Trace minerals play an important role in the body. Though required only in small quantities as compared to other nutrients, their deficiency may cause poor health and impaired performance. A trace mineral deficiency in the diet can reduce production efficiencies by 20-30%. As a result, trace element supplementation in animal diets has long been used to ensure rapid development, enhanced reproductive health, and improved immune response (Overton and Yasui., 2014).

Over the years trace elements have been supplemented in animal feeds as inorganic salts such as sulphates and chlorides. However, the bioavailability of trace elements from these inorganic sources is relatively lower than that of minerals from feed and fodder sources (Spears., 2003). Recent studies in mineral research indicate that absorption and utilization of trace elements is higher if they are supplemented in an organic form.


The classification of Organic trace minerals as done by the Association of American Feed Control Officials (AAFCO, 1998) is tabulated below. According to AAFCO organic minerals are metal ions chemically linked to an organic molecule such as an amino acid which forms a chemical structure with unique characteristics bringing about stability and high mineral bioavailability.


Metal polysaccharidesMetal polysaccharide complexes are formed by complexing of a soluble salt with a polysaccharide solution, e.g., Zn or Mn-polysaccharide complex.
Metal ProteinatesThe product resulting from the chelation of a soluble salt with amino acids and /or partially hydrolysed protein. e.g., Cu, Co and Mn proteinates.
Metal amino acid ComplexThe product resulting from complexing a soluble metal salt with an amino acid (s), e.g., Zn-Amino acid complex, K- Amino acid complex, and Cu- Amino acid complex.
Metal (Specific Amino Acid) ComplexThe product resulting from complexing a soluble metal salt with a specific amino acid. Minimum metal content must be declared. When used as commercial feed ingredient, it must be declared as specific metal, specific amino acid complex: e.g., Cu-lysine, Zn-lysine, Mn- methionine.
Metal amino acid ChelatesMetal amino acid chelates are available for Zn, Cu, Fe, Mn and Co in addition to the macro-minerals like Ca and Mg. The product resulting from the reaction of a metal ion from a soluble metal salt with a mole ratio of one to three (preferably two) moles of amino acids to form coordinate covalent bonds. The average weight of the hydrolysed amino acids must be approximately 150 and the resulting molecular weight of the chelate must not exceed 800 Da.



  • Molecular size is a major factor in determining the bioavailability of organic trace mineral.
  • The molecular size of organic trace minerals depends on the nature of the ligand and the molecular ratio of ligand to the metal.
  • The variations in the molecular size of an organic trace mineral affects  its bioavailability and consequently its ability to influence animal performance.


  • Solubility of an organic trace mineral is a key determinant of bioavailability.
  • Organic trace minerals that have low solubility in the intestine are not absorbed efficiently.
  • The solubility of an organic trace mineral generally decreases as the size of the ligand increases from a single amino acid to a dipeptide, tripeptide, and so on. If the size of the ligand exceeds a tetra or pentapeptide, the ligand is almost insoluble in the intestine.


  • Metal specific amino acid complexes result from complexing a soluble metal salt with a specific amino acid. They combine a specific single amino acid with a single metal ion to form a specific chemical entity. The end product is a new molecule containing one ion of the metal and one molecule of the specific amino acid.
  • An organic trace mineral containing only a small and specific ligand such as a single amino acid is likely to be absorbed intact, leading to a better bioavailability.
  • Studies evaluating the effect of amino acids and some “derivatives” on copper absorption showed that, in general, the Copper complexes of monomeric (one) amino acids are better absorbed than dimeric (two) or trimeric (three) or polymeric (four or more) amino acids (Kirchgessner and Grassmann, 1967, 1969).


  • The effectiveness of organic trace minerals is attributed to the association of the metal with the ligand. It is therefore imperative for the metal-ligand complex to remain stable in the digestive tract.
  • The pH in the digestive tract varies between 2 and 7. This means, that when ingested by an animal, an organic trace mineral faces the challenge of an acidic to a neutral environment.
  • This change in pH levels influences the stability of the organic plex as a reduction in pH  leads to an increase in  dissociation of the mineral and the ligand.

Organic trace minerals have a higher bioavailability resulting in better animal performance, health, production and immune response. Critical factors such as size, solubility, specificity and stability of an organic trace mineral ensure optimum absorption and bioavailability. If such factors are not taken into consideration, a deficiency in trace minerals may result in sub optimal performance affecting growth, egg production, milk production and more.

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