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Evaluation and Use of Pet Foods
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Clinical Nutrition
Evaluation and Use of Pet Foods: General Considerations in Using Pet Foods for Adult Maintenance
Francis A. Kallfelz, DVM, PhD*
Dogs and cats require the same basic nutrients as other nonherbivorous animal species, i.e., energy, protein (amino acids), minerals, vitamins, and water. Commercial pet foods are almost all "total mixed rations," designed to provide all needed nutrients in the correct proportions in a single feed. NUTRITIONAL REQUIREMENTS OF DOGS ENERGY
Most animals eat sufficient food to satisfy their caloric (energy) requirements. In the calculation of energy content of pet animal rations and of energy needs of dogs and cats, metabolizable energy (ME) values are frequently used. These are derived from approximations of metabolizable energy available from the ration for dogs and cats consuming average diets, assuming apparent digestibilities of 80 per cent for protein, 90 per cent for fat and 85 per cent for carbohydrate. Gross energy values are then corrected for the assumed digestibilities, including a urinary nitrogen energy loss for protein, to arrive at the approximations listed in Table 1. It can be seen that protein is an important energy source and that both protein and carbohydrate provide about 3.5 Cal of metabolizable energy per gram. Fats, both of animal and vegetable origin, provide about 2.25 times more energy per gram than is available from protein or carbohydrates. Fats are an important energy source for the working dog. Contrary to popular belief, working dogs do not need additional protein, but do need extra energy, which can be easily supplied by fat. Dietary fat is also a source of essential fatty acids (EFA). These substances are found mainly in unsaturated fats such as corn oil and • Diplomate, American College of Veterinary Nutrition; Professor, Veterinary Nutrition, New York State College of Veterinary Medicine; Chief, Clinical Nutrition, Veterinary Medical Teaching Hospital, Cornell University, Ithaca, New York
Veterinary Clinics ofNorthAmerica: Small Animal Practice-Vol. 19, No.3, May 1989
387
388
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Table 1. Caloric Content of Foods
Protein Carbohydrates Sugar Starches Fats Lard Tallow Vegetable fats (EFA)
TOTAL
AVAILABLE
5.65 4.15
3.5 Cal/gram 3.5 Cal/gram
9.40
8.5 Cal/gram
EFA = essential fatty acids
should constitute about 2 per cent of diet dry matter. Vegetable fat, however, does not contain arachidonic acid, which is an essential nutrient for the cat. The concerns about n-3 versus n-6 FA in humans are probably of little relevance to the nutrition of pet animals. It is generally assumed that the average-sized (30-lb) adult dog requires 30 Cal/lb per day of ME for maintenance. Smaller breeds require relatively more Cal/lb and larger breeds relatively less, e.g., 40 to 45 Calflb for a Chihuahua and 20 Cal/lb for an Irish wolfhound (Table 2). Commercial pet foods are formulated to ensure adequate intake of all required nutrients when the animal eats enough to satisfy caloric needs. The caloric content on a weight and volume basis does vary, however, among the various types of commercial foods (Tables 3 and 4). For example, assuming average values for the caloric content of a dry dog food, a 40-lb dog would be expected to consume 40 X 30 = 1200 Cal per day or 0.8lb/day (1200 Cal/1500 Cal/lb = 0.8 lb) of a dry dog food. 'On a dry matter basis, canned foods have a higher caloric density than dry or soft-moist foods. This is due to increased fat levels in these products. On an as fed basis, however, canned foods have the lowest caloric density, owing to their very high water content (75 per cent). On an as fed basis (i.e., by volume), soft-moist foods have the highest caloric density because they do not have air pockets in the food particles, as found in expanded dry foods, and have a much lower water content (33 per cent) than that found in canned products. Also, soft-moist foods may have a somewhat higher digestibility than do some other types. Thus, the Table 2. Estimated Maintenance Caloric (ME) Requirements of Dogs, Based on Size WEIGHT (LB)
CAL/LB/DAY
10 15 30 50 110
42 38 30 27 22
ME = metabolizable energy
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EvALUATION AND UsE oF PET FooDs
Table 3. Average ME Content of Dog Foods by Weight
Dry Soft-moist Canned
AS IS
DM
(CAL/LB)
(CAL/LB)
PER CENT H20
1500± 1300 ± 550±
1650± 1750± 1900±
10 33 75
ME = metabolizable energy; DM = dry matter basis
volume of soft-moist food required to meet daily maintenance requirements is only about half that required if dry or canned foods are being fed (see Table 4). The utilizable energy content of a commercial pet food on an as is basis can be calculated as shown in Table 5. This data can also be used to determine the approximate amount of a pet food that should be fed per day to a dog 9f a given weight. PROTEIN
Although almost everyone refers to animals (dogs or cats) as having a protein requirement, the actual requirement is for amino acids. About 20 different amino acids occur in proteins; however, of these only about 10 have been found to be essential dietary ingredients for the dog and cat; the remainder can be produced in the body from other substances. The protein quality of a pet food depends upon the levels of the various essential amino acids present in the protein sources used in its formulation, the total protein level in the product, and the caloric content. If overall caloric content is low, dietary protein will be used as an energy source. Many animal source proteins have high levels of all essential amino acids. Whereas individual vegetable source proteins may be deficient in one or more essential amino acids, combinations of vegetable protein sources can be used, which provide adequate levels of all essential amino acids. The actual protein level required in a dog food is dependent upon the total amount of the protein needed to supply adequate levels of all the essential amino acids; it also depends on the level of other energy sources. An experimental measurement called the biological value (BV) Table 4. Average ME Content of Dog Foods by Volume WT (LB)/CUP (8-oz VOL)
Dry Soft-moist Canned
0.2 0.35 0.5
ME = metabolizable energy
CAL/CUP
(8-oz VOL)
285 455
275
CUPS/DAY (30-LB DOG)
3t 2 3t
390
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Table 5. Calculation of Caloric Content (Canned Product) GUARANTEED ANALYSIS
Crude protein Crude fat Crude fiber Ash Moisture
10% X 3.5 = 35 Cal/100 g 4% X 8.5 = 34 Cal/100 g 1.5% 4% 72% 91.5%
100-91.5 = NFE = 8.5% X 3.5 = -30 -Cal_/'-1-0 -0 .: :cg . 99 99 X 4.54 = 450 Calflb as fed
NFE = nitrogen-free extract = carbohydrate
