Animal Factors

Cats with myocardial disease may be optimally conditioned or may be underconditioned or overconditioned depending on the severity and chronicity of the disease. Obesity results in blood volume expansion with elevated cardiac output, increased plasma and extracellular fluid volume, increased neurohumoral activation, reduced urinary sodium and water excretion, tachycardia, abnormal systolic and diastolic ventricular function, exercise intolerance, and systemic arterial hypertension.⁸⁶ This may result in progression of the disease. Likewise, cachexia may occur with myocardial failure. Cachexia associated with heart disease or failure results in negative nitrogen and energy balance.⁸⁹ The pathogenesis of cardiac cachexia is multifactorial, involving increased sympathetic tone, increased tumor necrosis factor and interleukin-1 levels, decreased physical activity with an increased resting energy requirement (RER), decreased tissue perfusion, venous congestion, and adverse effects of medications. Decreased nutrient intake and possibly increased nutrient losses (e.g., potassium loss with diuretic therapy) and loss of body weight and, more important, lean body mass occurs, resulting in an inability to respond to medical therapy and an increase in morbidity and mortality rates.

Cats have a dietary requirement for taurine because they have limited ability to synthesize it from cysteine and methionine and because it is used exclusively for bile acid conjugation. Taurine deficiency results in dilated cardiomyopathy in predisposed cats (Figure 18-1). The mechanism of heart failure in taurine-deficient cats is poorly understood. Taurine may function in osmoregulation, calcium modulation, and inactivation of free radicals.²¹³ Other factors are likely involved because many cats fed taurine-deficient foods for prolonged periods fail to develop myocardial dysfunction. Additionally, there is an association between taurine and potassium balance.⁶⁷ Inadequate potassium intake may induce significant taurine depletion, resulting in myocardial dysfunction. Male cats may be more prone to developing taurine deficiency–associated myocardial failure than are female cats, or male cats may be more prone to developing clinical signs at higher plasma taurine concentrations.⁸³

FIGURE 18-1 Dilated cardiomyopathy in a 4-year-old spayed female domestic shorthair cat with taurine deficiency.

l-Carnitine is a conditionally essential nutrient involved with transport of long-chain fatty acids from the cytosol into the mitochondria, where they undergo beta oxidation for energy production. l-Carnitine deficiency has been associated with dilated cardiomyopathy in some dogs¹³²; however, it has not been associated with this condition in cats.

Sodium intake is often restricted with heart disease; however, this may not be necessary until later in the course of the disease. Sodium restriction should occur concurrently with chloride restriction because chloride salt of sodium has more effect on blood pressure and plasma volume than non-chloride sodium salts.²⁶ Salt sensitivity has not been documented to occur in cats. Hypokalemia and hypomagnesemia are associated with arrhythmias, decreased myocardial contractility, and muscle weakness. Additionally, inadequate potassium intake may be associated with taurine deficiency.

Dietary Factors

Dietary recommendations for cats with cardiac disease are designed to optimize body condition and are summarized in Box 18-1. Commercial diets formulated for cats with cardiovascular disease are available.

Feeding Factors

Some cats require feeding of frequent small meals because of decreased appetite. Pharmacologic appetite stimulation (Table 18-1) or assisted feeding through the use of feeding tubes may be required. Additional nutrients that may be beneficial include coenzyme Q10, which is required for energy reactions and is an antioxidant, and other antioxidants, which may decrease oxidative stress with dilated cardiomyopathy.

TABLE 18-1 Appetite Stimulants for Use in Cats

Animal Factors

Oral disease occurs more commonly in older cats and usually is associated with systemic disease; therefore oral disease may be related to systemic effects of those disorders and to nutritional imbalances caused by those disorders or eating difficulties. Historical information should include diet, eating behavior, and access to toys and other foreign bodies. The veterinarian should perform a complete oral examination, which may require sedation or anesthesia, in addition to a physical examination to evaluate for systemic disease.

