Mineral availability of organic mineral complexes
A number of mineral chelates and complexes are available from a variety of manufacturers. A chelate is described as a metal complex in which the metal atom is held in the complex through more than one point of attachment to the ligand (chelating agent), with the metal atom occupying a central position in the complex. Natural digestion of foods produces numerous ligands that can complex (chelate) with minerals in the diet and facilitate their passage from the lumen of the intestine into the cells of the intestinal wall, where they eventually chelate with natural ligands that transport the minerals throughout the body. In theory, the introduction of chelated minerals will increase absorption and utilization of the mineral because of a more favorable binding or stability constant. Therefore, in an animal’s digestive system, organic trace minerals, those that are bound to an organic ligand such as protein, amino acids or carbohydrates, may be more biologically available than inorganic trace minerals. Naturally occurring chelating agents are widely distributed in all living systems in nature including carbohydrates, lipids, amino acids, phosphates (phytic acid), porphyrins (e.g., hemoglobin and chlorophyll) and vitamins (vitamin B12 and ascorbic acid). These are the typical forms in which we find minerals complexed in nature (plant material or grains). When commercially manufactured the number of ligands or chelating agents is more limited than that found in nature but still creates significant variability when we compare these sources for use in a mineral supplement. The basic classifications are as follows:
Metal - specific amino acid complexes (MSAA complexes)
These result from complexing a soluble metal salt (inorganic mineral as described above) with a specific amino acid. For instance, one of the most common metal complexes is zinc methionine which is produced by combining zinc sulphate with the amino acid methionine. Other common metal (specific amino acid) complexes include copper lysine and manganese methionine. The production of these types of complexes results in a very specific metal complex that is consistent in molecular size and stability and thus is consistent in how it is digested and absorbed by the animal. It is also probably the smallest particle given that it is one metal atom complexed with one amino acid. When considered with the consistency and stability, MSAA complexes are probably the most effectively and efficiently absorbed of all the complexes. When considering this type of complex it should be noted that of the metal amino acid complexes, proteinates, etc., these are also probably the most expensive to include in a supplement.
Metal -amino acid complex
Another similar process produces a different type of metal amino acid complexes. This a more general type of product which is characterized by a metal atom (zinc for instance) complexed with several single amino acids. Each individual molecule is still one metal ion and one amino acid but you have a variety of amino acids in the blend. For instance for a zinc complex in this category, the blend would include zinc methionine, zinc lysine, zinc leucine, zinc cystine, etc. with each molecule being specific but the whole product being a blend of these complexes. This process would hold true for other trace minerals as well, copper, manganese, etc. Similar to the specific amino acid complexes this process results in molecules that are also the smallest in size.
Metal proteinates (MPT)
These are formed from the chelation of a soluble mineral salt with amino acids and/or hydrolyzed (broken up) protein. The final product may contain single amino acids, dipeptides, tripeptides or other protein derivatives and probably contains some of all these classifications. In many cases, research has shown that the resulting mixture (i.e. the metal and the peptide ligand) may be bound too weakly to withstand the environment of the digestive tract. These types of compounds have shown high degrees of solubility in the rumen leaving them available to be bound to other compounds that may prove less available in the small intestine. Due to their molecular variability metal proteinates are not defined chemical entities. Metal proteinates tend to be less expensive than other organic mineral complexes
Metal amino acid chelates (MAAC)
These are formed from the reaction of a metal ion from a soluble metal salt with amino acids having a mole ratio of one mole of metal to one, two or three (preferably two) moles of amino acids to form coordinate-covalent bonds. More simply put, MAAC’s are produced by combining a given amount of a metal with one to three times the equivalent volumes by weight of amino acid or peptide ligands to form varying complexes. Somewhat similar to the proteinates in variability, they are normally a smaller and somewhat more stable molecule.
Metal polysaccharide complexes
These are formed by complexing a soluble salt with a polysaccharide (carbohydrate) solution declared as an ingredient of the specific metal complex. The product is more of an organic mineral matrix without any chemical bonding between the metal and the polysaccharide. These are larger molecules based on chains of simple sugars that are known to be highly soluble in the digestive tract.
