No matter the ingredients in a dog food, the raison d'tre is to supply nutrients in a form the dog can use to translate into growth, energy, and body repair. All organic bodies--plants and animals-- are made of nutrients that can also be used by other bodies to sustain life. Nutrients that are not used are simply recycled to the earth to feed plant life as the cycle of life continues.
Nutrients are chemicals ingested by living organisms that are necessary for survival. The six basic nutrients need by living things are protein, carbohydrate, fat, vitamins, minerals, and water. Fats, carbohydrates, and water are made of carbon, hydrogen, and oxygen molecules in different configurations; proteins include these elements and nitrogen. Minerals are themselves elements; vitamins are complex chemicals of different composition necessary for various life processes.
Proteins are chemicals made up of other chemicals known as amino acids. Dogs can manufacture some amino acids in their bodies and must be supplied others in their food. Proteins from animal sources -- meat and meat byproducts -- are more complete and easier to extract and digest than proteins from plant sources. Proteins form the enzymes that metabolize food into energy as well as the hormones that guide various body functions. They themselves can also be metabolized to provide energy. High protein feeds are recommended for puppies and working dogs, but too much protein can cause renal (kidney) disease and has been implicated in some temperament problems.
Fats are probably the most misunderstood of the nutrients, for they are popularly considered the cause of obesity. It's true that a food high in fat will cause obesity in a dog that has a low expenditure of energy, for fats are higher in calorie than either protein or carbohydrates. However, fats are essential for good health, particularly of the skin. Today's homes are well-heated and have dry air that can exacerbate dry skin conditions; the addition of Omega fatty acids to dog diets either in the formula or as a supplement, can help keep skin pliable and healthy.
Fats increase the palatability of food, provide a media for fat-soluble vitamins, and affect food storage. They also are essential for healthy coat and skin, reproductive efficiency, and kidney function.
Carbohydrates should make up about 50 percent of a balanced food for dogs, according to Donald Collins DVM, author of The Collins Guide to Dog Nutrition. The source of carbohydrates is an important consideration; corn is the most popular choice, with soybeans a close second. Other sources include rice and wheat, and the Iams Company now has a veterinary formula using potato starch. As long as the carbohydrate source is clean and of good nutritional quality, that is, it does not consist of floor sweepings or come from a poor quality harvest, it probably doesn't matter. Some dogs may be allergic to one or more of these sources, and some dogs may experience bloating or flatulence on soybean formulas, but most dogs do well on most sources of carbohydrate.
Vitamins and minerals are necessary for proper absorption of fats and carbohydrates and for the chemical reactions in the body. Not only do organisms need these nutrients, but they need them in proper amounts and ratios for optimum health. For example, unless calcium and phosphorus are in balance, neither will be properly absorbed or utilized, which can lead to bone or muscle problems.
Some dogs may need vitamin or mineral supplements at some time during their lives. Some breeders give extra Vitamin C to dogs recovering from injury and boost bitches with Vitamins C and E during pregnancy. However, dogs manufacture their own Vitamin C, so this may be redundant.
Dogs with dry skin may benefit from daily doses of Vitamin E, and dogs under stress or bothered by fleas or biting flies may improve if given Vitamin B-complex. The operative word is "may"; brewer's yeast, that oft-touted, but essentially effective treatment for flea problems is high in B-complex vitamins.
Vitamins are divided into fat-soluble and water-soluble types. Water soluble vitamins are excreted from the body if they are not used; fat soluble vitamins are stored in fatty tissue.
Water-soluble vitamins are the B-complex, including thiamine, riboflavin, pantothenic acid, niacin, pyridoxine, biotin, folic acid, choline, and B12, and C, ascorbic acid. B-vitamins help convert food to energy; C can be manufactured by the dog and supplementation is not necessary. However, some breeders insist that Vitamin C is helpful for dogs that are under stress.
Fat soluble vitamins are A, D, E, and K. They are involved in several body functions, including eyesight, bone formation and strength (with calcium), cell stability, and blood coagulation. Vitamin K can be synthesized by bacteria in the dog's intestine and does not need to be added to the diet under ordinary circumstances. Deficiencies of Vitamin E can cause muscle tissue breakdown, reproductive failure, and impairment of immune response. Vitamin A deficiency can cause several eye problems, including dryness, corneal ulcerations, and inflammation of the conjunctiva. Vitamin D deficiency causes rickets.
Fat soluble vitamins can build up in tissues and become toxic. Excess Vitamin A can lead to bone disease; too much Vitamin D can cause calcification of soft tissue, lungs, and kidneys. Evidence of toxicity in Vitamin E overdose is sketchy; there may be some adverse effects on blood coagulation or thyroid function, but more study is needed to ascertain the extent of such effect.
MInerals are essential for bone formation, muscle metabolism, fluid balance, and nervous system function. Minerals are divided into major and trace concentrations.
Calcium and phosphorus are necessary in particular ratio for bone formation and strength. An imbalance in the ratio will cause bone problems.
Potassium is found within tissue cells and is important in cellular activity; a deficiency causes muscle weakness and heart and kidney lesions.