Dietary Factors

Several dietary factors have been implicated with oral disease. Food texture and composition can directly affect oral cavity health through the following:

Claims of dry food being better for prevention of dental plaque than moist foods are unsubstantiated.³⁰ Likewise, there are no data to support the notion that natural diets and foods are better for oral health than commercial foods. Dietary texture can be modified by increasing fiber content with a size and texture that promotes chewing and mechanical cleansing of teeth.^30,161,272 Dental treats do not offer an advantage over dry foods; however, some contain hexametaphosphate, a calcium chelator, which may decrease calculus formation, although data are contradictory.^114,256 Hexametaphosphate has not been evaluated in cats. Many oral diseases are inflammatory, and modification of the inflammatory process may be beneficial. Antioxidants, vitamins E and C, and selenium may be beneficial, but data are lacking in cats. Nutritional deficiencies of such elements as calcium and vitamins A, B, C, D, and E are associated with oral cavity disease, but these are uncommon (see Chapter 17).

Nutrition has been implicated as a cause of feline tooth resorption. Acid coating of foods has been suggested to cause tooth resorption, although this has not been proved.^5,226,278 Dry food may cause microfractures that predispose teeth to infection and inflammation; however, this has not been proved. Dietary vitamin D has been implicated in tooth resorption. Evidence to support this assertion includes correlation between cats with tooth resorption and increased blood levels of 25-hydroxyvitamin D and histologic comparisons of the effects of excessive intake of vitamin D to the effects of bone resorption.^226,227 Although a direct effect of vitamin D has not been established, there is evidence of an active vitamin D signaling in the pathophysiology of tooth resorption.^27,28

Feeding Factors

Feeding a “dental” diet that carries the Veterinary Oral Health Council (http://www.vohc.org/) seal for plaque control may be beneficial for cats that are prone to periodontal disease. Additional recommendations include the following:

Animal Factors

Clinical signs associated with nutritional abnormalities include a sparse, dry, dull, and brittle hair coat that epilates easily; slow hair growth; abnormal scale accumulation; alopecia; erythema; crusting; decubital ulcers; and slow wound healing. Other clinical signs may be present with nutrient-deficient dermatoses (see Chapter 17). For more information on skin diseases, see Chapter 22.

Dietary Factors

Inadequate energy intake is associated with keratinization abnormalities, depigmentation, changes in epidermal and sebaceous glands, and increased susceptibility to trauma. Protein deficiency is associated with similar clinical signs. Essential omega-6 fatty acids include linoleic acid (>0.5% on a dry matter basis) and arachidonic acid (>0.02% on a dry matter basis).¹⁶⁹ Omega-3 fatty acids can supply part of the omega-6 fatty acid component. Clinical signs of essential fatty acid deficiency include scaling, matting of hair, loss of skin elasticity, dry and dull hair coat, erythema, epidermal peeling, otitis externa, and slow hair growth. Certain mineral deficiencies may affect the skin (see Chapter 17). Copper deficiency is associated with loss of normal hair coloration, decreased density or lack of hair, and rough or dull hair coat. Many dermatologic conditions may occur with zinc deficiency and respond to zinc supplementation. Dietary phytate binds zinc, resulting in clinical signs of deficiency. Clinical signs of zinc deficiency include erythema, alopecia, and hyperkeratosis. Certain vitamin deficiencies may affect the skin. Vitamin A deficiency is associated with skin lesions and focal sloughing of skin. Vitamin E deficiency occurs in cats in association with steatitis. Clinical signs include erythema and keratinization defects. Vitamin E–responsive dermatoses include discoid lupus erythematosus, systemic lupus erythematosus, pemphigus erythematosus, sterile panniculitis, acanthosis nigricans, dermatomyositis, and ear margin vasculitis. Dermatologic conditions also arise from food allergies (see Chapter 17).

