Mimicking Nature Boosts Trace Mineral Efficiency

Effective trace mineral nutrition is vital for healthy and active pets. Ensuring minerals are supplied in the most effective form for optimum bioavailability, stability and delivery will greatly improve the supply of trace minerals to all classes of pets.

Remember when you were young and the grown-ups told you to ‘eat your vegetables’? Other than the well-known addition of fibre to your diet, they also provide you with trace minerals. This natural presentation of trace minerals can bring significant benefits to the pet food industry. (Getty images)

Essential – but dangerous

Trace minerals play a role either structurally, catalytically or functionally with nearly every protein and biochemical process. Iron, zinc, manganese, copper and selenium all play essential roles in the body and supplying them effectively is crucial for healthy pets. Zinc, for example, is involved in more than 3,000 proteins in the body and in the very important processes of gas exchange, DNA transcription, redox, pH homeostasis and cell signalling.

As the name implies, ‘trace’ minerals are only required in very small quantities, and even small deviations in cellular content can result in dysfunction, disease and even death. Trace minerals are some of the most tightly controlled nutrients in the body, from both a legislative and nutritional perspective.

Mimicking nature

Trace element supply is a universal challenge across all pet species and all feed types and presentations, especially where the food is high in fat. Trace minerals are highly reactive with other compounds, resulting in the oxidation of fat, degradation of vitamins, or interaction with one another leading to reduced absorption. They need a strong bond to a partner that still allows them to be absorbed by the digestive system.

In nature, trace minerals begin their journey when rock and soil wear down and the trace minerals literally dissolve. In nature, microorganisms in the soil bind trace minerals to chelating agents. The term ‘chelation’ refers to the act of binding the trace minerals with a favourable organic (i.e. carbon-containing) partner. Strong chelation prevents the highly reactive trace minerals from acting against nutritionally valuable compounds. The now stabilised, yet soluble, trace minerals continue their journey to the roots of plants where they are absorbed.

The similarity between how plants and animals gain access to metals is striking and it is tempting to speculate that this is a general scheme in biology. (See table 1).

Table 1. Mechanisms used for acquiring metals by plants and animals are strikingly similar

Bound, but free

Trace minerals need to be bound to reduce their derogatory effects to other compounds, but to retain their functionality, they must remain available for absorption by the digestive system despite the bond. For that reason, they must remain soluble as solubility facilitates availability. By mimicking the way metals are delivered in nature it is possible to contain their reactivity throughout production, feed storage and digestion, and deliver them just where they are needed. Optimins® from Trouw Nutrition are strongly chelated trace minerals which allow delivery in the right part of the digestive system with high bioavailability, delivering significant benefits (See table 2).

Ideally, trace minerals should remain bound in the optimum form until absorbed by the animal. The strength of the bond is highly important. If the bond with the binding partner (ligand) is weak, then it can be broken and a bond will be made with another available ligand, for example fat, which is then oxidised. The loss in nutritional value is two-fold: less nutrition for the animal and money wasted on trace minerals that are not delivered.

Table 2. Benefits of Optimin® organic trace minerals

The challenge in delivering trace minerals

Essential trace minerals are not inert but are chemically active. Commonly used trace minerals in the pet food industry are in inorganic form, commonly sulphates and oxides. Most inorganic minerals disassociate easily during diet preparation, manufacture, or the digestion process. These dissociated minerals (charged ionic forms) can easily be tied up by dietary antagonists (e.g. phytates, tannins, phosphate, molybdenum) rendering the minerals insoluble and therefore effectively depressing their absorption by the intestinal cells (Erdman 1979; Fernandez and Philips, 1982).

Sulphates easily dissociate when in contact with moisture. Sulphates are also hygroscopic and bind moisture from the air, leading to degradation occurring in premixes before the minerals are used for manufacture of finished products. The attracted moisture can also cause lumps in the premix, and accelerate degradation of vitamins and oxidation of fats.

Oxides present concerns regarding availability. Iron oxide is known to have very poor bioavailability. For manganese there is no data in dogs and cats, but other species show lower bioavailability of oxide compared to sulphate, and chelates having enhanced bioavailability (Henry, 1995). Copper oxide has shown to have low availability in dogs (Fascetti AJ et al. 1998).

Zinc bioavailability is greatly affected by other components in the diet, but there are some studies suggesting zinc oxide has low availability and is prone to antagonistic reactions (Brinkhaus et al., 1998; Lowe et al. 1994; Lowe and Wiseman, 1998, Baker and Ammerman 1995, Lowe, J. A. & Wiseman, J. (1997)), while work in pigs reported similar availability between zinc sulphate and oxide (Baker, 1995).

Building strong bonds

There are various chemical factors affecting the strength of the bond between a trace mineral and its ligand. The major factors are:

1.) pH, the master regulator of speciation (choice of ligand)
2.) Redox potential, how easily electrons are moved between elements and the electrochemical behaviour with other compounds.
3.) Available ligands, types of ligands and ratios of ligands to trace mineral.
4.) Ionic strength, common and counter ions.

