness, decreased activity Decreased bone mass Degenerative joint changes Osteoarthritis, spondylosis Cardiovascular Decreased cardiac output, increased peripheral resistance, hypertension Cardiomyopathy, valvular regurgitation
Hypertension and end-organ damage
Valvular thickening Respiratory Reduced vital capacity and compliance Chronic respiratory disease Increased respiratory rate and residual air capacity Nervous Alterations in neurotransmitter levels Senility Progressive decline in cellularity of nervous tissues Decline in special senses Decreased reactivity to stimuli and cognition decline Behavioral changes Key: BMR = basal metabolic rate. 'As in any biologic system there is much individual variation. An individual aging animal may have few to many of these changes. Also, the age at which changes occur, and their severity, is quite variable.
Key Nutritional Factors For Older Cats
The nutrient requirements of older cats are unlikely to be significantly different from those of young to middleaged adult cats. However, the recommended range of nutrient allowances can be optimized to support changes in physiologic function and reduce risk factors for common age-related diseases.
Most common causes of mortality in cats. Cause of death
Proportion of deaths (%)
Feline infectious peritonitis
'Morris Animal Foundation. Animal health survey: Top five causes of death as reported by owners. Denver, CO. 1998.
Water is an often overlooked but critical nutrient in the health of older cats. Aging impairs thirst sensitivity, which is already low in cats compared with other species. In addition, the decline in renal function observed in many older cats may increase water losses due to impaired urine concentrating ability. Together, these characteristics predispose older cats to dehydration. Chronic dehydration can impair normal metabolic processes and exacerbate subclinical disease. In addition, dehydration reduces the cat's ability to thermoregulate. Water intake in healthy cats without increased losses is 200 to 250 ml per day. This intake comes from a combination of free water, metabolic water and water contained in food. The water content of food may be increased by changing to a moist food or adding water to the food (moist or dry). Offering low-salt broth, meat juices or "pet drinks" has been advocated as a means to enhance water consumption; however, the longterm effectiveness of this strategy is unknown. Clean fresh water should be continuously available and readily accessible to further encourage increased water intake.
Well-controlled studies to determine the energy needs of older cats have not been conducted. Reductions in lean body mass, basal metabolic rate and physical activity are factors that decrease energy requirements as animals age. "' In many species, the decline in lean body mass is counterbalanced by an increase in total body fat such that obesity becomes more prevalent with age. However, studies reveal the prevalence of obesity plateaus and then declines in cats after seven years of age, whereas the prevalence of underweight conditions increases dramatically after 11 years of age. This observation may be explained by the high occurrence of disease in this age group, reduced food intake due to impaired appetite or sensory function, an age-related decline in food digestion or assimilation or a combination of these factors. Although the prevalence of obesity declines after seven years, a significant proportion of older cats remain overweight. Both obesity and cachexia significantly increase the risk of mortality in cats over eight years of age, with obese cats nearly three times as likely to die as cats of optimal weight. Therefore, it is critical to recommend foods and feeding methods that will achieve optimal weight and body condition in individual older cats.
In a study of healthy cats, energy intake (ME) declined slightly until approximately 10 years of age. However, a sharp increase in food intake was observed in very old cats (12 years and older). A 10% reduction in fat digestibility was responsible for a similar reduction in total food digestibility in these very old cats. The digestibility of dietary fat declined significantly with age, whereas protein and carbohydrate digestibility remained stable. Thus, reduced fat digestibility in very old cats was offset by increased food intake, as a result digestible energy intake was not different between age groups. From these studies, it is not clear if changes in the metabolic rate of older cats are compensated for by a reduction in fat digestion, or if older cats simply compensate for impaired digestion by consuming more food. The latter seems more likely based on observations that weight loss is more prevalent than ,obesity in very old cats. A decline in pancreatic enzyme secretion is a common physiologic change associated with aging in many species and could be expected to reduce digestibility of dietary fat. In addition, hepatic changes seen in older cats may influence nutrient assimilation. Based on these studies, the energy density of foods formulated for senior cats should be between 3.5 to 4.5 kcal/g (14.6 to 18.8 kJ/g) DMB. Very old cats should be fed energy-dense foods (4.0 to 4.5 kcal/g [ 16.7 to 18.8 kJ/g] DMB) and caloric intake should not be restricted, except to prevent or treat obesity.