Feeding Factors

In cats with dermatologic disease, the veterinarian should evaluate the quality and quantity of the diet fed, including treats, snacks, and table food. A complete and balanced diet may be made incomplete or unbalanced when fed with other food stuffs. Homemade diets must be evaluated carefully.²²⁸ If a nutritional deficiency is suspected, the veterinarian should discuss with the owner the possibility of changing the diet to one of a higher quality. With suspected adverse food reaction, a diet change should be considered (see Chapter 17). If a specific nutrient deficiency is identified, the diet might be changed or supplemented accordingly. Zinc is supplemented for zinc-responsive dermatoses (zinc sulfate: 10 to 15 mg/kg per day by mouth; zinc methionine: 2 mg/kg per day by mouth). Vitamin A is supplemented for vitamin A–responsive dermatoses (tretinoin topically every 12 to 24 hours; isotretinoin: 1 to 3 mg/kg per day by mouth; etretinate: 0.75 to 1 mg/kg per day by mouth).

Fatty acid supplementation is often recommended for managing inflammatory skin disease. Cats have a limited capacity to convert 18-carbon long-chain fatty acids to 20-carbon long-chain fatty acids owing to low activity of delta-6-desaturase.²⁰¹ It is 20-carbon long-chain fatty acids that are incorporated into cellular membranes and subsequently metabolized to prostaglandins, leukotrienes, and thromboxanes. To alter levels of these cytokines in cats, it is necessary to supplement 20-carbon long-chain fatty acids. Insertion of omega-3 fatty acid (eicosapentaenoic acid [EPA]) into cell membranes results in production of cytokines of the odd-number series (e.g., prostaglandin E₃, leukotriene B₅) in place of the even-number series of cytokines produced from omega-6 long chain fatty acid, arachidonic acid (e.g., prostaglandin E₂, leukotriene B₄). These odd-numbered cytokines promote less inflammation and are more vasodilatory than the even-numbered cytokines. Cats being supplemented with omega-3 fatty acids must receive 20- and 22-carbon fatty acids owing to their limited ability to convert 18-carbon to 20-carbon fatty acids. The 20-carbon omega-3 fatty acid is EPA, and the 22-carbon omega-3 fatty acid is docosahexaenoic acid (DHA). Oils derived from marine life are high in EPA and DHA. Oils derived from plant life, such as flax seed and borage, contain primarily 18-carbon fatty acids, therefore limiting their conversion to the required 20-carbon fatty acid and their effectiveness in managing inflammation. There are no data on the effectiveness of omega-3 fatty acids in managing inflammatory skin diseases in cats.⁴¹

Types of Foods Used in Managing Gastrointestinal Disease

Animal Factors

Cats with pharyngeal or esophageal disease have difficulty swallowing food; these diseases are, however, uncommon in cats. Cats with gastric or small intestinal disease often vomit, and they may have diarrhea characterized by large-volume watery feces or inappetence. Poor body condition and weight loss may occur because of the inability to eat, vomiting, or loss of nutrients with diarrhea. Inflammatory bowel disease is the most common cause of small intestinal disease; however, other conditions, such as neoplasia and foreign body obstruction, may occur. Large intestinal disease is usually associated with small-volume firm feces with mucous and/or blood or with constipation or obstipation.

Dietary Factors

Cats with pharyngeal and esophageal disease should be given a high-protein food (>40% on a dry matter basis) because protein increases lower esophageal tone. Feeding a high-fat (>25% on a dry matter basis) diet increases the caloric density of the diet; however, it delays gastric emptying. Therefore if gastric motility and emptying is a concern, a high-fat diet may not be indicated.

