Evaluation of the nutritional adequacy of recipes for home-prepared maintenance diets for cats

Sarah A. Wilson 1Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Cecilia Villaverde 2Department of Molecular Biosciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Andrea J. Fascetti 2Department of Molecular Biosciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Jennifer A. Larsen 2Department of Molecular Biosciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Abstract

OBJECTIVE

To evaluate home-prepared maintenance diet (HPMD) recipes for cats and compare the nutritional profiles with National Research Council (NRC) recommended allowances (RAs) for essential nutrients for adult cats.

DESIGN

Evaluation study.

SAMPLE

114 recipes (obtained from books and online sources) for HPMDs for cats.

PROCEDURES

Computer software was used to determine nutrient concentrations of HPMD recipes for comparison with NRC RAs for essential nutrients for adult cats. Effects of recipe authorship (veterinarian vs nonveterinarian) and supplementation on the number of nutrient concentrations below RAs were evaluated.

RESULTS

Of the 114 HPMD recipes, 113 contained vague instructions regarding preparation, and 46 did not provide feeding directions. Only 94 recipes provided adequately detailed information for computerized nutritional analysis, although most (93/94) still required assumptions regarding ingredients, preparation, or supplementation. Nonveterinarian-authored recipes and recipes without supplement-type products had more nutrient concentrations below NRC RAs, but no recipe met all RAs. With assumptions, 5 veterinarian-authored recipes met NRC RAs for all assessed nutrients except choline; however, taurine adequacy in 2 of those recipes could not be confirmed. Crude protein concentration was below the RA in 6 of 94 (6.4%) recipes. Nutrients most frequently below RAs included choline, iron, thiamine, zinc, manganese, vitamin E, and copper (in 89.7%, 76.6%, 62.8%, 61.7%, 57.4%, 57.4%, and 45.7% of recipes, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

Problems with nutritional adequacy were identified in all evaluated HPMD recipes. Appropriate formulation of HPMDs requires specialized knowledge of nutrition and use of computer software to avoid potentially harmful nutrient deficiencies.

Abstract

OBJECTIVE

To evaluate home-prepared maintenance diet (HPMD) recipes for cats and compare the nutritional profiles with National Research Council (NRC) recommended allowances (RAs) for essential nutrients for adult cats.

DESIGN

Evaluation study.

SAMPLE

114 recipes (obtained from books and online sources) for HPMDs for cats.

PROCEDURES

Computer software was used to determine nutrient concentrations of HPMD recipes for comparison with NRC RAs for essential nutrients for adult cats. Effects of recipe authorship (veterinarian vs nonveterinarian) and supplementation on the number of nutrient concentrations below RAs were evaluated.

RESULTS

Of the 114 HPMD recipes, 113 contained vague instructions regarding preparation, and 46 did not provide feeding directions. Only 94 recipes provided adequately detailed information for computerized nutritional analysis, although most (93/94) still required assumptions regarding ingredients, preparation, or supplementation. Nonveterinarian-authored recipes and recipes without supplement-type products had more nutrient concentrations below NRC RAs, but no recipe met all RAs. With assumptions, 5 veterinarian-authored recipes met NRC RAs for all assessed nutrients except choline; however, taurine adequacy in 2 of those recipes could not be confirmed. Crude protein concentration was below the RA in 6 of 94 (6.4%) recipes. Nutrients most frequently below RAs included choline, iron, thiamine, zinc, manganese, vitamin E, and copper (in 89.7%, 76.6%, 62.8%, 61.7%, 57.4%, 57.4%, and 45.7% of recipes, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

Problems with nutritional adequacy were identified in all evaluated HPMD recipes. Appropriate formulation of HPMDs requires specialized knowledge of nutrition and use of computer software to avoid potentially harmful nutrient deficiencies.

Emerging human nutrition trends such as the popularity of organic foods, vegetarianism, or consumption of foodstuffs produced by sustainable agriculture have also been applied to the feeding of pets, and many dog and cat owners are placing an emphasis on their pets’ nutrition.1 A desire to provide a diet that is perceived as superior to commercial pet food in 1 or more aspects has resulted in the use of home-prepared diets.2,3 Reasons such as increased control of diet ingredients and strengthened human-animal bond have led some owners to search out internet and book sources for home-prepared diet recipes3 for their pets, which might not be adequate for long-term or sole-source feeding.

