All living organisms must eat. Dogs rely on their owner to provide a perfectly balanced diet every day. Some fifty nutrients are now considered essential for dogs, and the quality of a particular dog food is based on how well it solves and adapts the highly complex "puzzle" of canine nutrition.
Proteins (meat, fish, eggs), fiber (green vegetables), fats (plant and animal), minerals, and vitamins must be included in the ideal diet, and the amount of these various elements must reflect:

· The dog's size (obviously, a 2-kilogram (4 ½ pound) Chihuahua will not have the same diet as an 80-kilogram (175 pound) Saint Bernard!).

· The dog's physiological condition (dietary requirements are affected by growth, gestation, nursing, athletic activity, and old age).

· The dog's health (in many cases, nutrition has become an important tool in the medical treatment of disease).

Owners of canine athletes or utility dogs already know the importance of nutrition. For this reason, the present section will cover only the basic elements, in order to give all readers a good understanding of all the elements necessary to create the best possible nutritional balance.

50 Essential Nutrients with an Important Role

Just like humans, dogs are creatures whose survival depends on the hundreds of millions of cells that make up their body and work like tiny fires to provide energy. These "fires" are essential to life. They require a constant supply of fuel - food - and combustive - oxygen - , to produce heat and energy. The body thus maintains a constant temperature and can build and strengthen itself, and thereby survive, without ever ceasing to renew itself.
To feed a dog well, an owner must have a good understanding of the role of nutrition, defined as "all exchanges between an organism and its environment that allow the organism to assimilate foreign substances and produce the energy it needs to survive".

The Role of Nutrients

A nutrient is a simple element that must be included in a dog's diet in an amount that will help maintain the dog's health. Every day, dogs require each of the fifty essential nutrients because each has an important role, and their body cannot synthesize them.

Water: the Most Important of All
It may seem unnecessary to list water as a nutrient, but it is important to remember that while an organism can go weeks without eating, it cannot survive more than three days without drinking. A dog's body is two-thirds water, and all its tissues are bathed in water. Muscles, for example, are 80% water by weight.
While dogs can lose all their body fat and half their protein and still survive, a loss of only 10% of the water in their body leads to death. With its many significant functions, water is the most important nutrient for dogs and all other living organisms. Dogs on a maintenance diet require approximately 60 ml of water per day for each kilogram of body weight (and sometimes quite a bit more, in cases such as strenuous exercise, gestation, and lactation).

Protein: the Body's Building Blocks
Protein does have nutritional value, but it serves mostly as a building block for bones, muscles, nervous structures, etc. - in short, everything a dog needs to survive. A protein is a molecule consisting of amino acids, a sort of train made of cars (nonessential amino acids) and locomotives (essential amino acids). There are differences in the nutritional value, especially during digestion, of "good" proteins (red or white meat, fish, eggs, etc.) and "bad" proteins (tendons, connective tissue), which are indigestible and will be passed in the stools. A protein that is well-digested (and thus absorbed in the form of amino acids) will not necessarily be well-used (metabolized) by the organism. It may lack certain essential amino acids without which the dog's body cannot synthesize its own proteins. It is therefore useful to speak of the "biological value" of proteins and to compare essential amino acids to pieces of, red, white, and blue cloth: with enough of each color, American flags can be made, but if one color is lacking, this will not be possible. Similarly, when one essential amino acid is missing, protein synthesis ceases, and the remaining amino acids are wasted.
It is important to remember that a food high in protein is not necessarily high in quality. Instead, the type of protein used in a particular food must be considered.
Finally, insufficient calories in the diet can cause an organism to "burn" its proteins instead of saving them as building blocks. The balance of calories and proteins in a food is thus also essential.

Fats: Not just a Source of Calories

THE MAIN ROLE OF FATS IS TO PROVIDE ENERGY IN THE FORM OF CALORIES.

Dogs digest fats very well, much better than humans, and greatly enjoy the flavor (this can lead to overeating if a strict portion size is not adhered to). But the palatability of fats should never undermine the nutritional balance of a dog food. This explains why approximately 50% of the dogs in the United States are overweight, compared to only 25 to 30% of the dogs in Europe.
Chemically speaking, dietary fats consist of fatty esters and esters of glycerol that form a chain of a certain length and degree of saturation. A food's caloric content is based more or less on the amount of fat it contains. Carbohydrate-protein substitution is, in fact, nearly isocaloric in dogs, while any extra fat represents an additional 50 calories per kilogram. An increase in caloric density and fat content makes food more palatable to dogs. Because this can lead to overeating, it is necessary to exercise great vigilance over portion size.
While dogs can easily handle high levels of fat in their diet, fatty foods should be reserved for active dogs and dogs with high caloric requirements, such as lactating bitches. Depending on their origin, fats consist of various fatty acids and therefore have different nutritional values.
Fatty acids play a dual role:
- Primarily non-specific, in that they simply provide calories. All fatty acids contribute calories, but the so-called saturated fats in tallow (from ruminants) and lard (from pigs) do not play only this role.
- Specific, in that fatty acids play a structural role as a component of all cellular membranes, as well as a functional role as precursors of cellular and hormonal transmitters.