Several options exist for nutritional management of cats with inflammatory gastroenteritis.^106,280 In addition to pharmacologic therapy, cats may respond to elimination diets, whether it is a diet containing a novel protein source, a protein hydrolysate diet, or a homemade simple-ingredient diet. Inflammatory reactions are thought to occur through interaction of a protein with an antibody directed against it. Novel protein refers to a single dietary protein source that the cat has not been fed before; therefore an inflammatory response would not be evoked.¹⁰⁶ A protein hydrolysate diet involves feeding a diet where the protein has been hydrolyzed to a size that is not recognized by antigen processing cells and antibodies, typically below 12,000 daltons.⁴³ A homemade diet often comprises single unprocessed ingredients. In processing of foods, glycated protein end-products may be produced through the Mallard reaction and these glycated end-products may induce an inflammatory response. Feeding unprocessed foods decreases exposure to these glycation end products and subsequent inflammatory response.¹⁵⁶

Cats with large intestinal disease may respond to an elimination diet or to a higher fiber (>5% on a dry matter basis) diet.^{63,202,247,280} Dietary fiber increases fecal bulk, which stimulates colonic contraction; however, it increases fecal volume, which could exacerbate constipation.²⁴⁷ Dietary recommendations for cats with inflammatory bowel disease are summarized in Box 18-2.⁶¹

Feeding Factors

A change of diet or formulation of diet, including a homemade diet, may be necessary to manage cats with intestinal disease. Feeding smaller meals or restricting the amount consumed at a meal may be beneficial.

Animal Factors

Animals with liver disease may demonstrate a variety of clinical signs, from none to hepatoencephalopathy (characterized by ptyalism, vomiting, depression, and possibly seizures). Weight loss and poor body condition may or may not be present depending on the severity and chronicity of the underlying disease. Cats may or may not have hyperbilirubinemia.

Dietary Factors

Maintenance of body condition and weight is important; therefore adequate caloric intake is paramount. Hepatic lipidosis is a result of negative energy balance with mobilization of peripheral adipose tissue and accumulation of intrahepatic lipid.⁴⁶ In managing cats with hepatic lipidosis, reversing the negative energy balance is most important in reversing the disease process. Protein restriction is not necessary unless hepatoencephalopathy and hyperammonemia are present. Hypokalemia may occur with liver disease and has been reported in approximately one third of cats with hepatic lipidosis⁴⁶; therefore diet should be potassium replete. Many hepatic diseases are associated with oxidative stress that may induce further hepatocellular damage. Feeding diets with additional antioxidants or supplementing with antioxidants may be beneficial. Hepatic dysfunction entails a dysregulation of lipid metabolism; this is particularly prominent with hepatic lipidosis. l-Carnitine is involved with lipid metabolism, and although l-carnitine deficiency does not occur with hepatic lipidosis,¹²⁶ l-carnitine supplementation at 250 to 500 mg daily may be beneficial in cats with hepatic lipidosis.⁴⁴

Dietary recommendations for cats with hepatobiliary disease are summarized in Box 18-3.¹⁹⁴

Feeding Factors

Feeding small meals or facilitating food intake using pharmacologic stimulation or feeding tubes may be required. Caution must be exercised with administration of medications that require hepatic metabolism, such as appetite stimulants, because side effects may occur.

Animal Factors

The most important step is to recognize that a cat is overweight or obese. The veterinarian should compare the BCS with body weight, especially with historical data from annual examinations. Often a cat’s ideal body weight can be determined by finding its weight at about 1 year of age in the medical record. Cats that are obese may show clinical signs of related conditions such as diabetes mellitus, hepatic lipidosis, and osteoarthritis. The veterinarian should take a good dietary history, including the type(s) of food fed, amount(s), and frequency.¹⁹⁵ It is important to gather information about snacks, treats, and table foods that may be fed, as well as access to food in the outdoors if the cat is allowed access (Box 18-4). It may be helpful to have the owner keep a food diary for 1 or 2 weeks before the weight loss program is initiated. Collecting the information may help make owners aware of the role they play in the cat’s obesity, as well as provide useful information.

Dietary Factors

To achieve weight loss to ideal body weight, a change in diet is necessary. Feeding less of the same food is usually unsuccessful because the cat is used to eating the diet, it does not induce a shift in metabolism, and it may lead to deficiencies. There are two dietary strategies for inducing weight loss in cats:

Which dietary strategy will work in an individual cat is unknown. If one dietary strategy does not work, the veterinarian should switch to the other.

