Trace minerals: Time for change?

From the 1950s to the 1990s, most trace mineral supplementation of animal diets was in the form of inorganic minerals and these largely eradicated associated deficiency diseases in farm animals. However, since the 1960s, food animal production has intensified and genetic potential for growth and yield has improved.

This increase in demand on all aspects of nutrition has led to the use of new ingredients better able to meet the animal's growing needs. In the case of trace minerals, this has come in the form of organic minerals. Organic minerals is a loose term describing mineral sources bound in some way to an organic ligand. Chelated trace mineral technology allowed commercial application of these products to improve trace mineral status in the dairy herd with wide ranging benefits. Probably the best definition of chelates today is the AAFCO definition which splits chelates into five different groups:

• Metal Amino Acid Complex
• Metal (specific amino acid) Complex
• Metal Amino Acid Chelate
• Metal Polysaccharide Complex
• Metal Proteinate

The above descriptions are defined by the ligand binding and source, with soy-based peptide and amino acid bound trace minerals being the most commercially popular sources used in feed. This chelation technology is only possible with the transition metals (iron, copper, manganese, cobalt and zinc). The chemical state of the other two key trace minerals in dairy nutritioniodine and selenium make it impossible to produce a chelated version of these trace minerals.

Selenium differs

However, organic selenium sources have been available in the global feed industry since the early 1990s with the introduction of a selenium yeast product. The technology used in the production of this trace mineral source is different from the other organic minerals for the reasons stated above. Scientists took a lead from Mother Nature in understanding how plants accumulate selenium in their tissues. Selenium is taken up and stored in plant tissue by replacing sulfur in the sulphur-containing amino acids such as methionine or cystine.

Likewise, selenium-enriched yeast is produced by making selenium available in a sulfur deficient media used in the yeast propagation. The real technology here revolves around the selection of a yeast strain that will accumulate high enough levels of this bio-available selenium source to make supplementation in dairy diets cost effective.

The product landscape for organic selenium sources is much easier for the buyer than with chelates, with only a few selenium-yeast products available for use, and only one of these having gone through both FDA (USA) and European Union (EU) approval processes.

Optimum versus adequate

Dairy nutritionists aware of the low availability of inorganic forms commonly use high quantities of trace minerals in an effort to guarantee uptake of the required quantity by the animal. However, in recent years, research such as that at the University of Kentucky, United States (Figure 1), has shown that this practice does not yield the required uptake to maintain adequate mineral status.

Also questioned today is, “What is adequate?”, with recent research highlighting that trace mineral status needed to optimise immune function or fertility is much higher than that defined as a requirement by the NRC (Figure 2).

Lastly, a growing awareness of the environmental pollution caused by those unused trace minerals has led to concern and even new legislation in parts of the world controlling trace minerals in feed and manure levels.

Financial returns

For over 30 years, chelated minerals have been effectively used by nutritionists to address trace mineral deficiency issues. The cost implication is often significant when compared to inorganic supplementation; however, the financial return on benefits measured by the dairy producer warrant this investment.

Historically, research with organic minerals in dairy, as well as application, has focussed on the big three dairy diseases, namely lameness, infertility and mastitis. Probably the best example of how organic minerals can help relates to mastitis. The average cost of a single case of mastitis is reported (Esslemont et al., 2002) as £177 (ranging from £149 for a mild case to £1709 for a fatal case). These figures included both direct and indirect costs, though no account for any worsening of fertility. Further, Esslemont also showed that cows with one case were 1.6 times more likely to have a repeat case, bringing the total average cost per cow to £201.

