Although important for a variety of functions, minerals make up only a small part of the body weight. All together, minerals make up less than 2.0% of the body. Minerals can be grouped into two categories based on the amount required:

1. Macrominerals: inorganic nutrients needed in relatively high daily amounts for which the dietary requirements are best expressed as parts per hundred (pph).

2. Microminerals: inorganic nutrients needed in minute daily amounts for which dietary requirements are best expressed as parts per million (ppm).

As with vitamins, rarely would a dog or cat require a mineral supplement since almost all foods contain adequate amounts. Some of the problems in dogs and cats today are again caused by an overly concerned owner who supplements their pet's diet with extra calcium and phosphorus. Since many of these minerals have common pathways for absorption in the intestine, supplementing extra calcium often overloads the system and causes deficiencies of many of the trace minerals. This is why there must be a delicate balance. Attempting to supplement a diet often creates further secondary deficiencies and an imbalance.  

Macrominerals : inorganic nutrients needed in relatively high daily amounts for which the dietary requirements are best expressed as parts per hundred (pph)

Calcium (Ca) 

The primary role of calcium is building bones and teeth and more than 99% of the calcium in a pet's body is used to build these two structures. Calcium deficiencies while rare now, were more common in the 1950's and 60's and were primarily associated with animals fed all meat diets which contained almost no calcium. Now, calcium deficiencies are usually the result of owners feeding human food items to their pets like canned meats (for dogs) or tuna (for cats).

While calcium excess can occur, most problems are the result of high calcium intakes, which cause secondary trace mineral deficiencies, most notably iron, zinc and copper. This occurs because the calcium competes with these trace minerals for absorption in the intestine. Since calcium is required in the parts per hundred and the trace minerals are required in parts per million, even a small addition of calcium to a balanced diet can lead to a dramatic reduction in trace mineral absorption and a trace mineral deficiency. Typical signs are bone abnormalities, slow growth in young animals, and skin and haircoat problems.

Phosphorus (P) 

Phosphorus, like calcium, plays a major role in the development and maintenance of bones and teeth but also plays an important role in cell metabolism. The calcium to phosphorus ratio is also important, although in the past an excessive amount of emphasis has been placed on this ratio. In reality, animals are capable of performing normally on diets with fairly wide calcium to phosphorus ratios (cap - 0.7:1 to 2:1). Phosphorus in plant sources is usually present as phytate (i.e. phosphorus bound to carbohydrates) and only 1/4 to 1/3 of this phosphorus is available to the animal. In contrast, phosphorus from animal sources and mineral supplements are usually 100% available.

Magnesium (Mg) 

Magnesium participates in a variety of body functions from bone metabolism to acting as a co-factor in a variety of metabolic reactions. More focus has been placed on magnesium in the last 20 years than all the other minerals put together. This is because cats, and to a lesser degree dogs, are prone to urinary tract blockage, and one of the most common types of uroliths (stones) found in cats is composed of struvite, which is composed of magnesium, phosphorus and nitrogen. It was once thought that the best way to reduce the risk of these uroliths was to feed a cat a low ash/low magnesium diet. We now know that there are a variety of reasons cats develop urinary tract blockages and that simply feeding a low magnesium diet will usually not prevent uroliths. For a more detailed discussion on feline uroliths, see the section on FLUTD.

Sodium (Na), Potassium (K) and Chloride (Cl)

These minerals are grouped together because they are all electrolytes and thus share some common functions. Sodium is the major intracellular (within the cell) cation (positively charged ion), while potassium is the major extracellular (outside the cell) cation. All of these electrolytes play an important role in regulating fluid and acid-base balance in the body. While most young healthy dogs and cats excrete excess electrolytes via the urine, in some older animals or those with a pre-existing disease (heart or kidney disease) this process may be compromised. For these animals, sodium intake is important and should be adjusted accordingly. While sodium is a major health concern in human nutrition, much less is known concerning its effects in dogs and cats, although it will undoubtedly be studied more extensively in the future. 

Microminerals :inorganic nutrients needed in minute daily amounts for which dietary requirements are best expressed as parts per million (ppm)

Iron (Fe), Zinc (Zn), Copper (Cu), Manganese (Mn), Iodine (I) & Selenium (Se)

The primary functions of most of these trace minerals are as co-factors in various metabolic reactions. These metabolic reactions range from those that release energy from proteins, fats and carbohydrates to those involved in bone and cartilage formation. Iron plays a special role and is part of the hemoglobin molecule in red blood cells and thus responsible for transporting oxygen in the blood. Iodine functions as part of the hormone thyroxine and is involved in the regulation of energy metabolism.

Trace mineral deficiencies most often occur when:

•  One: owners supplement their animal's diet with too much calcium, which creates a secondary trace mineral deficiency

•  Two: owners institute high fiber diets that contain large amounts phytate that have not been fortified with extra trace minerals.

•  Three: when the less available forms of these minerals have been used as supplements.

In the 1960's and 70's a symptom known as "generic dog food" was reported which appeared to be the result of a zinc deficiency because the diets contained large quantities of phytate (organic acid) containing fiber. The symptoms included slow growth, flaky skin, poor haircoats and a very distinctive graying of the hair shaft, which was most noticeable in dogs with black haircoats.

The availability of trace minerals is generally a function of their solubility. For trace minerals the chelated (bound) forms (i.e. zinc amino acid chelate or zinc proteinate) have the highest availability, the sulfate forms (i.e. zinc sulfate) are next and the oxide forms (i.e. zinc oxide) last. In fact, some oxides, most notably iron/ferric oxide and copper/cupric oxide are virtually 100% unavailable. Although not available, iron oxide has often been used as a coloring agent, especially in cat foods.

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