Reasonable estimates of caloric needs in senior cats are 1.1 to 1.4 x RER (55 to 70 kcal/kg body weight [230 to 293 kJ/kg body weight]), with very old cats needing up to 1.6 x RER (80 kcal/kg body weight [344 kJ/kg body weight] ) Obese cats can be managed with standard weight-control programs appropriate for adult maintenance.
Dietary protein should not be restricted in apparently healthy older cats. Adequate protein and energy intake are needed to sustain lean body mass, protein synthesis and immune function in aging cats. Although controversial, the protein needs of older animals may be somewhat greater than those of young to middle-aged adults. In people, the recommended daily allowance of protein for the elderly is increased by 25% above that for adult maintenance. The equivalent increase in minimum protein requirement for cats is approximately to 18% DM protein or 15% protein calories using ideal proteins. The recommended protein allowance for healthy older cats fed commercial foods is 30% of the diet dry matter when the variable digestibility and protein quality of natural food ingredients are considered. An additional benefit to maintaining moderate protein concentrations in foods for older cats is the palatability-enhancing effect of animal proteins. Enhanced palatability resulting from animal proteins may conceivably improve food intake and weight maintenance in very old cats. However, the long-term effects of feeding foods with high dietary protein levels to healthy cats are still largely unknown. High-protein foods have been implicated in the progression of renal failure. Protein restriction in foods for older cats has been advocated because of the high prevalence of renal disease in this age group and the knowledge that renal failure is rarely diagnosed until at least threefourths of renal function is lost. The potential benefits of this restriction include a delay in age-related renal impairment and slowed progression of subclinical renal disease. In one study, investigators examining the effect of protein-calorie restriction in cats following five-sixths nephrectomy observed a reduction in proteinuria and glomerular injury in cats fed reducedprotein foods (27.6% DM) compared with high-protein foods (51.7% DM). A secondary finding was an increased occurrence of hypokalemia in cats fed the high-protein food. However, a subsequent study demonstrated no change in renal pathology following protein restriction and a slight benefit (i.e., reduced cellular infiltrates and tubular lesions) to caloric restriction (i.e., 56 kcal/kg body weight [low-calorie group] vs. 75 kcal/kg body weight [high-calorie group]). Unfortunately, these studies may not be directly comparable because the dietary protein sources were markedly different. Thus, there is no consensus about the role of protein reduction in slowing progression of feline renal disease.
Healthy older cats should receive sufficient protein to adequately meet protein needs and avoid protein-calorie malnutrition. Any additional protein needs of older cats can be fulfilled by improving protein quality without increasing protein intake. Until further research defines an optimal range of dietary protein for older cats, moderate levels of dietary protein (30 to 45%) are recommended.
Although weight loss is prevalent in very old cats, obesity still affects a large portion of the older cat population. Certain diseases associated with obesity are also common in older cats (e.g., diabetes mellitus, hypertension and heart disease). In addition, the risk of death increases nearly threefold in older obese cats (i.e., eight to 12 years). Moderate to low levels of fat are indicated to reduce the risk of obesity. However, very old cats need energy-dense foods and ample levels of essential fatty acids. Essential fatty acids (i.e., linoleic, arachidonic and possibly linolenic acid) help maintain normal skin and coat condition. As animals age, they tend to lose skin elasticity, develop epidermal and follicular atrophy and have reduced sebum secretion. 107 Marked reduction in dietary fat (i.e., calorie-restricted or "light" foods) is not ideal for older cats unless they are obese prone. Fat should be highly digestible in foods intended for older cats. As discussed above, fat digestion declines as cats age, which may account for the weight decline noted in very old cats. Dietary fat improves the palatability of food and contributes significantly to the energy density. Therefore, maintaining moderate fat concentrations improves food and caloric intake in older cats and enhances absorption of fat-soluble vitamins. Foods with lower fat levels are recommended for obese-prone cats, and foods with higher fat levels should be fed to thin cats (BCS <3/5) and cats with poor appetites. Essential fatty acids should be provided at levels at or above those recommended for young to middle-aged adults.
