Mineral Needs Of Broilers

Calcium and phosphorus make up about half of the total mineral needs. Calcium and phosphorus have been historically linked almost from the beginnings of nutrition as a science. The interrelationship of the two is widely documented and is generally given consideration when expressing requirements for either mineral. Calcium is one of the cheapest minerals to provide, and the tendency is often to overfortify. Excesses can be detrimental to the chicken as excess calcium forms complexes with phosphorus in the intestine that may inhibit P digestion. The ratio of calcium to phosphorus should not be allowed to become extreme. Excesses of calcium may also compete with zinc, magnesium, and manganese. Since these minerals are usually found in only small quantities, excesses of calcium may easily become antagonistic to these minerals, resulting in apparent deficiencies.

Supplemental sources of calcium include ground limestone and crushed marine shells. The limestone should be low in magnesium, as dolomitic limestones may cause diarrhea, although a certain amount can be tolerated. Oyster shell is similar in calcium content to ground limestone. Most phosphorus supplements also contain high levels of calcium that are highly digestible by chickens.

The primary role of phosphorus in poultry nutrition is for proper bone formation in growing animals. Phosphorus is also needed in a number of other roles, such as in energy metabolism, but the needs for these functions are small in relation to bone development.

Phosphorus from plant sources is poorly digested. Phytate phosphorus is an organic complex found in plants that includes phosphorus. On the average, about 70% of the phosphorus in plants is in this form. It is highly indigestible by monogastric animals and therefore is of limited use as a phosphate source. In order to break this molecule, the enzyme phytase is required. This enzyme is lacking or limited in monogastric animals. However, phytase enzyme is available for supplementing diets to release a portion of the bound phosphorus.

The majority of the phosphorus provided to the chicken is produced from phosphate rock. Most phosphate deposits contain high levels of fluorine, which can be toxic to animals. The rock is generally processed to remove much of the fluorine. The two most common phosphate supplements used in broiler diets are defluori-nated phosphate and dicalcium phosphate. In some areas, phosphate deposits with low levels of fluorine are found and are often used without processing. Quite often, the biological value of such phosphates is lower than that of the processed phosphates, but in certain areas, they may be more economical to use or may be the only sources available.

Sodium, chloride, and potassium function together as primary determinants of the acid base balance of the body and in maintenance of osmotic pressure between the intracellular and extracellular fluids. The relationship between these three is important and must be kept in proper balance, although no one agrees completely on what this balance should be. It is not generally considered necessary to supplement diets with potassium. Sodium and chloride are typically provided by the addition of salt.

Electrolyte balance refers to the balance between the positive and negative ions in the body. This has been calculated in different ways, the most common using the levels of sodium, chloride, and potassium to calculate electrolyte balance. One common formula used is as follows:

DEB (meq/kg) = (%Na x 434.98) + (%K x 255.74) - (%Cl x 282.06)

While no specific values are recommended, most starter diets will contain a DEB of 200 to 250 meq/kg, grower diets from 180 to 200 meq/kg, and finisher diets from 150 to 180 meq/kg. There is little evidence to indicate that levels other than these might improve or detract from performance.

Trace minerals are usually fully supplemented due to their relatively low cost, the need to provide a safety factor, the variability in composition of plants due to differences in geographical locations and fertilization rates, and the tendency for many to be bound by organic complexes and poorly digested. Most premixes would provide the entire needs for manganese, zinc, iron, copper, iodine, and selenium. In the United States, copper is often supplemented in levels far exceeding its nutritional needs. These high levels of copper have come under attack by environmentalists, and may also contribute to the development of gizzard erosion, where the lining of the gizzard is inflamed and irritated.

In general, trace minerals in the form of oxides and carbonates are less digestible, while sulfates or chlorides are more highly digestible. Organic chelates of various minerals are usually more biologically available; however, they are also considerably more expensive. Because many vitamins are subject to oxidation, mixing trace minerals and vitamins in a concentrated premix should be avoided to ensure adequate vitamin stability.

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