Tempting delicacies of meat or poultry, small slices of fresh filleted fish, first-quality cereals and sometimes a variety of different coloured chopped vegetables, such as carrots, potatoes and green beans: this is what is depicted on many packages of dog food and this is also what many dog food makers would like dog owners to believe they are buying when they purchase commercial dog food. But, as soon as one opens the can or pack of dog food, it becomes immediately clear that neither the appearance nor the smell of their content reflect what is depicted on the image of the package. So, what do really people buy when they purchase commercial dog food? And, most importantly, what does dog food contain and how is it made?
Before going into the details of how dog food is made, it would be worthwhile to remember that dog food is the result of a highly industrialized process, based on the use of well defined ingredients and of standardized processing methods, the main differences among different brands of dog food being the quality of the ingredients used and the quality standards followed by each manufacturer during dog food processing. However, under many aspects, the general recipe for commercial dog food is rather uniform.
The ingredients used to prepare commercial dog food can be divided into four main classes
- protein sources
- carbohydrate sources
- mineral and vitamin fortifiers
Protein sources in commercial dog food can be either animal or plant based, or both. Of course meat, broadly defined as the muscle tissue derived from cattle, swine, sheep, goats, poultry and fish, is one of the protein sources of the highest nutritional value, which provides the dog with all the essential amino acids it needs and in the right proportions. However meat is also an expensive ingredient for manufacturers, who often prefer to substitute it, in whole or in part, with less expensive protein sources, such as animal by-products (the parts of slaughtered animals that are not muscle meat and are not consumed by humans), meat, poultry and by-products meals (all obtained from the processing of animal materials not intended for human consumption) and vegetable protein, such as corn or wheat gluten meal and soybean meal. The real problem behind the use of these cheap protein sources relies on their poor nutritional value and/or their poor digestibility by dogs. For example, the main protein found in animal by-products such as intestines, lungs, livers, bones and ligaments, is collagen, which is characterized by a poorly varied amino acid composition, very far from that of the ideal protein. A similar remark can be made about gluten meal or other plant protein sources which, besides having an incomplete amino acid composition as it relates to the dog’s amino acid requirements, are also poorly digestible by dogs and can even be responsible for food allergy or intolerance reactions. A remarkable exception is meat or poultry meal obtained exclusively or predominantly by meat trimmings or meat mechanically separated from bones: in this case the protein value is fairly good, although not as high as that of fresh meat, since the high temperatures required to produce the meal can destroy or alter the proteins found in the raw ingredients.
Commercial dog food usually contains large amounts of complex carbohydrates (starch) in the form of rice, maize, wheat, oat and spelt, whose digestibility and nutritional value is improved through the processing methods of cooking or extrusion used to prepare wet and dry dog food, respectively. Although carbohydrates can be important sources of energy for dogs, it is important to note that they are not essential: dogs, in fact, get most of the energy they need from the protein and fats of the diet. The large amounts of cereal grains or flours that can be found in many commercial dog foods are usually intended to give the final product the desired texture, as well as to promote early satiety in dogs by using rather cheap ingredients. Certain dog foods also contain some sources of fiber, an indigestible complex carbohydrate that can help improve or maintain the intestinal function. The main sources of dietary fiber found in dog food include vegetables (carrots, peas, green beans) or less expensive ingredients such as wheat bran, peanut skins and beetroot pulp.
The fats most commonly added to commercial dog food include animal fats, such as lard and poultry fat, and vegetable oils, such as soybean, sunflower or corn oils. Added fats are not only an important source of energy and essential fatty acids, but they are also used to improve the palatability of dog food. In the last case, they are often sprayed on the surface of the finished product and are responsible for the characteristic pungent odour perceived at the opening of a dry dog food pack.
In order to ensure that dog food meets the dog’s nutritional requirements of minerals and vitamins, many manufacturers add a mix of these nutrients to the other ingredients before food is processed, to compensate for the unavoidable nutrient losses that occur during food processing and sterilization. In this way, it is guaranteed that commercial food contains the recommended doses of mineral and vitamin required by dogs.
A final mention should be made about preservatives and additives, the first added to ensure a long shelf life of the product, the second added to enhance palatability and give the product an inviting smell, colour and appearance. It seems unnecessary to say that dog foods of the best quality are those containing only natural preservatives (such as vitamin E and C) and no or minimal amounts of additives.
In order to understand how dog food is made, however, it is not enough to only consider the list of ingredients, but it is also necessary to consider how these ingredients are mixed and processed to give the final product. In general, after grinding and mixing all the ingredients in adequate proportions (which are usually computer calculated and controlled), the uncooked mix is processed through different methods depending on whether the final product is to be canned (wet) dog food or dry dog food. In the first case the mix of ingredients is preheated at 50-60 °C to allow the partial digestion of starches, and then placed into a sealable can in the form of chunks or pate. The sealed cans are then submitted to a cooking/sterilization process at a temperature of 120-130 °C, in order to guarantee the complete destruction of all food-borne pathogens. As regards dry food, this is prepared through a particular process called extrusion, in which the dough of ingredients is pulled trough a special machine (the extruder), where it is submitted to a rapid heat/high pressure process, which is responsible for its cooking and sterilization. As the dough exits the extruder, it is automatically cut into tiny pieces and the sudden exposure to the lower atmospheric pressure causes these pieces to expand and take their final shape.
It is important to note that the process of extrusion requires low moisture levels and the presence of adequate amounts of starch. This explains why dry dog food contains more dry ingredients such as meat meals, by-product meals and cereal flours than canned dog food does. It is clear therefore that how dog food is made only depends on its ingredients, which in turn determine the most suitable processing method.