can be used to determine the protein quality and thus the amount needed. The BV really depends on the level of the least prevalent essential amino acid in the food, assuming energy sources are adequate. Rough approximations of the protein requirements for maintenance of adult dogs and recommended levels of protein in the ration are given in Table 6. The BV of proteins in pet foods varies according to the source of the protein and on other factors, as previously mentioned. The biological values of some commonly used protein sources are shown in Table 7. In general, the higher the BV, the lower the actual protein requirement. The BV of animal source proteins is generally higher than that of vegetable source products. This leads to a marketing curiosity in that animalbased pet foods are much higher in protein' than vegetable-based products, even though the protein value in the canned foods is higher. Table 6. Protein Requirements for Dogs 4.8±* 22*
g/kg body weight per cent of ration (DM)
• Depends on the biological value (BV) of protein used and the protein-calorie ratio DM =dry matter basis
Table 7. Biological Value (BV) of Proteins PROTEIN
BV
Egg Milk Beef Fish Soy Rice Oats Yeast Wheat Corn
100 90 84
75 75 72 66 63 60 54
391
EvALUATION AND UsE OF PET FooDs
Table 8. Mineral Requirements of Dogs % OF FEED
MINERAL
Ca p Salt Potassium Trace minerals
(oM)
1.1 0.9 1.1 Generally adequate
MG/KG OF BODY WTjDAY
242
198 242 (may be less)
DM = dry matter basis
With regard to the protein/calorie ratio, as the percentage of calories from protein in a ration rises, the NPU (utilization of ingested protein) decreases, and as the nonprotein caloric intake increases, the NPU rises and then plateaus. While definitive data are unavailable, probably the NPU is optimal when the protein/calorie ratio is in the range of20 to 30 per cent (i.e., about 20 to 30 per cent of the calories in the food are from protein). For practical applications all commercial pet foods designed for general use contain far more protein than is needed (see Kallfelz, pp 433- 446). Thus, as long as a dog is eating a sufficient quantity of food to satisfy his caloric requirement, protein intake will undoubtedly be adequate. MINERALS
The currently accepted estimates of minimum major mineral requirements for maintenance of the adult dog are given in Table 8. It is probable that the levels recommended are higher than necessary, and revisions may be made as new information becomes available. The basic ration type may also alter dietary mineral requirements. For example the availability of a given calcium source from a ration containing mainly meat-source ingredients is probably higher than that from a ration containing mostly vegetable-source ingredients. Trace mineral levels are rarely a matter of concern. VITAMINS
The stated minimum fat-soluble vitamin requirements for maintenance of the adult dog are shown in Table 9. Vitamin A is necessary for Table 9,
Vitamin A VitaminD VitaminE VitaminK DM = dry matter basis
Vitamin Requiremepts of Dogs
PER KG DIET (oM)
PER KG OF BODY WT/DAY
5000 IU 500IU 50IU
110IU 11IU 1.1 IU
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normal function of connective tissue (cartilage, etc.) and epithelial tissue (skin, mouth, and intestinal lining, etc.), and, of cour!!e, for proper vision. Vitamin D is required for normal development of bones and controls other aspects of mineral handling by the body. Vitamin K is needed for normal blood clotting and is also involved in other functions. No requirement is listed for vitamin K, since it is manufactured by intestinal microorganisms. The requirement for water-soluble vitamins varies according to energy intake. Dogs and cats manufacture vitamin C in the liver and hence have no dietary requirement. It is possible, though probably very rare, that under certain conditions, a functional deficiency of vitamin C could occur and supplementation might be indicated. Water-soluble vitamins are needed for normal energy metabolism and for other functions. Requirements for water-soluble vitamins are rarely of concern, since virtually all pet foods contain added amounts of these nutrients. WATER
It is generally assumed that dogs require approximately 40 to 60 ml/kg/day (20 to 30 mljlb) under normal conditions. Water demands can be met by drinking, preformed water (in food), and with metabolic water (produced in the body) from metabolism of protein, carbohydrate, and fat.
COMMERCIAL DOG FOODS Commercial dog foods are available in three basic forms: dry, softmoist, and canned, as shown (Table 10). Since all of the nutrients are present in the dry matter of the product, canned foods represent a considerable expense, since on an as fed basis they are frequently the most expensive and consist of more than 70 per cent water. DRY FooDs Dry foods are available as: 1. Expanded products (almost all); e.g., Purina, Carnation, Science Diet 2. Kibbles (very few); e.g., Ken'L Ration Biscuit, Triumph
Table 10. Commercial Dog Foods TYPE
MOISTURE
DRY MATTER
Dry Soft-moist Canned
10% 33% 74%
90% 67% 26%
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EvALUATION AND UsE oF PET Fooos
Table II. Example of a Formula for an Expanded Product INGREDIENT
%
Ground corn Soybean meal Meat and bone meal Ground wheat Animal fat (preserved with BHA) Ground oats Ground grain sorghum Wheat mids Wheat germ Salt (iodized) Dried whey Vitamin mix (specified) Trace minerals (specified)
30.0 15.0 14.0 10.0 7.0 6.0 6.0 5.0 3.0 1.0 1.0 0.5 0.5
Reprinted from The Collins Guide to Dog Nutrition by Donald R. Collins, DVM. Copyright © 197 2 by Donald R. Collins, with special permission of the publisher, Howell Book House. ·
3. Meals or pelleted meals (almost none). Gaines Meal is, in fact, an expanded product. An example of a formula for a commercial expanded dry type product is shown (Table 11), and the caloric composition is demonstrated (Table 12). Dry type dog foods generally have the highest levels of vegetable-source proteins, are relatively low in fat, and have the lowest caloric density on a dry-matter basis. Many of these are maintenance products and, as such, may be bulk limited when used to feed stressed dogs. There are several, however, that meet the needs of growth as well as maintenance, and a few are designed for working dogs. These products, of course, contain additional fat. Dry type dog foods · represent about 50 per cent of pet foods produced. SoFT-MOisT PRoDucTs
Soft-moist or semi-moist dog foods are very similar to dry foods in nutrient content. The carbohydrate content of these products, however, Table I2. Caloric Content of Dry Dog Foods CALORIES INGREDIENT
(%AS IS)
(%DRY)
Protein Fat Fiber Ash Moisture NFE (carbohydrate)
25.0 8.0 4.0 6.5 10.0 46.5
27.8 8.9 4.4 7.2
454 327
27.9 20.1
51.7
844 1625
52.0
NFE = nitrogen-free extract
(PER LB)
(%)
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Table 13. Typical Formula for Soft-Moist Dog or Cat Food INGREDIENT
31.0 28.0 21.0 3.0 3.0 3.0 3.0 2.0 1.5 1.0 0.5 0.5 1.5
Soy Hour Meat by-products Sucrose Wheat bran Dical Meat Dried milk Tallow Propylene glycol Salt (iodized) Vitamin mix Trace mineral mix Other
Reprinted from The Collins Guide to Dog Nutrition by Donald R. Collins, DVM. Copyright © 1972 by Donald R. Collins, with special permission of the publisher, Howell Book House.
