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Distiller grains is a cereal coproduct from the distillation process. The starch in grain flour is converted into ethanol and carbon dioxide. The remaining nutrients (proteins, lipids, fiber, minerals, and vitamins) are relatively unchanged, but concentrated (Table 1). These nutrients end up in a coproduct, which is commonly known as distillers dried grains with solubles (DDGS; Liu, 2011).
Table 1. Nutrient composition of corn, wheat, and corn and wheat distillers dried grains with solubles (DDGS; NRC, 2012)
| Item, % | Corn | Corn DDGS | Wheat | Wheat DDGS |
| Crude protein | 8.24 | 28.89 | 14.46 | 36.61 |
| Crude fiber | 1.98 | 9.48 | 2.57 | 6.75 |
| Ether extract | 3.48 | 8.69 | 1.82 | 5.34 |
| Starch | 62.55 | 3.83 | 59.50 | 1.78 |
| NDF | 9.11 | 41.86 | 10.60 | 34.70 |
| ADF | 2.88 | 15.55 | 3.55 | 13.81 |
| Calcium | 0.02 | 0.08 | 0.06 | 0.16 |
| Phosphorus | 0.26 | 0.56 | 0.39 | 0.92 |
Corn is the primary grain used for ethanol production in the United States, but European and Canadian ethanol plants often use wheat or a combination of wheat and corn. Wheat DDGS usually contains more CP, but less ether extract, than corn DDGS (Table 1), and the digestibility of AA in wheat DDGS is variable and Lys is usually the AA with the greatest variability in digestibility (Cozannet et al., 2010). The reason for the variability in Lys digestibility is that some sources of DDGS are heat damage during drying (Stein et al, 2006). As a consequence, the nutritional quality of DDGS is impacted by the cereal source used as well as conditions during processing.
Amino acid digestibility in corn and wheat DDGS
A source of European wheat DDGS and corn DDGS were used to evaluate the standardized ileal digestibility (SID) of CP and AA. The diets contained 50% DDGS as the only source of protein. The diet with corn DDGS had less CP, but more Lys, compared with the wheat DDGS diet. However, the SID of CP and for all indispensable AA was greater in corn DDGS compared with wheat DDGS (Table 2).
Table 2. Standardized ileal digestibility of indispensable amino acids in distillers dried grains with solubles (DDGS) produced from wheat or corn
| Amino acid | Wheat DDGS | Corn DDGS | P-value |
| Arg | 74.31 | 82.83 | <0.01 |
| His | 71.16 | 78.28 | <0.01 |
| Ile | 70.20 | 75.27 | <0.001 |
| Leu | 77.76 | 86.52 | <0.01 |
| Lys | 33.07 | 58.45 | <0.01 |
| Met | 72.89 | 83.51 | <0.01 |
| Phe | 77.41 | 81.21 | <0.01 |
| Thr | 64.05 | 70.09 | <0.01 |
| Trp | 63.21 | 59.62 | <0.01 |
| Val | 68.14 | 75.35 | <0.01 |
| Mean | 70.67 | 78.67 | <0.01 |
Nutrient digestibility and growth performance of two sources of distillers dried grains with solubles produced from corn using two different processes
The SID of AA and the apparent total tract digestibility (ATTD) of NDF and acid hydrolyzed ether extract (AEE) were determined in conventional DDGS and in Dakota Gold DDGS. Growth performance and carcass characteristics of growing pigs fed diets containing the two sources of DDGS were also measured.
Dakota Gold is a low-oil DDGS produced by a heat-free process, using a cold fermentation technic called BPX, which may positively influence nutrient digestibility. Addition of fat to diets fed to pigs increases the digestibility of AA (Kil and Stein, 2011) and it is, therefore, possible that AA digestibility is affected by the reduced oil concentration in DDGS. Nutrient composition of both sources of DDGS is presented in Table 3, and the SID of indispensable AA as well as the apparent total tract digestibility of GE, NDF, and AEE, and the concentration of ME appear in Table 4.