Fiber facilitates GI health by a variety of mechanisms. Dietary fiber promotes normal intestinal motility and provides fuel for colonocytes via volatile fatty acids resulting from fermentation by colonic microbes. These effects can be attained by feeding small amounts (i.e., <5%) of soluble and insoluble fiber. Promoting intestinal motility may benefit older cats with constipation. Constipation is common in older animals because of a combination of factors, including reduced water intake, limited activity and reduced colonic motility. Although fiber should not be the sole factor in managing constipation, it is beneficial when provided regularly. Dietary fiber also is beneficial in the management of obesity, diabetes mellitus and hyperlipidemia.High levels of dietary fiber (>10%) reduce food dry matter digestibility and dilute caloric density. Very old cats appear to need energy-dense foods; therefore, high levels of dietary fiber are not recommended except to manage obesity and fiber-responsive diseases (i.e., diabetes mellitus, colitis and constipation).
Calcium and Phosphorus
After skeletal growth is complete, the nutritional requirement for calcium and phosphorus declines to levels needed by adult cats and is thought to remain relatively constant for life. Unlike the situation in people, osteoporosis is not commonly diagnosed in very old cats. Nevertheless, the bone mass of adult cats remains stable until seven years of age and then declines. The reason for the decline has not been characterized but is presumably related to the loss in lean and total body mass that occurs with aging. With loss of body mass, less bone mass is required for structural support. Alternatively, bone loss resulting from buffering chronic elevations of metabolic acids cannot be ruled out. Older cats have been reported to maintain a greater metabolic acid load and a significantly lower urinary pH compared with young adult cats. Interestingly, a lower urinary pH (i.e., higher metabolic acid load) is also a risk factor for development of calcium oxalate urolithiasis, which is most prevalent in older cats Older cats should receive foods with moderate levels of available dietary calcium to help maintain bone mass and possibly reduce the risk of calcium oxalate urolithiasis.In contrast to the moderate calcium needs during aging, reduction of dietary phosphorus is commonly recommended in foods designed for older cats. The recommendation is predicated on the fact that nearly 30% of older cats may have kidney disease. Further, in a survey of pet owners, kidney disease was the second leading cause of nonaccidental death in cats. As discussed in the section on feeding young and middleaged cats, renal insufficiency is rarely diagnosed until significant loss of renal function has occurred. Thus, a large proportion of older cats have subclinical renal damage and may benefit from reduced dietary phosphorus. It is commonly accepted that phosphorus restriction slows the progression of renal disease in cats. Phosphorus reduction helps decrease: 1) the renal excretory workload, 2) phosphorus retention, 3) renal secondary hyperparathyroidism and 4) the subsequent renal mineralization in cats with chronic renal insufficiency. Therefore, phosphorus levels should be reduced from levels typically found in commercial foods in the early nutritional management of renal disease in dogs and cats. Slowing progression of early renal disease in affected older cats should extend longevity. Phosphorus may be reduced to as low as 0.3% of the food (DM) for cats with overt renal disease, otherwise the general population of older cats should be fed foods containing 0.5 to 0.7% DM phosphorus. Although adult cats appear to be remarkably tolerant to perturbations in dietary calcium-phosphorus ratios, a ratio between 0.9:1 to 1.1:1 maximizes availability and ratios between 0.9:1 to 1.5:1 are recommended.
