Chapter 17. Types of Pet Foods
DRY PET FOODS
Dry pet foods contain between 6% and 10% moisture and 90% or more dry matter (DM). This category of pet foods includes baked kibbles, biscuits, meals, and expanded (extruded) products. Baked kibbles and biscuits are prepared in a similar manner, although the shape of the end product differs. In each case, all of the ingredients are mixed into a homogeneous dough, which is then baked. When biscuits are made, the dough is formed or cut into the desired shapes and the individual biscuits are baked much like cookies or crackers. When baked kibble is produced, the dough is spread onto large sheets and baked. After cooling, the large sheets are broken into bite-size pieces and packaged. Many dog and cat treats are baked biscuits, and a limited number of companies still produce complete and balanced baked kibble. Dry meals, the major type of dry pet food sold before 1960, are prepared by mixing together a number of dried, flaked, or granular ingredients. This type of product has almost completely disappeared from the commercial market.
The development of the extrusion process during the 1960s resulted in the almost complete replacement of meals and baked kibble with expanded pet foods. Today, expanded products represent the most common type of dry pet food produced and sold in the United States. The extrusion procedure involves mixing all of the ingredients together to form dough, which is then cooked under conditions of high pressure and temperature (80° to 200° C). 1 The machine that is used to cook and shape expanded foods is called an extruder. The dough moves very quickly through the extruder and is further mixed as it proceeds. The high cooking temperature, movement of the dough, and rising pressure causes cooking to occur very rapidly (within 10 to 270 seconds). When the cooked dough reaches the end of the extruder, it exits through a die (small opening). The die forces the soft product into the desired shape, and a rotating knife cuts the forms into the desired kibble size. Extrusion causes rapid cooking of the starches within the dough, resulting in increased digestibility and palatability. After cooling, a coating of fat or other palatability enhancer is usually sprayed on the expanded kibbles (a process called “enrobing”). Hot-air drying reduces the total moisture content of the product to 10% or less.
A certain level of starch must be included in expanded products to allow proper processing of the product. Similarly, baked biscuits often contain wheat as an ingredient because the starch and gluten of wheat contribute to the appealing texture and flavor of biscuits. The cooking process of both extruded and baked dry foods improves the digestibility of the complex carbohydrates in the product and enhances the food’s palatability. Heat treatment and storage can result in minor losses of some vitamins, so compensatory amounts of these nutrients are included by manufacturers when the diet is formulated. The heat used in the extrusion process also sterilizes the product, and the low amount of moisture that is present in dry foods aids in the prevention of growth of bacteria or fungus.
Ingredients commonly used in dry pet foods include a variety of cereal grains, meat, poultry or fish products, some milk products, vegetable fats/oils, and vitamin and mineral supplements (see Chapter 16 for a complete discussion). The caloric density of dry pet foods typically ranges between 3000 and 4500 kilocalories (kcal) of metabolizable energy (ME)/kilogram (kg), or between 1300 and 2000 kcal/pound (lb) on a dry-matter basis (DMB). Dry cat foods are often slightly higher in energy density than dog foods. The energy density of dry pet foods is somewhat limited by the processing and packaging methods used. However, most dry pet foods can easily meet the energy needs of the majority of companion animals. Products that are formulated for adult maintenance will only be bulk limited if fed to hard-working dogs or puppies that have very high energy requirements. In these cases, foods have been developed to meet the specific energy requirements of working dogs and growing puppies. Depending on the purpose of the food, the DM content of dry dog foods ranges between 8% and 22% fat and 18% and 32% protein (Table 17-1). Cat foods of all types contain slightly higher levels of protein than dog foods.