ESSENTIAL FATTY ACIDS
This dual role is played by so-called "essential" fatty acids - essential, because a dog's body cannot synthesize them and must obtain them from the diet. There are two families of essential fatty acids (also called polyunsaturated essential fatty acids), that are important to know despite their strange names:

- The "omega-6" series, more naturally found in vegetable rather than animal oils, except poultry. A deficiency in this type of fatty acid leads to skin dryness, desquamation, alopecia (hair loss), and a dull coat. This is one of the main nutrients for a beautiful coat.
- The "omega-3" series, found mainly in fish oils, play an important role in preserving cell membranes and in the functioning of the nervous and immune systems. These fatty acids now are also used for their anti-inflammatory qualities (in treating many cases of skin irritation) and their "oxygenating" properties (they improve oxygen flow in the cells and increase the deformability of red blood cells, interesting properties for sporting dogs and older dogs).

Whatever the type, all fats are particularly fragile raw materials that deteriorate rapidly. Rancidity leads primarily to the decreased palatability of food and especially to physiological ailments in dogs: digestive intolerance, pancreatic disorders, liver damage, etc. In commercial dog food, antioxidants are added to prevent dietary fat from becoming rancid. In the case of homemade dog food, it is best not to give a dog cooked fats.

Carbohydrates
Carbohydrates are nutrients consisting almost exclusively of plant matter; food ingredients of animal origin contain virtually no carbohydrates. The building blocks of carbohydrates are simple sugars, the most common of which is glucose, the primary component of starch and cellulose.
Other carbohydrates, such as pectins and gums, are more complex molecules consisting of uronic acid produced by the oxidation of simple sugars. Some carbohydrates (starches and sugars) can be digested and assimilated by a dog's body. Indigestible carbohydrates (fiber and cellulose) serve as bulk to stimulate and regulate intestinal flow. Like all other animals, dogs have a metabolic need for glucose, which is a primary source of energy for certain organs, including the brain, and is also an essential building block in many organic molecules.
Nevertheless, dogs and a few other animal species, have one basic difference: Their body can maintain its glycemia (the level of glucose in the blood) without any carbohydrates in the diet. Dogs and a few other animal species use certain amino acids found in proteins to synthesize glucose. For this reason, dogs are not at risk of glucose deficiency.

DIGESTIBLE CARBOHYDRATES
Among the digestible carbohydrates, lactose is fairly important for puppies. Canine mother's milk contains half the lactose of cow's milk. While puppies can use lactose, their ability to digest it is limited, and any excess leads to digestive problems. Replacement mother's milk for dogs therefore must not contain too much lactose. Adult dogs are even more lactose intolerant. In fact, milk consumption can lead to diarrhea in adults.

STARCH
Starch is a ramified complex of glucose polymers encased like a capsule called a "grain" (of starch). The shape of a particular starch depends on its botanical origin. A dog's body uses amylases, enzymes from the pancreas, to digest starch. Digestibility is greatly improved by cooking, which gelatinizes starch. Found in grains (wheat, corn, rice, etc.) and potatoes, starches provide the body with a quick source of energy, provided they are well-cooked. The rice used in homemade dog food should be "sticky" to ensure digestibility and prevent diarrhea. Two cooking methods are used for commercial dry dog foods: extrusion (kibble) and flaking (so-called "dinners"). These methods ensure that starch is cooked perfectly and therefore highly digestible.

DIETARY FIBER
Although dietary fiber cannot be assimilated by a dog's body, it is considered a necessary part of the canine diet. Dietary fiber consists of all carbohydrates that are not digested upon exiting the small intestine: cellulose, hemicellulose, lignin, pectic matter, etc. Some indigestible proteins, including keratin found in feathers, may also be included.
Fiber regulates the activity of the digestive tract, slowing it down or speeding it up when necessary. Since intestinal action in dogs is dependent of stress and activity level, the amount of dietary fiber in dog food must be adapted quantitatively. Fiber also serves as a substrate for the fermentation of intestinal flora and helps maintain the balance of this material in the large intestine. For this reason, any abrupt change in the source of dietary fiber can cause a temporary imbalance, with uncontrolled fermentation, flatulence, and diarrhea.
Although fiber is necessary for healthy digestion, it does have some drawbacks:

- Fiber decreases the digestibility of food (this is true especially of wheat bran).

- In combination with complex substances known as phytates, fiber can decrease the availability of certain minerals during digestion.