Recently, the first drug licensed for weight loss in veterinary medicine was approved for dogs. Dirlotapide (Slentrol, Pfizer Animal Health) is a selective microsomal triglyceride transfer protein inhibitor. The drug reduces fat absorption and increases satiety signals. However, dirlotapide is contraindicated in cats because it increases the risk of hepatic lipidosis. In multi-pet households in which a dog may be receiving the drug, client education is important to avoid administration of the drug to overweight or obese resident cats.

Feeding Factors

Weight-reduction programs are a multistep approach involving owner commitment, a feeding plan, and repeated communications and monitoring.^145,281 Owners must recognize that their cat is obese and understand associated health risks. Before instituting a weight loss program, the veterinarian should perform a thorough physical examination and obtain a minimum database (complete blood count, chemistry panel, urinalysis) to detect concurrent diseases. Then a feeding plan should be instituted. The veterinarian should first set the amount of calories to be fed on the basis of known or estimated energy requirements (see Chapter 15). Calculate the RER:

This number is multiplied by a factor of 0.8 to induce a weight loss of 1% to 2% body weight per week. The veterinarian should compare this estimated energy requirement with current caloric intake because some animals require further restriction to induce weight loss.²⁶⁸ The calculations for an 8-kg cat with an ideal body weight of 5 kg would be as follows:

Achieving a safe weight loss of 3 kg will take 5 to 9 months.

The veterinarian should choose a commercial diet, as previously described, and recommend that it be fed to meet the energy requirements estimated to induce weight loss. The veterinarian should eliminate or account for additional food and treats in the caloric intake, which should be less than 5% of total daily caloric intake. Some animals tolerate an abrupt change in diet with little problem, although some appear to have fewer gastrointestinal issues if food is gradually changed over a 7- to 10-day period. A new diet may be readily accepted by some cats, but patience will be required with others (Box 18-5).

The goal of weight reduction is to reduce the cat’s excess adipose tissue; however, loss of lean muscle mass occurs as well.⁹⁸ Feeding a high-protein diet is associated with less lean muscle loss.²⁶⁷ Additionally, increased dietary fiber is associated with decreased protein digestibility⁷⁵; therefore high-fiber diets are formulated to account for this. It is important that owners ensure that the obese cat continues to eat because of the risk of hepatic lipidosis. l-Carnitine (250 to 500 mg/day, by mouth) has been shown to be beneficial in preventing hepatic lipidosis with weight loss in obese cats.^24,48 Diets should contain more than 500 ppm.

Although meal feeding is associated with more consistent weight loss, this may not be possible depending on the cat. Providing a measured amount of food during a 24-hour period achieves the same goal. Using food puzzles or hiding food in various locations both provides a more stimulating environment and encourages energy expenditure (Figures 18-2 and 18-3). When feeding dry diets, some owners find using pre-weighed portions of food more acceptable than measuring the amount of food daily in a cup.²³ In multicat households the owner should strive to keep the obese cat from eating food provided for nonobese cats. This can be accomplished by separating the cats and limiting the time for meal consumption. Another strategy is to provide food for the nonobese cats in an area that the obese cat cannot enter (e.g., a box with a hole that only the nonobese cats can fit through). Many owners have become accustomed to using food and treats to enhance the bond with their cat and mistakenly believe that eating is a social event for cats, as it is for humans. In addition, owners often mistake any vocalization as a cry for food. Teaching owners to interact with their cats through play or training sessions may be an important part of the program. Environmental enrichment for indoor cats can be an integral part of a weight loss program.

FIGURE 18-2 Food puzzle to encourage energy expenditure by a cat to acquire food.

(Courtesy Steve Dale.)

FIGURE 18-3 Placing small amounts of food in different compartments of an egg carton encourages cats to expend energy to acquire food.

(Courtesy Steve Dale.)

