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May 28, 2004 Minerals, What They Are and Why They Are Important All too often, discussions of dairy nutrition are limited to nutrients such as energy and protein that have a direct impact on milk production, notes a North Dakota State University dairy specialist. But, what about minerals and why are they important? How much do cows need? What happens if we don't provide enough of a particular mineral? Can we provide too much? While varying mineral levels may not have the immediate impact of a major shift in energy or protein levels, the long-term effects on animal health, longevity and growth are significant. “Minerals are inorganic (not of plant or animal origin) elements required by the body for optimum growth and proper muscle and nerve function,” says J.W. Schroeder, NDSU Extension Service. “Minerals are essential components of body enzymes, hormones and body cells. Recommended mineral levels are not constant throughout the life of an animal. In fact, they vary with changing production, body size, environment and other dietary factors. In order to calculate a cow's true mineral need, it is necessary to know her physiological status by determining if she is pregnant, how much she is producing, what her maintenance needs are and how much she is growing.” Problems will first be observed in the areas of animal health and reproduction if mineral levels are not balanced, but the impact will not be immediate. Many mineral deficiencies are noticed only after a prolonged period of underfeeding has occurred. Although it may take awhile for clinical symptoms of a mineral deficiency to appear, subclinical deficiencies may have been impairing optimum performance for quite some time. The primary exception to this rule is mineral toxicity. Extremely high levels of copper, for example, may actually result in death. “The amount of mineral fed to a cow does not necessarily match the amount actually used, which complicates our ability to feed specific mineral levels,” Schroeder says. “In fact, mineral absorption is lower than absorption of most other nutrients. Mineral absorption varies from one mineral to another and by what form the mineral is. But even when we have determined how much of the right form of a particular mineral to feed, our job is not complete, as there are numerous known interactions between minerals (i.e., high levels of one will decrease utilization of another) to consider.” Known mineral interactions include copper-molybdenum, sulfur-selenium, calcium-phosphorus, calcium-zinc, calcium-manganese, and potassium-magnesium. With many minerals, absorption of the mineral decreases as the amount in the diet increases. It is also important to note that older animals have more difficulty absorbing minerals. To minimize costs, nutritionists should try to maximize the percent of minerals provided by typical feedstuffs. However, it is important to consider that mineral content in concentrates and forages are quite variable. Frequent forage testing (preferably through a wet chemistry analysis) is beneficial for economical mineral feeding. Generally, supplemental trace minerals are supplied through inorganic sources, typically in the form of sulfates, phosphates, chlorides, carbonates or oxide forms of the trace mineral. Some inorganic sources of trace minerals are more available than others (i.e., sulfates are generally more available than oxides). Organic minerals are often classified as chelates or proteinates and are bound to amino acids or proteins. “They are usually absorbed in the intestine by a different mechanism that may increase their bioavailability and provide a unique function when other minerals are interfering with the availability of a desired mineral,” Schroeder says. “Organic minerals are generally more expensive, but they may still be advantageous, particularly as related to immune and reproductive responses. As a rule of thumb, one-third to one-fifth of trace mineral supplementation should come from organic mineral sources, depending on the specific mineral desired.” Macrominerals are needed in higher amounts and are usually expressed as a percentage of the ration dry matter. Calcium, phosphorus, magnesium and sulfur are macrominerals that are important to the dairy cow. Microminerals are needed in smaller amounts and are generally expressed as parts per million (ppm). Iodine, zinc, iron, copper, molybdenum, fluorine, cobalt, selenium and chromium are examples. “Minerals are an integral part of any successful herd management program,” Schroeder says. “Often, correcting an imbalance in mineral levels can solve a nagging problem by improving reproductive performance or animal health, with very little additional cost. While research continues to redefine the forms in which minerals are delivered to the cow, their role in animal performance remains the same.” ### Source:
J W Schroeder, (701) 231-7663, allen.schroeder@ndsu.nodak.edu |
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