Biofuel co-products as livestock feed - Opportunities and challenges

140Biofuel co-products as livestock feed – Opportunities and challengescan contaminate the product. Old material that remainsfrom previous batches should be removed as it may havemould growth and can inoculate with spores fresh batchesdeposited on top. Similarly, WDGS that has been left outsidewith no cover can have been subject to precipitation,which modifies its moisture content and washes out solublenutrients before inclusion in livestock diets.If WDGS is not going to be fed to livestock within oneweek (3–4 days in summer), means of adequate storage needto be found. Covering with a weighted tarpaulin will protectWDGS from precipitation and exposure to light, but doesnot exclude air. Under these conditions WDGS will develop adark crust approximately 5 cm thick on the surface, which itis advisable to discard upon feed-out. If WDGS is protectedfrom air infiltration (e.g. in a silo bag), it will preserve well,either alone or blended with other feeds. Due to its highmoisture content and density, it is not advisable to storeWDGS in vertical structures such as silos. Storage can beeasily accomplished in bunkers, covered piles, or in silo bags.When storage is needed for prolonged periods (months),it is convenient to use silo bags to prevent extensive spoilage.Feeding out from bagged WDGS needs to followsimilar guidelines as feeding silage from a bag. Removalneeds to be approximately 30 cm in depth from the entireexposed surface at least every other day. Unloading WDGSat the farm on a firm surface, such as concrete or asphalt,prevents contamination with soil and seepage of mineralsinto the ground. The pile should be readily coveredto protect it from precipitation and, eventually, seepage.Precipitation not only refers to rain but also snow in coldclimates. When it leaves the ethanol plant, WDGS is usuallystill hot, with temperatures of around 60 °C not beingunusual upon arrival at the farm. If during transportationor just after unloading WDGS is snowed-upon, this temperaturewill melt the snow and nutrients will be lost withthe runoff.The method of choice for preservation depends notonly on the equipment available at the farm but also onthe number of animals to be fed daily. Small- to mediumsizedlivestock operations benefit the most from silo bagsbecause enough volume of WDGS can be removed fromthe exposed surface daily to keep ahead of potential spoilagelosses. Producers need to be careful not to overstretchthe bag as the lateral pressure can tear the bag open duringthe filling process.Storage of WDGS blended with foragesThe low pH of WDGS arriving from the ethanol plantis a positive factor when mixing WDGS with otherfeeds (Table 10). Studies conducted at the Dairy ScienceDepartment of South Dakota State University have shownthat the pH of these blends drops proportionally to thebuffer effect and/or original pH of the companion feedstuff.The pH of most dry feeds is neutral at best, and mixingthem 50:50 on a dry basis with WDGS reduces the pH ofthe blend to approximately pH 4. When compaction andair exclusion are adequate, this acidity supports adequatepreservation. In fact, WDGS preserves perfectly well on itsown without the need for such blends, but the blends helppreserve other feeds that otherwise would require an additionalstorage structure.Feeds that can ideally be mixed with WDGS are thosedeficient in the nutrients that WDGS supplies in excess.Feeds low in protein, fat and phosphorus are desirablecompanions because those nutrients are concentrated inWDGS. Examples of such feeds are soybean hulls, beetpulp, citrus pulp and crop residues such as maize stalks andsmall-grain straws. One additional advantage of the blendwith dry residues is that the moisture in WDGS softens thestructural carbohydrates, allowing for faster colonization byrumen bacteria. In addition, a practical advantage of blendingWDGS with fibrous residues is that the blend is moreeasily reduced to smaller particles during the winter, whenchunks of frozen DDGS can be difficult to incorporate intoa total mixed ration.Research conducted by the Dairy Science Departmentof South Dakota State University has demonstrated that tobe able to achieve adequate air exclusion through compactionthose blends should not exceed 50 percent DM. If thisrecommendation is to be followed then using “modified”WDGS (50 percent DM) would only work in blends withhigh moisture feedstuffs such as green chopped forages(e.g. maize plants). At the same time, the original WDGSwith 60 to 70 percent moisture would work better inblends with drier feeds. From this perspective, the genericterm “wet cake” is not descriptive enough and producersTABLE 10Wet distillers grain preserved in silo bagsParameterDay0 3 7 14 129 SEM1pH 3.1 3.1 3.2 3.2 3.1 0.04as % DMAcetic acid 0 0 0.11 0.30 0.23 0.16Propionic acid 0.30 0.30 0.32 0.30 0.33 0.02Lactic acid 0.90 0.95 0.97 1.02 0.98 0.02Notes: SEM = Standard error of mean. Source: Mjoun, Kalscheur and Garcia, 2011.