Maize distillery by-products are common ingredients for ruminants. In a forage and concentrate diet, DDGS can often replace most, if not all, of the protein supplement such as soybean meal and a significant amount of the grain (Schroeder, 2010). One particular benefit of DDGS over cereal grains is that, as their energy is primarily provided as readily digestible fibre and fat, they have a propensity to alleviate incidence and severity of acidosis, laminitis and fatty liver caused by rumen starch fermentation (Kelzer et al., 2011; Schroeder, 2010).
Wet and dried distillers grain are equivalent, but if the diet also contains moist feeds, such as maize silage, gut fill may limit total DM intake and production with diets that contain more than 20% of DM as wet DGS (Schingoethe, 2006).
Palatability
Dried DGS are palatable, and palatability may only become a problem with excess wet or dried DG in the diet (Schroeder, 2010).
Digestibility and energy content
The average OM digestibility was 73.5 ± 6.2% (6 samples collected from literature) which corresponds to a mean ME content of 12.6 MJ/kg DM (Feedipedia, 2011; Woods et al., 2003). This value is similar to the values of 12.6 and 12.7 MJ/kg DM proposed respectively by INRA (Sauvant et al., 2004) and NRC (NRC, 2001). Recent research in the USA suggests a much higher digestibility, about 85%, which corresponds to ME values of 14.6 to 15.9 MJ/kg DM. Wet DGS contained approximately 14.0 MJ/kg of ME and 9.5 MJ/kg of NEL, i.e. 10 to 15% more energy than published before (Birkelo et al., 2004). This could reflect either digestive interactions or a higher energy value for distillers grain obtained by recent processes, and notably those produced in bioethanol plants.
In sacco studies suggest that effective DM degradability of DDGS is higher than those of rapeseed meal and cottonseed meal, but lower than those of barley grain and beet pulp (Woods et al., 2003; Chapoutot et al., 2010).
Protein value and phosphorus
Since most of the degradable proteins in maize grain have been degraded during the fermentation process, the proteins in maize DDGS contains a higher by-pass fraction than that of the original grain. Values for rumen undegradability of protein (RUP) vary from 47% to 76%, with a mean value of 55% (44% in Sauvant et al., 2004) (Firkins et al., 1984; Woods et al., 2003; Kleinschmit et al., 2006a). If RUP values are quite high (e.g. more than 80%), it may be advisable to check for heat damaged, undigestible protein (Schroeder, 2010). Apparent small intestinal digestibility of DDGS (90%) appears to be lower than that of soybean meal and groundnut meal (96%) and higher than that of rapeseed meal (82%) and cottonseed meal (81%) (Yue Qun et al., 2007). The INRA-AFZ tables (Sauvant et al., 2004) propose a similar ranking of those ingredients.
When DDGS are included at high levels in the diet, other protein supplements may be needed because poor protein quality (lysine) and high phosphorus concentration become factors to consider (Schroeder, 2010).
Comparison with other concentrate ingredients
Distillers grain is estimated to have 120-150% of the energy value of dry-rolled maize grain in beef finishing diets, and this difference decreases as dietary DGS increases (Kononoff et al., 2006). However, the feeding value of DGS appears to be lower in finishing diets based on steam-flaked maize than in diets based on dry-rolled or high-moisture maize (Klopfenstein et al., 2008). In feedlot steers, including 15% maize DDG or sorghum DDG in steam-flaked maize-based diets did not affect apparent total tract digestibility (May et al., 2010). Dried DGS can effectively supplement barley-based beef cattle diets up to almost 20% of diet DM (Eun et al., 2009).
Feeding wet distillers grains with solubles (WDGS) and wet corn gluten feed together reduces some of the negative effects of feeding WDGS alone on nutrient digestion, purine derivative excretion, and N utilization in dairy cows (Gehman et al., 2010a).
With regard to protein, maize DDGS contain less protein than wheat DDGS but the protein of the latter is less degradable (Nuez-Ortin et al., 2010). A recent study with nylon bags incubated in the rumen suggested that the amino-acid availability of several distillers grain products is comparable with that of soybean products (Mjoun et al., 2010).
