This starch is converted into ethanol, an increasingly demanded form of biofuel, destined to provide the US with an alternative fuel source and alleviate the pressure imposed by current foreign fuel markets and politics. Ethanol has also been shown to reduce air pollution when compared to typical internal combustion automobile emissions. The resultant by product of ethanol manufacturing is what we refer to as DDGS. This corn derived by-product differs from corn in that the vast majority of starch is depleted and it has an alcohol aroma. Thus, with the removal of the predominant nutrient in corn, starch, all other nutrients in the resultant by-product DDGS are increased in their concentration.

Figure 1. DDGS samples from three different commercial sources.

It is estimated that the US currently produces 5 billion gallons of ethanol annually. It is also estimated that 1 new ethanol plant is opened weekly in the US. The majority of corn that used to be destined to supply animal feed mills in the US is now making its way into the more than 110 ethanol plants that are now operating, consuming approximately 50 millions tons of corn. As a result, a little more than 9 million tons of corn-originated DDGS were produced last year, and is expected that more than 16 million tons of DDGS will be produced this year. Obviously, as more ethanol plants become operational, this number will continue to increase proportionally.

The use of DDGS has created some problems for feed mills throughout the country. Unloading has been one of the most problematic operations regarding DDGS handling. Bridging and caking are not uncommon situations to encounter when unloading or moving DDGS. Depending on the degree of compactness, some rail cars can take 10 minutes to unload while others can take up to one and a half hours, thus creating logistical problems for any feed mill. In addition to the unloading problem, some concern has arisen with its flow ability characteristics. All these handling tribulations are likely the result of certain conditions such as moisture content of the ingredient, relative humidity, and the relatively higher fat content of the product.

Nutritionally, the feedstuff has shown some consistency problems as well. In swine, it was recently reported that 20% supplementation of DDGS affects belly firmness. In poultry, the ability to assign an energy value to the ingredient has created concern. In a study the true metabolizable energy (TME) of DDGS was evaluated (Batal and Dale, 2006). Seventeen samples obtained from six different plants in the Midwest gave a range of TME between 1,132 and 1,450 kcal/lb. A second study evaluated the TME of DDGS from five different plants in the Midwest (Fastinger et al., 2006), reporting a range in energy between 1,127 and 1,381 kcal/lb.

Amino acid content and digestibility has also been a cause for concern with DDGS. Fastinger et al. (2006) reported the amino acid content and digestibility of amino acids from 5 different plants from the Midwest (Table 1). As expected, there was some normal variation observed; however, lysine showed considerable variability, not only on its content (for those who formulate using total amino acid values) but also on its digestibility coefficient (for those who formulate using digestible values). Batal and Dale (2006) reported a range in lysine content from their 17 samples between 0.39 and 0.86%, and a range in digestibility coefficients between 46 and 78%. Of the critically limiting amino acids, lysine was likely the most affected based from these studies. The reduction in lysine digestibility and concentration is likely the result of heating damage endured during the fermentation process and perhaps some maillard reactions. Threonine and cystine also appear to be susceptible to the DDGS manufacturing process and thus their digestibilities.

Another nutrient that undergoes some bioavailability modification is phosphorus. DDGS are higher in nonphytate and available phosphorus than regular corn as a result of the fermentation process where some of the phytate complex bonds are cleaved, in turn generating more available phosphorus. This has resulted in a lower inclusion of inorganic phosphorus sources in formulation, generating a potentially more economical diet. However, the reduction in inorganic phosphorus use in feed mills has been linked to a lower feed mill throughput, a higher wear and tear at the pellet mill die, and higher electric power expenditure. This will likely off-set any potential cost savings in phosphorus and may create an obstacle in the amount of DDGS that may be included in poultry diets.
Other physical aspects have created concern with the use of DDGS. Variability in particle size is one of those aspects, where it has been observed to range between 612 and 2,125 microns. This was observed by Knott et al. (2004) after analyzing samples taken from 16 different plants. Such vast variations in particle size can have tremendous impact in pellet mill throughput and pellet quality. Additionally, diets with DDGS will also be bulkier, and has been estimated that for every 1% of additional DDGS inclusion, the volume of a diet will increase by 0.3%, when compared to corn-soybean meal diets. Another study analyzed the bulk density values of 72 different DDGS samples and observed them to range between 24 and 31 lb/ft³.

Color has also shown some noticeable differences between DDGS samples. Figure 1 shows 3 different sources of DDGS. This photograph also reveals the difference in texture previously discussed. Ergul et al., (2006) showed that lighter or yellower DDGS may result in higher digestibility of threonine, cystine, and particularly lysine, while darker or less yellow DDGS may result in a lower digestibility.

In Mississippi, some integrators have started using DDGS. Some feed mills are using DDGS but at inclusion levels lower than 5%. The main reasons for their lack of use have been a lack of availability of larger quantities and the freight costs associated with shipment from the Midwest. There is also the concern of inconsistency of the ingredient which has created some skepticism among nutritionists and integrators in general. The availability scenario is likely to change as more plants come online, particularly the one being built in Vicksburg, MS. That plant is expected to be operational early next year and will have a capacity of producing 60 million metric gallons of ethanol per year, and as a result approximately 150,000 metric tons of DDGS will be produced and available to the animal feed industry. With an increase in DDGS use there will also be an increase in research concerned about the efficiency of use for this ingredient by poultry. In addition to the institutions currently evaluating this ingredient, an increase in their numbers is expected. In the case of Mississippi, our lab and USDA-ARS Poultry Research Unit has initiated research towards the evaluation of this feed ingredient in broiler rations. Because of high feed ingredient prices, most integrators will have to include this feed-stuff in their diets. While this situation may create some concern due to the bird’s ability to properly utilize this ingredient without negative implications on growth, mortality, feed conversion and yields, we have reasons to feel optimistic about improvements in DDGS use by feed mills and by poultry.