Changes to distillers grains and the impact on feeding value

The most common method to remove corn oil is by centrifugation of the thin stillage. Historically, distillers grains plus solubles have about 11 to 13 percent fat, and this contributes to the improvement in feeding value relative to corn.

Matt Luebbe

Using this process reduces the oil of distillers grains plus solubles to approximately 7 to 8 percent. Based on more than 20 experiments, wet distillers grains with solubles has 130 to 135 percent the feeding value relative to corn.

Partially drying distillers grains to make modified distillers grains plus solubles results in a feeding value of approximately 125 percent of corn, and completely drying to 10 percent moisture to make dry distillers grains plus solubles decreases the feeding value to about 110 percent of corn.

Corn oil is energy-dense and generally has three times more energy than starch. All plants produce whole stillage, which is centrifuged into the wet grains and thin stillage. The thin stillage is condensed to make distillers solubles and then combined to the wet grains to produce wet, modified or dry distillers grains.

De-oiled distillers grains production includes an additional step where the thin stillage is centrifuged to remove the unbound or “free” oil. Typically, of the 12 percent fat or oil in distillers grains plus solubles, the solubles portion contains one-third of that oil, while the wet grains have two-thirds.

When the de-oiled solubles are combined with the grains, the resulting distillers grains with solubles product has approximately 4 percentage units less oil than the normal distillers. When de-oiled and full-oil distillers grains are compared in finishing diets, producers can expect to see a 1.5 percent decrease in feeding value relative to corn for every percentage unit decrease in oil content.

This is a relatively small change when we consider that corn oil, or “fat,” has three times more energy compared with starch. When feeding wet distillers grains at 30 percent of the diet on a dry matter basis, the feeding value may decrease from 130 percent of corn to 124 percent.

Some ethanol plants have the ability to use a more intense fractionation method before the grain is fermented. When these pre-fractionated byproducts are fed, the distillers grains have an energy value similar to corn grain.

Currently, ethanol plants are modifying production to fractionate a greater proportion of oil, protein and fiber. Some ethanol plants have already started this process by using traditional distillers grains as a secondary feedstock for cellulosic ethanol production.

Instead of the distillers grains available at this point for livestock feed, it goes into another fermentation process removing a portion of the fiber that makes up approximately one-third of the distillers grains.

At the same time, a greater proportion of corn oil is removed compared with the centrifugation method. While removing a portion of oil has a relatively small impact based on previous research, removing the fiber, protein and more oil will likely reduce the value of distillers grains to a greater extent.

An experiment conducted by the Iowa Beef Center compared traditional wet distillers grains with distillers grain that underwent a secondary fermentation process for cellulosic ethanol production.

The authors concluded that distillers grains produced using this process had a greater feeding value compared with corn grain (109 to 113 percent) but lower compared with traditional distillers grains, which is 130 to 135 percent the feeding value of corn.

One challenge we have is being able to predict the relative feeding value of byproducts produced with these different fractionation or fermentation processes. Until these processes are in place, we do not have access to the same type of byproduct for evaluation until it is available to producers.

Recent research at the University of Nebraska – Lincoln determined the impact of removing components of distillers grains (fat, fiber, protein, solubles) on the relative energy contribution of each nutrient alone or in different combinations.

To do this, it was necessary to mimic the components as they are found in traditional distillers grains. We used fractionated corn bran and germ meal to represent the fiber, corn gluten meal (65 percent crude protein) to represent the protein, condensed distillers solubles – or “syrup” – and full-fat corn germ to represent the two-thirds of oil found in distillers grains.

Our results show that each component contributes to the overall energy value of distillers grains. When all components are added back to the diet, we have the same performance as distillers grains.

However, individual component energy contributions were greater for fat and protein compared with fiber or solubles. It is logical that when fat is added back, the feeding value increased. However, the protein component is not always viewed as an energy source and does contribute to the overall feeding value.

When distillers grains are fed at inclusion levels above 20 percent, the byproduct meets the protein requirements, and the excess protein is used as an energy source. Carbohydrates (starch or cellulose) undergo fermentation in the rumen, and a portion is lost as methane and carbon dioxide.

This results in only 83 percent of the true energy content available to the animal from carbohydrates. Because a portion of the protein in distillers grains is not fermented and bypasses the rumen, it has a greater energy value when digested in the small intestine.

Ethanol plants will continue to modify production and maximize profitability by marketing components as separate commodities or for use in other processes.

Currently, we are combining results from our experiments and building a database that will allow us to estimate the feeding value of distillers byproduct that undergo a different fractionation or fermentation method before it is available to producers.

This will help producers determine how much can be paid for these new byproducts relative to traditional distillers grains or other competitive feedstuffs. Additional information about ethanol byproducts and other beef production tips can be found online (Beef Cattle Production).