Still, fiber can be used to decrease the digestibility of food for less active dogs or to lower the calorie content of food for overweight dogs. In these cases, the goal is to reduce the assimilation of food and obtain a degree of dilution that will not excessively limit bolus volume. Certain types of fiber can maximize these properties while limiting the drawbacks. Because of the decreased digestibility of high-fiber dog foods, it is necessary to raise the nutrient content of these foods.

Minerals: Many Functions

Minerals account for a very small proportion of a dog's weight, but each plays an essential role. For this reason, the mineral content in a dog's diet should be monitored very carefully. In addition, all minerals can interfere with each other in digestion or metabolism. Therefore, it is necessary not only to ensure that each is present in the proper amount, but also to avoid any imbalance, which can harm the organism as much as a simple deficiency.
In the field of nutrition, minerals are divided into two groups:

- Macronutrients, for which the dietary requirement is expressed in grams for a standard-sized dog, including calcium, phosphorus, magnesium, sodium, potassium, and chloride.
- Trace minerals, for which the dietary requirement is expressed in milligrams per day (or less), including iron, copper, manganese, zinc, iodine, selenium, fluorine, cobalt, molybdenum, etc.

Quantitatively speaking, calcium and phosphorus are the most important mineral elements: They are the building blocks of the skeleton and also have other important metabolic functions: For example, phosphorus is involved in energy transfer inside the cell. The skeleton is a substantial buffer reserve of phosphorus on which an organism can draw in the case of a deficiency. This explains the occurrence of bone disease when phosphorus and calcium levels in the diet are unbalanced. Magnesium is also involved in bone metabolism, but more importantly, it is found together with potassium in the intracellular fluid essential to many chemical reactions.

Generally speaking, trace minerals are necessary not only in the production of red blood cells, but also in oxygen transport, skin pigmentation and preservation, the functioning of enzymatic systems, the synthesis of thyroid hormones, etc. Each trace mineral fulfills one or more roles in a number of bodily functions.

Vitamins: Neither too Many nor too Few

Everyone has heard of vitamins, nutrients essential for life that include a wide variety of substances. When even a single vitamin is completely or partially lacking in the diet, an organism exhibits clinical symptoms of deficiency that can eventually lead to severe illness. As a group, vitamins have two distinguishing features:

- A dog's daily requirement for each vitamin is expressed in milligrams or even micrograms.
- Vitamins are organic substances, unlike trace minerals such as iron, iodine, and zinc, which are just as essential.

Vitamins are found in food and are either liposoluble (soluble in fats) or hydrosoluble (soluble in water).
Dogs require thirteen different vitamins. Each plays a specific role or roles, from ensuring good vision, proper growth, and the efficient use of fats, to preserving the skin and maintaining the blood vessels and nervous tissue.
It is important to note that excessive amounts of certain vitamins (particularly vitamins A and D) in the diet can be very dangerous. While these vitamins are necessary and useful in certain amounts, they are harmful and even toxic in others. However, some vitamins, including vitamin E, are well-tolerated even in large amounts. In fact, large amounts of vitamin E have a curative and preventative effect on cell membranes. So far, no signs of hypervitaminosis from this vitamin have been reported in dogs. Amounts of vitamin E above the physiological requirement may therefore increase the quality of a specific food.
Finally, owners should remember that brewers' yeast is a rich natural source of B vitamins, which can be a great aid to improving the appearance of the coat.

Prebiotics (FOS) in Dog Food
Fructo-oligosaccharides (FOS) are a certain type of sugar classified as fermentable fibers. These non-digestible sugars are rapidly fermented by the bacterial flora in the intestines. They stimulate production of volatile fatty acids (acetate, propionate, and butyrate), which maintain and promote growth of the cells that form the lining of the large intestine.
FOS favors the establishment of a healthful bacterial flora (bifidobacterium and lactobacillus). The benefits to the digestive tract are well known:
- they inhibit the growth of pathogenic bacteria;
- they stimulate the immune system

The Role of Probiotics in Canine Feeding
Probiotics are living microorganisms (bacteria or yeasts) that have a beneficial effect on the human or animal that ingests them. They are available as medications or dietary supplements (yeasts), or are present in food (yogurt).
While the beneficial effects of probiotic organisms on diarrhea in young children have long been known, their beneficial effects on human and animal health have been demonstrated only much more recently. The mechanisms of these effects have not yet been completely explained.
Probiotic organisms seem to act in three ways:
- Barrier effect: They allow a more favorable equilibrium to be established between the different organisms present in the intestinal microflora (they "suffocate" pathogenic organisms thanks to their superior numbers);
- Improved digestion: Through enzymatic action, they facilitate digestion of certain nutrients that resist the action of digestive juices;
- Stimulation of the host's immune defenses.
Probiotic organisms do not colonize the host's digestive tract, so to be effective, they must be consumed frequently and in sufficient doses.
Recent research has shown that an effective and practical way to get dogs to eat probiotic organisms is to add them to dry dog food. Once ingested, they improve the dog's health and increase its life expectancy.

Source : The Aniwa Encyclopedia