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.