Zinc is an essential trace mineral found to be an integral component of over 300 enzymes in metabolism (Dibley, 2001), as well as being documented to be involved in a number of healing processes in the dairy cow. Zinc absorption in ruminants declines with increasing parity though mechanisms that affect absorption have not been clearly defined. The teat canal is lined with keratin, a zinc dependent protein, which is a natural chemical and physical barrier to bacteria gaining entry to the mammary gland. Approximately 40 percent of the keratin lining is removed at each milking (Kellogg 2004) and, subsequently, requires constant regeneration between milkings. Bitman et al., in 1991, showed that keratin in the teat canal of holsteins before milking was 1.6 times greater than after milking. Zinc also has a role in immune function, being involved in Cu/Zn superoxide dismutase (SOD). This Cu/Zn SOD is responsible for prevention of lipid peroxidation.

The inclusion of supplemental zinc in the diet and the form of that zinc has been shown to help reduce the incidence of mammary infections and lower somatic cell count (SCC). Research by Spain et al. (1993) showed that mid-lactation cows given zinc proteinate are more resistant to bacterial infection than cows fed zinc oxide. It was also concluded that reduced susceptibility to bacterial invasion of the mammary gland might explain the reduced rate of new infection in treated vs. control cows. Further work by Kinal et al. (2005) reported that replacing 30 percent of the inorganic copper, zinc and manganese with organic sources for six weeks pre-calving until 305 days of lactation resulted in a 6.5 percent increase in milk yield, and a 34 percent reduction in SCC.

This positive impact of zinc on keratin production has led to widespread use of organic zinc to improve hoof health and thus reduce incidence of lameness. In 1998, Stern et al. investigated the effect of form of zinc supplementation on macroscopic clinical evaluation, microscopic coronary horn quality, and traction resistance in cows. Those animals receiving zinc proteinate tended towards better (P<0.1) clinical scores for microscopic horn quality and traction resistance. The organic zinc source also improved macroscopic clinical evaluation scores.

Steadily increasing milk yield over the last fifty years has resulted in a negatively correlated effect on fertility. Although there are a number of causes for this, trace mineral deficiency has contributed.

A number of trace mineral deficiencies manifest themselves through fertility problems, including anestrus behaviour with copper and manganese, and retained placenta with selenium. Research by O'Donoghue and Boland at University College Dublin, Ireland, highlighted a significant response on a number of reproduction parameters in cows fed a combination of organic copper, zinc and selenium from 14 days prior to calving till 12 weeks post calving (Table 1).

Similar commercial responses have led to widespread use of organic minerals in commercial dairy feed and mineral products as a partial replacement of inorganic trace mineral sources around the world.

Historically, it has been claimed that total replacement of inorganic trace minerals with organic sources was not only expensive but also nutritionally unsound. The rationale behind this was that protected organic mineral sources are theoretically unavailable to the rumen bacteria, potentially limiting rumen bacterial function. In reality, organic mineral sources are available to the intestinal microflora, which should not be a surprise, when we consider that prior to use of inorganic supplements, organic minerals found in grains, etc., were the only sources available to the animal.

Original research with organic selenium has clearly shown that 100 percent of the supplemented selenium can be made using organic sources, resulting in significant improvements in measured status parameters, such as blood, tissue, milk and hair. This has resulted in a recommended use of 100 percent organic selenium sources in all major farm species.

More recent research has focussed on chelated trace minerals, to see if a similar strategy could be followed. In work conducted at Harper Adams University College, UK, a 2.4 litre per cow yield response was recorded when organic zinc proteinate replaced an inorganic form at recommended levels (Figure 3). This work supports results seen in other species supporting total replacement of trace mineral supply with organic sources as a viable and cost effective strategy.

Significant impact

Genetic development, with the goal of improved herd performance will continue to be a necessity for a profitable dairy industry. As a result, improved lifetime nutrition must follow. Trace minerals may only make up a small portion of the ration, but have a significant impact on cow health and performance.

Development of organic trace mineral technology has led to widespread use in commercial dairies, benefiting the producer through improved fertility, udder and hoof health and overall production.

Future use of organic trace minerals as the sole source supplied will enable targeted use of the key nutrients designed to optimise production and performance, as well as environmentally responsible nutrition.