Previous studies have evaluated the clarity of instructions for preparation and the appropriateness of home-prepared diets for adult dog maintenance,4 dogs with cancer,5 and dogs and cats with chronic kidney disease6; however, to the authors’ knowledge, systematic assessment of HPMDs intended for adult cats has not been reported.

The NRC publishes a summary of available data on nutrient requirements of various species, including cats, and provides specific recommendations for the intake of essential nutrients to support various life stages. The NRC MR is defined as “the minimal concentration or amount of a bioavailable nutrient that will support a defined physiological state.”7 An NRC RA is defined as “the concentration or amount of a nutrient in a diet formulated to support a given physiological state” and “where applicable, includes a safety factor for nutrients with uncertain bioavailability.”7

The NRC RAs and MRs reflect recommended nutritional intakes derived from highly digestible whole food ingredients and purified nutrient sources and are often lower than the nutrient concentration minimum values for commercial pet foods as established by the Association of American Feed Control Officials.8 The Association of American Feed Control Officials nutrient profiles are intended to be practical for commonly used, complex pet food ingredients and are currently based on the NRC RAs with consideration of typical digestibility of nutrients from these ingredients as well as the known impacts of standard pet food processing.

The aim of the study reported here was to evaluate HPMD recipes to determine the appropriateness of each recipe on the basis of the NRC RAs and MRs for maintenance of adult cats.7 The HPMD recipes’ nutritional profiles were analyzed with computer software for comparison with NRC RAs for essential nutrients for adult cats. The HPMD recipes were also assessed to determine the effects of authorship by veterinarians or nonveterinarians and inclusion or noninclusion of supplement-type products on the number of nutrients with concentrations below their respective NRC RA. We hypothesized that many HPMD recipes would provide inadequate concentrations of multiple essential nutrients, but that veterinarian-authored recipes would have fewer nutrient concentrations below the NRC RAs. In addition, we hypothesized that details for formulation of the recipes would largely be insufficient, necessitating assumptions of ingredients, supplement-type products, or preparation methods to quantitatively evaluate them via computer analysis.

Materials and Methods

Veterinary textbooks, pet-care books for pet owners and veterinary care providers, and websites were searched for recipes for HPMDs for cats. Through Google and Yahoo search engines, recipes were identified with search terms that included *home-prepared OR *homemade OR *home-cooked, AND *diet OR *recipe, AND *cat OR *feline. Books with HPMD recipes were borrowed from local libraries or were purchased.

Recipes were included for evaluation if they did not specify intent for any medical condition, growth, lactation, or gestation or that they were to be used as a treat or as an intermittent or supplemental diet. Some books provided many recipes that met the inclusion criteria; in those situations, 10 recipes containing different ingredients were selected from each book for evaluation. All internet recipes identified in the web search that met the inclusion criteria were collected.

Qualitative analysis of recipes

Qualitative assessment of the HPMD recipes included evaluation of clarity (ie, specification and amounts of ingredients and supplement-type products and preparation and feeding instructions). In addition, authors were categorized as veterinarians (ie, persons with credentials including doctor of veterinary medicine or veterinary medical doctor) or nonveterinarians; anonymous authors were classified as nonveterinarians.

Quantitative analysis of recipes

Quantitative evaluation of the HPMD recipes required adequate detail to facilitate computerized assessment. This included specification of types and amounts of ingredients and supplement-type products as well as preparation methods. Weight measurements were preferentially used when provided. For recipes that allowed substitutions or provided range amounts of ingredients, mean values were used (eg, an ingredient listing of 60 g of rice or oatmeal was analyzed as 30 g of rice plus 30 g of oatmeal; an ingredient listing of 1 or 2 eggs was analyzed as 1.5 eggs). When multiple ingredient substitution options were given that included both commonly and less commonly available ingredients (eg, chicken or quail), the more commonly available ingredients were chosen because of the more complete nutritional database information. To address vague ingredient specifications, commonly available ingredients were chosen (eg, an ingredient listing of regular ground beef was analyzed as 85% lean ground beef). To address vague supplement-type product specifications (eg, multivitamin or cat vitamin), common, nationally available brands were used.a–l Supplement-type products were included in the analysis when listed as an optional component in a recipe.