| AF, As-fed; DM, dry matter; ME, metabolizable energy. | ||
| AF basis | DM basis | |
|---|---|---|
| Dry | ||
| Moisture (%) | 6-10 | 0 |
| Fat (%) | 7-20 | 8-22 |
| Protein (%) | 16-30 | 18-32 |
| Carbohydrate (%) | 41-70 | 46-74 |
| ME (kcal/kg) | 2800-4050 | 3000-4500 |
| Semimoist | ||
| Moisture (%) | 15-30 | 0 |
| Fat (%) | 7-10 | 8-14 |
| Protein (%) | 17-20 | 20-28 |
| Carbohydrate (%) | 40-60 | 58-72 |
| ME (kcal/kg) | 2550-2800 | 3000-4000 |
| Wet | ||
| Moisture (%) | 75 | 0 |
| Fat (%) | 5-8 | 20-32 |
| Protein (%) | 7-13 | 28-50 |
| Carbohydrate (%) | 4-13 | 18-57 |
| ME (kcal/kg) | 875-1250 | 3500-5000 |
Dry dog foods are very convenient for owners and continue to be the most common type of pet food bought by pet owners in the United States. 2 In general, these products are more economical to feed than wet or semimoist foods, and they store well because of their low moisture content. Large quantities of dry food can be purchased at one time, and dry products have a reasonably long shelf-life when stored under proper conditions. Many pet owners prefer feeding dry foods because they can leave a bowl of food available to their pet for a period of time without worrying about spoilage. In some cases, dogs and cats can be fed free-choice with a dry food and not overconsume. However, the high fat content and palatability of some of the foods marketed today coupled with the sedentary lifestyle of many pets preclude free-choice feeding for many dogs and cats. Dry pet food may also offer some dental hygiene advantages. The chewing and grinding that accompanies eating dry biscuits or pet food may aid in the prevention of plaque and calculus accumulation on teeth (see Chapter 34, pp. 442-445 for a complete discussion). 3
Dry dog foods are the most popular type of pet food purchased by consumers in the United States. Dry foods are economical and easy to store and feed, and they may be beneficial to dental hygiene. High-quality dry foods have high nutrient densities and digestibilities, meaning that less food can be fed, more nutrients will be absorbed and used, and stool volume will decrease.
A potential disadvantage of dry pet foods, when compared with semimoist or wet foods, is that dry foods may be less palatable to some dogs and cats. This disadvantage is especially true of foods that are low in fat or that contain poorly digestible or low-quality ingredients. However, dry pet foods that contain high-quality ingredients and moderate to high levels of fat do not demonstrate reduced acceptance in dogs and cats and are highly palatable to most companion animals. Because ingredients that are primarily low in moisture are used to formulate dry pet foods, harsh or improper processing of the ingredients can cause a reduction in nutrient availability and the loss of nutrients. As a result, poor-quality dry foods may have very low digestibilities and nutrient availabilities. Companies that manufacture high-quality, premium and super-premium foods only use properly treated ingredients and manufacturing methods to ensure that the digestibilities of their products remain high after processing.
WET PET FOODS
There are two primary types of wet pet foods—those that provide complete and balanced nutrition and those that provide a dietary supplement or treat in the form of a canned/pouched meat or meat byproduct. Complete and balanced wet foods may contain blends of ingredients such as muscle meats, poultry or fish meats or byproducts, cereal grains, texturized vegetable protein (TVP), and vitamins and minerals. Some of these products contain only one or two types of muscle meat or animal byproducts, with enough supplemental vitamins and minerals to make the product nutritionally complete. The second type of wet food, often referred to as “meat products,” consists of the same types of meat listed earlier but without supplemental vitamins and minerals. These foods are not formulated to be nutritionally complete and are intended to be used only as a supplement to an already complete and balanced diet. For example, some pet owners add a small amount of wet food to their pet’s complete and balanced dry food every day. The high fat content of the wet supplement enhances the texture and palatability of the pet’s diet. Although many complete and balanced dry foods are also highly palatable and provide a balanced diet, some pet owners believe that a dry diet alone becomes boring or bland to their pet. Adding a spoonful or two of a product that looks like meat or stew makes many owners feel they are making the meal more enjoyable for their pet.