is largely in the form of disaccharides such as sucrose, and they have lower levels of less soluble carbohydrates such as starches as compared with dry products. Protein in these products generally consists of more animal-source ingredients than is found in dry foods. They have a somewhat higher energy density on a dry-matter basis than do dry products. Also, stool production of animals fed soft-moist products is generally much less than that of animals fed dry rations but urine production is greater. The physical form of these products varies, to include patties, chunks, and so forth. This is a marketing gimmick and does not affect nutrient content. Almost all are balanced rations. The market percentage of these products is decreasing, currently representing only about 12.5 per cent of total pet food production. An example of a formula for a soft-moist product and the caloric content are shown in Tables 13 and 14. CANNED PRODUCTS
There is more variability in the formulation of canned products than in dry or soft-moist types. They may be balanced or not, depending on Table 14. Caloric Content of Soft-Moist Dog Foods CALORIES INGREDIENT
Protein Fat Fiber Ash Moisture NFE
%AS IS
%DRY
18.0 7.0 3.0 7.5 33.0 31.5
26.8 10.4 4.5 11.2
327 286
27.6 25.1
47.0
572 1185
48.3
NFE = nitrogen-free extract
(PER LB)
(%)
395
EvALUATION AND UsE oF PET FooDs
Table 15. Example ofa Fonnula for a Meat Type Canned Dog Food INGREDIENT
%
Meat by-products Meat Liver Steamed bone meal L~d
SBOM Corn Hour Beefblood Humectants Mineral and vitamin mix
35 20 15 7 6 5 4.5 4.0 2.0 1.5
SBOM = soy bean oil meal Reprinted from The Collins Guide to Dog Nutrition by Donald R. Collins, DVM. Copyright© 1972 by Donald R. Collins, with special permission of the publisher, Howell Book House.
the formula. The types available are balanced (mainly meat), balanced (other), and gourmet (mainly meat). Good quality balanced canned rations are higher in animal-source proteins and in fat but lower in carbohydrate content than dry or soft-moist products; they have the highest caloric density of all commercial products on a dry-matter basis. A typical formula of a meat-type canned dog food and the caloric composition are shown in Tables 15 and 16.
LABEL INFORMATION The label of any commercial pet food product has a Guaranteed Analysis statement and a list of ingredients (Table 17). The guaranteed analysis is taken from a proximate analysis of the product. The ingredients should be listed in terms of decreasing fractional content in the product. Be aware, however, that this is on an as is, not a dry matter, basis. Additionally, since the first of January, 1984, the label of all dog foods in interstate commerce are required to have a "statement and a validation of nutritional adequacy." Dog foods can be proven to be "complete and balanced" by one of two mechanisms: Table 16. Caloric Content of Canned Dog Foods INGREDIENT
Protein Fat Fiber Ash Moisture NFE
%AS IS
%DRY
PER LB
%
10.5 6.0 1.5 4.0 74.0 4.0
40.4 23.1 5.7 15.3
192 245
37.6 48.0
15.4
73 510
14.4
NFE = nitrogen-free extract
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Table 17. Guaranteed Analysis (Dry-Type Product) Crude protein Crude fat Crude fiber Moisture Ash
Minimum 2LO% Minimum 10.0% Maximum 4.0% Maximum 10.0% Maximum 8 .0%
Ingredients: Ground corn, meat by-product meal, soy grits, animal fat (preserved with BHA), wheat bran, brewers yeast, iodized salt, calcium carbonate, iron sulfate, zinc oxide, manganous oxide, copper oxide, cobalt carbonate, choline chloride, vitamin A palmitate, D-activated animal sterol, a-tocopherol, niacin, calcium pantothenate, riboflavin, thiamine, pyridoxine hydrocholoride, folic acid, biotin, vitamin B12 supplement
1. The manufacturer can prove by analysis that the product contains the minimum required levels ofall essential nutrients, as specified by the National Research Council (NRC) for maintenance, growth, and so forth. In this case a statement similar to that in italics will appear on the label. 2. The manufacturer can show by feeding trials (as specified by AAFCO) that the product supports maintenance, growth, and so forth, of dogs. In this case, a statement that the product has been shown by experiment to meet requirements for maintenance, and so on, will appear on the label. If the manufacturer has not evaluated the product as in (1) or (2), then a statement must appear that the product is "not intended for sole use." An exception to this is "dietary animal foods," which must have a statement that the product should be used only if recommended and supervised by a veterinarian. Thus, by reading the label, one can get useful information regarding the product (Table 18). However, the label may not specify all the information a user might want to know (Table 19). Frequently, the manufacturer will provide feeding guidelines for a product (how much to feed based on the weight of a dog) . In many cases a calculation of caloric content will show that the recommendations exceed the average caloric requirements for a dog of a specified weight. The owner is well advised to determine for himself the correct amount to feed. You should recommend that this be done on a weight, not a volume, basis. SUPPLEMENTATION Many dog owners supplement their animal's daily ration even though they are feeding adequate quantities of a complete and balanced Table 18. Information Available from Label Is product complete and balanced? Approximate caloric content Level of protein and fat Does the product C_?ntain meat (and, roug~ly, how much)?
EvALUATION AND
UsE OF PET Fooos
397
Table 19. Information Not Available from Label Overall digestibility Biological value (protein) Quality Contamination
ration. This is done for several reasons and can be accomplishecl in several ways (Tables 20 and 21). In most cases supplementation is tmnecessary and should be discouraged (see Kallfelz, pp 433-446). If a client insists on supplementing, a good recommendation is to supplement a balanced ration with a balanced ration (e.g., balanced fanned ration added to a balanced dry ration). In general, adding no more than 10 per cent by weight of almost any reasonable supplement to a balanced basic ration is acceptable, since a safety factor is used in formulation of commercial rations. SPECIFIC AS CoMPARED WITH GENERAL-PURPosE PRoDucTs
Many commercial products are complete and balanced for all phases of the life cycle (Table 22). Some products, however, are recommended for specific stages of the life cycle (growth, adult maintenance, older dogs, etc.). Conceptually, these specially designed products are preferable; however, the differences in formulation among these products are in most cases small and, in some, the basis for the formulation can be questioned, e .g., diets for older dogs generally contain reduced levels of protein, yet there is no evidence to suggest that "normal" older dogs cannot tolerate normal levels of protein.
PREMIUM PET FOODS Relatively recent additions to the pet food market are the "premium pet foods" represented by such lines as Purina Pro Plan, lams Eukanuba, Table 20. Rationale for Supplementation Lack of confidence in basic ration Increase palatability Meet individual requirements Provide extra nutrients during stress
Table 21. Methods of Supplementation Tablets, capsules, etc. (minerals and vitamins) Mixing foods (dry and canned) Meat (extra protein) Fat (for better skin and hair coat; extra energy) Table scraps Other (e.g., dried milk)
398
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Table 22.
A.
KALLFELZ
General-Purpose Products
Advantages Convenient Good results in average dog Owner confidence Disadvantages . Multipurpose product Designed for growth May overfeed maintenance animal if fed ad lib May be bulk-limited for working dog, etc.
