Good-quality Distillers’ Dried Grains with Solubles (DDGS) are high in energy and amino acid content and free of anti-nutritional factors such as mycotoxins and can support good egg production and egg quality. With inclusion rates of 3 to 5% for pullets and rates of up to 15% for layers, DDGS is widely recognized as an excellent feedstuff.
The greatest challenge in using DDGS in poultry diets is to work with accurate nutrition matrices. The nutritional composition and quality differ substantially between sources of DDGS. For example, the conditions during the drying process have a huge impact on the amino acid digestibility.
DDGS users are often tempted to use color as an indicator of DDGS quality, and energy and protein levels as the main criteria to decide whether they use it. However, there are more aspects to consider when birds are being fed with DDGS.
1. Amino acids digestibility
Visually we can have a rough idea of the effect of heat-damage on DDGS; a darker color indicates overheating and reduced protein quality and lower amino acid digestibility. However, a visual inspection by a human is subjective and heat-damage is not the only factor which can impact the color. DDGS is also influenced by the maturity of the grain, amount of solubles added to the DDG, storage conditions, presence of toxins, contamination due to sand and possible use of insecticides/fungicides, which give a dull and dusty appearance.
DDGS contains protein and carbohydrate levels which when exposed to high temperatures during the drying process, can form a chemical reaction (Maillard reaction) affecting its amino acid digestibility. Thus, more reliable heat-damage indicators than color are needed to evaluate the quality.
The amino acid, Lysine is very susceptible to heat damage and Maillard reaction. The reactive Lysine assay is very specific and measures only that amount of Lysine which did not participate in any Maillard reactions and thus, is potentially available to the animal. The reactive Lysine is an excellent indicator for heat-damage, and it correlates well with the changes in amino acid digestibility.
Classically, the reactive Lysine assay is a very demanding wet-chemistry method, but today Near-infrared Spectroscopy (NIR) calibrations are available to determine the reactive Lysine and to estimate the degree of heat-damage. Based on this estimation, a correction of the amino acid digestibility can be done. In summary, NIR is today a capable and powerful tool to identify and grade heat damage in DDGS giving reliable information on the real protein and amino acid quality.
2. Phosphorus availability
Although there is consistent evidence that excessive heating (dark color) during DDGS drying reduces the digestibility of amino acids, it may increase the relative bioavailability of phosphorus for poultry.
Studies suggest that the fermentation process which the corn undergoes improves phosphorus availability in the by-product. The synthesis of microbial phytase during fermentation and structural change caused by the drying process might increase phosphorus bioavailability.
Mycotoxins are one of the biggest concerns leading to low dietary inclusion rates of DDGS. Nutritionists try to minimize total mycotoxin content because they can have significant adverse health and performance effects.
Noticeably, the fungal contamination of grain used for the DDGS product, the drying equipment and storage could lead to high prevalence and concentrations of mycotoxins. During the fermentation process, the starch of corn is transferred into alcohol and the remaining components of corn are accumulated. Thus, DDGS typically contains three-times more nutrients like amino acids than corn, but this also applies for mycotoxins. Fungi toxins cannot be destroyed by heat during the drying process. If the source of corn is contaminated with fungi toxins, DDGS will be three-times higher in mycotoxin content as well.
4. Oil oxidation
DDGS are traditionally rich in fat and thus highly economically attractive when working with layers. Nutritionally the high fat content is also interesting, due to high concentrations of polyunsaturated fatty acids which are important for yolk formation, particularly linoleic acid that brings positive effects in egg weight at the production onset.
Unfortunately, polyunsaturated fatty acids are extremely susceptible to oxidation and drying processes accelerate this oxidation. Feeding diets with oxidized lipids has negative effects on the liver status and as a result on the egg quality and egg production.
NIR can be a fast and reliable way to assess the fat quality and determine the fatty acid contents of DDGS, together with other analytical methods, such as the TBARS (Thiobarbituric acid reactive substances) test that can give a good estimation of lipid peroxidation.
5. Yolk pigments
DDGS can be a good source of pigments for the yolk. Pigments like xanthophylls or carotenoids are liposoluble nutrients that cannot be synthetized by birds. Thus, they must be offered in the diet. DDGS inclusion levels have been shown to result in better distribution of color particles during feed mixing in comparison to smaller dose products. DDGS provides a good yellow pigmentation base and thus reduces diet cost while meeting consumers’ desired egg yolk color quality standards.
However, lighter colored DDGS is more likely to contain higher amounts of xanthophylls than darker colored DDGS, due to its liposoluble nature. Overheating of DDGS may cause oxidation of carotenoids resulting in lower concentrations. Therefore, complementing the yolk pigmentation using natural or synthetic products over a homogenized base of yellow from DDGS is recommended.
6. Sulfur content
Sulfuric acid is commonly added during the dry grind ethanol production process to keep pH at desired levels for optimal yeast propagation and fermentation for efficient conversion of starch to ethanol, as well as for cleaning purposes. However, sulfur is one of the core chemical elements needed for biochemical functioning and is an elemental macronutrient for all living organisms. Despite the importance, sulfur levels in poultry greater than 0.6% can produce wet litter problems, while 1.20% sulfur resulted in depressed growth.
However, it is very unlikely that DDGS will contain very high sulfur levels, but the general concern about the sulfur level in feeds and how it is influenced by using DDGS is reasonable. Therefore, it is important to consider the sulfur additivity of other feed ingredients too.
Carlos de la Cruz, Global Expert Egg Production, Evonik Health and Nutrition GmbH