From a processing standpoint, there are three general types of wet foods—loaf, chunks or chunks in gravy, and a chunk-in-loaf combination. Wet pet foods are prepared by first blending the meat and fat ingredients with measured amounts of water. Measured amounts of dry ingredients are then added and the entire mixture is heated. Canning occurs on a conveyor line. Most pet foods are typically sold in either 3-, 5.5-, or 13.2-ounce (oz) cans. After filling, the cans are then sealed with a double seam, washed, and labeled with a manufacturer code and date. Pressure sterilization of canned products is called retorting. Temperatures and times for retorting vary with the product and can size, but typically cans are held at around 250° C for 60 minutes. The high heat and pressure involved in processing canned foods kills harmful bacteria and causes some nutrient losses. Manufacturers of high-quality products conduct the research necessary to determine the extent of these losses and then adjust their formulations to compensate for them. After exiting the retort, the cans are cooled under controlled conditions to ensure the sterility of the product and the integrity of the sealed cans. To designate the product, paper labels are then applied during the final step of production. Wet foods are also sold in pouches and trays. These containers are more delicate and so retorting procedures are adjusted to prevent damage to package structures and seals. Generally, the cooking pressure is lower and more tightly controlled to ensure that rupture or shrinkage of the packaging does not occur.
In general, wet foods are more palatable and digestible than many dry pet foods, and they contain a higher DM proportion of protein and fat (see Table 17-1). 4 When measured on a DMB, the caloric content of wet pet foods generally ranges between 3500 and 5000 kcal/kg or about 1600 and 2300 kcal/lb. The fat content of wet pet foods ranges between 20% and 32%, and protein levels are usually between 28% and 50%. Most wet products contain a relatively small proportion of digestible carbohydrate when compared with that in other types of pet foods (see Table 17-1). Wet foods are also more expensive than dry pet foods. Although expense is often not a concern for owners of cats or small dogs, it can become significant when feeding large dogs or multiple pets. Nutrient and price comparisons between wet and dry pet foods should always be made on either a DMB or a caloric-density basis because wet foods contain a very large proportion of water (see Chapter 15, p. 132). In the United States the moisture content of pet foods can be as high as 78%, or equal to the natural moisture content of the ingredients used, whichever is greater. 5 On average, wet pet foods contain about 75% water; this amount can be compared with dry pet foods, which contain approximately 6% to 10% moisture.
Some advantages of wet pet foods include their long shelf-life and high acceptability. The sterilization and sealing of the cans and pouches allows these products to be kept for long periods before opening, without the need for special storage considerations. Because of their nutrient content and texture, wet foods tend to be highly palatable to dogs and cats. However, this can be a disadvantage for some companion animals. Dogs and cats that have moderate to low energy requirements may be predisposed to the development of obesity when fed exclusively wet pet foods. If fed free-choice, the high palatability of these products can override an animal’s inherent tendency to eat to meet its caloric requirements, resulting in the overconsumption of energy. Conversely, dogs and cats that have increased energy needs or reduced interest in food because of illness may benefit from the high palatability and energy density of wet food. Feeding a wet diet is also an approach to ensuring adequate water intake in cats that are at high risk of developing lower urinary tract disease (see Chapter 30, pp. 365-366).
Gourmet-type wet cat foods are especially popular with cat owners. These products may or may not be nutritionally complete, and they contain primarily animal tissues such as fish, shrimp, tuna, or liver. These foods are often sold in small, one- or two-serving cans and appeal to owners’ desires to give their cat “something special.” There may some degree of risk in the exclusive feeding of these products to some cats. More so than dogs, which have an evolutionary history of scavenging and consuming a wide variety of food types, cats appear to be more susceptible to the development of neophobia, the rejection of foods that have not been previously encountered. This is more likely to develop if a cat is fed a diet of a certain type or that contains a single type of ingredient starting early in life and continuing for a long period of time. 6. and 7. Some cats eventually accept only this one food item and will refuse to eat any other type or flavor of food. This can be a problem if the food is not complete and balanced, or if the cat experiences a health condition that warrants a change in diet. Therefore, if wet foods are used with cats, it is advisable to feed complete and balanced rations that contain more than one principal ingredient and to occasionally offer different flavors of food. The gourmet products can be used as supplemental feeding, but they should not make up the entire diet.