Quantitative analysis of the recipes was performed with computer softwarem and both proprietaryn and public-sourceo nutrient analysis databases. Recipes were assessed for total energy, energy density, moisture content, caloric distribution on an ME basis (proportion of calories from protein, fat, and carbohydrate), and most essential nutrient concentrations. These were compared with the respective NRC RA (units/1,000 kcal of ME) and, when available, the MR (units/1,000 kcal of ME) for maintenance of adult cats.7 Concentrations of total fat, linoleic acid, arachidonic acid, sodium, zinc, and vitamins A and D were also compared with NRC SULs where applicable. Lack of a specific nutrient concentration for an ingredient in a database was treated as a missing value for that nutrient in the recipe unless adequacy could be verified from contributions of other ingredients. As such, total concentrations for essential nutrients determined for each recipe represented known minimums. Physiologic fuel values (kcal/g of metabolized fat, protein, and carbohydrate) applied to recipe analyses were those for specific human foods as provided in the database.9 Iodine, chloride, biotin, and vitamin K content could not be assessed because of a paucity of analysis data for these nutrients in many of the ingredients. Linoleic acid and arachidonic acid were the only fatty acids assessed. Overall, 38 essential nutrients were assessed.

Statistical analysis

Descriptive statistics (median and range) were calculated with computer-based software.p The denominators used to calculate percentages were the numbers of recipes for which data were available for that variable. Comparisons for effects of recipe authorship (veterinarian vs nonveterinarian) and supplement-type products (inclusion or noninclusion) were performed with a Wilcoxon test in computer-based software.q The level of significance was set at a value of P < 0.05.

Results

A total of 114 recipes from internet (n = 48) and book (66) sources were collected. Of the 48 recipes obtained from 11 internet sources,10–20 6 were associated with 4 veterinarian authors and 42 were associated with 10 nonveterinarian authors. Of the 66 recipes obtained from 10 book sources,21–30 44 were associated with 7 veterinarian authors and 22 were associated with 3 nonveterinarian authors. Most recipes (113/114 [99.1%]) contained vague instructions, which necessitated at least 1 assumption regarding the ingredients, preparation method, or supplementation details to enable analysis.

Of the 114 HPMD recipes evaluated, 46 (40.4%) did not provide any feeding instructions and the remaining 68 (59.6%) gave poorly detailed or unclear feeding instructions. These included imprecise measurements (terms such as a whisker of catnip and some shrimp) and wide-ranging feeding instructions based on volume amounts (statements such as 1 to 1.5 cups of food/d, more if your cat is very active).

Eight of the 114 (7.0%) HPMD recipes included potentially toxic ingredients such as garlic, onions, and leeks (2 recipes provided by veterinarian authors recommended garlic extract, whereas 6 recipes provided by nonveterinarian authors recommended whole garlic cloves, onions, or leeks). Eleven (9.6%) recipes did not include meat or fish but did include plant- or dairy-based protein sources (or both) or eggs (3 recipes were associated with veterinarian authors and 8 recipes were associated with nonveterinarian authors). Furthermore, 25 (21.9%) recipes either did not recommend any preparation method or provide feeding instructions. Some recipes recommended feeding the meals raw (22/114 [19.3%]) or with whole or ground bones (7/114 [6.1%]); of those, 9 recipes were associated with veterinarian authors and 13 recipes were associated with nonveterinarian authors.

Some HPMD recipes (20/114 [17.5%]) could not be quantitatively evaluated owing to either vague instructions even with assumptions (statements such as 1-part vegetable mixture, 3-parts meat mixture) or the inclusion of ingredients not found within the available databases (eg, bones, chicken backs, or necks). As such, quantitative assessment was possible for 94 recipes from internet (n = 38) and book (56) sources, all but one of which also required assumptions. Of the 38 recipes obtained from 7 internet sources, 4 were associated with 3 veterinarian authors and 34 were associated with 4 nonveterinarian authors. Of the 56 recipes obtained from 8 book sources, 36 were associated with 6 veterinarian authors and 20 were associated with 2 nonveterinarian authors.

