Trace elements may be needed only in small amounts, but their influence on animal health is anything but small. From growth and immunity to fertility and overall productivity, these micronutrients play vital roles in keeping ruminants performing at their best. In this Ask the Vet column, Drs Willie Smith and Lourens Havenga explain why trace elements matter, how they function in the body, and why ensuring optimal levels, especially before critical production stages, is essential for every livestock farmer.
Question: Why are trace elements important to ruminants?
Answer: Seven trace elements are officially recognized by the American Food and Drug Administration (FDA) and the National Research Council (NRC) as being essential for normal production and reproduction, namely zinc (Zn), manganese (Mn), selenium (Se), copper (Cu), cobalt (Cb), iron (Fe) and iodine (I). This means that if ruminants do not ingest a specified minimum of these seven trace elements, in a biologically available form, they will not be able to produce and/or reproduce optimally. Chrome (Cr) would probably be classified as the eighth essential trace element and is regarded as absolutely essential for all ruminants in stressful situations (feedlot cattle and top-producing dairy cows). Silicon (Si) could possibly, infuture, be classified as essential.
New research indicates that silicon supplementation results in stronger and healthier bones and joints, especially in horses, and also prevents arthritis in humans. The “biological availability” of trace elements is defined as the degree to which an ingested trace element from a specific source is absorbed in a form that can be used by an animal in metabolic processes. Biological availability values of trace elements are usually expressed relative to the response obtained using a standard reference material. This is called the “relative biological availability value”. So zinc sulphate is used as the reference source for zinc and a value of 100 is assigned to it.
In one study, in cattle, it was shown that zinc methionine (a sulphur-containing amino acid) has a “relative biological availability value” of 133. This means that, in this specific study, the zinc from zinc methionine was absorbed 33% more efficiently than from zinc sulphate and in a form that could be used in the animal’s metabolic processes.
Broadly speaking, trace elements have three functions, namely structural, catalytic and regulatory.
Structural trace elements form structural components of body organs and tissues; for example, zinc, manganese and copper in bones and teeth. These trace elements are of the utmost importance for ensuring – along with calcium and phosphate – that bones and teeth are healthy and strong.
Catalytic trace elements serve as catalysts (fuel for certain processes) in enzyme and hormone systems. During the last two decades, many metalloenzymes (chemical messengers in the body, which consist of one of the minerals mentioned above, plus proteins) have been identified.
The importance of trace elements in enzymes involved particularly in natural resistance and reproductive efficiency is now better understood and, as a result, the absolute necessity of the optimal status of trace elements to these functions is taken far more seriously. It is of great practical value to know that the optimal metalloenzyme levels in the animal, which make the real difference to natural resistance and reproductive efficiency, are only achieved about 20 days after the optimal trace element status has been attained. There is thus no “quick fix” and the trace element supplementary programme has to be planned in such a way that the metalloenzyme functions are always optimal before critical times such as the drying-up of dairy cows, calving of dairy and beef cattle, lambing of ewes, mating or artificial insemination (AI) of cows or ewes, and stressful times, such as adapting to feedlots and active growing periods.
Regulatory trace elements, such as zinc, regulate cell reproduction, as well as other processes in the body. For this reason, they need to be present in optimal quantities in the animal’s body, particularly before the advent of critical events, in order to ensure that important regulatory processes are not hindered. New information about trace elements, revealed during the past two decades, should reawaken the animal reproduction world to the essential role that trace elements play in the production and reproductive processes of ruminants.
Trace element principles, particularly the underrated, but essential, roles they play as catalysts in countless enzyme and hormone systems, need to be understood and acknowledged, particularly by the older generation. (Many of these substances were largely unknown 20 years ago.) Higher production goals in ruminants genetically reproduced for this purpose, in combination with largely nutrient-depleted food sources, make it, in practical terms, more essential now than in the past to supplement trace elements more effectively, and to ensure that trace element functions are at optimal levels in advance of critical events (such as drying up, calving, lambing, artificial insemination (AI), adapting to the feedlot and quick growth), in order to ensure the final result – namely economically efficient animal production – is successful.
References: Underwood, E. J. & Suttle, N. F., 1999. The Mineral Nutrition of Livestock. 3rd Edition. CABI Publishing, 10 E. 40th Street, Suite 3203, New York, NY 10016, USA.
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