Advantages and disadvantages of feeding distilled grains to dairy cows

The extensive development of the ethanol industry from grain, which began in 2005, has been able to increase the supply of byproducts for animal feed. The availability of corn distillers’ grains (DG), which are mostly called distillers’ grains, has increased significantly, as a result of which the desire to use these feeds in the diet of dairy cows has also increased.

Production and storage of distilled grains:

Traditionally, distilled grains are produced in connection with the production of alcohol for human consumption. While the traditional and modern ethanol production processes are generally similar, the advancement of technology, the difference in ethanol consumption, and the knowledge of raising livestock as important consumers of by-products have led to the creation of a new generation of distillers.

Ethanol can be fermented from any carbohydrate substrate such as sugarcane, corn, etc. with different degrees of efficiency. Currently, the main carbohydrate used for this fermentation is corn starch. The first step to produce ethanol is grinding corn. With this process, corn kernels are ground into small and medium particles, and water and enzymes are added to break down starch into glucose. This mixture is cooked and sterilized to kill bacteria. The sterilized flour is cooled and the inoculum containing yeast is added to it in order to ferment glucose and convert it into ethanol and carbon dioxide. Then the ethanol is distilled, and the remaining solids and water are processed into wet distillate grains (WDG) and the remaining distillate grains with solvent. Solvents are usually combined with wet distillate grains, which eventually leads to the production of solvent wet distillate grains (WDGS). Solvent-wet distillate grains can be dried and converted into solvent-dried distillate grains (DDGS). Each of these by-products is fed to dairy cows.

The easiest product to produce ethanol for transportation and storage is DDGS. Since this product is in a dry form, it can be transported anywhere and even stored indefinitely under normal conditions. Drying distillers grains requires a lot of energy, time and money, which is why DDGS is more expensive than WDGS on a dry matter basis. However, WDGS is more difficult to transport and store due to its moisture and perishability. As a result, WDGS will typically only be applicable to farms located within close proximity of ethanol plants. Spoilage usually occurs in five to seven days after production, which itself depends on the ambient temperature. Also, equipment for storing WDGS can be problematic due to its higher moisture content (typically 35% dry matter). However, storage losses of WDGS can be high. By limiting oxygen during storage, the shelf life of WDGS can be increased.

Nutrient composition of distilled seeds:

Since ethanol fuel is produced by removing starch from corn, in most cases, the composition of distillate grains can be predicted from the composition of corn. As a general rule, except for starch (which is removed first), the nutrient composition of distillers grains is approximately 3 times their concentration in corn kernels. This is because starch makes up about two-thirds of the weight of corn. If converting the nutrient composition of corn to distillers grains is always correct, because the nutrient composition of corn has little variability, the nutrient composition of distillers grains will have little variation. Anyway, this issue has always been discussed among ethanol production factories. The reasons for differences in the composition of nutrients can be related to small differences in processing steps over time and processes between factories. In addition, solvents added to the distillate grains at different ratios increase the chemical diversity in both WDGS and DDGS. Such factors can make significant differences in DDGS.

Distillates are mainly considered as supplementary sources of crude protein (CP) {especially rumen non-degradable protein (RUP)}. In addition to crude protein, distilled grains contain high levels of neutral detergent insoluble fiber (NDF) and ethereal extract (EE) and phosphorus (P). In addition, the concentration of sulfur may exceed one percent of dry matter. The concentration of this nutrient is higher and completely variable compared to corn, which is due to the addition of sulfuric acid during the production process. The NDF in distilled grains has high digestibility. Because the crude protein of distilled grains is mainly composed of zein protein, they are broken down at a lower rate in the rumen. According to the absence of amino acid lysine in zein, the amino acid composition of crude protein in distilled grains is similar to corn, where amino acid lysine is considered a limiting amino acid for milk production in most cases. It seems that the variation between the maximum and minimum nutrient composition of distillers grains is very large for many components. This is especially true for crude protein and the undegradable protein fraction in the rumen, which is a major reason for using DDGS in dairy cattle diets.

In most cases, factories producing DDGS will have a special analysis according to the specific process of ethanol production. Important process characteristics include plant design, processing or grain size, extent of fermentation, and drying temperature. Additionally, experience has shown that a significant amount of variability in DDGS analysis can result from differences in the corn (source and quality) used.

