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Winter Mineral Nutrition

By Adele Harty and Kenneth Olson
Winter supplementation often focuses heavily on meeting cow protein and energy requirements and tends to leave mineral nutrition as almost an afterthought. In reality, meeting all nutrient requirements, including energy, protein, minerals, vitamins, and water are equally important. Missing the mark in any of these five nutrient categories can have equally negative effects on cattle health and performance. 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.
During winter months, locally grown forages are typically the basis of cattle diets with important considerations being the amount and availability of minerals in these forages. Various factors play a role in forage nutrient content, including quantity and timing of precipitation, timing of harvest, harvest conditions, and storage. The amount of each mineral in the forage is based on mineral content of the soils they are grown on, which is highly variable. Not only does this affect mineral status from one region to another, but it can change quickly on a local basis, to the point that mineral content of forages can vary from one pasture to the next. Additionally, mineral content and availability are not the same thing, with mineral interactions playing a key role. Another key characteristic of forages that drives mineral availability is digestibility. Higher quality forages that have higher digestibility will have greater availability of the minerals they contain than mature forages such as dormant winter range, crop residues, or CRP hay.
Depending on individual situations, modifications may be needed to ensure that mineral requirements of cattle are being met. To fully evaluate a mineral program, the forage, water and supplemental feeds will need to be sampled and analyzed for mineral content, then compare the mineral supply to requirements and find or formulate a supplement that matches needs. This is not a one and done exercise, but additional feed and water testing and monitoring of animal responses are needed to fine-tune the formulation. While this involves a considerable amount of up-front effort and expense, it has several potential advantages, including improved cattle performance, reduced mineral costs by avoidance of excess mineral feeding, prevention of interactions/antagonisms and prevention of toxicity.
Supplemental feeds play an important role in the mineral profile of the diet. For example, distiller’s grains are commonly fed as a protein supplement, but can present challenges with mineral nutrition because it is high in phosphorus and sulfur. In general mineral nutrition is challenging as minerals can interact with one another. These interactions can be positive, however there are some negative ones that are of great concern in the western part of South Dakota, including sulfur, molybdenum, copper and iron. When these antagonisms occur, the bioavailability of the minerals to the animal is reduced. In other words, it may be necessary to feed an excess of one mineral in order to overcome an antagonism with another. Secondly, excess minerals can cause toxicity and potentially death. Therefore, it is critical that minerals are not supplemented needlessly because of cost and toxicity concerns. In general, if distiller’s grains are being fed as the protein supplement, make sure the mineral supplement does not contain high levels of phosphorus or added sulfur, but does contain additional calcium and copper. There are multiple mineral supplements available that are formulated to be fed with ethanol co-products and these supplements are high in calcium, low in phosphorus and high in copper with no added sulfur.
To speak in generalities of forage mineral levels, calcium levels are adequate and phosphorous levels tend to be low and often inadequate, especially in mature, dormant forages. Thus, phosphorous supplementation is often necessary, especially with low quality forages such as winter range, crop residues, or low quality hay. The specifics of the mineral program can vary greatly depending on the total ration mineral composition. Some basic recommendations for winter mineral supplementation programs are: Provide a supplement that contains 8-12% phosphorous when forage is dormant unless distiller’s grain or another high phosphorus co-product is being used as a supplement, then depending on the level of distillers fed, the phosphorus may be able to be reduced to 4%. Copper deficiency is common in South Dakota, so providing supplemental copper will benefit the calf in utero as well as the cow herself. A guideline for copper is 2000 to 2500 ppm for a 4 oz intake or 4000-5000 for a 2 oz intake. Always provide free-choice salt at a minimum. Because off-the-shelf mineral and salt products are formulated to meet generalized conditions, it is important to take the time to find product that matches needs or create a custom-blended mineral formula for a specific ranch.
Minerals are important nutrients that need to be properly balanced in the diet. In general, mineral supplementation is necessary at some level year round, but due to the amount and availability of minerals in dormant, low quality forages, it is more important in the winter months. However, mineral supplements are often expensive so careful attention should be given to providing the right supplement to ensure the biggest bang for the buck.