Computerized assessment revealed wide ranges in total energy provided by each of the 94 HPMD recipes (median, 630 kcal [range, 36 to 4,638 kcal]); median energy density was 5,137 kcal/kg [2,335 kcal/lb] of dry matter (range, 3,245 to 6,636 kcal/kg [1,475 to 3,016 kcal/lb] of dry matter). Median moisture content was 70.1% (range, 47.9% to 92.1%), and median caloric distribution on an ME basis for protein was 37.9% (range, 11.4% to 63.0%). Median percentages of fat and carbohydrate were 48.2% (range, 8.9% to 76.3%) and 10.8% (range, 0.1% to 72.4%), respectively. In addition, there were wide ranges of concentrations of crude protein and amino acids (Table 1) as well as concentrations of total fat, arachidonic acid, linoleic acid, vitamins, and minerals (Table 2).

Table 1—

Concentrations of crude protein and essential amino acids in recipes for HPMDs for adult cats and comparison of those concentrations relative to the NRC feline maintenance RA7 for each component.

VariableNRC RA (units/1,000 kcal)Median (units/1,000 kcal)Range (units/1,000 kcal)No (%) of recipes in which the component concentration was below RA
Crude protein (g)50.0091.3031.17–148.166 (6.4)
Arginine (g)1.935.632.04–10.180
Histidine (g)0.652.670.69–4.410
Isoleucine (g)1.084.041.41–7.490
Methionine (g)0.432.420.72–4.000
Methionine and cystine (g)0.853.421.17–5.780
Leucine (g)2.557.052.42–11.731 (1.1)
Lysine (g)0.857.411.60–13.170
Phenylalanine (g)1.003.611.64–6.360
Phenylalanine and tyrosine (g)3.836.732.74–11.564 (4.3)
Threonine (g)1.303.741.37–6.390
Tryptophan (g)0.330.960.36–1.670
Valine (g)1.284.501.81–7.710
Taurine (g)0.100.240–10.7513 (22.4)

Concentration data are reported as median and range. In total, variables were analyzable in 93 recipes with the exceptions of crude protein concentration, which was analyzable in 94 recipes, and taurine concentration, which was analyzable in 58 recipes.

Table 2—

Concentrations of total fat, linoleic acid, arachidonic acid, and selected vitamins and minerals in recipes for HPMDS for adult cats and comparison of those concentrations relative to the NRC feline maintenance RA7 for each component.

VariableNRC (units/1,000 kcal)Median (units/1,000 kcal)Range (units/1,000 kcal)No (%) of diets in which the component concentration was below RANo (%) of diets in which the component concentration was < 50% of the RA
Total fat (g)22.5053.7210.19–86.404 (4.3)1 (1.1)
Linoleic acid (g)1.406.511.09–31.502 (2.1)0
Arachidonic acid (g)0.0150.380.00–3.354 (4.3)4 (4.3)
Minerals
 Calcium (g)0.720.950.05–3.1735 (37.2)23 (24.5)
 Phosphorus (g)0.641.360.53–3.172 (2.1)0
 Magnesium (mg)100.00161.5039.00–706.0010 (10.6)1 (1.1)
 Sodium (mg)170.00824.5080.00–4,666.004 (4.3)1 (1.1)
 Potassium (g)1.301.490.50–11.1331 (33.0)3 (3.2)
 Iron (mg)20.0011.722.16–44.4672 (76.6)39 (41.5)
 Copper (mg)1.201.350.06–57.2943 (45.7)25 (26.6)
 Zinc (mg)18.5014.612.42–61.9758 (61.7)34 (36.2)
 Manganese (mg)1.201.060.06–10.8354 (57.4)29 (30.9)
 Selenium (μg)75.00135.008.00–1,208.0018 (19.1)1 (1.1)
Vitamins
 Retinol (μg)250.00283.210.00–29,029.3241 (43.6)25 (26.6)
 Vitamin D (U)70.00193.250.00–2418.0123 (27.1)12 (14.1)
 Vitamin E (mg)10.008.140.44–190.4754 (57.4)31 (33.0)
 Thiamine (mg)1.400.980.06–24.1959 (62.8)33 (35.1)
 Riboflavin (mg)1.002.050.24–25.6814 (14.9)3 (3.2)
 Pyridoxine (mg)0.632.070.20–25.564 (4.3)1 (1.1)
 Niacin (mg)10.0030.510.33–105.899 (9.6)4 (4.3)
 Pantothenic acid (mg)1.445.910.78–43.482 (2.1)0
 Cobalamin (μg)5.6025.600.50–347.9121 (22.3)13 (13.8)
 Folic acid (μg)188.00230.6719.14–1,981.8939 (41.5)14 (14.9)
 Choline (mg)637.00350.9611.05–1,955.4878 (89.7)37 (42.5)

