An Overview of Various Types of Organic Trace Minerals in Poultry Nutrition

Marked deficiencies are unlikely to occur in modern commercial production systems; however, marginal deficiencies could arise under certain conditions such as poor feed formulation or low feed intake. The occurrence and severity of mineral deficiencies are influenced by the duration of time that deficient diets are fed, prior mineral status, and the physiological state of the animals (Hill,2000).

What are Organic Trace Minerals?

Organic Trace Minerals, considered the third generation of trace minerals, are increasingly utilized globally. Their advantages stem from the chelates' unique chemical structure, consisting of central ions (or atoms) and ligands. In these compounds, the central ion is located in the centre and is surrounded by ligands in a specific spatial arrangement, connected by chemical bonds. The central ions, such as zinc, iron, copper, manganese, and chromium, are termed the forming bodies, while amino acids are ligands. This molecular structure results in stable compounds that are resistant to chemical reactions with other substances and exhibit excellent solubility in animals. Due to their moderate stability constant, these compounds are easily absorbed through the small intestinal mucosa of animals.

The main difference between organic and inorganic zinc sources is the presence of carbon. Inorganic sources lack carbon, while organic sources contain carbon and carbon-hydrogen bonds (Jahanian et al.,2010). Frequently, the terms "complex" and "chelate" are mistakenly used interchangeably. A metallic ion combined with a ligand forms a complex. This complex can be as simple as a single bond or can involve multiple bonds. When multiple bonds are present, it's specifically referred to as a chelate (Byrne et al.,2022).

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Definition of Organic Trace Minerals:

a).According to the Association of American Feed Control Officials (AAFCO), several types of organic trace minerals are defined as follows:

57.142 – Metal Amino Acid Chelate

This is produced from the reaction of a metal ion from a soluble metal salt with amino acids. It typically has a mole ratio of 1 mole of metal to 1-3 moles of amino acid (preferably 2) to form coordinate covalent bonds. The average molecular weight of the amino acids should be around 150 daltons, and the chelate's molecular weight should not exceed 800 daltons. When used as a commercial feed ingredient, it must be declared as a specific metal amino acid chelate.

57.150 – Metal Amino Acid Complex

This product results from complexing a soluble salt (such as potassium or manganese) with amino acids. The minimum metal content must be specified. When used commercially, it should be declared as a specific metal amino acid complex, such as potassium amino acid complex, copper amino acid complex, zinc amino acid complex, iron amino acid complex, cobalt amino acid complex, calcium amino acid complex, or manganese amino acid complex.

57.151 – Metal (Specific Amino Acid) Complex

This is formed by complexing a soluble metal salt with a specific amino acid, with the minimum metal content needing to be declared. When used in commercial feed, it should be declared as a specific metal, specific amino complex, such as copper lysine, zinc lysine, ferric methionine, manganese methionine, or zinc methionine.

57.23 – Metal Proteinate

This product results from chelating a soluble salt with amino acids and/or partially hydrolyzed proteins. It must be listed as a specific metal proteinate when used as a feed ingredient, such as copper proteinate, zinc proteinate, magnesium proteinate, iron proteinate, cobalt proteinate, manganese proteinate, or calcium proteinate.

57.29 – Metal Polysaccharide Complex

This is produced by complexing a soluble salt with a polysaccharide solution and must be declared as a specific metal complex, such as copper polysaccharide complex, zinc polysaccharide complex, iron polysaccharide complex, cobalt polysaccharide complex, or manganese polysaccharide complex.

57.28 – Metal Methionine Hydroxy Analogue Chelate

This results from the reaction of a metal salt with 2-hydroxy-4-methylthiobutanoic acid (HMTBa), with a chelated molar ratio of one mole of metal to two moles of HMTBa to form coordinate covalent bonds. This ingredient is used as a source of trace minerals and must be declared as a specific metal chelate for a metal methionine hydroxy analogue chelate.

57.160 – Metal Propionate

This is the product of the reaction between a metal salt and propionic acid, prepared with an excess of propionic acid at an appropriate stoichiometric ratio. It must be declared as a specific metal propionate when used as an ingredient, such as copper propionate or zinc propionate.