Tip: There are two primary types of wet pet foods—those that provide complete and balanced nutrition and those that do not. Complete and balanced wet foods contain vitamins and minerals in addition to muscle meats, poultry, meat, or fish byproducts, cereal grains, and/or texturized vegetable protein. Foods that are not complete and balanced do not contain all the necessary vitamins and minerals and should be considered as a dietary supplement only.
SEMIMOIST PET FOODS
Semimoist pet foods contain 15% to 30% water and include fresh or frozen animal tissues, cereal grains, fats, and simple sugars as their principal ingredients. These products are softer in texture than dry pet foods, which contributes to their acceptability and palatability for some animals. Several methods of preservation are used to prevent contamination and spoilage of semimoist foods and permit an extended shelf-life. The inclusion of humectants such as salt, simple sugars, glycerol, or corn syrup reduces the water activity of the food, which prevents the growth of contaminating organisms. 8 Further protection is provided by preservatives such as potassium sorbate, which prevents the growth of yeasts and molds. Small amounts of organic acids may also be included to decrease the pH of products and inhibit bacterial growth.
The high simple sugar content of many semimoist dog foods and treats contributes to the palatability and digestibility of these products. Although dogs have been shown to enjoy the taste of simple sugars, cats are less likely to select sweet foods. 9.10. and 11. Semimoist pet foods that contain a high proportion of simple carbohydrates have digestibility coefficients that are similar to those of wet foods. However, because of their lower fat content, the caloric density of semimoist foods is usually less. The ME content of semimoist foods typically ranges between 3000 and 4000 kcal/kg on a DMB, or about 1400 to 1800 kcal/lb. Semimoist foods contain between 20% and 28% protein and between 8% and 14% fat on a DMB. The proportion of carbohydrate in semimoist foods is similar to that of dry foods (see Table 17-1). However, an important difference is that the carbohydrate in semimoist pet foods is largely in the form of simple carbohydrates, with a relatively small proportion present as starch.
Semimoist pet foods appeal to some pet owners because they generally are less odorous than wet foods, and many come in convenient single-serving packages. These foods are also available in a large variety of shapes and textures that often resemble different types of meat products, such as ground beef, meat patties, or chunks of beef. Although these different forms do not necessarily reflect nutrient content or palatability for the pet, they do appeal to the tastes of many pet owners. Semimoist foods do not require refrigeration before opening and have a relatively long shelf-life. The cost of these foods when compared on a DMB is usually between the cost of dry and wet products. However, products sold as single-serving packages are often comparable in price to wet pet foods. Because they are lower in energy density than wet foods, semimoist diets can be fed free-choice to some pets. However, these products dry out and lose appeal when left in a pet’s bowl for an extended period of time.
