Mineral nutrition for grazing beef cows
November 30, 2009
We often focus heavily on meeting the protein and energy requirements of livestock and tend to leave mineral nutrition as almost an afterthought. In reality, meeting all of the nutrient requirements, including energy, protein, minerals, vitamins, and water are equally important. Yes, water is a nutrient, but that’s a subject for another column. Missing the mark in any of these five nutrient categories can have equally negative effects. 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. For example, phosphorous is critical to energy metabolism, so a phosphorous deficiency can create an energy depleted animal even if dietary energy is adequate.
There are at least 18 mineral elements that livestock require in their diets. This could quickly become a long and boring column if I try to cover every one of them. Instead, my intention is to discuss some important mineral characteristics in cattle diets and discuss a few specific mineral situations that tend to be important in the Tri-State region.
In general, we group minerals into two categories: the macro minerals are needed in relatively large amounts (i.e. a percentage of the diet) and the micro or trace minerals are needed in relatively small amounts (parts per million). Besides having a minimum requirement in the diet, excesses of most minerals can become toxic, so we have to be concerned about both deficiency and excess. This is especially true for the trace minerals.
Another important characteristic of minerals is that they interact with each other and can be antagonistic, meaning that they can bind with each other and reduce availability to the animal. Thus, we sometimes have to feed excess of a particular mineral to overcome an antagonism. For example, excess phosphorous can interfere with calcium absorption. The classic problem that this can create is water belly (urinary calculi) in steers. This can easily be overcome by adding a supplemental source of calcium, such as limestone, to the diet.
Another important interaction concern in this region involves sulfur, molybdenum, iron, and copper. Copper tends to be deficient, while molybdenum and sulfur can be excessive. Molybdenum and sulfur both reduce copper availability, so local forages are often deficient in available copper. On the other hand, copper can reduce molybdenum toxicity if it is excessive. Additionally, excessive sulfur can often reach toxic levels, especially from water sources. Excess copper can be toxic, so it is important not to supplement it needlessly. If copper deficiency symptoms appear, including poor growth, rough or faded hair coat (reddish hair on black cattle), black goggles appearance around eyes, diarrhea, lameness, or infertility, then blood serum or liver copper levels should be monitored to verify it. Mineral analysis in these samples should include all of the interacting minerals so that copper levels can be adjusted to overcome antagonisms.
Because locally grown forages are the basis of cattle diets, important considerations are the amount and availability of minerals in forages. The amount of each mineral in the forage is based on mineral content of the soils they are grown on, which is highly variable because of variation in the geologic parent material the soils come from. Not only does this affect mineral status from one region to another, but it can be highly variable on a local basis, to the point that mineral content of forages can be vary from one pasture to the next. Additionally, mineral content and availability are not the same thing, with the interaction among minerals that we already discussed playing a key role.
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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 or crop residues.
Despite this variability, there are a few glaring generalities about forage mineral levels. In general, calcium levels are adequate in forages and phosphorous levels tend to be low and often inadequate, especially in mature forages. Thus, phosphorous supplementation is often necessary, especially with low quality forages such as winter range or crop residues.
Magnesium levels can be deficient, especially in lush, green grass. At the same time, potassium levels are extremely high, leading to another interaction problem. This combination can cause grass tetany. Supplementing magnesium in the spring helps to prevent this.
Based on these glaring generalities, basic mineral supplementation recommendations are: Always provide trace mineralized salt as a minimum. Supplement phosphorous when forage is dormant. Supplement magnesium when forage is green and lush. Supplement copper if symptoms are present, but be sure to monitor copper status to be sure deficiency is solved without reaching toxic levels.
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. This is accomplished by sampling forages and water throughout the year, testing them for mineral content, comparing mineral supply to livestock requirements, and formulating to overcome specific seasonal deficiencies and interactions.
After initial formulations, further feed and water sampling and monitoring animal response are important to fine-tune the formulation. While this involves a considerable amount of up-front effort and expense to sample and measure forage mineral content, 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.
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. This 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.