The potassium requirement for older cats is thought to be greater than that for young to middle-aged cats. This impression has come from anecdotal reports of low serum potassium levels and improved attitude, appetite, muscle strength and renal function following oral potassium supplementation in older cats. However, the potassium requirement of healthy older cats has not been determined and an increased need remains speculative. Nevertheless, factors common in older cats that support the need for increased dietary potassium include: 1) kaliuresis as a result of kidney disease, high dietary protein or high metabolic and/or dietary acid load, 2) reduced food intake and 3) increased intestinal loss. Older cats with normal appetite and renal function probably do not benefit significantly from increased dietary potassium levels. However, hypokalemia can cause signs ranging from mild lethargy to marked polymyopathy or nephropathy Thus, increasing dietary potassium to support moderate losses may benefit some older cats. Levels as low as 0.3% resulted in hypokalemia when provided in high-protein or acidified foods. Dietary potassium levels for older cats should be at least 0.6% of the diet dry matter.
Increased losses of magnesium, similar to those seen with potassium, may affect magnesium balance in older cats. Hypomagnesemia has also been associated with refractory hypokalemia, particularly in cats with diabetes mellitus. The benefit of limiting dietary magnesium in cats is a reduced risk of struvite-mediated lower urinary tract disease. However, the risk of struvite-mediated disease is low in older cats. Further, foods containing very low levels of magnesium have been associated with the development of calcium oxalate uroliths in an epidemiologic survey of cats and deficiency is known to increase urolith formation in rats. Therefore, magnesium should be provided at moderate levels and severe magnesium restriction should be avoided (less than 0.04% DM).
Sodium and Chloride
Avoiding excessive sodium intake to reduce risk factors appears even more important in older cats than in young to middle-aged cats. Although the sodium and chloride requirements of older cats are not likely to be different from those of young to middle-aged adults, the prevalence of chronic diseases associated with hypertension (e.g., renal disease, hyperthyroidism, cardiac disease) increases with age. The exact prevalence of secondary hypertension in the feline population is unknown, but it appears highest in older cats. In one study, systolic arterial pressures were significantly higher in older cats than in middle-aged or younger cats. Further, hypertension affects 60 to 65% of cats with renal disease and 23% of cats with hyperthyroidism. Chronic hypertension results in end-organ damage and progression of renal and cardiac disease; therefore, control of risk factors for salt-sensitive individuals is desirable. Unfortunately, accurate monitoring of blood pressure in all feline patients is uncommon and hypertension is rarely diagnosed until clinical signs are evident. Therefore, nutritional needs for sodium and chloride should be met, but excesses should be avoided.
Regulation of acid-base homeostasis and normal plasma osmolality depends, in part, on adequate sodium and chloride intake. Deficiencies of sodium and chloride can have deleterious effects in older cats; therefore, over-restriction should be avoided. The minimum dietary requirement of sodium for adult cats is 0.08% DM. AAFCO recommends an intake of 0.2% of the diet dry matter, or 2.5 times the minimum requirement. Some commercial moist foods exceed 1.0% dietary sodium (DM) or 12.5 times the requirement. Sodium intake at this level is markedly above that needed for optimal health. Chloride is now recognized as a co-determinant in salt-sensitive hypertension, thus control of dietary excess is equally important. Unfortunately, little information is available about the chloride requirement of cats. An intake of 0.2 to 0.6% DM sodium is recommended to ensure sodium adequacy and simultaneously avoid excess in older cats. Minimum chloride levels of 0.19% are suggested; however, more typically, chloride values are approximately 1.5 times the concentration of sodium.
Urinary pHOlder cats frequently have clinical or subclinical renal disease that can impair their ability to compensate for acid-base alterations resulting from metabolic or dietary influences. In a study in which cats were fed a food with higher urinary acidifying potential (pH 6.39 vs. pH 6.6 in the control food), older cats lost more weight, had lower red cell counts and had greater systemic acid loads than younger cats. This observation, combined with the reduced risk of struvite urolithiasis, increased risk of calcium oxalate urolithiasis and high frequency of kidney disease in older cats, supports the idea that foods fed to older cats should have a lower urine acidifying potential (i.e., higher published urinary pH averages) than foods for young and middle-aged adults. A safe range of measured urinary pH values in older cats is still between 6.2 to 6.5.
