Minerals are present in small amounts in the tissues of all living things. Teeth, bones, muscles, and nerves have especially high mineral content. Although the AAFCO provides guidelines for the minimum amounts of minerals necessary for canine growth and development, each dog’s mineral requirements depend on the current nutritional state. For example, if a dog is iron deficient, he will need and absorb more iron from the intestinal tract. Working dogs and ill or stressed dogs may also have higher requirements.
Minerals can be divided into two groups: major minerals and trace minerals. The major minerals are required in gram amounts each day, whereas the trace minerals are required in milligram or microgram amounts per day. Of the trace minerals, several are known to be required for canine health, and the roles of others are less understood.
Your dog’s body needs to maintain a delicate balance between the various major and trace minerals. For several trace minerals, the line between the required amount and toxic levels is a thin one. So supplementing an already balanced dog food with minerals can create more problems than it solves.
Table Sources of Minerals lists the different minerals your dog needs and which foods are good sources of these minerals.
Table Sources of Minerals
|Calcium||Dairy products, poultry, meat bone|
|Phosphorus||Meat, poultry, fish|
|Magnesium||Soybeans, corn, cereal grains, bone meals|
|Sulfur||Meat, poultry, fish|
|Zinc||Beef liver, dark poultry meat, milk, egg yolks, legumes|
|Manganese||Meat, poultry, fish|
|Iodine||Fish, beef, liver|
|Selenium||Grains, meat, poultry|
|Cobalt||Fish, dairy products|
The four major minerals are calcium, phosphorus, magnesium, and sulfur. Calcium and phosphorus are the most important minerals in all dogs’ diets, especially in the diets of growing puppies. Calcium is needed for muscle contraction, nerve transmission, and blood coagulation. It is also required to activate numerous enzymes that affect virtually every process in the cell. Phosphorus plays a part in nearly all chemical reactions in your dog’s body. Both strengthen your dog’s bones and teeth.
Although the ratio of calcium to phosphorus in a dog food is important, the total amount of calcium ingested may be more important. Excess calcium is thought to contribute to the development of hip and elbow dysplasia, osteochondrosis dissecans (degeneration of the joint cartilage), and other bone and joint problems. Calcium deficiencies frequently occur in dogs who are fed all-meat diets. A severe deficiency of calcium can cause rickets and bone malformations. A moderate deficiency can cause muscle cramps, impaired growth, and joint pain.
As of this writing, all premium-quality adult maintenance dog foods produced by major manufacturers have enough calcium to support the healthy growth of puppies, including those of giant breeds. Resist the urge to provide extra supplementation of vitamins and minerals, particularly those containing calcium, to your growing puppy on a premium dog food.
Never add bone meal to a complete and balanced diet. Not only are you likely to alter the critical calcium to phosphorus ratio, but you also risk decreasing your dog’s ability to absorb and utilize many of the other minerals he needs.
Magnesium is essential for many enzymatic reactions. It also helps promote the absorption and metabolism of many other vitamins and minerals, including vitamins C and E, calcium, and phosphorus. As with calcium and phosphorus, magnesium is important in bone growth and development. In fact, 70 percent of the magnesium in your dog’s body is in his bones. Magnesium is rarely deficient in complete and balanced diets. However, its absorption can be impaired when the diet is too high in calcium and phosphorus.
Your dog needs sulfur for the synthesis of a variety of components in his body, most notably proteins. Sulfur is also an important constituent of joint fluid and cartilage and, thus, is important for proper joint health.
Your dog needs only very small amounts of trace minerals in her diet. Trace minerals are found in meat and grains and are provided as a supplement in complete and balanced premium dog foods. A balanced diet is still the best source for all the vitamins and minerals required for optimum health.
The trace minerals include the following:
• Iron: Iron is present in every cell in the body. It is particularly important, along with protein and copper, for the production of red blood cells, which are responsible for transporting oxygen from the lungs to every part of the body. Dogs with iron deficiency develop anemia. But remember, iron is needed in only small amounts, so it is important that you not supplement with iron unless you have a prescription.