SNACKS AND TREATS
Snacks and treats have become increasingly popular with pet owners in recent years. A survey conducted in 1965 showed that Nabisco’s Milk Bones dominated the treat market, and the choice of snacks at that time was extremely limited. However, today almost every major pet food company markets one or more types of dog and cat snacks. This increase can be theorized to reflect some of the changing roles that dogs and cats have had in our society within the last few decades. Pet owners purchase treats not because of their nutritional value but as a way of showing love and affection to their pets. Feeding and caring for a pet is a nurturing process, and giving pets “special” snacks generates the positive feelings that accompany nurturing and the expression of affection. Pet owners also use treats as training aids to reinforce desired behaviors, at times of arrival or departure, as a means of providing a sense of variety in the pet’s diet, and as an aid to proper dental health. 12
Because emotional benefits are a primary motivator for buying treats, palatability to the pet is of chief importance. Owners are less concerned with the nutritional value of a snack than they are with its appearance and acceptability. In the early years, all dog treats were in the form of baked biscuits. Over time, different shapes, sizes, and flavors of biscuits were developed and marketed. Because treats are often purchased on impulse or because of novelty, owners are more likely to try a new flavor or type of treat than they are to completely switch dog or cat food. To capitalize on this, manufacturers have continued to develop new types of dog and cat snacks. Today, treats can be categorized into four basic types—semimoist, biscuits, jerky, and rawhide products. Cat treats are usually in the form of either semimoist or biscuit products, while rawhides and jerky products are highly palatable to many dogs. Many treats are made to resemble foods that humans normally eat, such as hamburgers, sausage, bacon, cheese, and even ice cream. Examples of several popular treat concepts include snacks that are made with all-natural ingredients, biscuits that promote dental health, and chews made from livestock body parts such as ears, hooves, and even noses.
Although treats and snacks do not have to be nutritionally complete, a significant proportion of these products are formulated to be complete and balanced, and some biscuits and semimoist treats carry the same nutritional label claims as dog and cat foods. In general, treats and snacks are highly attractive to pets and cost significantly more than other types of pet foods when compared on a weight basis. Part of this cost is a reflection of the larger amounts of marketing effort and money directed toward making the product attractive to pet owners. 13
PET FOOD CLASSIFICATIONS
In addition to classifying pet foods according to the type of processing method that is used, they can also be classified with respect to overall quality, the types of ingredients that are included (or excluded), availability, and cost. A recent survey of the consumer habits of pet owners reported that the continuing devotion and commitment to companion animals is reflected in increased interest in “premium” and “super-premium” products, those that are on the higher end of the pet care spectrum. 14 A wide variety of new pet food products have also been introduced in recent years. Some of these target the needs of consumers in niche markets and are formulated to contain or eschew a specific type or quality of ingredient (organic foods, “natural” foods, and vegetarian food), while others employ a particular method of preparation or processing (raw diets and homemade diets). Pet owners select these foods for a variety of reasons. These may include beliefs about the wholesomeness and safety of foods; a desire to follow a prescribed “food philosophy” that reflects a religious, ethical or personal belief system; or beliefs about the therapeutic value of certain types of ingredients. 15 For example, according to a recent report, the market segment of raw, frozen, organic, and natural pet foods, while still relatively small, is growing at a rapid rate. 16 The primary motivator (or “driver”) for this growth is a belief among pet owners that these foods are more healthful and of higher quality than more conventional products.
Today, pet owners enjoy a wide variety of pet foods to choose from. The premium and super-premium foods provide consumers with a guarantee of quality ingredients and high nutrient availability. Other foods are marketed to cater to pet owners’ needs to provide a food that is all-natural, organic, vegetarian, or comprised of raw ingredients.
Premium and Super-Premium Brands
The term premium pet food refers to products developed to provide optimal nutrition for dogs and cats during different stages of life. These foods target companion animal owners, hobbyists, and professionals who are very involved with their companion animal’s health and nutrition. In general, quality ingredients that are highly digestible and have good to excellent nutrient availability are used in these products. Manufacturers of most premium pet foods formulate and market products for different stages of life and lifestyles and for different breed sizes (dogs). For example, dog foods have been developed for hard-working dogs (performance diets), adult dogs during maintenance, growing dogs of different sizes, and for females during lactation and gestation. Super-premium foods are those that include high-quality ingredients along with various types of functional ingredients or nutrients that provide specific health benefits. Examples include foods that contain joint protective agents for large-breed dogs and foods that are formulated to support immune health and proper body condition in senior pets. The companies that produce premium and super-premium foods also provide educational materials about their products and about companion animal nutrition and feeding to pet owners and professionals. Although some of these products can be found in grocery stores, many are only available through pet supply stores, feed stores, or veterinarians.
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