Table 3. Analyzed concentration of dry matter (DM), gross energy, nutrient composition in two sources of distillers dried grains with solubles (DDGS)
| Dakota Gold DDGS | Conventional DDGS | |
| Dry matter, % | 87.77 | 82.26 |
| Gross energy, kcal/kg | 4,442 | 4,831 |
| Crude protein, % | 29.5 | 28.67 |
| Ether extract, % | 4.49 | 7.91 |
| Acid hydrolyzed ether extract, % | 6.82 | 9.54 |
| NDF, % | 29.4 | 37.59 |
Table 4. Standardized ileal digestibility of indispensable amino acids, apparent total tract digestibility of gross energy, NDF, and acid hydrolyzed ether extract (AEE), and the concentration of ME in conventional distiller dried grains with solubles (DDGS) and Dakota Gold DDGS
| Dakota Gold DDGS | Conventional DDGS | SEM | P-value | |
| Standardized ileal digestibility | ||||
| Arg | 93.3 | 87.2 | 1.2 | 0.013 |
| His | 86.6 | 82.1 | 1.1 | 0.043 |
| Ile | 84.7 | 79.8 | 1.4 | 0.051 |
| Leu | 90.5 | 86.9 | 1.2 | 0.075 |
| Lys | 68.1 | 53.0 | 4.6 | 0.007 |
| Met | 89.3 | 85.4 | 0.9 | 0.007 |
| Phe | 88.4 | 84.2 | 1.1 | 0.017 |
| Thr | 80.8 | 77.4 | 1.1 | 0.052 |
| Trp | 79.1 | 76.7 | 2.7 | 0.582 |
| Val | 83.2 | 77.6 | 1.5 | 0.026 |
| Apparent total tract digestibility | ||||
| Gross energy, % | 67.9 | 67.2 | 0.505 | |
| NDF1, % | 49.9 | 60.6 | 0.002 | |
| AEE1, % | 51.9 | 68.4 | 0.001 | |
| Concentration of ME, kcal/kg | 2,743 | 2,965 | 0.001 | |
1NDF: neutral detergent fiber; AEE: acid hydrolyzed ether extract.
Greater SID of Arg, His, Lys, Met, Phe, and Val were observed in Dakota Gold DDGS compared with conventional DDGS. The reduced heat treatment used in processing of the Dakota Gold DDGS, therefore, appear to positively influence AA digestibility because of reduced heat damage in this source of DDGS. However, the ATTD of NDF and AEE, and the concentration of ME was greater in conventional DDGS than in Dakota Gold DDGS, but there was no difference in the ATTD of gross energy between the 2 corn sources of DDGS. The increased ME in conventional DDGS, therefore, is a result of the increased gross energy in conventional DDGS compared with Dakota Gold DDGS.
For the growth performance and carcass characteristics experiment, diets were formulated to contain the same level of SID Lys; therefore synthetic Lys was added to the diet containing conventional DDGS. However, no attempt to equalize ME was made. As a consequence, the ME in diets containing conventional DDGS was slightly greater than for diets containing Dakota Gold DDGS. There were no differences between pigs fed diets containing Dakota Gold DDGS and pigs fed diets containing conventional DDGS in growth performance (Figure 1) or in any of the carcass characteristics measured (hot carcass weight, dressing percentage, backfat, longissimus muscle are, and percentage of fat-free lean; results not presented). The effect of reduced ME in diets containing Dakota Gold DDGS was not reflected in the growth performance.
From these 2 experiments it is concluded that:
- Corn DDGS has greater SID of CP and indispensable AA compared with wheat DDGS.
- The process to obtain the DDGS may change nutrient digestibility, but not growth performance, or carcass characteristics. The SID of most AA were greater in Dakota Gold DDGS than in conventional DDGS, but the ATTD of NDF and acid hydrolyzed ether extract and concentrations of ME were less in the Dakota Gold DDGS than in the conventional DDGS fed to growing pigs. Nonetheless, use of the 2 sources of DDGS in diets fed to weaning to market did not affect growth performance or carcass characteristics, but fewer synthetic AA are needed if Dakota Gold DDGS was used.