Sodium is found in fluids outside the tissue cells and performs a function similar to potassium. It is usually found in the diet as sodium chloride -- salt -- and is rarely deficient. Excess sodium has been linked to hypertension in dogs.
Magnesium is found in soft tissue and bone; it interacts with calcium to provide proper heart, muscle, and nervous tissue function and aids in metabolism of potassium and sodium. Deficiency leads to muscle weakness and sometimes convulsions.
Trace elements are iron, copper, manganese, zinc, iodine, selenium, and cobalt. Although dietary requirements are minimal, they are essential to general good health.
Iron is critical for healthy red blood cells and an essential component of some enzymes. Iron from animal sources appears to be more readily absorbed than that from vegetable sources. There is some evidence that feeds high in soy products could interfere with iron absorption, leading to a recommendation that soy-based foods be supplemented with a higher than normally required iron supplement.
Zinc is heavily involved in skin and coat health, enzyme function, and protein synthesis. Deficiencies lead to poor growth, anorexia, testicular atrophy, and skin lesions.
Copper is necessary in production of melanin, the pigment that colors coat and skin, and is linked with iron metabolism. Deficiencies can cause a bone disorder and anemia even if iron intake is normal. Bedlington Terriers can store toxic amounts of copper in the liver, causing hepatitis and cirrhosis. A genetic link to copper toxicosis in the breed has officially been discovered.
Little is known about the need for manganese and selenium in the dog, but they are known to be necessary for a variety of reactions.
The preservatives battle rages on, with anecdotal evidence supporting a closer look at the antioxidant ethoxyquin and more and more companies formulating one or more foods preserved with vitamins.
Just as "natural" is in the perception of the beholder, so is the "danger" associated with chemical preservatives in the absence of scientific study. Actually, in the case of ethoxyquin, several studies attest to the benefits of its use as an antioxidant, including cost efficiency and increased shelf life for the product. However, chemical additives of all sorts from pesticides to coloring and flavoring agents to preservatives are undergoing increased scrutiny as potential culprits in a plethora of canine and human health problems.
News stories abound with stories of dangerous chemicals. This causes cancer, that collects in the fatty tissue, and the other can cause nerve damage. Toxic dumps, contaminated water, residue in food -- it all adds up to a growing fear of chemicals.
But without some use of chemicals, food will spoil, even dog food.
Preservatives are necessary in foods that contain animal fats to prevent rancidity. The fats used in dry kibble for palatability, a source of fatty acids, and a carrier for fat-soluble vitamins can cause dog food to become toxic if they break down. Dog food manufacturers use several chemicals called antioxidants to prevent that breakdown, including BHA, BHT, ethoxyquin, and Vitamins C and E.
Vitamins are used in "all natural" and "organic" feeds. They are more expensive than other chemicals and not as efficient at the job. Foods preserved with vitamins have a shorter shelf life than food preserved with BHA, BHT, and ethoxyquin.
BHA and BHT are often used in concert and are Generally Recognized as Safe (GRAS) by the US Food and Drug Administration although very high doses have been implicated as carcinogens in some studies. These are the most common preservatives in human foods.
Ethoxyquin is an antioxidant that has come under much criticism in the past few years. Like many chemicals, it comes in several forms. One form is used to prevent breakdown of rubber; another has been used to protect apples from scale insects. Food grade ethoxyquin is used as a preservative in dogs foods.
Ethoxyquin is manufactured by Monsanto Chemical Company. It has been used in dog food for many years in the US but is banned in Europe. Some vocal breeders and competitive dog food manufacturers have blamed ethoxyquin for a variety of maladies, including skin, reproductive, and nerve problems. The complaints led to a review of the scientific literature on ethoxyquin studies by the FDA and a recommendation of new tests. However, the chemical was not removed from the market.
As with most chemicals, the story of ethoxyquin is surrounded by anecdotal evidence and emotional reactions. There are many things that can cause skin problems and reproductive failure; even if a change in dog food clears up the problem, there's no way to tell without controlled scientific research if the chemical was at fault. Reproductive problems can be caused by nutrient imbalance and environmental conditions; skin problems can be caused by poor diet, allergies, and autoimmune disease. Since no two dog foods are alike, the mere fact that a condition improved when the diet was changed means nothing except that the new food is more balanced for that particular dog.
Major dog food manufacturers make every effort to provide a balanced diet of proper nutrients in usable form, but in the end the choice of a dog food is personal, preferably done as a result of careful consideration, not scary stories. If a natural food meets your dog's nutritional needs, your emotional needs, and your budget, buy it. As long as the food meets these requirements and keeps the dog healthy, there's no reason to spend time researching the hundreds of available brands and varieties. If the dog's coat is dull and brittle, if his skin is dry or flaky, if he's not maintaining his weight, if his energy level is low, and if medical conditions have been ruled out, then try a different food.
Much of the information for this article was gleaned from Waltham Book of Dog and Cat Nutrition, edited by A.T.B. Edney and published in 1988 by Pergamon Press of Oxford, England. Studies were done at the Waltham Centre for Pet Nutrition, Waltham-on-the Woods, Melton Mowbray, Leicestershire, United Kingdom.
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