The acidifying potential of commercial foods is not typically tested for in older cats, despite the fact that older cats generate a significantly lower urinary pH than younger cats fed the same foods. To achieve a normal urinary pH, the acidifying potential of foods for older cats should be lower than that of foods for young to middle-aged cats. Published urinary pH averages should be greater for foods for older cats than for foods for young to middle-aged adults, unless the foods have been specifically tested in old (senior) or very old cats and found to be safe. Providing food with less acidifying potential helps avoid metabolic acidosis and its complications in older cats.
Palatability and Digestibility
Reduced smell or taste, the presence of oral disease or metabolic disturbances, the use of medications or a combination of factors can impair appetite and food intake in older cats. Foods for very old cats should be highly palatable and highly digestible to lessen concerns about weight loss and inadequate food intake.
Assess The Food(s) and Feeding Method
After assessing the cat and identifying key nutritional factors, the food(s) and feeding methods should be assessed as described for young and middle-aged cats. Foods currently being fed should be evaluated as discussed previously.
Ensure feeding tests have been conducted (i.e., review package label for statement).
Compare the nutrient content of the current food with the cat's nutrient needs and the key nutritional factors.
Identify discrepancies between the key nutritional factors and the food currently fed.
It may not always be necessary to change the food and feeding method when managing healthy geriatric cats. However, a thorough evaluation includes verification that an appropriate food and feeding method are being used. Older cats should be re-evaluated at each examination because nutrition and health needs change with disease status, risk factors and overall health.Determine a Feeding Plan
Older cats are more prone to weight loss, cardiac disease, renal disease and metabolic aberrations and usually have a decreased activity level than younger cats. The feeding plan should be based on the information obtained in the assessment as well as detected risk factors. Nutritional surveillance and therefore the number of contacts per year should be increased for older cats. Although goals remain the same as those listed in the introduction, each animal should be evaluated individually.Select a Food(s)
Several nutrients are of particular interest because of their role in the management of health risks or age-related disease or because older cats poorly tolerate and adapt to wider variations in nutrient concentrations. The nutrient profile of the current food should be compared with the appropriate key nutritional factors to determine if the food is satisfactory.
An important goal when managing the nutrition of older cats is to ensure proper food intake. There is little need to change the form of food a cat eats well simply because of age. In fact, some cats will refuse to eat a new form or texture of food. However, cats with poor intake may benefit from changing food forms if the new food is more palatable and easier to chewDetermine a Feeding Method
As mentioned above, healthy senior cats may be fed free choice, meal fed or fed by a combination of methods. Obese cats should be offered measured amounts of food. The measured quantity may be fed in meals or dispensed at one time to allow continuous access throughout the day. Underweight cats should be allowed to eat free choice. Only dry and semi-moist foods may be fed free choice and these foods are typically less palatable than moist foods. Older cats may have reduced olfaction and taste perception; therefore, it may be preferable to feed moist and warm foods to encourage food intake. Providing dry foods for free-choice consumption and moist foods in several meals throughout the day may optimize food intake. Adding broth or canned meat juices to dry foods may enhance food and water intake in geriatric cats.
Although most cats do not experience digestive upsets with typical food changes, a gradual transition to a new food may benefit older cats. Progressively exchanging the new food for the usual food over four to seven days will minimize untoward effects and food refusal.
Veterinarians should examine and conduct a nutritional assessment of geriatric cats regularly. The frequency of monitoring depends on the overall health of the cat and the presence or absence of chronic diseases. Annual veterinary examinations are usually recommended for older cats, whereas biannual check-ups are recommended for very old cats.
The owner should evaluate body condition every two to four weeks. Although lean body mass tends to decline as cats reach extreme geriatric age (older than 16 years), significant loss of muscle mass or body weight warrants immediate evaluation by a veterinarian. Owners should also monitor daily food and water intake and stools and urination. Any persistent change, whether increased or decreased, should prompt the veterinarian to assess the cat and perform diagnostics as indicated.
Dental disease is the most frequent diagnosis made in geriatric cats. Therefore, a dental health program should be part of every older cat's preventive health care plan.
Main Subject Index