Crude protein quality:

As a by-product of corn, the crude protein of distilled grains is relatively non-degradable in the rumen. This situation is especially seen in products that have been heated and dried twice. According to the analysis table provided by NRC 2001, the increase of non-degradable protein in the rumen has a linear relationship on milk production and milk protein. This result has been confirmed in distiller’s grains. Milk and milk protein production increases when RUP in the form of distillers grains replaces soy protein.

It has been stated that the amino acid lysine is limiting in distilled grains. The researchers found that when DDGS was fed 15% dry matter along with corn silage and alfalfa forage or an equal mixture of both, milk production increased with increasing levels of alfalfa in the forage portion of the diet.

It has been determined that the amino acid lysine is the first limiting amino acid for mammary glands for cows fed diets containing corn silage or diets containing corn silage/alfalfa forage, while the amino acid methionine is the first limiting amino acid for diets containing alfalfa forage. It is believed that supplementing diets containing a lot of corn silage with passable lysine can be beneficial.


Although distillers grains are usually fed as a source of crude protein, the energy concentration of distillers grains is equal to or greater than that of corn kernels. Although the energy of distilled grains is provided by fat, digestible fiber and crude protein instead of starch. It can effectively affect the rumen environment and reduce the occurrence of acidosis.

Insoluble fibers in neutral detergent (NDF):

The major carbohydrate fraction in distillers grains is NDF. Feeding high levels of distiller’s grains will increase the NDF concentration of the diet. Numerous experiments have shown that distillers grains are comparable to forage as an effective fiber source. Due to forage portion size considerations, using higher levels of distillers grains in the diet to replace effective forage fibers is likely to be limiting. Although the NDF concentration of these rations is higher than the rations containing corn, the milk production is equivalent or even higher than the rations without distillers grains.


There are high levels of distillers’ grain fat. Diet fat levels should be balanced to less than 5% of dry matter (excluding trans fats) to avoid rumen dysfunction. Variation in DDGS fat levels can be problematic and must be controlled for normal rumen function. If other fat-containing food sources (whole soybeans and cottonseeds) are used in the diet, the amount of distillers grains fed should be limited.

Phosphorus and sulfur:

Nutrient management programs are mostly designed around nitrogen and phosphorus removal. Phosphorus concentration in distilled grains is much higher than the needs of cattle. Probably, due to the hydrolysis of phytate during the fermentation process of distilled grains, it seems that the availability of phosphorus in these products is more than that of corn. According to this case, it is suggested that if sufficient levels of distilled grains are used in the diet, the inorganic phosphorus supplement can be reduced or eliminated in the diet. However, in order to meet nutrient management goals, it is necessary to control the level of phosphorus in the final diet. Usually, the phosphorus in DDGS is twice the level of phosphorus in corn kernels. Feeding high levels of DDGS may increase phosphorus excretion in the herd.

The level of sulfur in distilled grains is high and variable. It is usually recommended that the diet of ruminants has 0.3% sulfur dry matter. Diets often formulated for higher sulfur concentrations (especially when feeding anionic salts) are often without problems. It is important to control the level of sulfur in the final ration. In total, DDGS has four times the sulfur of corn grain, which should be paid special attention to when adjusting rations.

Maximum level of distilled grains:

The usual maximum recommended level of distillers grains for dairy cows is 20% of the dry matter of the diet. However, due to the other characteristics and composition of DDGS discussed in this article, the feeding level is often limited to 10-15%.

  The researchers replaced corn and soybean meal with distilled grains at 0, 10, and 20% dry matter levels of the diet. The consumption of dry matter in the diet containing distilled grains decreased, milk production as well as the production of protein and milk fat was higher for cows consuming diets containing distilled grains. This itself leads to improved feed conversion efficiency (feed efficiency) for cows fed diets containing distillers grains.

Fungal toxins in distilled grains:

The presence of fungal toxins (mycotoxins) is one of the potential risks in the production of ethanol from corn seeds. Several types of mycotoxins can be found in corn kernels and its products, such as aflatoxins, dioxyvalone (DON), fumonisins, T-2 toxins, and zearalenone.

If there is mycotoxin in corn, its concentration increases. Mycotoxins can contaminate distillers grains and reduce animal performance, and if their levels are high, they can be transferred to milk. According to the information presented, it seems that the maximum level of distilled grains in the ration of dairy cows is limited as a result of the composition of nutrients in the whole ration.

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