Managing mineral variation in forages – Kyle Taysom, Dairyland Laboratories, Inc.
The impacts of forage minerals extend far beyond milk fever. Front-line revenue is impacted by minerals through their influence on milkfat percent and yield, but more subtle impacts can also be seen on rumen pH, dry matter (DM) intake, fiber digestibility, and reproductive outcomes, like conception rates and onset of puberty in heifers. While minerals are relatively inexpensive to supplement, failing to account for the variation of minerals within forages can lead to substantial over- or underfeeding.
Know your forages’ mineral content
Potassium has the highest concentration and variation with values ranging from 0.2 to 4.2 percent of DM in common forages, as you can see in Figure 1 above. Its impact on diet formulation is compounded by the fact that it is a strong cation, which pushes diet DCAD balances higher. Chloride and sulfur have the opposite effect, resulting in a lower DCAD balance, but their concentrations are much lower and less variable in forage. For most dairy diets, calcium needs are largely determined by the relative amount of alfalfa and corn silage in a diet, but, even within alfalfa, concentrations can range from 0.5 to 2.4 percent of DM.
When considering testing options for minerals, it’s important to understand NIR methods are inherently limited when predicting mineral concentrations. Since minerals are inorganic, NIR cannot see them directly and only makes an educated guess by looking at related nutrients.
For example, sulfur and amino acid content are related because both methionine and cysteine contain sulfur. For a highly variable mineral, like potassium in alfalfa, NIR can have six times the error of chemistry testing. If that alfalfa is destined for a DCAD-sensitive group of animals, the extra $15 for mineral chemistry testing could be worth the improved confidence. The accuracy of mineral testing methods is shown in Figure 2 below.
Managing your minerals
Strategies for managing mineral variation are similar to strategies for managing other nutrients. First, consider which feeds are appropriate for each group of animals being fed. For example, it may make sense to limit alfalfa and grass to close-up groups that are sensitive to DCAD variations.
Second, remember that variation has more consequence when working with high-inclusion rate ingredients. Cutting the inclusion rate of a feed in half reduces its impact on diet variation by a factor of four.
Finally, use the analysis of multiple samples when making diet changes. For nutrients that exhibit a wide range of variation, it’s unlikely that one sample provides an accurate representation of an entire silo, bag or pile. Analyzing multiple samples allows the diet formulator to compensate for the impact of sampling variation through averaging or statistical process control.
Both NIR and chemistry mineral analyses are available through all five Dairyland Laboratories, Inc. locations in the Midwest, as well as through more than 20 of our worldwide laboratory partners. All Midwest locations offer same-day or second-day mineral chemistry, as well as same-day, oven-dried NIR analyses.
Feed quality and nutrition
Forage storage and management