Grazing Mineral Nutrition For Beef Cows Back »

With the recent moisture that much of South Dakota received, grass is growing and many cattle have been moved to summer pasture. With that move and change in feed, ranchers need to be aware of the nutrient requirements of their livestock and ensure they are all being met, including energy, protein, minerals, vitamins, and water. All are equally important but may not be observed as closely during the months in which animals are grazing. However, deficiencies in any of these nutrients can cause negative effects on animal production. In reality, all nutrients interact, and deficiencies in mineral nutrition can create deficiencies in availability of other nutrients, even if those nutrients are adequate in the diet.

Mineral content of grasses and forbs is determined by mineral content of the soil, plant species, and plant maturity. Legumes, such as alfalfa and clovers, tend to be higher in calcium, magnesium, and potassium, as well as iron, copper, zinc, and cobalt than grasses. As plants mature, mineral content changes such that phosphorus and potassium decrease, but not at an equal rate across all plant species, as this decrease is less pronounced in legumes than grasses.

In general calcium levels are adequate in forages, while phosphorus levels tend to be low and often inadequate, especially in mature forages. In regards to potassium, these levels tend to be excessive, while magnesium levels can be deficient, especially in lush, rapidly growing pastures. Therefore a “one-size fits all” mineral package rarely meets the needs of the livestock depending on plant diversity, soil mineral content, plant maturity, and supplemental feeds. There can be a measurable difference within a pasture, let alone across an entire ranch or state. Table 1 shows the difference in two mineral supplements and how they can vary from eastern South Dakota to western South Dakota. Table 2 shows the seasonality differences in a mineral supplement for an eastern South Dakota ranch, with forage type being range in the summer and corn stalks in the winter.

Table 1: Custom mineral supplement based on mineral content of summer forages from an eastern and western South Dakota ranch.

  Eastern Western
Mineral % or ppm % or ppm
Calcium 1 0.18% 4.87%
Phosphorous 8.93% 6.38%
Potassium 0.03% 29.90%
Sodium 19.41% 0.62%
Magnesium 0.27% 4.60%
Zinc 6973 ppm 1677 ppm
Copper 3500 ppm 286 ppm
Manganese 138 ppm 570 ppm
Cobalt 20 ppm 5 ppm
Iodine 200 ppm 25 ppm
Iron   5024 ppm
Selenium   10 ppm

ppm = parts per million

Table 2: Winter and summer custom mineral supplement for eastern South Dakota ranch.

  Winter Summer
Mineral % or ppm % or ppm
Consumption 2.7 oz 2.5 oz
Calcium 10.18% 12.89%
Phosphorous 8.93% 0.57%
Sulfur 0.00% 0.43%
Potassium 0.03% 0.00%
Sodium 19.41% 12.00%
Magnesium 0.27% 11.18%
Zinc 6973 ppm 4100 ppm
Copper 3500 ppm 4600 ppm
Manganese 138 ppm 7 ppm
Cobalt 20 ppm 30 ppm
Iodine 200 ppm 666 ppm

ppm = parts per million

Mineral interactions also complicate the issues. One of the more common and challenging mineral interactions that occurs particularly in western South Dakota is the three-way interaction between sulfur, molybdenum, and copper. Many soils in South Dakota are high in molybdenum while water and by-product feeds can be high in sulfur. This results in copper being tied up and unavailable for absorption by the animal. Copper is one of the key nutrients for reproduction and immunity, therefore an adequate amount of copper needs to be available in the mineral supplement to overcome this interaction.

Because off-the-shelf mineral and salt products are formulated to meet generalized conditions, it is often beneficial to create a custom-blended mineral formula to meet localized deficiencies or toxicities of a specific ranch and the needs of that ranch throughout the year.

Developing a custom mineral formulation has many potential advantages, including avoiding excess mineral feeding, which results in less environmental contamination, more opportunity to prevent or overcome interactions and antagonisms, prevent toxicity, and save money. There is a substantial upfront time and money investment, but in the long run, the savings from eliminating unneeded minerals and the additional income from improved performance can make it worth the up-front investment.

There are three main steps in developing a custom formulation:

  1. Sample.
  2. Compare minerals in feeds to requirements.
  3. Formulate the supplement.

When sampling standing forage, observe animals grazing a new pasture and collect grab samples of the same type of plants they are eating at approximately the same level. Typically as cattle walk through a pasture grazing, they will clip the top part of the plant, so observe how much this is and collect samples accordingly. Also sample water sources and any supplemental feed and have a full mineral analysis performed. 

The second step is to compare the minerals in the feed and water to the animal requirements to determine where there are deficiencies, toxicities, or interactions. Just because the level reads that it is adequate on the lab report does not mean it is available to the animal. Work with a nutritionist or Extension Field or State Specialist to work through this process to determine what the supplement needs to contain. This individual should then also help with the final step, formulation of the supplement.

Minerals are important nutrients that need to be properly balanced in the diet. If dietary feedstuffs do not contain adequate minerals or contain an imbalance, then mineral supplementation is necessary, which is usually the case. However, mineral supplements are often expensive and careful attention to providing the right supplement can be key to ensuring that we get the biggest bang for the buck, and this may be through a ranch specific custom blend.


For more information, contact Adele Harty at the Rapid City Regional Extension Center at 605.394.1722 or contact any SDSU Extension Cow/Calf Field Specialist or Beef Extension Specialist.

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