• Zinc: Zinc is important in the metabolism of several vitamins, particularly the B vitamins. It is also a component of several enzymes needed for digestion and metabolism, and it promotes healing as well. Your dog needs zinc for proper coat health. Some breeds of dogs, particularly the northern breeds such as Siberian Huskies, appear to have problems with absorption and/or utilization of zinc. These dogs develop poor coats and dry, scaly skin with sores (particularly on the nose and mouth) and stiff joints unless they are supplemented with zinc.
• Copper: Copper is a trace mineral that has many different functions. It is needed for the production of blood and for the proper absorption of iron. It is also involved in the production of connective tissue (the cells and extracellular proteins that form the background structure of most tissues) and in healing. Copper is found in fish, liver, and various grains. The amount of copper in a grain is related to the level of copper in the soil where the grain was grown. A copper deficiency can result in anemia and skeletal abnormalities. Some breeds of dogs, such as Bedlington Terriers and Doberman Pinschers, can have a genetic problem that interferes with the metabolism of copper. In these dogs, copper is stored in the liver to toxic levels, resulting in hepatitis.
• Iodine: Iodine is critical for the proper functioning of the thyroid gland, which regulates the body’s metabolism and energy levels and promotes growth. Iodine is found in high levels in fish. It is added to most dog foods to make the levels sufficient for canine health.
• Selenium: Selenium works with vitamin E to prevent oxidative damage to cells. It is needed in only minute amounts in the diet. Meats and cereal grains are good sources of selenium. In dogs, an excess of selenium results in death of the heart muscles, as well as damage to the liver and kidney. Deficiency results in degeneration of heart and skeletal muscles.
• Manganese: Manganese is a component of many different enzyme systems in the body. Most important, it activates enzymes that regulate nutrient metabolism. It is found in legumes and whole-grain cereals; animal-based ingredients are not a good source of manganese.
• Cobalt: Cobalt is a part of vitamin B12, which is an essential vitamin. Cobalt does not appear to have any function independent of vitamin B12.
In addition to these trace minerals, other trace minerals known to be important in laboratory animals but with an unclear role in dogs include molybdenum, cadmium, arsenic, silver, nickel, lead, vanadium, and tin.
As scientists discover more about the nutritional needs of dogs, they are beginning to recognize that our canine companions may need different nutrient levels for optimal health than they need just to prevent deficiencies. Be sure to discuss nutritional questions with your veterinarian — and take a vet’s advice over anyone selling dog food, because stores may push the brands that give them a bigger profit margin. And if you have a question about a specific dog food, call the manufacturer.
How dog food is made
How do some cows or chickens and a pile of grains turn into your dog’s dinner? First the animals are slaughtered and the body parts not used for human consumption are put into bins according to which parts of the body they do or do not contain. These are either shipped directly to the dog food manufacturer or are rendered and the meal (what remains after the fats are removed) is shipped to the manufacturer. Similarly, either grains or the meal (what remains after the oils have been extracted for use in human foods) may be shipped to the dog food manufacturer. If whole grains are sent, the manufacturer grinds and separates the grains into their different components. For example, wheat may be separated into wheat flour, wheat germ meal, wheat bran, and wheat middlings.
The ingredients are then mixed in proper proportions and added to the extruder, a large tube containing a screw that mixes the ingredients with steam and water under pressure, and then squirts out the mixture through holes at the end, like a pasta maker squeezes out spaghetti. A knife cuts the ribbon into small pieces, which are then moved along a conveyor belt through a dryer/cooler until the right amount of moisture remains. The food is then coated with fat, vitamins, and flavorings.
The high temperature at which dry dog foods are processed breaks down proteins and may change their structure and quality. In addition, the heat destroys any enzymes that were in the food components. Vitamins that have been destroyed during processing have to be sprayed back onto the food after it cools. But whether the components that are added back are really the same as those that were present in the unprocessed food components is unclear, and this is why some people prepare foods for their dogs at home. As a trade-off, however, processed dog food is virtually sterile. None of the common bacteria present on beef and poultry, such as salmonella and E. coli, remain after the food is processed.
Semi-moist foods are not dried as much, and they have more preservatives and sugar added. Canned dog foods are heated but not sent through an extruder. Thus, they tend to retain more of the natural proteins, fats, vitamins, and enzymes.