Metal propionates (MPP)
First recognized in 1891, are the result of combining soluble metals with soluble organic acids such as propionic acid. The resulting products are highly soluble and generally disassociate in solution.
Yeast derivative complexes
Another sources of organic trace elements that is showing promise are those integrated into a yeast cell for feeding as a trace mineral-enriched yeast. The most common of these at this time is selenium yeast with the selenium found largely to be complexed with a methionine molecule (selenomethionine). Use of element-specific amino acid complexes (i.e. specifically zinc or copper or manganese, etc.) reduced vitamin destruction in a vitamin-trace mineral premix compared to inorganic trace mineral sources. When other antagonists are involved, if there is high dietary molybdenum, copper in chelated form has an advantage over an inorganic form as it may escape the digestive system complexing among molybdenum, copper and sulphur.
Interestingly, some studies have shown no benefit from chelated and complexed minerals, but most have shown positive responses compared to inorganic sources. One study suggested that at adequate levels of dietary zinc, bioavailability of supplemental zinc sources may be less important than under conditions of limited dietary zinc or if very high levels of supplemental zinc are fed. Dietary copper from sulphate and lysine sources had similar results for cattle with adequate copper status. However; copper lysine at 16 mg of copper per kg diet appeared to be more beneficial for animals that were borderline to deficient in copper status. Organic copper provided a more bioavailable form of supplemental copper than copper sulphate for postpartum first-calf heifers. Organic trace minerals are generally of very high bioavailability, and they are particularly attractive for high-producing or stressed animals or for problem areas (e.g., high dietary molybdenum for ruminants) where cheaper inorganic sources are less effective.
Providing proper protein nutrition
The relationship of an animal protein and energy status is a key component in proper mineral utilization. Protein aids in absorption, transport and metabolism and is critical in maintaining the absorption function of trace elements in the intestinal tissues. Carrier proteins are essential for effective transport of trace elements. Copper and zinc transport involve very specific proteins.
Biomarkers for mineral status assessment
Sub-clinical or marginal deficiency of minerals are very widespread and are likely to be more economic significance than are easily recognized cases with prominent clinical signs as with inadequate intake of minerals, the animals have lower growth and milk production and lower reproductive efficiency without readily recognizable symptoms. Parameters like growth rate, tissue and physiological fluid concentration, enzyme concentration and activity, chemical balance and mobilizable stores are some of the indeces for assessing mineral status. The recommended requirement of zinc is 30 mg Zn/kg diet, a concentration which should satisfy requirements in most situations. Zinc deficiency can adversely affect reproductive processes in females from estrus to parturition. Inadequate Zn levels in gestating cows may result in abortion, fetal mummification, lower birth weight or altered myometrial contractility with prolonged labor. Other effects reported include impaired growth, delayed puberty and decreased appetite in Zn deficient bull calves. A loss of appetite results in lowered mineral ingestion, which further decreases, feed utilization due to impaired nutrient metabolism. Relative bioavailability of zinc from grains and legume seeds averages about 60-70%. Supplemental sources like zinc sulphate and zinc oxide are well utilized and their relative bioavailability is 100%.
Blood and its specific nutrient concentrations provide useful but frequently inadequate index. Specific biochemical and physiological measurements including enzyme activity, such as glutathione peroxidase, selenoprotein, selenoprotein mRNA levels for Se, acute phase protein (Ceruloplasmin), Cu/Zn-superoxide Dismutase (Cu/ Zn-SOD), Cu chaperone CCS and other cupro-enzymes for Cu, hair and cells concentrations, alkaline phosphatase and Zn-binding protein (metallothionein), Zn- metaloenzymes, metallothionein mRNA for Zn, Cu/Zn-superoxide dismutase for Cu and Zn, urinary iodine, blood concentration of thyroid stimulating hormone and thyroglobulin for I status provide useful endpoints for assessing the mineral status of animals. The potential for identifying suitable biomarkers using high-throughput technologies such as transcriptomics and proteomics are essentially needed if search for mineral biomarkers are to be successful.