The first, diet pH, is by far the most important regulator for speciation and solubility throughout pet food manufacture and the digestive process. Trace mineral chelates and amino acid complexes that are resistant to pH and redox fluctuations are well suited for pet diets. Redox potential is more important for iron and copper and accounts for many of the shelf-life and feeding problems associated with trace minerals. Manganese can be influenced by pH and redox but this has not yet been found to be a major problem in pet foods. Selenium is less affected by these factors because it prefers covalent bonds.

In the late 1950’s organic trace minerals were developed, which were found to reduce many of the problems related to feeding mined minerals. They have several chemical characteristics that make them more suitable than inorganic minerals for pet food such as resistance to chemical changes created by pH and redox fluctuations. In the 1980s, work done by Bo Lonnerdal changed the general thinking about minerals and metal nutrition, leading to the development of organic minerals which more closely replicated natural processes.

It is extremely important to know how different organic sources will respond to a pH challenge. Zinc proves a great subject to illustrate bond strength. Poorly chelated zinc sources can change chemical partners as pH varies during digestion. When changing ligands, zinc can easily lose its ability to remain soluble, reducing its bioavailability to the pet. Unfortunately, not all commercially available organic zinc minerals are resistant to a physiologically relevant pH challenge (Figure 1).

Figure 1. Proportion of zinc remaining bound to its ligand during a physiologically relevant pH challenge

An organic mineral must be able to maintain its structure at reduced pH levels to have any opportunity to survive the harsh environment of manufacture, the gut environment and digestion. Simple complexes such as zinc methionine, which does not qualify as a chelate, cannot survive the pH challenge. Other organic minerals with less appropriate amino acid partners were partially protected from pH modification and had intermediate stability values. However, only Optimins® remained stable when exposed to different physiologically relevant pH levels.

Optimins® organic trace minerals are unique in being bound to multiple oligo-peptides and amino acids rather than single amino-acid linked compounds. Optimins® are the most strongly chelated minerals on the market. Optimins® trace minerals are therefore stable throughout pet food manufacture and do not affect shelf life of the product, while delivering nutritional superiority.

Conclusion

A major challenge of effective trace metal nutrition in pet foods is bonding with a chemical partner, which can occur during diet preparation and digestion. These exchanges can influence metal solubility, redox activities and ultimately the accessibility of the metal for absorption. Both the source of the metals and the composition of the diet can influence the outcome of these interactions.

The sheer number of inorganic and organic trace mineral choices on the market make the process of choosing a trace mineral source even more confusing. There is no class of supplemental essential nutrients with more choices than those found for trace minerals. Trace minerals made utilising chelation avoid many of the hazards regarding metal solubility that can occur during diet preparation and digestion. Chelation strength is directly correlated to the ability of a natural chelate to evade these hazards and potential problems. Optimins® trace elements deliver optimum nutrition for pets where it is needed most.

References

Erdman, J. 1979. Oilseed phytates: Nutritional implications. Journal of the American Oil Chemists’ Scoety 56:736-741.
Fernandez, R., and Philips, S. 1982. Components of fiber impair iron absorption in the dog. American Journal of Clinical Nutrition 35:107-112.
Henry, P. 1995. Manganese bioavailability. Pp. 239-256 in Bioavailability of Nutrients for Animals: Amino Acids, Minerals, Vitamins, C. Ammerman, D. Baker, and A. Lewis, eds. New York: Academic Press.
Fascetti AJ, Morris JG, Rogers QR. (1998) Dietary Copper Influences Reproductive Efficiency of Queens. Journal of Nutrition 128 (12):2590S-2593S.
Brinkhaus, F., Mann J., Zorich, C., and Greaves, J. 1998. Bioavailability of zinc propionate in dogs. Journal of Nutrition 128 (supplement):2596S-2597S.
Lowe, J., Wiseman, J., and Cole, D. 1994. Zinc source influences zinc retention in hair growth in the dog. Journal of Nutrition 124(supplement):2575S-2576S.
Lowe, J., and Wiseman, J. 1998. A comparison of the bioavailability of three dietary zinc sources using four physiologic parameters in dogs. Journal of Nutrition 128(supplement):2809S-2811S.
Baker, D. H. & Ammerman, C. B. (1995) Zinc bioavailability. In: Bioavailability of Nutrients for Animals (Ammerman, C. B., Baker, D. H. & Lewis, A. J., eds.). Academic Press, San Diego, CA.
Lowe, J. A. & Wiseman, J. (1997) The effect of the source of dietary supplemental zinc on tissue copper concentration in the rat. Proceedings of the British Society for Animal Science, p. 67.
Baker, D. 1995. Zinc bioavailability. Pp. 367-398 in Bioavailability of Nutrients for Animals: Amino Acids, Minerals, Vitamins, C. Ammerman, D. Baker, and A. Lewis, eds. New York: Academic Press.