Although trace minerals make up a very small portion of the diets of high-producing dairy cows, they have a tremendous impact upon each animal’s health, reproduction and milk production status.
Minerals play vital roles in the activation of enzyme systems that drive almost every biochemical reaction in the cow’s body. Of particular importance are trace minerals such as copper, zinc, manganese and selenium, which might be contained at high levels in a well-balanced dairy diet, but are of no nutritional use to dairy cows unless they have a high degree of bioavailablity. Reliable sources of these trace minerals with superior bioavailability should be fed in the dairy barn, so their natural benefits are profited.
Bioavailability of trace minerals in dairy cows usually refers to an essential trace mineral source that is consumed, digested and absorbed by dairy cow in a form that can be metabolized and finally utilized in order to meet the dairy cow’s specific trace mineral requirements.
The feed industry has routinely supplemented commercial dairy feeds with different inorganic mineral salts with varying degrees of “bioavailability.” These compounds have different solubility, molecular mass, electrical charge, pH properties and chemical reactive states that affect the way and degree in which they are absorbed and retained in the cow. For instance, dairy research shows the relative bioavailabilities of “rock” sources of dietary copper follows the rank of highest to lowest absorption: copper sulphate (bluestone), copper carbonate and copper oxide (virtually unavailable).
Despite feeding a dairy diet with a good suitable level of essential trace minerals (often based on NRC requirements), there are many dietary factors that will adversely reduce trace mineral bioavailability and thus affect how much essential mineral the dairy animal finally receives or can utilize. Some of these dietary factors bind ingested trace minerals in the gut and make them unavailable for absorption in the small intestine. For example, high levels of molybdenum in the dairy diet combine with copper digested from the feed in the rumen and render it insoluble for absorption.
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Chelated trace minerals
In response to these biochemical obstacles to good trace mineral absorption and metabolism in dairy cattle, the use of “chelated organic” trace minerals in dairy diets has become mainstream nutrition.
Chelated/organic mineral compounds are positively charged trace minerals chemically bound to organic compound. They are produced by a specialized manufacturing process that takes a metal element (i.e. copper) from inorganic rock sources and attaches it to an organic molecule; often derivatives of a protein molecule such as a peptide or amino acid. Examples include: zinc methionine, copper lysine, and manganese methionine as well as non-specific trace mineral proteinates. It should be noted that selenium cannot be truly chelated. Rather, organic selenium is produced by feeding inorganic selenium to yeast, which incorporates it into their body proteins.
Similar to these organic metallo-proteins, a new category of chelates known as hydroxyl trace minerals have been introduced as a new source of bioavailable copper, zinc and manganese. They are well-defined crystalline structures held together by covalent bonds (similar to those found in proteinated trace minerals), which render them non-hydroscopic (do not absorb water), and non-oxidative (non-reactive with other nutrients such as fats and vitamins). Unlike organic trace minerals, which contain between 10-15 per cent specific trace mineral, hydroxyl trace minerals are available in higher trace mineral concentrations such as: copper chloride (54 per cent copper), zinc hydrochloride (55 per cent zinc) and manganese hydroxylchloride (44 per cent manganese).
Regardless of chelated source, some scientists think a trace mineral chelate’s superior bioavailablity has more to do with its reduced electrical charge that makes it less reactive with other molecules that might otherwise make it unavailable for absorption. Organic mineral compounds are also believed to be less susceptible to possible changes in pH, which tends to also affect inorganic mineral absorption.
Studies aimed at demonstrating the visible benefits of feeding chelated minerals with higher bioavailablity than inorganic minerals to dairy cattle have been variable.
In one experiment, researchers at North Carolina State University fed marginal copper-deficient heifer replacement calves either organic chelated copper, inorganic copper sulphate, or inorganic copper carbonate. The researchers concluded that organic copper may have the same bioavailability as inorganic copper sulphate under normal dietary conditions.
However in a second NCSU experiment, they fed the same treatments, but in the presence of high dietary molybdenum, known to be antagonistic toward dietary copper. As a result, the organic copper was then shown to have greater intestinal absorption and liver retention in the animals than the inorganic copper sources. Such evidence pointed to the advantage of using chelated minerals under special conditions in dairy nutrition.
To help iron out these inconsistencies, a new statistical review technique called meta-analysis has been applied to such practical field studies in order to determine common patterns, areas of disagreements among treatment results and any significant experimental interactions. For example, a meta-analysis examined 20 dairy research papers and reports (2010) performed by the Zinpro Corp (re: manufacturer of organic chelated minerals for livestock). The meta-results of this review demonstrated that organic chelated trace mineral supplementation in dairy diets improved health status, milk production and reproduction performance in lactation dairy cows.
These field trial reviews are useful in demonstrating the source of essential trace minerals for dairy cattle should contain high bioavailablity. It also suggests precious time, effort and money are not wasted by ineffective over-formulation of dairy diets with inorganic minerals, but rather fine-tune the dairy diet with various sources of essential trace minerals. Reliable rock trace mineral sources might work satisfactorily in modest situations, while chelated trace minerals with higher bioavailabilities are effective for more high-performance or challenging environments.
Successful dairy cows should not only consume adequate amounts of an essential trace mineral, but one that can be effectively absorbed, retained and metabolized in its body that ultimately contribute to high performance and financial rewards.