ANF, Science Diet, and so forth . These products are generally composed of high-quality, meat-source ingredients, have a high digestibility, and generally contain more fat than standard manufactured dry pet foods. They are sold exclusively through non-grocery outlets such as pet supply stores and animal hospitals. Currently, sales of these products are increasing at a rate of about 15 per cent per year, even though they are more expensive than standard pet foods. For most adult maintenance situations, it is unnecessary to use such products, although their use is certainly acceptable. If a client prefers such a product, calculate the caloric need and recommend an amount to be fed daily. These products do tend to be very palatable, thus the probability for excessive weight gain may be increased if they are fed free choice. Because of their relatively high fat content, they have a good caloric density and can be recommended during periods of physiological stress. In some cases, the improved digestibility and utilizability of such products results in decreased required feeding amounts, which could offset the price premium. GENERIC PET FOODS The other new addition to the line of pet food products is that of the generic pet foods; these are at the opposite end of the spectrum from the premium products. Virtually all are guaranteed to be complete and balanced for maintenance, but this is validated in almost all cases only by chemical analysis, not by animal-feeding experiments. A few papers have reported that generic foods are inferior to standard products in terms of animal growth rates, nutrient content, apd so forth. Excessive nutrient content and rapid growth rates of dogs fed a given product should not necessarily be considered desirable characteristics of a good pet food. The biggest problem with the generic products is palatability. Since they tend to be low in fat and animal-source protein, they are not well accepted by many pups. The cost of additives needed to improve palatability could well outweigh the initial economic advantage of purchasing a generic type pet food. THE BEST COMMERCIAL DOG FOOD Frequently veterinarians are asked for a recommendation as to what hP.st dol! food. There is no valid answer to this question. There are
i-: th P
EvALUATION AND UsE OF PET Fooos
399
many good commercial dog foods, and the choice of which to use depends on many factors, including age of dog, size of dog, number of dogs, management conditions, (constant versus restricted food availability, etc.), economic factors, and so forth. A veterinarian should be able to make recommendations to individual owners about adequate products available in his or her practice area, based on the above factors. "NATURAL" DOG FOODS In the last few years, several so-called natural dog foods have appeared on the market; they supposedly contain no artificial ingredients. A basic difference between these and the usual products is that many of the "natural" products do not contain a fat preservative (BHA or BHT). The shelf life of these products is therefore theoretically reduced, since the fat will become rancid in a shorter time period than in products with fat preservatiyes. These products also often contain special ingredients such as herbs, etc. While proponents of such products claim these "natural" additives are valuable, there is little objective scientific evidence to support a recommendation for their use. In some cases, the special ingredients may have pharmacological action or may be toxic, which could result in adverse side effects. HOME-FORMULATED DOG FOODS As previously mentioned, there are many excellent commercial products available. Even so, for whatever reasons, some owners insist upon the use of home-formulated rations. It is difficult, but possible, to formulate a balanced ration for the dog, using ingredients available in the home. Two publications are extremely valuable in this regard: Nutrient Requirements ofDogs, available from the National Research Council, and Nutritive Value of American Foods, available from USDA. The first is needed to ascertain the nutrient requirements of dogs and the second to provide information on the nutrient content of human foodstuffs. A chart (Table 23) is very handy to use in formulating a ration and should include, at least, estimates of protein, fat, calories, calcium, phosphorus, salt, vitamin A, and thiamine. The assumption is that if intakes of these nutrients are adequate, it is probable that other essential ingredients are also present in adequate amounts. Protein sources should be chosen to supply the protein requirement; then other ingredients should be added to supply additional calories and other essential nutrients. NUTRITIONAL REQUIREMENTS OF CATS (SPECIFIC CONSIDERATIONS) In a general sense, the nutrient requirements of cats are similar to those of dogs. A few differences do exist, as follows:
Table 23. INGREDIENT
Chart for Home-Formulated Ration Calculation* p
AMOUNT FED
DM
PROTEIN
FAT
ENERGY
(g)
(g)
(Cal)
(g)
NaCl (g)
VITAMIN A
(g)
Ca (g)
THIAMINE
(oz)t
(mg)
(IU)
0.011
0.2I7
O.I58
0.09
I9 566
Cooked lean ground beef
3t
40
27.3
I0.7
208
Dry powdered milk
It
50
I3.2
I3.8
25I
0.455
0,354
0.505
O.I4
Cooked rice
It
I3.7
54
0 .005
O.OI5
0.467
O.ol
0.586
1.13
0.24
I Turns tablet Total
1.2
0.500
2 6.3.
•
I05.7
41.7
24.5
Formula: t Cooked lean ground beef t Dry powdered milk t Cooked rice 2 Turns tablets I
5I3
0.971
585
DM=51.8% Protein = 39.5% DM Calories= 115Iflb, as is Fat=23% DM Ca=0.92%DM P=0.56%DM
• Sample calculation for an adult maintenance ration. Feed I oz per 2.5lb body weight/day.
f By weight DM = dry matter basis Adapted from Nutrient Requirements of Domestic Animals: Nutrient Requirements of Dogs. Printing and Publishing Office, National Academy of Sciences, 2IOI Constitution Ave., N.W., Washington, DC 20418; and Nutrient Value of American Foods. Agricultural Handbook No. 456, Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402
401
EvALUATION AND UsE OF PET FooDs
PROTEIN
The protein requirement of the cat is higher than that of the dog. It is recommended that protein levels in adult-maintenance cat foods be at least 30 per cent on a dry matter basis. Also, since palatability appears to be of more importance in affecting food intake in cats, cat foods generally contain more meat-source proteins. The cat also has a unique requirement for taurine, a sulfonic acid amine, frequently lacking in protein sources commonly used in dog foods (see Hayes, pp 403-413). Seafood products contain the highest levels of taurine. Based on new data it is recommended that cat foods contain 0.15 per cent taurine on a dry matter basis. ENERGY
The energy requirements of the average-sized (10-lb) adult cat is higher than that of the average-sized (30-lb) dog. It is generally assumed that 45 Cal/lb/day of ME is the maintenance energy requirement of the adult cat. As is also true in the dog, carbohydrate has not been shown to be an essential nutrient for maintenance of the adult cat, although sugars and starches are commonly used in the formulation of commercial cat food products. High fat content in rations (up to 60 per cent fat on a dry matter basis) has been found to increase palatability. The fat requirement of the cat is also somewhat unique in that the cat cannot convert linoleic acid to arachidonic acid, which is an EFA. Since vegetable fats contain no arachidonate, some animal-source fat is essential for the cat.
MINERALS
Mineral requirements of cats are similar to those of dogs. Little experimental evidence is available. VITAMINS
The cat cannot convert carotene to vitamin A; therefore, dietary vitamin A is essential. This is of no consequence when commercial rations are fed, since vitamin supplements are added by the manufacturer. Also, the cat cannot convert tryptophan to niacin, thus dietary niacin is essential. Niacin is also added as a supplement to most commercial rations.
WATER
The water requirements of cats are similar to those of dogs (20 to 30 ml/lb/day) under normal conditions. There is no experimental evidence to support the hypothesis that cats become relatively dehydrated when fed dry rations, as long as an adequate amount of clean water is available.
402
FRANCIS
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COMMERCIAL CAT FOODS The manufacturing procedures used in the pr;pQuction of cat foods are similar to those used in the dog food industry. However, there are many more gourmet (and, therefore, unbalanced) canned cat-food products on the market than dog food products. The veterinarian must advise the cat owner to be certain that a balanced ration is fed.