Communication and monitoring are important. The cat should be weighed every other week and the body weight charted. Owners should be aware that it may be necessary to adjust the amount of food, especially given that cats often lose weight steadily at the outset of the diet and then plateau. Many obese cats will require up to 12 months for safe weight loss. Many owners find that the cat’s learned hunger behaviors (e.g., vocalizing, attention seeking) increase in frequency and intensity once a weight loss plan is in place, and some are unable to cope with this. It is important for the owner to have realistic expectations and to understand and anticipate some of the problems that may arise.

The veterinarian should use positive reinforcement with the client and reward successes. Charting the cat’s weight loss on a graph will make progress more apparent. A photograph of the cat can be taken before and after weight loss is achieved and then displayed in the waiting room. Some clients are motivated by certificates of achievement. Once the target body weight has been achieved, the food intake should be adjusted to maintain that weight. It is important that the owner does not revert to old habits, such as letting the cat eat ad libitum, feeding it treats, and not ensuring that it get exercise. Owners must understand that long-term portion control will be necessary.

Prevention of obesity is easier than treating obesity in cats. The veterinarian should teach owners how to keep their cat’s body condition from lean to optimally conditioned during growth.^{9,19,111,120,182} It will be necessary to adjust food intake after neutering because gonadectomy reduces energy requirements, although food intake increases within weeks of surgery. At every veterinary visit, a cat’s body weight and BCS should be recorded in the medical record.^111,129,233

Animal Factors

Insulin is a major anabolic hormone involved with energy, protein, carbohydrate, and lipid metabolism. With insulin deficiency or insulin antagonism, anabolic metabolic pathways are disrupted, resulting in polyuria/polydipsia, polyphagia, weight loss, muscle mass loss, decreased body condition, and clinical signs of ketoacidosis with progression of IDDM (e.g., vomiting, anorexia, seizures). Cats with NIDDM are typically obese and do not generally develop ketoacidosis. Risk factors identified for NIDDM in cats include indoor confinement and decreased physical activity, likely resulting in obesity and insulin resistance; type of food consumed is not necessarily a risk.^223,248

Dietary Factors

Dietary management of cats with diabetes mellitus depends in part on whether IDDM or NIDDM is present. For cats with IDDM, timing of meals with insulin administration is advantageous; however, some cats with diabetes mellitus eat small meals even when fed ad libitum.¹⁸⁰ Diets that are higher in fiber may increase insulin sensitivity and blunt postprandial hyperglycemia.^135,203 In cats that are underconditioned as a result of unregulated IDDM, feeding a calorically dense diet to increase body weight and condition may be necessary while regulating the IDDM with insulin.

Because cats with NIDDM are typically obese, weight loss is an important component of management. Many cats can go into diabetic remission with a combination of weight loss and insulin treatment¹⁷⁸ or weight loss alone. Traditional diabetic cat diets have been fortified with fiber to reduce postprandial glucose absorption and control weight.^135,203 Many cats respond to being fed low-carbohydrate, high-protein diets. In studies so far, low-carbohydrate, high-protein diets are associated with improved remission rates compared with higher-fiber diets (68% versus 41%) and maintain more lean body mass during weight loss.* However, in cats that do not go into remission and require long-term therapy, there appears to be little difference between the diets. In addition, some cats respond better to high-fiber diets, and weight control may be easier with a less calorically dense food. Canned food is preferred in diabetic cats to maintain hydration, lower carbohydrate content, and improve satiety. Dietary recommendations for cats with diabetes mellitus are summarized in Box 18-6.²⁷⁹

The following supplements have been suggested for the management of cats with diabetes mellitus, although they are for the most part unproven:

Feeding Factors

The goal is to achieve and maintain optimal body condition and body weight. For cats with IDDM, dietary intake should be matched with insulin administration. For cats with NIDDM, body weight should be decreased from obese body condition to optimal body condition.

