Canine Nutrition

April, 1998

Proper diet is among the more important considerations in maintenance of our pets’ health and can also be used in management of many diseases. This month’s article deals with the basics of nutrition by describing the different nutrient categories.
Water may be considered a nutrient, as it is a component of all foods and is required by the body in a larger amount than any other nutrient. A 10% loss of total body water (dehydration) results in serious disease, and a 15% loss results in death. As a general rule, water of good quality should be available to the animal at all times. Dogs usually prefer it cooler than room temperature. When consuming only dry dog food, containing only about 9% moisture, an animal will usually drink more of his free choice water than when consuming all canned dog food. This ensures that the total amount of water entering the body stays the same, regardless of the form of the food. Dry foods and canned foods are of equal value nutritionally, as both should provide a complete and balanced diet. However, dogs consuming only dry food usually have less dental disease, because less plaque is deposited on the teeth than with canned food.
Carbohydrates are often classified into 2 groups, based on disgestibility. Sugars and simple starches are considered digestible or soluable carbohydrates. On pet food labels, this fraction is sometimes refereed to as NFE, or Nitrogen-Free-Extract. Their main function is to supply energy to the body. Fiber is the relatively indigestible or insoluble carbohydrate portion of the diet. In the dog and in humans, fiber is broken down, by fermentation, to a very limited degree. This is accomplished by enzymes produced by bacteria that inhabit specialized areas of the GI tract. Ruminants (grazing animals such as cattle, sheep or deer) can actually obtain energy from the fiber they consume. The largest part of their 4-chambered stomach is well developed for this fermentation by bacteria. Other animals (such as horses and rabbits) are called hind-gut fermenters, because this process takes place in the cecum, a structure in the lower part of the intestinal tract. Mongastric animals (including humans and dogs) have only a very small cecum and therefore obtain almost no energy from insoluble carbohydrates. However, dietary fiber serves other purposes in those species. I affects colonic function by increasing stool bulk and prevents hard, dry stool due to its water-holding capacity. A lot of emphasis has been placed on adding fiber to the diet of humans for preventing intestinal cancer, decreasing fat absorption and increasing cholestorol excretion. Similar benefits would not be expected by adding fiber to our dogs’ diets because most dog foods already contain 3 or 4 times the fiber content of the typical human diet.
The functions of proteins in the diet have been discussed in a previous article (SPO Magazine, Sept. 1997). These functions include serving as componenets of enzymes, hormones, a variety of body secretions and structural components (such as muscle, hair and nails). Therefore, inadequate dietary protein can lead to weight loss and poor haircoat.
Fat is another improtant component of the diet. Twenty-five to fifty percent of the dietary energy of dogs can come from fat. Fats are also needed for the absorption of some vitamins (the “fat-soluble” vitamins: A, D, E and K) and are a source of essential fatty acids. The essential fatty acids have the potential to become oxidized (rancid) if sufficient amounts of anti-oxidants are not present). Deficiencies can alter the oil film on the skin, leading to flaky skin and a lusterless coat and may also predispose to skin infections. In suspected cases of fatty acid deficiencies, they can be supplemented by adding 1 teaspoon of soy or corn oil to each cup of dry food. Capsules containing fish oils have a more profound effect on the skin and hair coat. One of the most important functions of the fat content of dog foods is to enhance palatability, or acceptability, of the food. A well balanced diets does no good if the dog won’t eat an adequate amount. Both dogs and people tend to like the taste of fatty foods. Some manufacturers of dry dog foods use a technique more commonly used with dry cat foods. A coating of fat is sprayed on the outside of each kibble after it has been dried. Other pet food companies will spray the dry food with a material called “digest”. Digest is partially degraded animal tissue such as ground viscera of poultry, fish liver and beef lungs. Either of these techniques can enhance the palatability of pet food and does not detract from its nutritional values. However, it is a good idea not to purchase a bag of dry dog food with evidence of fat soaking through to the outside (“grease out”).
A number of minerals are required by the body in small amounts, but they serve a number of important functions, including muscle contraction, nerve conduction and structural integrity of bones. The proportions of different minerals, especially the calcium phosphorus ratio, is crucial to their function. Dog foods are formulated to contain the proper amounts and proportions of minerals. Indiscriminate supplementation by well-meaning owners is the main cause of mineral imbalances in dogs.
Vitamins are another class of nutrient required in small amounts, less than 1% of the entire diet. They all serve as enzymes, substances which regulate chemical reactions in the body. These reactions include digestion of all other nutrients, nerve and muscle function as well as energy utilization. Routine vitamin supplementation is usually unnecessary when a healthy dogs is eating a quality commercial diet.
I have presented here an overview of the different nutrients and their functions. Canine nutrition is obviously very similar to human nutrition, but formulating a balanced diet for the dog by using only table foods can be difficult. Fortunately, there is a variety of good quality dog foods available to choose from. A future article will deal with feeding dogs for different purposes and with different disease conditions.

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