Minerals are defined as all the inorganic elements in a food, and when all of the organic matter in a food has been burned, the remaining ash is composed of those minerals.  The body needs minerals for a number of functions.  They:  1) provide building blocks for organs and tissues; 2) are responsible for muscle contraction and cell membrane permeability; 3) help maintain pressure balance between the inside and outside of the  blood vessels; and 4) act as catalysts and cofactors in many enzymatic and hormonal processes.

Minerals are divided into two categories.  The macrominerals are those that are present in the body in large quantities.  They are measured in percentages.  The microminerals, also referred to as trace elements, are present in very small amounts.  They are measured in parts per million (ppm).  While the amounts are small, they are still vital for survival.  Both types of minerals are more readily absorbed in the intestinal tract if they are attached to one or more amino acids.  These minerals are referred to as "chelated."  Inadequate or excessive intake of any mineral can cause varying symptoms of deficiencies or toxicities.  Twelve minerals have been identified as being essential nutrients for (dogs) (cats).  While each of these minerals has more than one function in the body, only the major roles will be discussed in this article.

Macrominerals

Calcium has several important functions.  It plays a major role in the formation of bones and teeth.  It is crucial to the communication between individual cells which are responsible for muscle contraction, and response to nerve impulses, hormones, and other chemical messengers.  In addition, calcium plays a part in blood clotting.  Its two major functions in bone are to provide a matrix for structural support, and serve as a reservoir when the body needs more calcium than is being supplied by the diet.  The majority of the body's calcium (approximately 99%) is stored in the bones.    Calcium carbonate, calcium chloride, calcium phosphate, calcium sulfate and bone meal are the most common calcium supplements used in pet food. 

Phosphorus plays a role in several essential activities.  Approximately 86% of the body's phosphorus is stored in the bones where, along with calcium, it makes the skeleton solid.  Phosphorus is incorporated in DNA and RNA, the molecules which are responsible for the cells' genetic instructions.  It is an important component of cell membranes and high-energy compounds (adenosine triphosphate or ATP).  Meat is an excellent source of phosphorus.  Supplements include calcium phosphate, sodium phosphate, and phosphoric acid.

Magnesium, along with calcium and phosphorus, is also part of the mineral structure of bones and teeth.  It is involved in the metabolism of carbohydrates and lipids, and the production of energy at the cellular level (ATP).  Magnesium is also required for the efficient functioning of the nervous system.  Bone meal and beet pulp are natural sources of magnesium.  Supplements commonly used are magnesium oxide and magnesium sulfate.

Sodium and Chloride help maintain the pressure balance inside and outside of cells.  They also control the movement of nutrients into cells, and are involved in transmitting nerve impulses and muscle contractions.  Sodium regulates the body's water balance, i.e. sends signals for thirst and urination.  Fish, eggs, and soy isolate are high in both sodium and chloride.  Supplements include salt (sodium chloride), sodium phosphates, calcium chloride, and potassium chloride.

Potassium helps maintain the pressure balance inside and outside of cells.  It is vital for cardiac function, muscle contraction, and energy metabolism.  It facilitates synthesis of protein and carbohydrate metabolism.  Very little potassium is stored in the body so it must be supplied daily in the diet.  While meat is a good source of this mineral, common dietary supplements include potassium citrate, potassium chloride, and potassium sulfate.

Microminerals or Trace Elements

Iron is found more than any other trace element in mammals.  Its main function is to facilitate the transport of oxygen from the lungs to the rest of the body.  In fact, approximately 70% of iron in the body is part of hemoglobin, a protein molecule in red blood cells that functions in oxygen transfer.  Iron also is critical for DNA synthesis and energy metabolism.  Very little iron is lost from the body, and what is not being used by the red blood cells is stored in the spleen, liver, bone marrow, and certain white blood cells.  Liver and meat are rich sources.  Supplements include ferrous sulfate, ferric chloride, and ferrous carbonate.

Zinc has many different roles and functions.  More than 200 enzymes are dependent on zinc for proper activity.  It is plays a part in protein synthesis and carbohydrate metabolism.  It stimulates the immune system and helps to promote healthy skin and coats.  It is very important for reproduction as it plays a part in production of the hormone testosterone.  Zinc is also involved in cell replication and differentiation, both of which are vital processes during embryonic and fetal development.  Most meats and other animal products are naturally high in zinc.  Supplements include zinc gluconate, zinc chloride, and zinc sulfate.

Copper is important for the intestinal absorption of iron and its association with hemoglobin.  It plays a role in the formation of red blood cells and is utilized for the prevention and treatment of anemia.  Copper also has a part in the development of connective tissue and the outer layer which covers nerves.  While hair and nails contain significant amounts of copper, the majority of this mineral is stored in the liver.  Most organ meats (especially liver), lamb, pork, and duck some are natural sources of copper.  Supplements include cupric sulfate and cupric chloride.

Manganese is an enzyme activator and plays a role in the production of cellular energy.  It also helps in the formation of bone and cartilage.  Manganese is necessary for reproduction and the metabolism of lipids.  Natural sources are grains and fruit.  Supplements include manganese chloride, manganese sulfate, and manganese carbonate.

Selenium, in conjunction with Vitamin E, is a potent antioxidant and provides cell membranes protection from free radicals.  It also helps to maintain normal thyroid and iodine metabolism.  Fish, eggs, and liver are natural sources.  Supplements include sodium selenite and sodium selenate.

Iodine is a component of thyroid hormones.  These hormones are vital for regulating metabolism.  They are also crucial for reproduction, growth, and development to occur normally.  Natural sources of iodine are fish, eggs, and iodized salt.  Supplements include calcium iodate, potassium iodide, and cuprous iodide.

Minerals need to be provided by the diet or in the form of supplements.  They must be maintained in the proper concentration for ideal fertility, development and growth, and overall health. 

References available upon request.