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b) According to the European Union (EU) definitions:

57.23 – Metal Proteinate

Form: Powder
Minimum Metal Content:

10% for copper, iron, manganese, and zinc

Chelation:

Minimum 50% for copper, iron, and manganese
Minimum 85% for zinc

Chemical Formula: M(x)1–3. nH₂O

M = metal
x = anion of protein hydrolysates containing any amino acid from soya protein hydrolysate

57.142 – Metal Amino Acid Chelate

Form: Powder
Minimum Metal Content:

10% for copper and zinc
9% for iron
8% for manganese

Chelation:

Metals and amino acids from soya protein are chelated via coordinate covalent bonds
Maximum 10% of the molecules exceeding 1500 Da

Chemical Formula: M(x)1–3. nH₂O

M = metal
x = anion of any amino acid from soya protein hydrolysate

57.151 – Metal (Specific Amino Acid) Complex

Form: Liquid or Powder

Liquid:

Minimum 6% for copper
Minimum 7% for zinc

Powder:

Minimum 15% for copper, iron, zinc, and manganese
Maximum moisture content:

13% for copper
10% for iron, zinc, and manganese

Chemical Formula: M(x)1–3. nH₂O

M = metal (Cu or Zn)
x = anion of glycine

Mode of action:

Minerals bonded to amino acids may potentially be absorbed more efficiently by the gut wall, although conclusive evidence is still lacking. For instance, a study demonstrated that adding methionine to a human diet doubled copper absorption (Goff, 2018). The mechanisms of absorption for bonded metals remain uncertain: some studies suggest that the metal separates from the ligand during absorption, while others propose that the metal-ligand complex is absorbed intact. Research by Gao et al. (2014) strongly suggested that amino acid-bonded metals are absorbed more readily and possibly through non-standard inorganic transporters, based on findings using Caco cells in vitro. Another supplier's research indicated that their glycinates were absorbed more effectively than sulfates in a similar model. However, it remains unclear whether these observations hold universally true across different conditions and biological systems.

In general, chelates are categorized based on their stability constants (Qf values). Here's a breakdown:

- Chelates with a Qf value below 10 are considered weakly chelated.

- Moderately strong chelates typically have Qf values in the range of 10 to 100.

- Chelates with Qf values above 100 are considered strongly chelated.

The stability constants indicate how tightly the metal ion is bound to the ligands (such as amino acids) in the chelate complex. A higher Qf value generally suggests greater stability and resistance to dissociation, which can influence the bioavailability and effectiveness of the chelated mineral in animal nutrition (Cao et al.,2000 & Byrne et al.,2022).

Points to be considered while selecting an organic trace mineral:

Bond strength
Chemical form and purity of the mineral sources
Differences in dissociation rates of the mineral form from the ligand
Particle size of the mineral
Processing conditions/manufacturing method
Solubility
Stability
Bioavailability

Conclusion:

In poultry diets, selecting the optimal form of organic minerals is critical for maximizing nutrient utilization and overall bird health:

Bioavailability and Absorption: Choose organic minerals with high bioavailability and proven absorption rates in poultry species, ensuring efficient utilization of essential nutrients.
Chelate Stability: Prioritize forms with stable chelation properties, indicated by moderate to strong stability constants (Qf values), which support resilience through digestive processes.
Formulation Compatibility: Select mineral forms (e.g., amino acid chelates, amino acid complexes, proteinates) that integrate smoothly into poultry feed formulations, enhancing dietary consistency and efficacy.
Supplier Reliability: Source from reputable suppliers known for quality assurance and transparency in product specifications, ensuring reliability in nutrient content and performance.
Cost-Effectiveness: Balance the benefits of enhanced mineral bioavailability and poultry performance against the cost of the chosen organic mineral source, optimizing overall feed efficiency and economic viability.

By prioritizing these factors in poultry nutrition, producers can effectively enhance nutrient uptake, growth rates, and overall health outcomes in their flocks.