Foods can be categorized according to their nutrient content, the purpose for which they are formulated, and the quality of ingredients they contain.
The majority of pet owners feed their companion animals commercially prepared pet foods. These products are available in several forms that vary according to the processing methods used, the ingredients included, and the methods of preservation.
One of the broadest classifications of commercial pet foods divides products according to processing method, methods of preservation, and moisture content . these categories are the dry, wet, and semi moist foods.
In recent years, a variety of foods have been developed to meet specific needs of some pet owners. These include natural and organic foods, raw food diets, and vegetarian products.
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 food, biscuits, meals, and expanded (extruded) products.
Baked dry Pet Foods
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.
Extruded Dry Pet Products
Process
The development of the extrusion process s 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 World.
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). 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.
General Ingredients used in Dry Foods
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 .
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 (See the table). Cat foods of all types contain slightly higher levels of protein than dog foods.
Dry dog foods are the most popular type of pet food purchased by consumers .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 digestibility, meaning that less food can be fed, more nutrients will be absorbed and used, and stool volume will decrease.
NUTRIENT CONTENT OF DRY,SEMIMOIST, AND WET DOG FOODS
| Content | AF Basis (as Fed Basis) | DM Basis (Dry Matter) |
| Dry Food | ||
| Moisture % | 6-10 | 0 |
| Fat % | 7-20 | 8-22 |
| Protein % | 16-30 | 18-32 |
| Carbohydrates % | 41-70 | 46-74 |
| Metabolised Energy Kcal/kg | 2800-4050 | 3000-4500 |
| SEMIMOIST | ||
| Moisture | 15-30 | 0 |
| Fat % | 7-10 | 8-14 |
| Protein % | 17-20 | 20-28 |
| Carbohydrates % | 40-60 | 58-72 |
| Metabolised Energy Kcal/kg | 2500-2800 | 3000-4000 |
| Wet | ||
| Moisture % | 75 | 0 |
| Fat % | 5-8 | 20-32 |
| Protein % | 7-13 | 28-50 |
| Carbohydrates % | 4-13 | 18-57 |
| Metabolised Energy Kcal/kg | 875-1250 | 3500-5000 |
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 by-product.
Complete and balanced wet foods may contain blends of ingredients such as muscle meats, poultry or fish meats or by-products, 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 by-products, 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.
Processing of Wet foods
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. After filling, the cans are then sealed with a double seam, washed, and labelled with a manufacturer 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.
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. 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.
Advantages of Wet Foods
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. .
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.
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 .
SEMIMOIST PET FOODS
Semi moist 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 semi moist 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.
Further protection is provided by preservatives such as potassium sorbate, which prevents the growth of yeasts and moulds. 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.
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.
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, semi moist 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.