Organically Inorganic - Minerals

In recent years, copper levels have become a hot topic in the pet food industry, as copper-associated liver hepatopathy has been a topic of discussion as of late. This disease is a result of an inherited defect in copper metabolism in specific dog breeds, thus, the question lingers if other dog breeds might have this condition from dietary copper accumulation. While there is limited scientific data on this subject in pets, we need to understand the sources of copper, or any mineral, being fed. There is no better place to dig deeper than research done on livestock animals. As animal agriculture migrates towards more cognizant feeding strategies in an era of cereal uncertainty in livestock diets, feeding management needs to maintain the delicate balance of doing more with less. This philosophy combines two important principles. Nutrient output is reduced through efficient nutrient management strategies, while diet design maintains a healthy and efficiently producing animal. As diets are formulated, ingredient and supplement choices are made based on available knowledge regarding nutrient bioavailability, environmental impact, and price. Trace mineral premixes contain an array of mineral concentrations and sources which are often based on growth studies or other experimental data. In agricultural nutrition, premixes contain copper (Cu) and zinc (Zn); for example, 20-50-fold above their requirements for pharmacologic growth stimulation. Even at non-pharmacologic concentrations, trace minerals, such as copper, are still routinely fed five times above the pig’s requirement,¹ with equal biological impact and bioavailability assumed between mineral sources. Some may be aware of the confusing wording on “organic”- and “inorganic“ minerals, so let’s start there and discuss “bioavailability” in subsequent articles.

It is important to understand that not all mineral sources are equal in their bioavailability and biological impact. Choices between mineral sources can become overwhelming, not even to mention other nutrient interactions which can be both antagonistic and protagonistic. Formulators must choose to incorporate either ‘inorganic’ Cu sources such as salt, copper sulfate, or ‘organic’ Cu sources. The term ‘organic’ is often used to describe a mineral attached to an organic ligand, that can be chelated or complexed in at least five different variations including metal amino acid (AA) complexes, metal AA chelates, metal polysaccharide complexes, or metal proteinates. Copper salts such as Cu- sulfate (CuSO4), oxide (CuO), carbonate, acetate, and chloride have been traditionally added to animal and human diets to meet or exceed nutritional recommendations. Traditionally, Cu sulfate has been used to supplement growth-promoting levels in weanling pig diets, as Cu oxide is ineffective as a growth promotant.² Liver Cu concentrations of pigs fed either CuSO4 or CuO were 137- or 16- mg/kg Cu, indicating large effective differences between inorganic sources, as well as increased bioavailability from CuSO4. It is no surprise that the Association of American Feed Control Officials (AAFCO) does not recommend utilizing Cu oxide as a source of pet food.

Organic minerals can be bound in a variety of structurally different ways and are unified by their ‘organic’ carriers. The term chelated stems from the Greek word chele, meaning crab’s claw. A chelated mineral provides a ligand that surrounds a metal ion by coordinating covalent bonds, forming a ring-like structure. A ‘complexed’ mineral is one in which the ligand is bound by covalent bonds, without the ring-like structure.³ Many variations of ‘organic’ minerals can be formed, such as mineral AA complexes, specific mineral AA complexes (avg MW of AA must be ~150), metal AA chelates, metal polysaccharide complexes, or metal proteinate. According to AAFCO,⁴ a mineral chelate refers to the products “resulting from the reaction of a metal ion from a soluble metal salt with amino acids with a molecular ratio of one mole to one to three (preferably two) moles of amino acids to form coordinate covalent bonds”. Similarly, complexing a soluble metal salt with amino acids(s) or hydrolyzed protein results in a metal amino acid/proteinate complex. Copper can be bound to a variety of AA, and the type of amino acid affects the stability of the chelate, with preferential utilization of basic amino acids arginine, histidine, or lysine. It is this coordination chemistry, which surrounds the structure of metal ions that greatly influences how available the mineral will be for utilization by the animal. As the American architect, Louis Sullivan once wrote in 1896, and was later promoted by Frank Lloyd Wright:

“It is the pervading law of all things organic and inorganic, of all things physical and metaphysical, of all things human and all things super-human, of all true manifestations of the head, of the heart, of the soul, that the life is recognizable in its expression, that form ever follows function. This is the law.”

The simplistic beauty of this notion is easily translatable to organic- and inorganic-ly bound minerals, as the form refers to the role ligand coordination chemistry plays towards the function, or impact it will have in being digested, absorbed, utilized, and impact the animal.  Understanding mineral chemistry will help us better understand bioavailability, nutrient interaction, and absorption mechanisms in future articles, but mainly help us evaluate data to provide sound guidance in the area of nutrition.

References

1. 1998. Nutrient Requirements of Swine. 10th ed. National Academy Press, Washington, DC.
2. Cromwell G.L., Stahly, T.S., Monegue, H.J. 1989. Effects of Source and level of copper on performance and liver copper stores in weanling pigs. J. Anim. Sci. 67:2996- 3002.
3. Ashmead, H.D., Graff, D.J., Ashmead, H.H. 1985. Intestinal absorption of metal ions and chelates. C.C. Thomas, Springfield, Illinois.
4. 2001. Official Publication. Association of American Feed Control Officials, Oxford, IN.

About the author: Dr. Blaire Aldridge is BSM Partners Director of Nutrition. Prior to this, she was one of the industry’s primary innovators in companion animal nutrition, leading teams at Nestle Purina to groundbreaking products and solutions, in addition to her innovations in Equine nutrition.
Her PhD studies at Purdue University focused on mechanisms of nutrient absorption and gene expression before moving on to post-Doctoral work in Human Nutrition at Washington University Medical School. Blaire prides herself in the cultivation of a wide perspective, open conversation among peers, and above all, integrity of purpose and profession.

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