REFERENCES 1. Collins DR: The Collins Guide to Dog Nutrition. New York, Howell Book House, Inc,
1972 2. Nutrient Requirements of Cats. Washington, DC, National Academy of Sciences, 1986 3. Nutrient Requirements of Dogs, revised 1985. Washington, DC, National Academy of Sciences, 1985 New York State College of Veterinary Medicine Cornell University Ithaca, NY 14853
Clinical Nutrition
Evaluation and Use of Pet Foods: General Considerations in Using Pet Foods for Adult Maintenance
Francis A. Kallfelz, DVM, PhD*
Dogs and cats require the same basic nutrients as other nonherbivorous animal species, i.e., energy, protein (amino acids), minerals, vitamins, and water. Commercial pet foods are almost all "total mixed rations," designed to provide all needed nutrients in the correct proportions in a single feed. NUTRITIONAL REQUIREMENTS OF DOGS ENERGY
Most animals eat sufficient food to satisfy their caloric (energy) requirements. In the calculation of energy content of pet animal rations and of energy needs of dogs and cats, metabolizable energy (ME) values are frequently used. These are derived from approximations of metabolizable energy available from the ration for dogs and cats consuming average diets, assuming apparent digestibilities of 80 per cent for protein, 90 per cent for fat and 85 per cent for carbohydrate. Gross energy values are then corrected for the assumed digestibilities, including a urinary nitrogen energy loss for protein, to arrive at the approximations listed in Table 1. It can be seen that protein is an important energy source and that both protein and carbohydrate provide about 3.5 Cal of metabolizable energy per gram. Fats, both of animal and vegetable origin, provide about 2.25 times more energy per gram than is available from protein or carbohydrates. Fats are an important energy source for the working dog. Contrary to popular belief, working dogs do not need additional protein, but do need extra energy, which can be easily supplied by fat. Dietary fat is also a source of essential fatty acids (EFA). These substances are found mainly in unsaturated fats such as corn oil and • Diplomate, American College of Veterinary Nutrition; Professor, Veterinary Nutrition, New York State College of Veterinary Medicine; Chief, Clinical Nutrition, Veterinary Medical Teaching Hospital, Cornell University, Ithaca, New York
Veterinary Clinics ofNorthAmerica: Small Animal Practice-Vol. 19, No.3, May 1989
387
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Table 1. Caloric Content of Foods
Protein Carbohydrates Sugar Starches Fats Lard Tallow Vegetable fats (EFA)
TOTAL
AVAILABLE
5.65 4.15
3.5 Cal/gram 3.5 Cal/gram
9.40
8.5 Cal/gram
EFA = essential fatty acids
should constitute about 2 per cent of diet dry matter. Vegetable fat, however, does not contain arachidonic acid, which is an essential nutrient for the cat. The concerns about n-3 versus n-6 FA in humans are probably of little relevance to the nutrition of pet animals. It is generally assumed that the average-sized (30-lb) adult dog requires 30 Cal/lb per day of ME for maintenance. Smaller breeds require relatively more Cal/lb and larger breeds relatively less, e.g., 40 to 45 Calflb for a Chihuahua and 20 Cal/lb for an Irish wolfhound (Table 2). Commercial pet foods are formulated to ensure adequate intake of all required nutrients when the animal eats enough to satisfy caloric needs. The caloric content on a weight and volume basis does vary, however, among the various types of commercial foods (Tables 3 and 4). For example, assuming average values for the caloric content of a dry dog food, a 40-lb dog would be expected to consume 40 X 30 = 1200 Cal per day or 0.8lb/day (1200 Cal/1500 Cal/lb = 0.8 lb) of a dry dog food. 'On a dry matter basis, canned foods have a higher caloric density than dry or soft-moist foods. This is due to increased fat levels in these products. On an as fed basis, however, canned foods have the lowest caloric density, owing to their very high water content (75 per cent). On an as fed basis (i.e., by volume), soft-moist foods have the highest caloric density because they do not have air pockets in the food particles, as found in expanded dry foods, and have a much lower water content (33 per cent) than that found in canned products. Also, soft-moist foods may have a somewhat higher digestibility than do some other types. Thus, the Table 2. Estimated Maintenance Caloric (ME) Requirements of Dogs, Based on Size WEIGHT (LB)
CAL/LB/DAY
10 15 30 50 110
42 38 30 27 22
ME = metabolizable energy
389
EvALUATION AND UsE oF PET FooDs
Table 3. Average ME Content of Dog Foods by Weight
Dry Soft-moist Canned
AS IS
DM
(CAL/LB)
(CAL/LB)
PER CENT H20
1500± 1300 ± 550±
1650± 1750± 1900±
10 33 75
ME = metabolizable energy; DM = dry matter basis
volume of soft-moist food required to meet daily maintenance requirements is only about half that required if dry or canned foods are being fed (see Table 4). The utilizable energy content of a commercial pet food on an as is basis can be calculated as shown in Table 5. This data can also be used to determine the approximate amount of a pet food that should be fed per day to a dog 9f a given weight. PROTEIN
Although almost everyone refers to animals (dogs or cats) as having a protein requirement, the actual requirement is for amino acids. About 20 different amino acids occur in proteins; however, of these only about 10 have been found to be essential dietary ingredients for the dog and cat; the remainder can be produced in the body from other substances. The protein quality of a pet food depends upon the levels of the various essential amino acids present in the protein sources used in its formulation, the total protein level in the product, and the caloric content. If overall caloric content is low, dietary protein will be used as an energy source. Many animal source proteins have high levels of all essential amino acids. Whereas individual vegetable source proteins may be deficient in one or more essential amino acids, combinations of vegetable protein sources can be used, which provide adequate levels of all essential amino acids. The actual protein level required in a dog food is dependent upon the total amount of the protein needed to supply adequate levels of all the essential amino acids; it also depends on the level of other energy sources. An experimental measurement called the biological value (BV) Table 4. Average ME Content of Dog Foods by Volume WT (LB)/CUP (8-oz VOL)
Dry Soft-moist Canned
0.2 0.35 0.5
ME = metabolizable energy
CAL/CUP
(8-oz VOL)
285 455
275
CUPS/DAY (30-LB DOG)
3t 2 3t
390
FRANCIS
A.
