Biofuel co-products as livestock feed - Opportunities and challenges

Feeding biofuel co-products to dairy cattle 1392125 µm (Shurson, 2007). Particles on the lower end of themicron spectrum will be more prone to caking problems andreduced flow. In short, and in order to minimize “caking”problems, it is suggested to purchase DDGS from plantswith particle size standardized towards the higher end ofthe spectrum (around 2000 microns), with fat contents notexceeding 10 percent, and that offer a co-product thatconsistently tests under 10 percent moisture.Fat content in DDGS varies and it can be as high as 15 percentdepending on the amount of solubles added back to thestarch-expended mash before being dried to DDGS. Duringthe normal ethanol production process, maize kernels areground prior to fermentation. This allows for greater accessof the yeast’s (Saccharomyces cerevisiae) enzymes to the nutrientspreviously protected by the grain cuticle. Once WDGS isdried to DDGS, these non-starch nutrients remain exposed.The germ in particular is very rich in lipids that, when exposedto air, can undergo auto-oxidation at varied speed dependingon environmental conditions. This process can consume naturalantioxidants present in the original grain, such as tocopherols(vitamin E). In the presence of air, the conjugated dienescombine with oxygen to produce peroxyl radicals. Theseradical can further remove hydrogen from adjacent fattyacids, causing an autocatalytic chain reaction (propagation)to produce lipid peroxides. The termination stage requires thepresence of an antioxidant such as -tocopherol (vitamin E),which is the chain-breaking molecule.In addition to auto-oxidation, the fat in DDGS canundergo photo-oxidation, which is even faster thanauto-oxidation. Light acts on the oxygen molecule toform a radical called “singlet oxygen”, which reacts withdouble bonds of fatty acids in DDGS to produce hydroperoxides.From then on the propagation and terminationstages will continue similar to the process described asauto-oxidation above (Cyberlipid Center, no date). Afterthis process, the DDGS become rancid and the presenceof these lipid peroxides leads to reduced palatability inruminant animals. It is clear that exposure of DDGS andWDGS to sunlight and oxygen has to be reduced as muchas practically possible.One other aspect related to the conservation of distillersgrain is the potential for mycotoxin contamination.Mycotoxins are not destroyed during the ethanol fermentationprocess or the distillers grain production processes,but instead augmented almost three-fold from their initialconcentration in the original kernel. Inadequate storageconditions may also increase their concentration due toinoculation by mould spores present in the environment.The use of mycotoxin-contaminated distillers grain in dairycattle diets poses a risk to human health because of thetransfer to milk of the carcinogenic metabolite aflatoxinM1. Even when the toxin concentration is within acceptablestandards for distillers grain, the additive nature ofthe mycotoxins does not preclude the potential for toxicitywhen other slightly affected feeds are also included in thediet. In the presence of borderline-acceptable levels of aflatoxinB1 in DDGS, testing the TMR and/or individual feedsis recommended to ensure milk will not be contaminated.If a feed ration has been found to have high mycotoxinconcentration, the producer could include various feedadditives to bind mycotoxins, and reduce absorption by theanimals. For example, β-glucans, zeolyte and other bindershave been reported to be effective. At the time of writing,the United States Food and Drug Administration does notrecognize the potential “binding” properties of these additives,which can only be commercialized by the respectivecompanies as “anti-caking” agents.Storage of wet distillers grain with solublesWhen ethanol plants are relatively close to the farms,WDGS is usually an attractive alternative. They are usuallypriced around one-third to one-quarter the price of DDGSand, on a dry basis, their nutrient content is practically thesame as DDGS. However, WDGS has advantages otherthan just a competitive price, as WDGS helps improve theoverall diet, increasing its palatability and reducing feedsorting, particularly when dry forages and concentratespredominate. These advantages are not such when otherfermented feeds are included at high levels in the diet (e.g.maize silage, high-moisture maize, hay crop silage) as theinclusion of WDGS may result in excessively wet or acidic,or both, rations that may reduce intake. An additionaldrawback in the field is that the term WDGS or “wet cake”is applied loosely to any wet product coming from theethanol plant that is not DDGS, regardless of its moisturecontent. The DM content of WDGS ranges in most casesbetween 30 and 40 percent.Another product that has become quite popular amongethanol plants is the “modified” WDGS, with reducedwater compared with WDGS. Modified WDGS has a DMconcentration between 45 and 55 percent. On a drybasis, the nutritive quality of WDGS can be affected byprocessing, handling and storage. Mishandling betweenproduction at the plant and utilization on the farm can turnan excellent product into a lower quality or even healththreateningfeedstuff.From processing at the ethanol plant to delivery on thefarm, there are critical time constraints that may challengeWDGS quality. Granted, WDGS does not remain for extendedperiods at the plant before being shipped. Oftentimes itleaves the plant still warm from the fermentation process.Temporary storage at the plant is usually done on concretesurfaces, so these surfaces should be maintained cleanand protected from the weather. In addition, WDGS is notonly palatable to livestock but also to birds, vermin andeven companion animals (including dogs), whose faeces