Dairy cattle
Since the 1990s, numerous experiments have been carried out with corn distiller grain in dairy cow rations. Dried DG(S) is mainly used as a protein supplement, and milk production response to DDG(S) was either unaffected (Clark et al., 1993; Owen et al., 1991) or increased (Powers et al., 1995; Nichols et al., 1998). Dairy rations can be successfully formulated to include 15% (diet DM) of maize distillery by-products (DDGS or high-protein DDG) while maintaining or increasing DM intake, milk production, and yields of milk components (Kelzer et al., 2009). Balanced diets for dairy cattle can include up to 25% WDGS and result in increased microbial protein synthesis, milk production, and milk protein yield (Gehman et al., 2010b). As a rule, a maximum of 20% (diet DM) distillers grain should be included in the ration. At higher levels, potential palatability and excessive protein consumption problems often exist, though amounts may approach 30 % when diets are properly formulated (Schroeder, 2010).
Dried DG was also a good energy source for dairy cows when the diet contained approximately 28% NDF and 5% fatty acids (Leonardi et al., 2005). Higher production was observed when cows were fed either wet or dried DGS than when fed the control diet (Anderson et al., 2006). Similar milk production was observed for wet and dried maize DGS but maize DGS resulted in a higher milk production than sorghum DGS (Al-Suwaiegh et al., 2002).
Milk composition is usually not affected by feeding DGS when feeding sufficient amounts of forage fibre. Some field reports and publications reported instances of milk fat depression when diets contained more than 10% (diet DM) of wet DGS (Hutjens, 2004; Cyriac et al., 2005, Kleinschmit et al., 2006b). However, a meta-analysis of 24 studies conducted between 1982 and 2005, involving 98 treatment comparisons, showed that there were no decreases in milk fat content when diets contained wet or dried DGS up to a level of 40% of DM intake (Kalscheur, 2005).
Corn distillers solubles (CDS) are usually blended with the distillers grain before drying to produce DGS, but the solubles may be fed separately. In lactating cows fed wet (28% DM) condensed corn distillers solubles (CCDS) at 0, 5, and 10% (diet DM), milk production increased when fed the CCDS (34.1, 35.5 and 35.8 kg/d for 0, 5, and 10% CCDS diets), although milk fat content (3.54, 3.33, and 3.43% respectively) was slightly lower and milk protein content (2.93, 2.97 and 2.95% respectively) was unaffected by the diets (da Cruz et al., 2005). Dairy cows could be fed as much as 20% of the total ration DM as CCDS (4% added fat from the CCDS) with no apparent adverse affects on DM intake or milk composition (Sasikala-Appukuttan et al., 2006). CCDS supplementation improves nutrient availability and use of low-quality forages (Gilbery et al., 2006).
Beef cattle
Beef cattle have been successfully fed as much as 40% (diet DM) of wet or dried DGS without affecting meat tenderness or palatability (Roeber et al., 2005). Growing cattle fed moderate levels (15% diet DM) of DDGS had similar growth performance and carcass characteristics to animals fed the control diet (Depenbusch et al., 2009). In growing and finishing beef cattle, wet and dried DGS resulted in similar performances (Ham et al., 1994).
Interactions were observed between maize grain processing (dry rolling, high moisture and steam-flaking) and the inclusion rate of WDGS. These interactions could be due to the decreased rumen ratio of acetate/propionate in dry-rolled maize and high-moisture maize diet with 40% WDGS (Corrigan et al., 2009b). Feeding strategies of steers aimed at increasing rumen pH may improve digestion of DDGS in steam-flaked maize-based finishing diets (Uwituze et al., 2010). In steers, apparent total tract digestibility of DDG was negatively affected by association with processed (dry-rolled or steam-flaked) maize grain (May et al., 2009).
Dried DGS may be similar to tallow and high-moisture maize grain in finishing diets containing 20% DDGS. The greater energy value of WDGS compared with maize grain may be due to higher propionate production, higher fat digestibility, and more unsaturated fatty acids reaching the duodenum (Vander Pol et al., 2009).
The level of condensed distillers solubles (CDS) may affect the performance of growing steers as CDS depressed average daily gain and gain/feed. There was no obvious explanation for the interaction between DDG supplementation and the CDS level on growing steer performance (Corrigan et al., 2009a).
Sheep and goats
Dried DGS is a viable supplement to enhance the nutrition of sheep consuming moderate-quality forages (Archibèque et al., 2008). DDGS achieved higher average daily gains and lower feed costs per kg gain compared to lambs on a control diet (Iliev et al., 2008). In growing lambs, DDGS included at 20% (diet DM) could replace a mixture of barley grain and rapeseed meal without adversely affecting average daily gain and carcass characteristics. Including triticale DDGS also improved the fatty acid profile of subcutaneous fat (McKeown et al., 2010).
