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Understanding bioavailability in a supplementation program

Ben Neale for Progressive Cattleman Published on 30 May 2019
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Good nutritional status is an important factor for quality of life and health of all living things, including cattle. Yet, because many of the signs of poor nutrition are subclinical, they are often overlooked.

There is one aspect of animal nutrition, however, that seems to be the least appreciated and understood that contributes significantly to nutritional health, and that is bioavailability.

Bioavailability is conventionally defined as the fraction of a given dose of an unchanged nutrient or drug that reaches systemic circulation. For dietary supplements and other nutrients that are administered orally, bioavailability designates the amount of the ingested dose that is absorbed. 

Many factors can affect bioavailability of a nutrient regarding the physiology of the animal. Overall gut health, specifically the absorption that occurs in the intestinal tract, are key in nutrient uptake. This includes the interactions of a healthy microbiome and supplemental nutrients. Factors that can affect the strength and health of these connections are age, sex, stress, pregnancy, present antagonists, physical activity, metabolic disorders and nutrient form. 

If the form of the nutrient presented in a supplement cannot be readily absorbed, it has little economic or therapeutic value. Also, the form is even more vital when an animal’s digestive system and overall health is compromised or stressed due to one of the first seven factors listed above. 

Bioavailability for feed supplements should be further considered looking back on the history of the past few decades. Since the 1950s, animal feeds have been supplemented with essential trace minerals such as copper (Cu), iron (Fe), iodine (I), manganese (Mn), molybdenum (Mo), selenium (Se) and zinc (Zn). Initially, such supplementation was by means of inorganic salts or the plain rock form of essential trace elements.

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From the 1960s onward, genetic improvement in size of farm livestock resulted in increased nutritional requirements for these nutrients. Chelated minerals were developed in the 1980s and 1990s, creating a more concentrated, more bioavailable supplement form. Trace mineral chelates have been proven in numerous studies to be better than inorganic minerals in meeting the nutritional needs of modern farm animals.

However, not all chelates are created equal, as some chelated minerals are more bioavailable than others. The main point for consideration is what makes a chelate different than an inorganic mineral and why it matters. By definition, a chelate is a chemical compound in which a metal molecule (mineral) and an organic molecule (ligand) are combined. The ligand is a critical component of a chelate that actually transforms the previously inorganic molecule into an organic mineral form, like one found naturally in plants, thus making it more bioavailable to the body. 

Considerations when comparing differing mineral products is important because of bioequivalence. In pharmaceuticals, the FDA defines bioequivalence as the absence of a significant difference in the rate and extent to which the active ingredient becomes available at the site of drug action when administered at the same dose under similar conditions. In other words, for products to be comparable, they should be of the same quality, safety and strength under similar circumstances. 

In application, bioavailability is one of the most important factors in a supplementation program. A practical example is a free-choice mineral supplement tag. The metal molecule amount that is on an animal feed tag in parts per million (ppm) states the nutrient amount. However, it does not state of that amount what percentage is in what form to know its bioavailability or how much will be working in the animal and not just passing through it. Therefore, although the expectation is the same because the tag appears the same, the therapeutic effect can vary greatly across products with similar tags because of their vast differences in absorption and systemic effects. 

As the economic importance and scrutiny of financial returns for nutritional supplements continues, it should increase the accountability for critically evaluating the therapeutic and environmental impact of nutritional supplements, and to do so, a good understanding of bioavailability is essential.  end mark

PHOTO 1: Bioavailability is one of the most important factors in a supplementation program and is influenced by several different factors.

PHOTO 2: Some factors that influence bioavailability include age, sex, stress, pregnancy, present antagonists, physical activity, metabolic disorders and nutrient form. Photos courtesy of Alltech.

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