Part 2 in a Series
In the last article we started a discussion of mineral sources or “complexes” as they are used in mineral programs for cattle. As we have discussed previously, the most common sources of minerals, macro and micro, are those found in the forage and feed material that the animal consumes. These minerals are bound into the organic (carbon-based) food or fiber material and are the most available sources of these nutrients. Research has shown us, however, balance or amounts of the various minerals in plants and feed ingredients seldom matches the needs of the animal and that the availability in these forages and feeds does vary. The actual amount of mineral content is variable depending on plant maturity, presence of antagonistic compounds and when the forage or grain is produced on land that may have been under production for years and in which many of the minerals have been extracted through plant growth and harvest. Thus there is a need for supplementation, essentially year-round, in virtually all cases.
Over the years mineral supplementation has taken a number of forms but the most common types have been from inorganic sources. Inorganic sources are either “natural” (mined from the earth and ground or refined into a usable form) or manufactured (chemical processes resulting in an end product) origins. These are products such as Calcium Carbonate, Monocalcium Phosphate, Magnesium Oxide, Potassium chloride, Zinc Sulfate, Copper Sulfate, Cobalt Carbonate and many others. All of these products can be classified as “salts” or inorganic
One of the first things we have to recognize when designing a mineral supplement is that chemical and physical forms of mineral elements affect their availability for animals. For instance, iron oxide (the ingredient used to give many minerals their red color) is virtually unavailable for animals and therefore of little or no uses (see discussion in the previous article). This can be compared to the high iron availability from ferrous sulfate. Likewise, copper oxide is unavailable as included in a regular diet or free-choice mixture. However, copper oxide as copper needles is available due to the slow release and acid conditions of the abomasum. Sulfur from potassium or magnesium sulfate is highly available when compared to the low bioavailability of calcium sulfate. At this point it would be useful to point out that in many areas high availabilities of iron or sulfur in a mineral supplement is undesirable since they interfere with the absorption of other minerals, particularly copper, and this is a problem we commonly are trying to overcome anyway.
As this discussion illustrates, there are significant variations in the availability in the base minerals as related to their chemical form. Nutritionists and researchers have searched for years for ways to improve biological availability of many, if not all, of the minerals under a variety of circumstances. This has created the catalyst for interest in organic or chelated minerals.
Some Background on Organic Mineral Complexes
A number of mineral chelates and complexes are available from a variety of manufacturers. A chelate is described as a metal complex in which the metal atom is held in the complex through more than one point of attachment to the ligand (chelating agent), with the metal atom occupying a central position in the complex. Natural digestion of foods produces numerous ligands that can complex (chelate) with minerals in the diet and facilitate their passage from the lumen of the intestine into the cells of the intestinal wall, where they eventually chelate with natural ligands that transport the minerals throughout the body. In theory, the introduction of chelated minerals will increase absorption and utilization of the mineral because of a more favorable binding or stability constant. Therefore, in an animal's digestive system, organic trace minerals, those that are bound to an organic ligand such as protein, amino acids or carbohydrates, may be more biologically available than inorganic trace minerals. Naturally occurring chelating agents are widely distributed in all living systems in nature including carbohydrates, lipids, amino acids, phosphates (phytic acid), porphyrins (e.g., hemoglobin and chlorophyll) and vitamins (Vitamin B12 and Ascorbic acid). These are the typical forms in which we find minerals complexed in nature (plant material or grains). Unfortunately, significant quantities of minerals are complexed with ligands that are inefficiently absorbed and, therefore, lost by excretion.
Because many factors work against an animal as its body tries to absorb trace minerals, it is essential to realize that bioavailability of trace mineral sources varies widely. Blood samples are commonly used to assess mineral status in the animal but, currently, the best tool for determining trace mineral status is liver biopsy. Liver biopsies are simple, safe and relatively inexpensive, and yield valuable information. To develop a true baseline level, about 10-15 percent of the herd needs to be sampled. A qualified veterinarian should help perform the liver biopsies and can provide information on where to send the samples.
Commercially Produced Complexes
When commercially manufactured the number of ligands or chelating agents is more limited than that found in nature but still creates significant variability when we compare these sources for use in a mineral supplement. The basic classifications are as follows:
Metal (specific amino acid) Complexes (MSAA Complexes), result from complexing a soluble metal salt (inorganic mineral as described above) with a specific amino acid. For instance, one of the most common metal complexes is zinc methionine which is produced by combining zinc sulfate with the amino acid methionine. Other common metal (specific amino acid) complexes include copper lysine and manganese methionine. The production of these types of complexes results in a very specific metal complex that is consistent in molecular size and stability and thus is consistent in how it is digested and absorbed by the animal. It is also probably the smallest particle given that it is one metal atom complexed with one amino acid. When considered with the consistency and stability, MSAA complexes are probably the most effectively and efficiently absorbed of all the complexes. When considering this type of complex it should be noted that of the metal amino acid complexes, proteinates, etc., these are also probably the most expensive to include in a supplement.