Concentration data are reported as median and range. In total, variables were analyzable in 94 recipes with the exceptions of vitamin D concentration, which was analyzable in 85 recipes, and choline concentration, which was analyzable in 87 recipes.

None of the 94 HPMD recipes that were evaluated quantitatively provided all essential nutrients in adequate concentrations to meet the NRC RAs for maintenance of adult cats. With assumptions, 5 recipes that were associated with veterinarian authors met the NRC RAs for adult cats for all assessed nutrients except choline; 3 of those recipes provided choline in amounts that met the NRC MR. However, the taurine adequacy of 2 of those 5 recipes could not be confirmed because of unknown contributions from ingredients expected to provide this nutrient (eg, certain fishes and some cuts of beef or poultry). Most recipes (80/94 [85.1%]) had concentrations of 3 or more nutrients below the respective RA, with a median of 7 nutrients (range, 1 to 19 nutrients) at inadequate concentrations. The most common nutrients in the recipes that were below RAs were choline (78/87 [89.7%] recipes), iron (72/94 [76.6%] recipes), thiamine (59/94 [62.8%] recipes), zinc (58/94 [61.7%] recipes), manganese (54/94 [57.4%] recipes), vitamin E (54/94 [57.4%] recipes), and copper (43/94 [45.7%] recipes). One recipe relied on a protein source with no defined amino acid concentrations in the database (beef heart); however, other than taurine, all other recipes met the NRC RAs for all essential amino acids except leucine (concentration was inadequate in 1/93 recipes) and phenylalanine and tyrosine (combined concentration was inadequate in 4/93 recipes; Table 1).

Taurine concentrations of some ingredients were not available in the databases despite the use of previously published values for many food entries.31 If taurine adequacy could not be verified on the basis of the contributions of other ingredients, it was treated as a missing value. Many HPMD recipes (50/94 [53.2%]) had an insufficient concentration of taurine. However, 36 of those 50 recipes had 1 or more ingredients without a defined value for taurine concentration in the database but were likely to provide some taurine (eg, certain fishes and some cuts of beef or poultry). Therefore, minimal taurine concentration was confirmed for 58 recipes. Taurine supplementation was stated to be optional or conditional (eg, when the diet had been frozen > 1 week) in 6 of 94 (6.4%) recipes. In these instances, the taurine supplement-type product was included in the analysis. Most recipes (74/94 [78.7%]) did not include a specific taurine supplement-type product. All recipes (20/94 [21.3%]) that contained a taurine supplement-type product met the NRC RA for taurine for adult cats. Of the recipes that provided taurine concentrations for all ingredients expected to supply it, 13 of 58 (22.4%) were below the NRC RA for taurine for adult cats.

Similar to taurine, some ingredients in the databases did not have defined values for vitamin D and choline concentrations but could be expected to contribute these essential nutrients (eg, meat or organs providing vitamin D and lecithin providing choline). If vitamin D or choline adequacy could not be confirmed on the basis of contributions of other ingredients, these were treated as missing values (9/94 [9.6%] and 7/94 [7.4%] recipes, respectively). Of the 85 HPMD recipes that had defined values for all ingredients expected to provide vitamin D, 23 (27.1%) had a vitamin D concentration below the NRC RA. Likewise, choline concentration was confirmed to be below the NRC RA in 78 of 87 (89.7%) recipes.

Among the HPMD recipes evaluated, those that provided nutrients in concentrations < 50% of their respective NRC RAs were common, but no recipe was that low in crude protein or amino acid concentrations other than taurine. The nutrients that were most commonly present in concentrations < 50% of their respective RA included choline (37/87 [42.5%] recipes), iron (39/94 [41.5%] recipes), zinc (34/94 [36.2%] recipes), thiamine (33/94 [35.1%] recipes), vitamin E (31/94 [33.0%] recipes), and manganese (29/94 [30.9%] recipes; Table 2).