KALLFELZ
Table 5. Calculation of Caloric Content (Canned Product) GUARANTEED ANALYSIS
Crude protein Crude fat Crude fiber Ash Moisture
10% X 3.5 = 35 Cal/100 g 4% X 8.5 = 34 Cal/100 g 1.5% 4% 72% 91.5%
100-91.5 = NFE = 8.5% X 3.5 = -30 -Cal_/'-1-0 -0 .: :cg . 99 99 X 4.54 = 450 Calflb as fed
NFE = nitrogen-free extract = carbohydrate
can be used to determine the protein quality and thus the amount needed. The BV really depends on the level of the least prevalent essential amino acid in the food, assuming energy sources are adequate. Rough approximations of the protein requirements for maintenance of adult dogs and recommended levels of protein in the ration are given in Table 6. The BV of proteins in pet foods varies according to the source of the protein and on other factors, as previously mentioned. The biological values of some commonly used protein sources are shown in Table 7. In general, the higher the BV, the lower the actual protein requirement. The BV of animal source proteins is generally higher than that of vegetable source products. This leads to a marketing curiosity in that animalbased pet foods are much higher in protein' than vegetable-based products, even though the protein value in the canned foods is higher. Table 6. Protein Requirements for Dogs 4.8±* 22*
g/kg body weight per cent of ration (DM)
• Depends on the biological value (BV) of protein used and the protein-calorie ratio DM =dry matter basis
Table 7. Biological Value (BV) of Proteins PROTEIN
BV
Egg Milk Beef Fish Soy Rice Oats Yeast Wheat Corn
100 90 84
75 75 72 66 63 60 54
391
EvALUATION AND UsE OF PET FooDs
Table 8. Mineral Requirements of Dogs % OF FEED
MINERAL
Ca p Salt Potassium Trace minerals
(oM)
1.1 0.9 1.1 Generally adequate
MG/KG OF BODY WTjDAY
242
198 242 (may be less)
DM = dry matter basis
With regard to the protein/calorie ratio, as the percentage of calories from protein in a ration rises, the NPU (utilization of ingested protein) decreases, and as the nonprotein caloric intake increases, the NPU rises and then plateaus. While definitive data are unavailable, probably the NPU is optimal when the protein/calorie ratio is in the range of20 to 30 per cent (i.e., about 20 to 30 per cent of the calories in the food are from protein). For practical applications all commercial pet foods designed for general use contain far more protein than is needed (see Kallfelz, pp 433- 446). Thus, as long as a dog is eating a sufficient quantity of food to satisfy his caloric requirement, protein intake will undoubtedly be adequate. MINERALS
The currently accepted estimates of minimum major mineral requirements for maintenance of the adult dog are given in Table 8. It is probable that the levels recommended are higher than necessary, and revisions may be made as new information becomes available. The basic ration type may also alter dietary mineral requirements. For example the availability of a given calcium source from a ration containing mainly meat-source ingredients is probably higher than that from a ration containing mostly vegetable-source ingredients. Trace mineral levels are rarely a matter of concern. VITAMINS
The stated minimum fat-soluble vitamin requirements for maintenance of the adult dog are shown in Table 9. Vitamin A is necessary for Table 9,
Vitamin A VitaminD VitaminE VitaminK DM = dry matter basis
Vitamin Requiremepts of Dogs
PER KG DIET (oM)
PER KG OF BODY WT/DAY
5000 IU 500IU 50IU
110IU 11IU 1.1 IU
392
FRANCIS
A.
KALLFELZ
normal function of connective tissue (cartilage, etc.) and epithelial tissue (skin, mouth, and intestinal lining, etc.), and, of cour!!e, for proper vision. Vitamin D is required for normal development of bones and controls other aspects of mineral handling by the body. Vitamin K is needed for normal blood clotting and is also involved in other functions. No requirement is listed for vitamin K, since it is manufactured by intestinal microorganisms. The requirement for water-soluble vitamins varies according to energy intake. Dogs and cats manufacture vitamin C in the liver and hence have no dietary requirement. It is possible, though probably very rare, that under certain conditions, a functional deficiency of vitamin C could occur and supplementation might be indicated. Water-soluble vitamins are needed for normal energy metabolism and for other functions. Requirements for water-soluble vitamins are rarely of concern, since virtually all pet foods contain added amounts of these nutrients. WATER
It is generally assumed that dogs require approximately 40 to 60 ml/kg/day (20 to 30 mljlb) under normal conditions. Water demands can be met by drinking, preformed water (in food), and with metabolic water (produced in the body) from metabolism of protein, carbohydrate, and fat.
COMMERCIAL DOG FOODS Commercial dog foods are available in three basic forms: dry, softmoist, and canned, as shown (Table 10). Since all of the nutrients are present in the dry matter of the product, canned foods represent a considerable expense, since on an as fed basis they are frequently the most expensive and consist of more than 70 per cent water. DRY FooDs Dry foods are available as: 1. Expanded products (almost all); e.g., Purina, Carnation, Science Diet 2. Kibbles (very few); e.g., Ken'L Ration Biscuit, Triumph
Table 10. Commercial Dog Foods TYPE
MOISTURE
DRY MATTER
Dry Soft-moist Canned
10% 33% 74%
90% 67% 26%
393
EvALUATION AND UsE oF PET Fooos
Table II. Example of a Formula for an Expanded Product INGREDIENT
%
Ground corn Soybean meal Meat and bone meal Ground wheat Animal fat (preserved with BHA) Ground oats Ground grain sorghum Wheat mids Wheat germ Salt (iodized) Dried whey Vitamin mix (specified) Trace minerals (specified)
30.0 15.0 14.0 10.0 7.0 6.0 6.0 5.0 3.0 1.0 1.0 0.5 0.5
Reprinted from The Collins Guide to Dog Nutrition by Donald R. Collins, DVM. Copyright © 197 2 by Donald R. Collins, with special permission of the publisher, Howell Book House. ·
3. Meals or pelleted meals (almost none). Gaines Meal is, in fact, an expanded product. An example of a formula for a commercial expanded dry type product is shown (Table 11), and the caloric composition is demonstrated (Table 12). Dry type dog foods generally have the highest levels of vegetable-source proteins, are relatively low in fat, and have the lowest caloric density on a dry-matter basis. Many of these are maintenance products and, as such, may be bulk limited when used to feed stressed dogs. There are several, however, that meet the needs of growth as well as maintenance, and a few are designed for working dogs. These products, of course, contain additional fat. Dry type dog foods · represent about 50 per cent of pet foods produced. SoFT-MOisT PRoDucTs
Soft-moist or semi-moist dog foods are very similar to dry foods in nutrient content. The carbohydrate content of these products, however, Table I2. Caloric Content of Dry Dog Foods CALORIES INGREDIENT
(%AS IS)
(%DRY)
Protein Fat Fiber Ash Moisture NFE (carbohydrate)
25.0 8.0 4.0 6.5 10.0 46.5
27.8 8.9 4.4 7.2
454 327
27.9 20.1
51.7
844 1625
52.0
NFE = nitrogen-free extract
(PER LB)
(%)
394
FRANCIS
A. KALLFELZ
Table 13. Typical Formula for Soft-Moist Dog or Cat Food INGREDIENT
31.0 28.0 21.0 3.0 3.0 3.0 3.0 2.0 1.5 1.0 0.5 0.5 1.5
Soy Hour Meat by-products Sucrose Wheat bran Dical Meat Dried milk Tallow Propylene glycol Salt (iodized) Vitamin mix Trace mineral mix Other
Reprinted from The Collins Guide to Dog Nutrition by Donald R. Collins, DVM. Copyright © 1972 by Donald R. Collins, with special permission of the publisher, Howell Book House.
