Mineral Concentration in Forages
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Amy Myers: Today we're talking about mineral concentration of forages. Hello, I'm Amy Taylor and welcome to Farm and Family. Today we're speaking with Rocky Lemus, Mississippi State University Extension Service Forage Specialist. So, Rocky, what types of minerals in the forage system are important for livestock production?
Rocky Lemus: Amy, the nutrition of grazing animals is a complicated interaction between soils, plants, and animals. The performance health of grazing livestock is dependent on the adequacy and availability of essential minerals elements, from pastures. From the forage and livestock point of view, minerals are classified in two groups, micro-minerals, and trace minerals. Micro-minerals are required in high concentrations in the ration. Micro-minerals include calcium, phosphorus, sodium, potassium, and magnesium. On the other hand, trace minerals are needed in the ration in low concentrations. Trace minerals include iron, zinc, copper, manganese, cobalt, molybdenum, selenium, and iodine.
Amy Myers: And what factors effect mineral composition in the forage?
Rocky Lemus: Minerals also tend to be area specific and factors like climate, soil type, forest species, agronomic practices, maturity, season, soil-mineral concentration, [inaudible 00:01:24] yield and the amount and type of fertilizer nutrients applied ultimately affect the nutritive value of forages for livestock. Seasonal availability can markedly affect the dietary intake of minerals, as a result of changes in composition, such as the stage of growth, availability of pasture, and to changes in the moisture content of the soil. Forage mineral concentrations is also affected by maturity, generally there is a rapid uptake of minerals during early growth, and gradual dilution as the plant matures.
Amy Myers: Now, how do mineral concentrations vary among legumes and grasses?
Rocky Lemus: Mineral concentrations in forages vary more than do protein and energy concentration. Leaves have higher concentrations of minerals than stems, except for potassium. Legumes on the other hand are generally higher than grasses in calcium, potassium, magnesium, copper, zinc, and cobalt. And in contrast, grasses tend to have a higher concentration of manganese than legumes, and also molybdenum, and most common grasses to Mississippi are marginal to deficient in copper and zinc.
Amy Myers: And how can mineral interactions affect their availability?
Rocky Lemus: Many types of forage contain antagonistic effect that reduce the availability of minerals. There are many mineral to mineral interactions that increase requirements, such as high molybdenum to sulfides, increase the requirement for copper. And as the dietary potassium increases, magnesium requirement increases as well. In addition to mineral interaction, there is significant interaction between minerals and organic constituents found in plants. Many organic acids may be present that have shown to reduce the bioavailability of the forage minerals. For example, I saw this in Arkansas, have indicated forage growing in poorly amended soils had too little magnesium and copper, which would put the cows in danger of developing grass tetany, or to suffer from copper deficiency. The combination of all this factor makes it extremely difficult for livestock producer to determine the actual mineral status of the herd, whether or not mineral supplementation's necessary, and the degree of supplementation that might be needed to meet the production goals.
Amy Myers: So if there's a forage mineral imbalance, how would that affect livestock production?
Rocky Lemus: Mineral imbalances usually might be deficiency or excess of specific mineral in soils and forages, that have been associated with low ... and they have been associated with low reproductive rates in animal production among grazing ruminants. The ability of the forage minerals to meet grazing livestock's requirements depend on quantity, which is usually the concentration of the mineral on the plant, and the bioavailability of those minerals. Amount that the cows can absorb from the digestive tract. Although mineral concentrations in the forage might be adequate, the percent that is available to the livestock might be much lower. Mineral availability dependent on the various factors including digestive tract interactions, mineral solubility, and digestive tract PH. Factors such as also low protein, high degree of lignification, or reduce digestibility of the forages can also reduce total mineral consumption. However, simply knowing the animal's requirement is only one component in alleviating an animal's mineral status.
Amy Myers: Thanks, Rocky. Today we've been speaking with Dr. Rocky Lemus, Mississippi State University Extension Forage Specialist. I'm Amy Taylor, and this has been Farm and Family. Have a great day.
Announcer: Farm and Family is a production of the Mississippi State University Extension Service.