Of the 94 HPMD recipes, 43 (45.7%) contained at least 1 (median, 0; range, 0 to 3) nutrient at a concentration that exceeded the SUL. Nutrient concentrations that exceeded their respective NRC SUL included arachidonic acid (34 [36.2%] recipes), linoleic acid (12 [12.8%] recipes), retinol (1 [1.1%] recipe), and total fat (1 [1.1%] recipe). No recipes provided sodium, zinc, or vitamin D at concentrations greater than their respective SUL.

The number of nutrients for which the recipe concentration was below RA was evaluated on the basis of HPMD recipe authorship. Forty veterinarian-authored recipes were compared with 54 nonveterinarian-authored recipes. Veterinarian-authored recipes had significantly (P < 0.001) fewer numbers of nutrients at concentrations below their respective RAs (median, 3.5; range, 1 to 12), compared with findings for nonveterinarian-authored recipes (median, 10; range, 3 to 19).

For purposes of analysis, only a small number of recipes (15/94 [16.0%]) did not necessitate any assumptions regarding supplementation. With regard to vitamins and minerals, all but 1 veterinarian-authored recipe (39/40 [97.5%]) included supplement-type products, whereas many nonveterinarian-authored recipes (37/54 [68.5%]) did not include supplement-type products. Home-prepared maintenance diet recipes that included vitamin and mineral supplement-type products had significantly (P < 0.001) fewer nutrients at concentrations below their respective RA (median, 5 nutrients; range, 1 to 14 nutrients), compared with recipes with no supplement-type products (median, 11 nutrients; range, 3 to 19 nutrients). Only 4 recipes specifically suggested inclusion of a pet or feline supplement-type product, although no specific brand was recommended. All remaining recipes that included supplements recommended human adult or child vitamin and mineral supplement-type products.

Discussion

To the authors’ knowledge, this was the first study to assess the nutritional adequacy of recipes for HPMDs for adult cats. Consistent with the results of similar studies of recipes for dogs,4–6 results of the present study indicated that none of the evaluated recipes provided all essential nutrients in amounts that met the NRC RAs, as determined by computer software analysis. In most HPMD recipes, multiple essential nutrients were at concentrations below their respective RAs, regardless of recipe source or category of author (veterinarian vs nonveterinarian). In addition, preparation and feeding instructions were often inadequate and almost all recipes required at least 1 assumption to enable analysis. These concerns were further compounded by recommendations for foods known to be toxic to cats (eg, garlic, onions, and leeks), consumption of which could lead to development of hemolytic anemia.32 Additional concerns were raised by the recommendation of raw animal products in some recipes; most of those recipes did not mention the risk of contamination of raw animal products with harmful bacteria and other organisms, thereby neglecting to inform readers of important potential hazards commonly associated with this feeding practice.33,34 Moreover, some recipes that included bones did not advise to grind the bones to reduce risk of traumatic injury to teeth or gastrointestinal tract perforation or obstruction. Many recipes also neglected to specify preparation methods, which can influence nutrient concentrations. For example, whether fat drippings rendered from meat during cooking are included could impact the calorie content and nutrient profile of the diet; likewise, meat can leach essential nutrients, such as taurine, during boiling, which may result in a diet that is nutrient deficient.31