Animal Factors

Hyperthyroidism is a clinical condition associated with excessive production and secretion of thyroxine (T₄). Most cats are older, with an average age at diagnosis of 13 years. Clinical signs associated with hyperthyroidism are usually polyphagia with weight loss, loss of muscle mass, polyuria/polydipsia, and hyperactivity; hyperthyroidism is also associated with cardiomyopathy. Because hyperthyroidism occurs in older cats, it may be associated with other diseases, most commonly chronic kidney insufficiency, which may become unmasked when the hyperthyroidism is treated. For more information on hyperthyroidism, see Chapter 24.

Dietary Factors

Most cats with hyperthyroidism are underweight and underconditioned; therefore feeding a calorically dense diet may be helpful in restoring body condition and weight. Increasing the fat content of the diet increases the caloric content. Underweight cats should receive a diet containing higher levels of protein; however, caution is necessary because of the association of renal disease with hyperthyroidism. Concentrations of blood urea nitrogen and creatinine should be monitored. If renal azotemia develops with treatment of hyperthyroidism, then dietary protein should be restricted (see the section on renal disease). Nutritional recommendations for feeding underweight cats with hyperthyroidism are summarized in Box 18-7.²⁷⁹

Nutritional factors have been implicated in the pathogenesis of hyperthyroidism, although the etiopathogenesis is not known. Epidemiologic studies have identified consumption of commercial canned foods, especially fish or liver and giblets, as a risk for development of hyperthyroidism, which suggests that a goitrogenic compound may be present in the diet.^{130,181,207,270} However, no specific goitrogenic factor has been identified. Iodine is one potential dietary goitrogen; however, most commercially prepared cat foods contain adequate amounts of iodine. It is important to note that such studies show association but not necessarily a cause-and-effect relationship. Additional non-nutritional risk factors have been identified, including use of cat litter; being an indoor cat; sleeping on the floor; presence of dental disease; presence of a smoker in the house; use of flea products; and exposure to herbicides, pesticides, or plant pesticides.^{130,181,207,270}

Feeding Factors

Cats with untreated hyperthyroidism are often ravenous, although some may show hyporexia (so-called “apathetic hyperthyroidism”), and they often vomit. With treatment appetite often decreases; therefore clients must ensure adequate dietary intake during treatment. Additionally, medical therapy with methimazole or unmasking of renal disease with therapy may occur, resulting in hyporexia or anorexia.

Animal Factors

OA occurs more commonly in cats older than 10 years of age. In one study of cats older than 12 years that were examined for reasons other than lameness, 90% of radiographs taken demonstrated OA.¹⁰⁹ Overweight cats are approximately 3 times more likely to present for lameness not associated with cat bite abscess.²⁴¹ Obesity may cause excessive forces on joints and articular cartilage, resulting in inactivity and further weight gain; however, obesity is a proinflammatory condition.^{38,69,105,282} Therefore obesity may result not only in abnormal mechanical forces on joints but also in production of adipokines, and upregulation of inflammatory pathways associated with obesity may promote joint inflammation and progression of OA.²²²

Dietary Factors

There is a paucity of information concerning nutritional management of OA in cats. Weight loss is an important component of nutritionally managing OA in cats (see the section on obesity). In one study consumption of a diet containing high levels of n3 fatty acids (eicosapentaenoic and docosahexaenoic acid) and supplemented with green-lipped mussel extract and glucosamine/chondroitin sulfate improved activity in cats with OA.¹⁴⁹ There are no studies evaluating supplementation with n3 fatty acids, glucosamine/chondroitin sulfate, antioxidants, or nutraceuticals in cats with OA. As mentioned, n3 fatty acids may alter inflammation through production of odd-numbered cytokines.^15,38,246 Antioxidants scavenge free radicals that are increased with OA and may be beneficial.^17,38 Chondromodulating agents such as chondroitin sulfate and glucosamine may slow progression or alter processes involved with OA, including stimulating cartilage matrix synthesis, inhibiting catabolic enzymes, and increasing fluidity of synovial fluid.^17,38

Feeding Factors

Obesity should be managed if present. This may require changing from ad libitum feeding to meal feeding or changing the diet.