Trace minerals – zinc, copper, manganese, cobalt, iron etc. are essential nutrients in animal nutrition. They can exist in more than one oxidation states and thus has capability to participate in various kind of metabolic redox reactions.
These trace minerals exhibits wide range of activities and performs various functions within the body, being involved individually or collectively in general metabolism, reproduction, the immune system, growth, development and repair of various tissues etc.
These trace minerals are present in the natural feed stuff such as corn, wheat, soybean, millet etc. However, these they are often in lesser bio-available form and in inadequate concentrations leading to gap between the metabolic need of the animal and the quantity fed through feed stuff.
Trace minerals normally exists as chelates or salts within the grain as plenty of ligands like peptides and proteins and salt forming compounds like fatty acids, flavanoids, lecithins etc. are available in the system. As an example iron is largely available in the bio-available chelate form as iron-ferrin, ferrin being a protein. However, in general, because of competition of plenty of ligands and fatty acids available in the system, it is very difficult to predict resultant bio-availability of the mineral, which further gets complicated by variation in breed of the grain, nutritional management during crop production and the season.
Mineral deficiency generally reduces disease resistance and exposes the cells to oxidative stress. To overcome trace mineral deficiencies, inorganic salts are being generally supplemented to the animal feed.
Trace element bioavailability, or the degree to which or rate at which it is absorbed after administration, varies based on a number of circumstances. For example, the reasons for variations are influenced by the different digestive tract anatomies between the species. In addition, trace element bioavailability depends further on a number of factors, such as: the status of the trace element; its ability to form chemical bonds; the trace element’s dosage; and the antagonists which inhibit absorption.
The various feed additives approved as trace element sources can be distinguished in terms of their availability for the animal. The best known and largely used inorganic trace minerals, sulphates and oxides, vary mainly due to their solubility in the aqueous medium of the digestive tract. A product with very low solubility, e.g. copper oxide, should therefore be avoided in livestock feed.
However, the high solubility of sulphates provides the disadvantage of very reactive copper ions, i.e. a strong pro-oxidant initiator and thus hurries oxidation, which promotes adverse reactions with feed components. This causes the degradation and damage of sensitive ingredients, such as vitamins and fat, as well as leads to formation of harmful free radicals and peroxides and consequent reduction in palatability of feed.
In contrast to inorganic, organically bound trace elements, or chelates, are stable in the diet and improve absorption due to their chemical structure. The advantage is not only lower solubility in aqueous medium when compared to inorganic trace elements, but also reduction of absorption-inhibitory responses in the digestive tract. The positive effects of organically bound versus inorganic trace elements have been confirmed in numerous scientific studies.
Chelate is defined as a form of organic mineral which are formed by complexation of the inorganic salts with one or more organic ligands. Chelated trace minerals are the safe choice which increase the bio-availability by reducing ionic nature of the associated metals and hence increasing its absorption across the intestinal cell barriers.
Much trial work has been carried out in monogastrics where stable trace element sources, e.g. chelates or hydroxy trace minerals, confirmed better effects when compared to sulphates with regards to an improved bioavailability, intestinal efficacy and gut health.
In case of ruminants some of the trace mineral chelates provides additional advantage of trace mineral bypassing the rumen to reach the intestine. Few chelates available in market are bound with ligands susceptible for rumen fermentation and they behave like naked ionic minerals. Protein hydrolysate, amino acid ligands belong to this kind of category and they under perform seriously from the view point of bioavailablity of trace minerals to the ruminants.
Another factor that need to be considered while choosing chelates is its stability constant. As we know, the chelate forms with its reduced polarity when compared to its precursor ionic form, have better passage capability through cell wall leading to enhanced bioavailability, but may vary in its stability constants depending on nature of metal ion, ligand and medium. To cite an example, we have highly stable EDTA chelate which do not release metal ion even under extreme conditions making it useless from the view point of requirement of the intestinal cells. The other extreme is highly unstable pseudo-chelates formed from carboxylic acids and some hydroxy acids.
Based on chemistry, kinetics of hydrolysis of chelates and gut conditions and numerous in-vitro simulation and field trials it has been shown that chelates made out of specific amino acids enhances bio-availability. However the best comes from hydroxy analogs of amino acid chelates both in ruminants as well as non-ruminant species because of extra-stability of these hydroxy analogs of amino acids in acidic pH conditions.
Hydroxy analog amino acid chelates with trace minerals like Cu, Mn, Zn and Fe have been standardized to assure superior bio-availability and is being extensively used as part of productive animal nutrition programs.