Costs and Spoilage Losses

Costs and Spoilage Losses Costs of storage in either a bag or bunker are difficult to estimate. Many factors need to be addressed. In Table 2, a cost budget is shown that can assist producers in estimating the cost of storing WDGS (or other coproducts). A cost budget analysis spreadsheet is also available for download at beef.unl.edu under the "byproduct feeds" tab.

Using an example of purchasing WDGS at a cost of $30/ton (as-is) at a DM percentage of 34%, the cost of mixing 15% wheat straw with 85% WDGS on an as-is basis and storing it for 150 days is calculated. The costs of the wheat straw, WDGS and the DM and as-is quantities of each are needed in this cost budget and are shown at the top of Table 2. Similarly, estimates of labor, equipment costs, interest, and shrink are required to make appropriate estimates of costs. While these costs can be difficult to estimate, the spreadsheet on the website can assist in these calculations. Ultimately, the cost of storage has to be evaluated on a dollars-perton as-is basis and DM basis to make fair comparisons to alternative stored and purchased feeds. The economic costs of storage can add up, thereby making these calculations critical for producers to make sound decisions on whether to store wet co-products for feeding at a later date.

Shrink or spoilage losses are likely lower for bagging compared to bunker storage; however, few data are available to make this comparison. Spoilage losses measured as DM weight put into the bag versus DM weight removed from the bag likely vary from 2% to 15% with a few examples measured from 8% to 12%. Shrink is challenging to measure and will vary among different operations depending on storage method, compaction and likely particle size of the forage. In many cases, producers are willing to risk shrink due to the cost of the co-product relative to other feed ingredients. It is prudent to assume 10-15% shrink in the absence of measurements on your own operation and to include these in your cost estimates of storage. Another approach is to assume that storage losses will be similar to silage storage, which is 3-6% for bags and 10-14% for covered bunker storage facilities.

Mold production and foul odor may occur during storage of wet co-products, especially when piled and left uncovered. Figure 18 illustrates piling WDGS on the ground with no cover. After weeks of storage, some color change is noted (Figure 19) as well as some mold growth at the surface (Figure 20). If the pile "seals" itself, the material below the suface may be good quality. Our experience is that the amount of mold is directly proportional to the oxygen permeability of the plastic covering the storage site, with thicker plastics resulting in less visible mold. Given concerns over the dangers of feeding moldy corn grain to livestock one might reasonably question the safety of feeding moldy coproduct to livestock.

As part of our efforts to evaluate different storage techniques, we have analyzed samples from four different storage sites for mycotoxin concentrations. Each sample was safe in terms of mycotoxins. We tested for the presence of aflatoxins, ochratoxins, vomitoxin, zeralenol, zearalenone, T-2 toxin and fumonisin — all the major mycotoxins found in grains and potentially grain byproduct feeds. Only fumonisin was found to be present in any of the samples — but at a low level. The site with the greatest concentration of fumonisin was 1.4 ppm, with the average in all four samples being 0.8 ppm. The Food & Drug Administration recommends total fumonisins in rations not exceed 30 ppm. Thus, the levels of fumonisins observed in our stored piles are considered safe. For comparison, the FDA considers 3 ppm the safe threshold for human foods. Because the fresh distillers were not tested, it is not possible to determine whether the fumonisins were produced during storage or whether they were present in the corn grain before entering the ethanol plant and were in WDGS prior to storage. The bottom line from our experience is that mycotoxins are a minimal concern at least based on limited data thus far.

For more information or to request additional copies of this manual, contact the Nebraska Corn Board at 1-800-632-6761 or e-mail kelly.brunkhorst@nebraska.gov

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Date published: May, 2008