Whether an individual animal would develop clinical signs related to inadequate intake of essential nutrients would depend on many factors including the animal's overall nutritional status, magnitude of the nutrient deficiency in the diet, duration of feeding the nutrient-deficient diet, dietary concentrations of other nutrients, and overall bioavailability of the nutrients in the diet. Among the nutrients that were present in HPMD recipes at concentrations below their respective RA identified in the present study were choline and iron; clinical signs among cats fed those diets might include weight loss and lipid accumulation in the liver associated with choline deficiency7 and anemia, pallor, lethargy, and weight loss associated with iron deficiency.7 Many nutritional deficiencies are associated with nonspecific clinical signs that may be difficult to attribute to diet; for example, the clinical signs associated with zinc deficiency include poor growth, depressed immune function, and poor wound healing.7 Signs of thiamine deficiency can also be variable and nonspecific; weight loss and anorexia are typically the first noted signs.35 However, cardiac and neurologic signs can develop and may even be fatal if inadequate thiamine intake persists.7,36 Vitamin E deficiency is associated with signs of depression and anorexia as well as splenomegaly and steatitis,7 and development of these problems as a consequence of inadequate intake of vitamin E in cats consuming unbalanced home-prepared diets has been reported.37 In the 94 recipes evaluated in the present study, copper and calcium concentrations were also commonly below their respective NRC RA, and 25 (26.6%) and 23 (24.5%) of the HPMD recipes provided < 50% of their RA, respectively. Signs of copper deficiency include poor reproductive performance, discoloration of hair, skeletal malformations, oxidative damage, and anemia. Signs of calcium deficiency are most commonly associated with skeletal abnormalities, such as bone pain related to osteopenia and even pathological fractures,7 but neurologic signs and severe, fatal vertebral fractures in cats eating unbalanced home-prepared diets have previously been reported.38 Given that several of the nutrients most commonly identified from the recipes as being present in the diets at inadequate concentrations (ie, below their respective RA) in this study (specifically choline, iron, thiamine, zinc, and vitamin E) were also those present at < 50% of their respective RA in at least a third of the recipes, development of clinical signs in cats consuming these HPMDs may be likely.

Although the HPMD recipes evaluated in the present study varied widely with regard to crude protein content (31.2 to 148.2 g/1,000 kcal) and the concentrations in 6 recipes were found to be below the crude protein NRC RA, dietary crude protein and essential amino acid adequacy was less of a concern than was dietary adequacy of vitamins and minerals. Concentrations of most amino acids were adequate in all recipes evaluated. This was likely attributable to the widely known fact that cats are obligate carnivores and require dietary protein in greater amounts, compared with protein intake in dogs.39 In addition, most of the recipes used meat, fish, or eggs as the protein source in the diets.

Although most dietary inadequacy concerns identified in the present study related to insufficient amounts of essential nutrients, there were also recipes wherein nutrient concentrations exceeded their respective NRC SUL. In an otherwise balanced diet, concentrations of total fat and fatty acids that exceed SULs are not likely to result in adverse effects, and none have been reported to date to the authors’ knowledge.7 However, an excess of retinol was evident in 1 recipe, and potential clinical signs associated with consumption of that diet might include skeletal malformation and pathological fractures as well as reproductive defects and neurologic abnormalities.7 The source of the high concentration of retinol in that recipe was liver, which is commonly used in both commercial and home-prepared diets because of its high nutrient density and palatability. However, this ingredient must be used in formulation of diets with a clear understanding of its nutritional profile to avoid causing development of hypervitaminosis A, which has been detected in cats consuming home-prepared diets containing high amounts of liver.40

It is important to emphasize that even when a detailed and balanced recipe is used by pet owners, inherent variability in ingredients, differences in interpretations of the ingredients or instructions, or other food and owner-related factors likely lead to differences in the nutritional profile of the resulting diet.41 Further, long-term compliance with regard to nutritional management plans that incorporate home-prepared diets is generally poor.42,43 We determined that many assumptions were required to quantitatively evaluate most recipes; assumptions would also have to be made by cat owners attempting to prepare the diet at home. In addition, although veterinarian-authored recipes contained comparatively fewer nutrients at concentrations below their respective RA than did nonveterinarian-authored recipes, presumably in part because they were more likely to include supplement-type products, concentrations of components of each recipe were still below RA regardless of the category of author. In addition, all but 1 recipe required assumptions for quantitative analysis, and it is possible that dietary concentrations of 1 or more nutrients would be even lower with different assumptions. This underscores the importance of expertise specific to diet formulation when developing recipes for home-prepared pet diets. We recommend that home-prepared diets be formulated by a board-certified veterinary nutritionist or an animal nutritionist with advanced training to ensure nutritional adequacy.44