Metal Amino Acid Complex. Another similar process produces a different type of metal amino acid complexes. This a more general type of product which is characterized by a metal atom (zinc for instance) complexed with several single amino acids. Each individual molecule is still one metal ion and one amino acid but you have a variety of amino acids in the blend. For instance for a zinc complex in this category, the blend would include zinc methionine, zinc lysine, zinc leucine, zinc cystine, etc. with each molecule being specific but the whole product being a blend of these complexes. This process would hold true for other trace minerals as well, copper, manganese, etc. Similar to the specific amino acid complexes this process results in molecules that are also the smallest in size. However, since we see some variation in the amino acids we will also see some variation in absorption not as common in a pure blend.
Metal proteinates (MPT) result from the chelation of a soluble mineral salt with amino acids and/or hydrolyzed (broken up) protein. The final product may contain single amino acids, dipeptides, tripeptides or other protein derivatives and probably contains some of all these classifications. In many cases, research has shown that the resulting mixture (i.e. the metal and the peptide ligand) may be bound too weakly to withstand the environment of the digestive tract. These types of compounds have shown high degrees of solubility in the rumen leaving them available to be bound to other compounds that may prove less available in the small intestine. Due to their molecular variability metal proteinates are not defined chemical entities. Metal proteinates tend to be less expensive than other organic mineral complexes
Metal amino acid chelates (MAAC) are formed from the reaction of a metal ion from a soluble metal salt with amino acids having a mole ratio of one mole of metal to one, two or three (preferably two) moles of amino acids to form coordinate-covalent bonds. More simply put, MAAC's are produced by combining a given amount of a metal with one to three times the equivalent volumes by weight of amino acid or peptide ligands to form varying complexes. Somewhat similar to the proteinates in variability, they are normally a smaller and somewhat more stable molecule. Once again, however, metal amino acid chelates are not specified chemical entities.
Metal polysaccharide complexes result from complexing a soluble salt with a polysaccharide (carbohydrate) solution declared as an ingredient of the specific metal complex. The product is more of an organic mineral matrix without any chemical bonding between the metal and the polysaccharide. These are larger molecules based on chains of simple sugars that are known to be highly soluble in the digestive tract.
Metal propionates (MPP). First recognized in 1891, are the result of combining soluble metals with soluble organic acids such as propionic acid. The resulting products are highly soluble and generally disassociate in solution. Care should be taken here in differentiating the very similar spelling of proteinates when discussing the various sources.
Yeast Derivative Complexes.
One other source of organic trace elements that is showing promise are those integrated into a yeast cell for feeding as a trace mineral-enriched yeast. The most common of these at this time is selenium yeast with the selenium found largely to be complexed with a Methionine molecule (selenomethionine).
In general the selection of an organic trace mineral complex should be based on four factors. These include:
• Cost Effectiveness
Generally, organic trace minerals are made by mixing a hydrolysate (broken up fragments down to individual amino acids) of plant or animal proteins, carbohydrates or amino acids with a soluble salt, usually a sulfate of a trace mineral. The details of the complete process vary with the manufacturer. However, the quality of the starting material, the type of mineral-ligand binding and the stability constant of the resulting compound substantially affect the quality of organic trace mineral products. In general organic trace minerals have high stability and do not react as readily as single ions. These forms do not interact with vitamins (as can inorganic trace minerals) and other ions and are effective at low levels. Not only do organic trace minerals not react with vitamins in the digestive tract but do not react with vitamins in premixes.
Use of element-specific amino acid complexes (i.e. specifically zinc or copper or manganese, etc.) reduced vitamin destruction in a vitamin-trace mineral premix compared to inorganic trace mineral sources. When other antagonists are involved, if there is high dietary molybdenum, copper in chelated form has an advantage over an inorganic form as it may escape the digestive system complexing among molybdenum, copper and sulfur.
Interestingly, some studies have shown no benefit from chelated and complexed minerals, but most have shown positive responses compared to inorganic sources. One study suggested that at adequate levels of dietary zinc, bioavailability of supplemental zinc sources may be less important than under conditions of limited dietary zinc or if very high levels of supplemental zinc are fed.
Dietary copper from sulfate and lysine sources had similar results for cattle with adequate copper status as shown by researchers in 1999. However, copper lysine at 16 mg of copper per kilogram appeared to be more beneficial for animals that were borderline to deficient in copper status. Organic copper provided a more bioavailable form of supplemental copper than copper sulfate for postpartum first-calf heifers.
Much more needs to be learned about the selectivity of organic trace minerals, the most effective kind and quantity, their mode of action and their behavior with different species of animals and with varying diets. Dietary requirements for minerals may be greatly reduced by the addition of organic trace elements to animal diets, but it is generally more economical to use higher levels of inorganic mineral sources than the more expensive mineral chelates and complexes. Nevertheless, organic trace minerals are generally of very high bioavailability, and they are particularly attractive for high-producing or stressed animals or for problem areas (e.g., high dietary molybdenum for ruminants) where cheaper inorganic sources are less effective.
Dr Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at firstname.lastname@example.org.