is largely in the form of disaccharides such as sucrose, and they have lower levels of less soluble carbohydrates such as starches as compared with dry products. Protein in these products generally consists of more animal-source ingredients than is found in dry foods. They have a somewhat higher energy density on a dry-matter basis than do dry products. Also, stool production of animals fed soft-moist products is generally much less than that of animals fed dry rations but urine production is greater. The physical form of these products varies, to include patties, chunks, and so forth. This is a marketing gimmick and does not affect nutrient content. Almost all are balanced rations. The market percentage of these products is decreasing, currently representing only about 12.5 per cent of total pet food production. An example of a formula for a soft-moist product and the caloric content are shown in Tables 13 and 14. CANNED PRODUCTS
There is more variability in the formulation of canned products than in dry or soft-moist types. They may be balanced or not, depending on Table 14. Caloric Content of Soft-Moist Dog Foods CALORIES INGREDIENT
Protein Fat Fiber Ash Moisture NFE
%AS IS
%DRY
18.0 7.0 3.0 7.5 33.0 31.5
26.8 10.4 4.5 11.2
327 286
27.6 25.1
47.0
572 1185
48.3
NFE = nitrogen-free extract
(PER LB)
(%)
395
EvALUATION AND UsE oF PET FooDs
Table 15. Example ofa Fonnula for a Meat Type Canned Dog Food INGREDIENT
%
Meat by-products Meat Liver Steamed bone meal L~d
SBOM Corn Hour Beefblood Humectants Mineral and vitamin mix
35 20 15 7 6 5 4.5 4.0 2.0 1.5
SBOM = soy bean oil meal Reprinted from The Collins Guide to Dog Nutrition by Donald R. Collins, DVM. Copyright© 1972 by Donald R. Collins, with special permission of the publisher, Howell Book House.
the formula. The types available are balanced (mainly meat), balanced (other), and gourmet (mainly meat). Good quality balanced canned rations are higher in animal-source proteins and in fat but lower in carbohydrate content than dry or soft-moist products; they have the highest caloric density of all commercial products on a dry-matter basis. A typical formula of a meat-type canned dog food and the caloric composition are shown in Tables 15 and 16.
LABEL INFORMATION The label of any commercial pet food product has a Guaranteed Analysis statement and a list of ingredients (Table 17). The guaranteed analysis is taken from a proximate analysis of the product. The ingredients should be listed in terms of decreasing fractional content in the product. Be aware, however, that this is on an as is, not a dry matter, basis. Additionally, since the first of January, 1984, the label of all dog foods in interstate commerce are required to have a "statement and a validation of nutritional adequacy." Dog foods can be proven to be "complete and balanced" by one of two mechanisms: Table 16. Caloric Content of Canned Dog Foods INGREDIENT
Protein Fat Fiber Ash Moisture NFE
%AS IS
%DRY
PER LB
%
10.5 6.0 1.5 4.0 74.0 4.0
40.4 23.1 5.7 15.3
192 245
37.6 48.0
15.4
73 510
14.4
NFE = nitrogen-free extract
396
FRANCIS
A.
KALLFELZ
Table 17. Guaranteed Analysis (Dry-Type Product) Crude protein Crude fat Crude fiber Moisture Ash
Minimum 2LO% Minimum 10.0% Maximum 4.0% Maximum 10.0% Maximum 8 .0%
Ingredients: Ground corn, meat by-product meal, soy grits, animal fat (preserved with BHA), wheat bran, brewers yeast, iodized salt, calcium carbonate, iron sulfate, zinc oxide, manganous oxide, copper oxide, cobalt carbonate, choline chloride, vitamin A palmitate, D-activated animal sterol, a-tocopherol, niacin, calcium pantothenate, riboflavin, thiamine, pyridoxine hydrocholoride, folic acid, biotin, vitamin B12 supplement
1. The manufacturer can prove by analysis that the product contains the minimum required levels ofall essential nutrients, as specified by the National Research Council (NRC) for maintenance, growth, and so forth. In this case a statement similar to that in italics will appear on the label. 2. The manufacturer can show by feeding trials (as specified by AAFCO) that the product supports maintenance, growth, and so forth, of dogs. In this case, a statement that the product has been shown by experiment to meet requirements for maintenance, and so on, will appear on the label. If the manufacturer has not evaluated the product as in (1) or (2), then a statement must appear that the product is "not intended for sole use." An exception to this is "dietary animal foods," which must have a statement that the product should be used only if recommended and supervised by a veterinarian. Thus, by reading the label, one can get useful information regarding the product (Table 18). However, the label may not specify all the information a user might want to know (Table 19). Frequently, the manufacturer will provide feeding guidelines for a product (how much to feed based on the weight of a dog) . In many cases a calculation of caloric content will show that the recommendations exceed the average caloric requirements for a dog of a specified weight. The owner is well advised to determine for himself the correct amount to feed. You should recommend that this be done on a weight, not a volume, basis. SUPPLEMENTATION Many dog owners supplement their animal's daily ration even though they are feeding adequate quantities of a complete and balanced Table 18. Information Available from Label Is product complete and balanced? Approximate caloric content Level of protein and fat Does the product C_?ntain meat (and, roug~ly, how much)?
EvALUATION AND
UsE OF PET Fooos
397
Table 19. Information Not Available from Label Overall digestibility Biological value (protein) Quality Contamination
ration. This is done for several reasons and can be accomplishecl in several ways (Tables 20 and 21). In most cases supplementation is tmnecessary and should be discouraged (see Kallfelz, pp 433-446). If a client insists on supplementing, a good recommendation is to supplement a balanced ration with a balanced ration (e.g., balanced fanned ration added to a balanced dry ration). In general, adding no more than 10 per cent by weight of almost any reasonable supplement to a balanced basic ration is acceptable, since a safety factor is used in formulation of commercial rations. SPECIFIC AS CoMPARED WITH GENERAL-PURPosE PRoDucTs
Many commercial products are complete and balanced for all phases of the life cycle (Table 22). Some products, however, are recommended for specific stages of the life cycle (growth, adult maintenance, older dogs, etc.). Conceptually, these specially designed products are preferable; however, the differences in formulation among these products are in most cases small and, in some, the basis for the formulation can be questioned, e .g., diets for older dogs generally contain reduced levels of protein, yet there is no evidence to suggest that "normal" older dogs cannot tolerate normal levels of protein.
PREMIUM PET FOODS Relatively recent additions to the pet food market are the "premium pet foods" represented by such lines as Purina Pro Plan, lams Eukanuba, Table 20. Rationale for Supplementation Lack of confidence in basic ration Increase palatability Meet individual requirements Provide extra nutrients during stress
Table 21. Methods of Supplementation Tablets, capsules, etc. (minerals and vitamins) Mixing foods (dry and canned) Meat (extra protein) Fat (for better skin and hair coat; extra energy) Table scraps Other (e.g., dried milk)
398
FRANCIS
Table 22.
A.
KALLFELZ
General-Purpose Products
Advantages Convenient Good results in average dog Owner confidence Disadvantages . Multipurpose product Designed for growth May overfeed maintenance animal if fed ad lib May be bulk-limited for working dog, etc.