In the present study, both qualitative and quantitative assessments of a large sample of recipes for home-prepared diets for cats that are readily available to pet owners were undertaken, and limitations were recognized. Computerized analysis is dependent on a complete and accurate database; in the present study, certain essential nutrients in some ingredients included in the HPMD recipes were undefined, especially those not essential for humans, such as taurine. In addition, because laboratory analysis and animal feeding trials were not performed, it was not possible to fully assess the diets including determination of the digestibility and bioavailability of essential nutrients. Laboratory analysis is costly, but there is evidence that computerized assessment of pet recipes is reasonably predictive of the nutritional profiles of home-prepared diets.4 Also, when recipes provided raw amounts of ingredients to be fed cooked, those raw amounts were used for analysis; therefore, potential losses of nutrients during cooking were not taken into account. Although care was taken in the present study to choose commonly available ingredients when assumptions were necessary, it was possible that we may have inadvertently chosen more appropriate ingredients because of an unrecognized bias; thus, the number of nutrients determined to be at concentrations below their respective RA could have been potentially decreased. Although every effort was made to make consistent ingredient choices for the recipes when necessary, this was not a blinded study and there could have been bias for aspects such as ingredient choice. Despite these limitations, the HPMD recipes assessed in the present study were largely nutritionally inadequate, and the ingredient and preparation choices that a typical cat owner may make when following a recipe may further exacerbate deficiencies in a diet already lacking in multiple essential nutrients.

In the present study, problems with nutritional adequacy were identified in all veterinarian- and nonveterinarian-authored recipes evaluated. On the basis of these recipes, the resultant diets cannot be considered appropriate for long-term feeding of adult cats. Home-prepared diets can be an appropriate option for adult cats, but diet formulation (including selection of ingredients and methods of preparation) requires advanced nutrition and diet formulation training, specialized computer software, and specific detailed information to ensure the development of complete and balanced diets. In a clinical setting, when one encounters a cat that is fed a home-prepared diet, it is recommended that the advice of a board-certified veterinary nutritionist is sought regarding evaluation of the recipe and its preparation method; with such consultation, the risk of development of health problems associated with the consumption of an unbalanced diet can be reduced. It is also important to be aware that owner-driven recipe modifications or substitution or omission of ingredients can result in an unbalanced diet.1,42 A complete diet history, including details of the specific types and amounts of the ingredients and any supplement-type products, preparation instructions, and amount of the diet fed to the cat in question should be obtained at every visit, to identify patients at risk for problems related to consumption of an unbalanced diet.45

ABBREVIATIONS

HPMD

Home-prepared maintenance diet

ME

Metabolizable energy

MR

Minimal requirement

NRC

National Research Council

RA

Recommended allowance

SUL

Safe upper limit

Footnotes

a.

NOW Daily Vits Multi Vitamin & Mineral, NOW Foods, Bloomingdale, Ill.

b.

Centrum Kids Multivitamin/Multimineral Supplement, Pfizer Inc, Kings Mountain, NC.

c.

GNC UltraMega Multivitamin Plus Yummy Chicken Flavor, GNC Holdings Inc, Pittsburgh, Pa.

d.

GNC B Complex Big 100, GNC Holdings Inc, Pittsburgh, Pa.

e.

NOW Taurine Powder, NOW Foods, Bloomingdale, Ill.

f.

NOW Vitamin E – 400, NOW Foods, Bloomingdale, Ill.

g.

Nordic Naturals Cod Liver Oil, Nordic Naturals Inc, Watsonville, Calif.

h.

NOW Calcium Carbonate Powder, NOW Foods, Bloomingdale, Ill.

i.

Solgar Bone Meal Powder with Vitamin B12, Solgar Inc, Leonia, NJ.

j.

Morton Iodized Salt, Morton Salt Inc, Chicago, Ill.

k.

Morton Lite Salt Mixture, Morton Salt Inc, Chicago, Ill.

l.

Morton Salt Substitute, Morton Salt Inc, Chicago, Ill.

m.

Balance IT Autobalancer, Davis Veterinary Medical Consulting Inc, Davis, Calif.

n.

Davis Veterinary Medical Consulting Inc, Davis, Calif.

o.

USDA National Nutrient Database for Standard Reference Release 28.2016, USDA Agricultural Research Service, Beltsville, Md.

p.

Microsoft Office Excel 2016, Microsoft Corp, Redmond, Wash.

q.

R Development Core Team, R Foundation for Statistical Computing, Vienna, Austria.

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