“Nutritional importance of zinc”
Zinc is present in every body tissue and every tissue fluid. Among trace minerals in the body, only iron is found in greater concentration. Zinc serves two broad purposes; enzyme function and protein synthesis. In human medicine, patients deficient in zinc have shown improved wound healing following oral zinc supplementation. It has also been reported that skin absorption of zinc increases at wound healing sites. and that tensile strength of healing skin is greater when zinc is supplemented. When dogs need zinc for healthy coats and skin in the diet is necessary for normal pigmentation of the coat – a concern of many dog breeders.
Zinc deficiency in dogs is characterized by one of more of the following clinical signs:
-skin lesions -slow and sparse hair growth
-poor growth -abnormal sexual development
“Dermatosis : A special zinc deficiency problem” dermatosis caused by zinc deficiencies has been discussed frequently in veterinary literature. The Dermatosis caused by zinc deficiencies has been discussed frequently in veterinary literature. The Merck Veterinary Manual (6th Ed.) notes that “dermatosis may be associated with nutritional deficiencies, especially those of proteins, fats and trace elements (including zinc)”.
Simply because zinc is in a dog’s diet does not necessarily mean tat the mineral is available to the animal. Even well fed dogs can be zinc deficient if absorption of zinc is hindered by certain nutrients or foods. Scientists have noted that high levels of calcium interfere with zinc assimilation. Zinc absorption is also inhibited by high levels of copper, cobalt, phytates (salts produced by phytic acid, and acid in cereal grains like wheat and soybeans), phosphorous, starch, and fibre.
“Process of zinc absorption”
Absorption and clearance of zinc from the plasma occurs quickly after ingestion by way of homeostatic control. Both extracellular and intracellular factors determine the amount of dietary zinc that reaches the plasma from the intestinal lumen. Zinc in ionic form does not cross the membranes off mucosal cells in significant amounts. To cross these lipoid barriers, zinc must first form complexes with organic molecules known as zinc binding ligands (ZBL).
Amino acids form complexes with zinc and other cations which can cross the mocosal cell membrane readily. The mucosal cell contains proteins known as metallothioneins, which bind zinc ions. Intracellular concentrations of these proteins can change rapidly in response to an animal’s zinc status and dietary zinc intake. Increased intracellular concentrations of zinc metallothionein is in reserve for transport. Zinc metallothioneins provide the mechanism of homeostatic control governing the amount of zinc that reaches the bloodstream. Absorption of zinc ions from the intestinal lumen into the mucosal cells is controlled by several factors:
-Solubility of dietary zinc source. Zinc oxide is relatively insoluble in water, and its rates of dissolution depends on the PH of the contents of the gastrointestinal tract. Zinc sulfate and zinc chloride are readily soluble in water, and provide ionic zinc; however, they irritate gastrointestinal membranes.
-Presence of ZBL’s, which form complexes with amino acids to be absorbed. The amount of zinc absorbed depends upon the fraction of zinc ions present as absorbable complexes.
-Presence of chelating agent, which form unabsorbable complexes. Absorption of dietary zinc is adversely affected by high dietary levels of phytates, calcium, phosphorous and fibre. Also, trace minerals such as copper and iron in high levels compete for ligands, leaving less ZBL to form complexes with zinc ions.
“Problems with conventional zinc compounds”
Synthetically chelated zinc products are usually excreted in the urine shortly after ingestion. As a result, most of the zinc and many other heavy metals are wasted. Zinc chelated with hydrolyzed protein is bound by more than one amino acid and must be altered by the body before it can be absorbed.
Inorganic compounds such as zinc oxide and zinc sulfate cannot be used by the body as sources of zinc until complexes have been formed with specific organic compounds in the gastrointestinal tract.
Sometimes these complexing compounds are not present in sufficient concentrations for adequate zinc absorption. Giving an animal excessive amounts of organic zinc compounds can create an imbalance or deficiency of other metals like copper or iron.
Zinc methionine, the compound contained in Availa®Zn overcomes many of the problems encountered in administering zinc supplements. A unique, patented compound, zinc methionine contains the amino acid methionine, zinc and the acid sulfate anion in a 1:1:1 ration. In this well defined organic compound the zinc ion is coordinated with amino and carboxyl groups of the amino acid methionine. The acid sulfate anion (HS04) and water molecules occupy the remaining vacant bonds in the coordination sphere of zinc. Because of its chemical structure, zinc methionine does not need ZBL; it can be absorbed directly and carried to the target organ as zinc methionine. In addition, zinc methionine is free from the adverse dietary effects of phytates, calcium, phosphorous, and fibre, and it does not compete with copper and iron for ZBL. Unlike chelated zinc or inorganic zinc compounds, zinc methionine is a soluble organic complex that is a readily bioavailable source of zinc for dogs.