ANF, Science Diet, and so forth . These products are generally composed of high-quality, meat-source ingredients, have a high digestibility, and generally contain more fat than standard manufactured dry pet foods. They are sold exclusively through non-grocery outlets such as pet supply stores and animal hospitals. Currently, sales of these products are increasing at a rate of about 15 per cent per year, even though they are more expensive than standard pet foods. For most adult maintenance situations, it is unnecessary to use such products, although their use is certainly acceptable. If a client prefers such a product, calculate the caloric need and recommend an amount to be fed daily. These products do tend to be very palatable, thus the probability for excessive weight gain may be increased if they are fed free choice. Because of their relatively high fat content, they have a good caloric density and can be recommended during periods of physiological stress. In some cases, the improved digestibility and utilizability of such products results in decreased required feeding amounts, which could offset the price premium. GENERIC PET FOODS The other new addition to the line of pet food products is that of the generic pet foods; these are at the opposite end of the spectrum from the premium products. Virtually all are guaranteed to be complete and balanced for maintenance, but this is validated in almost all cases only by chemical analysis, not by animal-feeding experiments. A few papers have reported that generic foods are inferior to standard products in terms of animal growth rates, nutrient content, apd so forth. Excessive nutrient content and rapid growth rates of dogs fed a given product should not necessarily be considered desirable characteristics of a good pet food. The biggest problem with the generic products is palatability. Since they tend to be low in fat and animal-source protein, they are not well accepted by many pups. The cost of additives needed to improve palatability could well outweigh the initial economic advantage of purchasing a generic type pet food. THE BEST COMMERCIAL DOG FOOD Frequently veterinarians are asked for a recommendation as to what hP.st dol! food. There is no valid answer to this question. There are
i-: th P
EvALUATION AND UsE OF PET Fooos
399
many good commercial dog foods, and the choice of which to use depends on many factors, including age of dog, size of dog, number of dogs, management conditions, (constant versus restricted food availability, etc.), economic factors, and so forth. A veterinarian should be able to make recommendations to individual owners about adequate products available in his or her practice area, based on the above factors. "NATURAL" DOG FOODS In the last few years, several so-called natural dog foods have appeared on the market; they supposedly contain no artificial ingredients. A basic difference between these and the usual products is that many of the "natural" products do not contain a fat preservative (BHA or BHT). The shelf life of these products is therefore theoretically reduced, since the fat will become rancid in a shorter time period than in products with fat preservatiyes. These products also often contain special ingredients such as herbs, etc. While proponents of such products claim these "natural" additives are valuable, there is little objective scientific evidence to support a recommendation for their use. In some cases, the special ingredients may have pharmacological action or may be toxic, which could result in adverse side effects. HOME-FORMULATED DOG FOODS As previously mentioned, there are many excellent commercial products available. Even so, for whatever reasons, some owners insist upon the use of home-formulated rations. It is difficult, but possible, to formulate a balanced ration for the dog, using ingredients available in the home. Two publications are extremely valuable in this regard: Nutrient Requirements ofDogs, available from the National Research Council, and Nutritive Value of American Foods, available from USDA. The first is needed to ascertain the nutrient requirements of dogs and the second to provide information on the nutrient content of human foodstuffs. A chart (Table 23) is very handy to use in formulating a ration and should include, at least, estimates of protein, fat, calories, calcium, phosphorus, salt, vitamin A, and thiamine. The assumption is that if intakes of these nutrients are adequate, it is probable that other essential ingredients are also present in adequate amounts. Protein sources should be chosen to supply the protein requirement; then other ingredients should be added to supply additional calories and other essential nutrients. NUTRITIONAL REQUIREMENTS OF CATS (SPECIFIC CONSIDERATIONS) In a general sense, the nutrient requirements of cats are similar to those of dogs. A few differences do exist, as follows:
Table 23. INGREDIENT
Chart for Home-Formulated Ration Calculation* p
AMOUNT FED
DM
PROTEIN
FAT
ENERGY
(g)
(g)
(Cal)
(g)
NaCl (g)
VITAMIN A
(g)
Ca (g)
THIAMINE
(oz)t
(mg)
(IU)
0.011
0.2I7
O.I58
0.09
I9 566
Cooked lean ground beef
3t
40
27.3
I0.7
208
Dry powdered milk
It
50
I3.2
I3.8
25I
0.455
0,354
0.505
O.I4
Cooked rice
It
I3.7
54
0 .005
O.OI5
0.467
O.ol
0.586
1.13
0.24
I Turns tablet Total
1.2
0.500
2 6.3.
•
I05.7
41.7
24.5
Formula: t Cooked lean ground beef t Dry powdered milk t Cooked rice 2 Turns tablets I
5I3
0.971
585
DM=51.8% Protein = 39.5% DM Calories= 115Iflb, as is Fat=23% DM Ca=0.92%DM P=0.56%DM
• Sample calculation for an adult maintenance ration. Feed I oz per 2.5lb body weight/day.
f By weight DM = dry matter basis Adapted from Nutrient Requirements of Domestic Animals: Nutrient Requirements of Dogs. Printing and Publishing Office, National Academy of Sciences, 2IOI Constitution Ave., N.W., Washington, DC 20418; and Nutrient Value of American Foods. Agricultural Handbook No. 456, Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402
401
EvALUATION AND UsE OF PET FooDs
PROTEIN
The protein requirement of the cat is higher than that of the dog. It is recommended that protein levels in adult-maintenance cat foods be at least 30 per cent on a dry matter basis. Also, since palatability appears to be of more importance in affecting food intake in cats, cat foods generally contain more meat-source proteins. The cat also has a unique requirement for taurine, a sulfonic acid amine, frequently lacking in protein sources commonly used in dog foods (see Hayes, pp 403-413). Seafood products contain the highest levels of taurine. Based on new data it is recommended that cat foods contain 0.15 per cent taurine on a dry matter basis. ENERGY
The energy requirements of the average-sized (10-lb) adult cat is higher than that of the average-sized (30-lb) dog. It is generally assumed that 45 Cal/lb/day of ME is the maintenance energy requirement of the adult cat. As is also true in the dog, carbohydrate has not been shown to be an essential nutrient for maintenance of the adult cat, although sugars and starches are commonly used in the formulation of commercial cat food products. High fat content in rations (up to 60 per cent fat on a dry matter basis) has been found to increase palatability. The fat requirement of the cat is also somewhat unique in that the cat cannot convert linoleic acid to arachidonic acid, which is an EFA. Since vegetable fats contain no arachidonate, some animal-source fat is essential for the cat.
MINERALS
Mineral requirements of cats are similar to those of dogs. Little experimental evidence is available. VITAMINS
The cat cannot convert carotene to vitamin A; therefore, dietary vitamin A is essential. This is of no consequence when commercial rations are fed, since vitamin supplements are added by the manufacturer. Also, the cat cannot convert tryptophan to niacin, thus dietary niacin is essential. Niacin is also added as a supplement to most commercial rations.
WATER
The water requirements of cats are similar to those of dogs (20 to 30 ml/lb/day) under normal conditions. There is no experimental evidence to support the hypothesis that cats become relatively dehydrated when fed dry rations, as long as an adequate amount of clean water is available.
402
FRANCIS
A.
KALLFELZ '
COMMERCIAL CAT FOODS The manufacturing procedures used in the pr;pQuction of cat foods are similar to those used in the dog food industry. However, there are many more gourmet (and, therefore, unbalanced) canned cat-food products on the market than dog food products. The veterinarian must advise the cat owner to be certain that a balanced ration is fed.
REFERENCES 1. Collins DR: The Collins Guide to Dog Nutrition. New York, Howell Book House, Inc,
1972 2. Nutrient Requirements of Cats. Washington, DC, National Academy of Sciences, 1986 3. Nutrient Requirements of Dogs, revised 1985. Washington, DC, National Academy of Sciences, 1985 New York State College of Veterinary Medicine Cornell University Ithaca, NY 14853